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HomeMy WebLinkAboutReso 95-057 - Approve Woodward0Clyde Federal Serv Agreemnt for the Preparation of Seismic Risk Assessment RESOLUTION NO. 95-57 A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF REDDING APPROVING THE WOODWARD-CLYDE FEDERAL SERVICES AGREEMENT FOR THE PREPARATION OF A SEISMIC RISK ASSESSMENT AND AUTHORIZING THE MAYOR TO SIGN SAID AGREEMENT. BE IT RESOLVED by the City Council of the City of Redding, that: 1 . The City Council hereby approves the Woodward-Clyde Federal Services Agreement providing for preparation of a Seismic Risk Assessment for a fixed, not-to- exceed, amount of $24,136. 2. The Mayor of the Redding City Council is hereby authorized and directed to sign all necessary documents on behalf of the City Council. 3. A true copy of the Agreement referred to herein is attached hereto and made a part hereof. I HEREBY CERTIFY that the foregoing resolution was introduced and read at a regular meeting of the City Council of the City of Redding on the 7th -day of March, 1995, and was duly adopted at said meeting by the following vote: AYES: COUNCIL MEMBER: P. Anderson, Kehoe, McGeorge, Murray and R. Anderson NOES: COUNCIL MEMBER: None ABSENT: COUNCIL MEMBER: None ABSTAIN: COUNCIL MEMBER: None _130 T C. ANDERSON, Mayor City of Redding ATTEST: (;ONNIE MAYER, Ci C erk FORM APPROVED: DOUGLAS . CALKINS, Interim City Attorney d:\rest\w-cfs.cc � s CLIENT-CONSULTANT AGREEMENT FOR THE PREPARA TION OF A SEISMIC RISK ASSESSMENT THIS AGREEMENT, made and entered into the 7th day of March, 1995, by and between the CITY OF REDDING, a municipal corporation of the State of California, hereinafter referred to as "City" and the firm of WOODWARD-CLYDE FEDERAL SERVICES, hereinafter referred to as "Consultant" for professional consulting services for the project known as the Seismic Risk Assessment to aid City in updating its Seismic Safety Element of the General Plan. I s�al�� of woRK Consultant will prepare a Seismic Risk Assessment to provide as complete an assessment of all probable and potential risks relating to seismic activity as possible based on existing and easily obtainable information. Any seismic source which can potentially cause significant or damaging shaking to the City of Redding should be considered. Consultant will attend a minimum of one (1 ) scoping session with City staff and one (1) public meeting to present the findings of the Seismic Risk Assessment. Consultant will provide all services and meet all timelines as represented in Sections 4 and 5 of the proposal submitted to the City dated January 6, 1995, which is hereby attached as Exhibit A. C[. C0 PENSATI N Total payment for services rendered under this Agreement shall not exceed 524,136. Payments shall be made on a reimbursement basis upon completion of tasks outlined in Section 4 of Exhibit A. No more than 50 percent of the total Agreement amount shall be disbursed until the Administrative Draft Seismic Risk Assessment has been approved by City staff. ........................................ ftl, TINykNG Upon approval of this Agreement by the City and receipt of authorization to proceed, the Consultant shall begin work within 15 days after the date of execution of the Agreement and in accordance with the schedule presented in Section 5 of Exhibit A and thereafter diligently pursue the same to completion. The schedule presented in Section 5 of Exhibit A is modified to reflect that the Notice to Proceed is dated March 8, 1995 and that the Final Report is due on June 1 , 1995. tU iNETN0 pF PAYMEI All requests for payment shall be by invoice, and are due and payable upon presentation and verification of performance of work. If the City decides to abandon or suspend the project before its completion, the Consultant is to be paid AGREEMENT FOR PROFESSIONAL SERV/CES Page 2 for the service performed prior to receipt of written notice from the City of such abandonment or suspension together with reimbursements then due based on personnel hours expended and costs incurred to the date of discontinuance. V.' TERNt€NATtUItI QF Ct7TRAC"t' I`E)R CAUSE __.. ......... ............. If, through any cause, the Consultant shall fail to fulfill in a timely and proper manner his obligations under this Agreement, or if the Consultant shall violate any of the covenants, agreements, or stipulations of this Agreement, the City shall thereupon have the right to terminate this Agreement by giving written notice to the Consultant of such termination and specifying the effective date thereof, at least five (5) days before the effective date of such termination. In such event, all finished or unfinished documents, data, studies, surveys, drawings, maps, photographs and reports prepared by the Consultant under this Agreement shall, at the option of the City, become its property and the Consultant shall be entitled to receive just and equitable compensation for any work satisfactorily completed hereunder. 1; TERMIN-TION ICOR CONVEI�IE(! CE ? T1HE , CENC The City may terminate this Agreement at any time by giving at least ten (10) days notice in writing to the Consultant. If the Agreement is terminated by the City as provided herein, the Consultant will be paid for the time provided and expenses incurred up to the termination date. V1 CAN ES _ . ....................................... ........ The City may, from time to time, request changes in the scope of the services of the Consultant to be performed hereunder. Such changes, including any increase or decrease in the amount of the Consultant's compensation, which are mutually agreed upon by and between the City and the Consultant, shall be incorporated in written amendments to this Agreement. The fee schedule presented in Section 6 of Exhibit A shall be used as the basis of any increase or decrease in amount of Consultant's compensation. No verbal agreement or conversation with any officer, agent, or employee of the City, either before, during, or after the execution of this Agreement shall affect or modify any of the terms or obligations herein contained, nor shall such verbal agreement or conversation entitle the Consultant to any additional payment whatsoever under the terms of this_Agreement. Wit'::::*:.:: PEHSO. EI A. The Consultant represents that he has, or will secure at his own expense, all personnel required to perform the services under this Agreement. Such 0 AGREEMENT FOR PROFESSIONAL SERVICES Page 3 personnel shall not be employees of or have any contractual relationship with agencies providing funds for the project. B. All of the services required hereunder shall be performed by the Consultant or under his supervision and all personnel engaged in performing the services are to be fully qualified and shall be authorized or permitted under State and local law to perform such services. All professional personnel, including subcontractors engaged in performing services for the Consultant under this Agreement, are identified in Section 9 of Exhibit A. C. Except as otherwise agreed to in this Agreement, no other portion of the work or services under this Agreement shall be assigned, transferred, conveyed, or subcontracted without the prior written approval of the City. Any work or services subcontracted hereunder shall be specified by written agreement and shall be subject to each provision of this Agreement. D. Any changes or substitutions in the Consultant's personnel, as set forth herein, must be made known in writing to the Director of Planning and Community Development prior to execution and written approval granted by same before said change or substitution can become effective. t?( ' A���SIG;I'dABiL[T ...............................................................: ................................................................ The Consultant shall not assign any interest in this Agreement, and shall not transfer any interest in the same (whether by assignment or novation), without the prior written approval of the City; provided, however, that claims for money due or to become due to the Consultant from the City under this Agreement may be assigned to a bank, trust company, or other financial institution without such approval. Written notice of any such assignment or transfer shall be furnished promptly to the City. ...................................................... X: 11 5 JRA ........... ._... . ..................................................... Consultant shall procure and maintain for the duration of the contract insurance against claims for injuries to persons or damage to property which may arise from or in connection with the performance of the work hereunder by Consultant, its agents, representatives, or employees. 1 . Commercial general liability insurance (at least as broad as ISO form CG0001), with limits no less than 51 ,000,000 per occurrence/ $2,000,000 aggregate for bodily injury, personal injury, or property damage. 2. Automobile liability (at least as broad as ISO form CA0001), covering owned, non-owned and hired vehicles, with limits no less than $1 ,000,000 per accident for bodily injury and property damage. � 4 AGREEMENT FOR PROFESSIONAL SERV/CES Page 4 3. Professional liability insurance appropriate to Consultant's profession, with limits no less than $1 ,000,000 per occurrence. Architects and engineers coverage is to be endorsed to include contractual liability. 4. Worker's compensation insurance as required by the State of California and employers' liability insurance, the latter with limits no less than 51 ,000,000 per accident for bodily injury or disease. The general liability and automobile liability policies are to contain or be endorsed to contain the following provisions: 1 . The City, its officers, officials, employees, and volunteers are to be covered as insureds as respects: liability arising out of work or operations performed by or on behalf of the consultant; or automobiles owned, leased, hired or borrowed by the consultant. 2. For any claims related to this project, the consultant's insurance coverage shall be primary insurance as respects the City, its officers, officials, employees, agents and volunteers. Any insurance or self-insurance maintained by the City, its officers, officials, employees, agents or volunteers shall be excess of the consultant's insurance and shall not contribute with it. Each insurance policy required by this clause shall be endorsed to state that coverage shall not be canceled except after thirty (30) days prior notice has been given to the City. Insurance is to be placed with insurers admitted in the State of California with a current A. M. Best's rating of no less than A:VII, unless otherwise acceptable to the City. Consultant shall furnish the City with certificates of insurance and original endorsements effecting coverage required by this article. The endorsements are to be signed by a person authorized by that insurer to bind coverage on its behalf. All endorsements are to be received and approved by the City before work commences. At the request of the City, the Consultant shall provide a certified copy of each policy at no cost to the City. . ... ............................. . .. fl 1' ( E) lI*1CX 1flN Consultant agrees to protect, defend, indemnify, and hold harmless City, its officers, agents, and employees from and against any and all liability, damages, claims, suits, liens, and judgments, of whatever nature, including claims for contribution and/or indemnification, for injuries to or death of any person or persons, or damage to the property or other rights of any person or persons, arising out of or alleged to have arisen from the negligent acts, errors, or omissions of the 0 AGREEMENT FOR PROFESSIONAL SERV/CES Page 5 Consultant in the performance of this Agreement. Consultant's obligation to protect, defend, indemnify, and hold harmless, as set forth hereinabove, shall include any matter arising out of any actual or alleged infringement of any patent, trademark, copyright, or service mark, or any actual or alleged unfair competition, disparagement of product or service, or other business tort of any type whatsoever, or any actual or alleged violation of trade regulations. Consultant further agrees to protect, defend, indemnify, and hold harmless the City, its officers, agents, and employees from and against any and all liability for compensation under the Workmen's Compensation Act arising out of injuries sustained by any employee of Consultant. Xll INIDEPENDEN,T CONTRACTOR Consultant, in accordance with his status as an independent contractor, covenants and agrees that he will conduct himself consistent with such status, that he will neither represent himself as, nor claim to be an officer or employee of the City by any reason hereof, and that he will not by reason hereof make any claim, demand, or application to or for any right or privilege applicable to an officer or employee of the City, including, but not limited to, Workmen's Compensation coverage, unemployment insurance benefits, social-security coverage, or retirement membership credit. XIII: R POi TS ANQ INFORM AVON:: The Consultant, at such times and in such form as the City may require, shall furnish the City such periodic reports as it may request pertaining to the work or services undertaken pursuant to this Agreement, the costs and obligations incurred or to be incurred in connection therewith, and any other matters covered by this Agreement. Xl O ICER H1P UBLI IO1AT[ON REPRf}Q�CT�ON..`AN .USE All documents and materials prepared pursuant to this Agreement are the property of the City. The City shall have the unrestricted authority to publish, disclose, distribute, and otherwise use, in whole or in part, any reports, data, or other materials prepared under this Agreement. The City will give credit to the Consultant for his services in any public relations bulletin that may be published concerning the project. XV.*.*,:: COPYRIGHT ..................................................... ..................................................... No report, maps, or other documents produced in whole or in part iunder this Agreement shall be the subject of an application for copyright by or on behalf of the Consultant. AGREEMENT FOR PROFESSIONAL SERVICES Page 6 XW RECOR0S AND AUDITS' ...................................................................................... The Consultant shall maintain accounts and records, including personnel, property and financial records, adequate to identify and account for all costs pertaining to the Agreement and such other records as may be deemed necessary by the City to assure proper accounting for all project funds. These records will be made available for audit purposes to the City or any authorized representative, and will be retained for three years after the expiration of this Agreement unless permission to destroy them is granted by the City. X . All of the reports, information, data, etc., prepared or assembled by the Consultant under this Agreement are confidential and the Consultant agrees that they shall not be made available to any individual or organization without the prior written approval of the City. ........ .__ .... .. _.... .. ..._. _.. .... ..-..... _..._.... X1llit COMPLIANCE WITH U.CAL L.A. .. ..... ... ......... ... ...... _ _. ..................................................................................................................... .................................................................................................................... The Consultant shall comply with all applicable laws, ordinances and codes of the State and local governments. XIX 1tiIQNOISCRfM.W. IRTIOi .................................................................................. .................................................................................. ........._...... ........ ....... ... ...... . During the performance of this Agreement, the Consultant agrees as follows: A. The Consultant will not discriminate against any person or group of persons because of race, color, religion, sex, or national origin. B. The Consultant will cause the foregoing provision to be inserted in all subcontracts for any work covered by this Agreement so that such provision will be binding upon each subcontractor, provided that the foregoing provision shall not apply to contracts or subcontracts for standard commercial supplies or raw materials. E PLO The Consultant covenants that he presently has no interest and shall not acquire interest, direct or indirect, in the study area or any parcels therein or any other interest which would conflict in any manner or degree with the performance of his services hereunder. The Consultant further covenants that in the performance of this Agreement, no person having any such interest shall be emploYed. AGREEMENT FOR PROFESSIONAL SERVICES Page 7 NOTicES. Any notice provided for in this Agreement shall be given by mailing such notice to Consultant at WOODWARD-CLYDE FEDERAL SERVICES, 500 12th Street, Suite 100, Oakland, CA 94607-4014 or at such other address as Consultant may designate by notice to City; and any notice to City shall be given by mail as follows: City of Redding Department of Planning & Community Development 760 Parkview Avenue Redding, California 96001 IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be executed by Consultant the day of 1995, and by City the 7th day of March, 1995. ACCEPTED: CITY OF REDDING By: ROBERT C. ANDERSON, Mayor CONSULTANT By: IVAN G. WONG, Vice President A TTEST. By: CONNIE STROHMAYER, City Clerk FORM APPROVED: By: DOUGLAS H. CALKINS, Interim City Attorney cseismic.agr P R O P O S A L EXHIBIT "A" 0 0 0 SEISMIC RISK 41.00 ASSESSMENT ale • t • .;• :�� :• ••�o ; FOR THE 40.75 ' •�' • • goesaq CITY OF REDDING, • • • ••ass• ••' •f• • '•_ o Redd • 'x z=' 4''. ;,. CALIFORNIA • p 40.50 • • • • • • °0 a•�.=�a� ••.• • • B ° ass ° d�•I • • o .• • % • • Z • ~ • •b •P P : ° •cQ `* Prepared for 1 b . •0. . . ° •� ° O°� •°' oQ o°°. 100°: • Department of Planning& 4000 • • ° •° Community Development -123.00 -122.75 -I2250 -122.25 -122.00 City of Redding January 6,1995 Woodward-Clyde vw mi Woodward-Clyde Consultants 500 12th Street Suite 100 Oakland, California 94607-4014 PSK9501 Woodward-Clyde W -,gmee'^g 3 sciences scones'o gra=aeh 1 s acv,ronme�t January 6, 1995 Mr. Larry Morgon Associate Planner City of Redding Department of Planning & Community Development 760 Parkview Avenue Redding, CA 96601 Subject: Proposal for Seismic Risk Assessment Dear Sir. Woodward-Clyde is pleased to submit this proposal in response to the subject Request for Proposal. We wish to express a strong and enthusiastic interest in providing seismological, geological, and geotechnical and earthquake engineering services to the City of Redding for updating the Seismic Safety Element of the General Plan. Woodward-Clyde is a worldwide firm with more than 2,400 employees in more than 60 offices. Our demonstrated management capability and depth of experience in seismic hazard studies have resulted in proven performance on projects with expedited schedules such as yours. Woodward-Clyde is internationally known for its capabilities in geology, seismology, geophysics, and earthquake engineering, and has advanced many state-of-the-art techniques in the evaluation of seismic hazards. We are one of the few firms in the U.S. that has strong in-house capabilities in all these fields. Woodward-Clyde also has developed an outstanding reputation for the siting of critical facilities including some of the most world renown such as the Trans-Alaskan Pipeline and Aswan Dam. For this proposed project, we have assembled an outstanding Project Team of earth scientists and engineers. The Team includes Mr. Ivan Wong, Vice-President and Manager of our Seismic Hazards Branch and our proposed Project Manager, seismologist Mr. Doug Wright; earthquake engineer Dr. Joseph Sun; and geologist Dr. Clark Fenton. Our Project Team is fully committed to working on this interesting project and providing the required deliverables on time. In summary, we trust that our proposal responds fully to your needs. We can assure you that we will commit the resources of Woodward-Clyde to the fullest extent necessary to ensure HNM0P0SAL%PSK9467.2U M0106951651 Woodward-Clyde Federal Services-A subsidiary of Woodward-Clyde Group,Inc. 500 12th Street, Suite 100.Oakland,California 94607-4014 510.893-3600 Fax 510-874-3268 Woodward-Clyde _ Federal Services Mr. Larry Morgon January 6, 1995 Page 2 the successful completion of all contractual work. Please call Ivan Wong at (510) 874-3014 if you have any questions or require further information regarding this proposa,[. Regards, WOODWARD-CLYDE FEDERAL SERVICES Ivan G. Wong Vice-President and Manager Seismic Hazards Branch H-.NM0P0SALN?SK 67,E N40106951651 TABLE OF CONTENTS Section Page 1.0 INTRODUCTION 1 2.0 STATEMENT OF QUALIFICATIONS 3 3.0 PROJECT EXPERIENCE 11 4.0 SCOPE OF SERVICES 12 5.0 SCHEDULE 16 6.0 CURRENT RATE SCALE AND FEE ESTIMATE 17 7.0 INSURANCE COVERAGE 20 8.0 CONFLICT OF INTEREST STATEMENT 21 9.0 KEY PERSONNEL 22 APPENDIX - SELECTED PUBLICATIONS H.'MOYOSALTSK9501.21d 11 M0106951620 1.0 INTRODUCTION Woodward-Clyde is pleased to submit this proposal in response to the Request for Proposals for a Seismic Risk Assessment, City of Redding to update the Seismic Safety Element of the General Plan. Woodward-Clyde has a long history as an earth science, environmental and geotechnical engineering firm in the United States with extensive experience in seismic hazard evaluations both throughout the United States and overseas for numerous critical facilities. The combination of our experience and expertise has gained Woodward-Clyde an international reputation for our capabilities in addressing unique and site-specific seismic hazard issues. Woodward-Clyde is a group of full-service companies providing all aspects of engineering and sciences applied to the earth and its environment. We are an independent, employee- owned firm. Founded in 1950, the firm has grown to employ about 2,400 professionals and support staff in more than 60 offices worldwide with offices in major cities throughout the United States. Woodward-Clyde Group, Inc. is the parent company for three engineering subsidiaries: Woodward-Clyde Consultants, Woodward-Clyde Federal Services, and Woodward-Clyde International. Woodward-Clyde provides services in seismic geology, seismology, earthquake and geotechnical engineering, engineering geology, environmental sciences, and hazardous waste management. Our seismic hazards and earthquake engineering staff is composed of skilled, dedicated professionals under the direction of leaders in the earth sciences and engineering. Our technical leadership is maintained by an excellent in-house professional development program, significant research activities, and leadership and participation in national professional organizations. We have assembled a project team that specializes in earthquake-related studies and includes highly-skilled, professionally recognized individuals in the disciplines of seismology, seismic geology, and geotechnical earthquake engineering. We believe our project team has more than the necessary technical capability and depth to perform a seismic hazard assessment that will satisfy the needs of the City of Redding. H:\PROPOS4kL\PSK9501.3\1 l M0106951604 This proposal describes our approach, ability and experience to perform state-of-the-art seismic hazard assessments. Section 2.0 comprises a Statement of Qualification. Section 3.0 discusses previous project experience relevant to the Seismic Risk Assessment for the City of Redding. Section 4.0 details our Scope of Service, including the Project Goals and Approach. Section 5.0 describes the Project Schedule. Section 6.0 details Woodward- Clyde's Standard Schedule of Fees and Charges along with our General Conditions for Professional Services. Section 7.0 provides a summary of Woodward-Clyde's insurance coverage. Section 8.0 is a Conflict of Interests Statement . Appendix A contains published research by Woodward-Clyde personnel relevant to the Seismic Risk Assessment for the City of Redding. H:\PROPOSAL\PSK9501.3\2 2 M0106951604 2.0 STATEMENT OF QUALIFICATIONS Woodward-Clyde has conducted earthquake hazards evaluations for bridges, industrial complexes, office buildings, hospitals, power plants, dams, national laboratories, nuclear waste repositories, and lifelines in various tectonic environments. Our experience includes integrated evaluations of seismic geology, seismology, and geotechnical earthquake engineering for hundreds of facilities worldwide. Woodward-Clyde has the capability to perform complex work in a short time frame if needed. We bring: • A large network of experienced personnel throughout the firm who can be assembled into specialized teams for specific tasks • Extensive experience in managing multidisciplinary projects • Quality assurance/quality control to provide a high standard of services • A long history of successful project performance on public and private projects As a multidisciplinary firm, Woodward-Clyde can provide a single consultant or a team of consultants with specialized expertise to suit the special needs of a particular project. We can address a problem in sufficient detail to find solutions ranging from simple regulatory compliance to highly complex engineering designs. We can provide consultation services on various phases of a project from initial site selection through design, construction, and operation as well as services for upgrading or retrofitting existing facilities. Un particular, Woodward-Clyde has 40 years of experience on seismic hazards-related and engineering projects nationwide. As a nationwide, full-service firm, Woodward-Clyde has successfully managed both large and small contracts by using an approach to project management that is effective in meeting established schedules and is responsive to our clients' needs and expectations. W\PROPOSAL\PSK9501.313 3 M0106951604 Woodward-Clyde has conducted earthquake hazards evaluations for bridges, industrial complexes, office buildings, hospitals, power plants, dams, national laboratories, nuclear waste repositories, and lifelines in various tectonic environments. Our experience includes integrated evaluations of seismic geology, seismology, and geotechnical earthquake engineering for hundreds of facilities worldwide. SEISMIC HAZARD ASSESSMENTS Woodward-Clyde is a leader in the field of seismic hazards evaluation. Seismic hazards include ground shaking and ground rupture caused by earthquakes, as well as their secondary effects, such as tsunamis, soil liquefaction, and landsliding. A seismic hazards analysis iden- tifies seismic sources (such as active faults), assesses their potential for earthquakes, and estimates the ground motions or fault displacement they may generate. Possible secondary effects can also be assessed. Our projects have ranged from small preliminary investigations to comprehensive multidisci- plinary studies, and have spanned a wide range of geographic regions both nationally and worldwide. Many of our approaches represent state-of-the-science technology. Woodward- Clyde's professional staff includes over 30 seismic geologists, seismologists, earthquake engineers, and probability analysts. Because of our experience, we can make rapid evaluations by assembling teams of specialists in these complementary disciplines. Our Seismic Hazards Group has pioneered the development of many of the field techniques, analytical procedures, and computer models that are widely used by the geological, seis- mological, and engineering professions. The group's experience and a practical approach are used to develop realistic criteria and solutions. We employ experts who can perform a full range of services in any of the following disciplines. SEISMOLOGY Seismology is the study of earthquakes and of the propagation of seismic waves through the earth. From the analysis of seismic waves, aspects of the earthquake source are estimated such as location, depth, faulting mechanism, rupture area, and magnitude. Analysis of H:\PR0P0SAL\PSK9301.3\4 4 M0106951604 seismic waves also provides information about the structure and material properties of the portion of the earth through which the waves travelled. Woodward-Clyde possesses an extensive earthquake computer database used for assessing historical seismicity. We have performed numerous evaluations of historical seismicity in regions worldwide as well as seismicity recorded by modern seismographic networks. The results of our analyses of seismicity patterns, focal mechanisms, seismotectonic setting, and associations between earthquakes and geologic structures have been published in numerous scientific papers. In addition to studies of natural seismicity, Woodward-Clyde has extensive experience in the evaluation of man-induced seismicity including earthquakes caused b, reservoir impoundment, mining, and fluid injection or withdrawal. We have developed at first-of-its- kind probabilistic approach to evaluating reservoir-induced seismicity. Woodward-Clyde has developed advanced methods for the computer modeling; of seismic source characteristics and seismic wave propagation, and uses these capabilities n1 estimating strong ground motion characteristics in situations where suitably recorded data are sparse. Strong motion evaluations can be done on either a regional or site-specific basis. To support studies of earthquake ground motions and seismic stability, we have an extensive computerized database of strong-motion accelerograms recorded during earthquakes throughout the US. This unique data bank includes documentation of pertinent data on the strong-motion records and the causative earthquakes including earthquake magnitude, focal depth, distance from the earthquake source to the recording station, and the site conditions at the recording station. Woodward-Clyde is one of the few firms in the world that possesses a major seismological instrumentation capability. We have installed and operated seismographic instruments for the purposes of evaluating contemporary seismicity, crustal structure and attenuation, and local site response. Networks have been operated by Woodward-Clyde in the United States, Central and South America, and the Middle East. H:\PROPOS4,L\PSK9501.3\5 5 M0106951604 J � • SEISMIC GEOLOGY Seismic geology integrates many disciplines to evaluate earthquake hazards. Adequate and effective evaluation of earthquake hazards requires a comprehensive approach involving paleoseismology, tectonics, engineering geology, Quaternary stratigraphy, geomorphology, and structural geology. Key questions to answer are when, where, and how large were prehistoric earthquakes and what types of effects did they cause? At Woodward-Clyde, we have the breadth of expertise and knowledge to comprehensively answer these questions. Our geologists have developed and refined tools for fault detection and evaluation of prehistoric fault displacements including low-sun-angle aerial photography and techniques in exploratory trenching. In addition, our capabilities in interpreting all types of remote imagery, geologic mapping, computer mapping, acquisition and analysis of drilling data, and applying dating methods allow us to apply the most effective means to evaluate earthquake hazards. Woodward-Clyde has conducted seismic geology evaluations on both large and small scales for critical facilities in different tectonic environments throughout the world. Our experience includes a number of large multidisciplinary seismic hazards investigations, such as for the High Dam at Aswan, Egypt, and scaled-down investigations for smaller facilities, such as hospitals and schools. EARTHQUAKE ENGINEERING Earthquake engineering is the evaluation of the effects of earthquakes on soils and structures and the development of designs to accommodate those effects. Woodward-Clyde has extensive experience in assessing earthquake ground motions throughout the world. Engineering characterizations of earthquake ground motion include design response spectra or acceleration time histories, evaluation of soil failure potential, and recommendations for remedial measures, if needed. Our earthquake engineers have used and improved analytical techniques for evaluating soil- structure interaction and have applied them to nuclear power plants, seawalls, buried W\PROPOSALTSK9501.3\6 6 M0 1 0695 1 604 structures, and tanks. Woodward-Clyde has played a leading role for the past 25 years in the study of earthquake effects on dams and other earth structures. Woodward-Clyde has conducted evaluations of liquefaction potential for a wide variety of facilities. The scope of our services typically includes an assessment of the consequences of liquefaction and subsequent development of remedial schemes for those cases where evaluations indicate that liquefaction is likely to occur. Woodward-Clyde has applied its geologic, geotechnical, and earthquake engineering skills to evaluate the seismic stability of slopes and possible remedial actions to improve the stability of marginally stable slopes, existing landslides, ancient landslides, and slopes modified by man. By combining probability theory with our geologic, seismologic, and engineering knowledge, our earthquake engineers have performed many seismic risk evaluations. These tools allow a reasonable and comprehensive hazard assessment in areas where large earthquakes occur but not very frequently. SERVICES Characterization of Seismic Sources The first step in any deterministic or probabilistic seismic hazards analysis is to identify and evaluate potential seismic sources in the site region. The characterization of seismic sources and assessment of fault activity, maximum earthquakes, and recurrence for seismic hazard evaluations can be accomplished through geologic, seismologic, and geophysical techniques. The geologic characterization of seismic sources can be based on: (1) a review of geologic literature, particularly of previous seismotectonic studies and seismic hazards evaluations in the area; (2) discussions with scientists familiar with the seismotectonic setting of the region of interest; (3) development of a regional tectonic model; (4) aerial reconnaissance and analysis of aerial photographs (including low-sun-angle photography) and satellite imagery; (5) ground. reconnaissance and mapping of selected geologic features; and (6) site-specific H:\PROPOSAL\PSK9501.3\7 7 M0106951604 studies including detailed mapping, paleoseismic trenching, drilling, geophysical surveys, and Quaternary studies. The historical and contemporary seismicity in a region can be evaluated to characterize earthquake sources. Seismicity data can be examined for spatial trends and possible associations with geologic structures. Often we will re-evaluate seismicity data to refine earthquake locations and determine focal mechanisms. Probabilistic assessments of earthquake hazard require that all seismic sources and the random background seismicity be characterized by earthquake recurrence relationships that define the frequency of occurrence of earthquakes of various magnitudes up to the maximum. Typically, both seismologic and geologic data are used to constrain recurrence relationships, depending on the availability of data. Fault Evaluations Evaluations of potentially active faults form the basis of seismic hazards investigations. The purpose of a fault evaluation is to assess the potential for surface faulting at a site and/or to characterize fault activity and geometry. To evaluate surface faulting hazards, active fault traces on associated zones of deformation are identified and accurately located in order to recommend appropriate setback distances for engineered structures. A number of criteria are required to characterize fault activity, including timing, displacement, and length of prehistoric fault ruptures. From this information, maximum magnitudes, slip rates, recurrence intervals and potential activity can be assessed. Key to such studies is professional judgment with respect to tectonic setting, amount, rate, and recency of Quaternary deformation used to define an active fault. Application of these criteria requires constraint of the timing of the most recent faulting episode, either by direct geologic evidence, such as age of the youngest faulted and oldest unfaulted deposits, or by indirect inference from geologic and geomorphic expression when no suitable datable deposits overlie the fault. Evaluation of associated seismicity and tectonic association with other active structures, and the relation of structures to the modem stress field are also used to characterize fault activity. Gathering data for fault investigations include aerial photographic interpretation, detailed mapping and surveying of fault zone structure and H:TROPOSALTSK9501.34 8 M0106951604 tectonic geomorphology, trenching and detailed logging of stratigraphic offsets, fault scarp profiling, and application of a variety of dating methods. Geophysical profiling, including seismic refraction, high-resolution seismic reflection, and ground penetrating radar, may also be used to detail the three-dimensional structure of faults. Characterization of Earthquake Ground Motions Ground shaking generally causes the most damage during earthquakes and so it is generally the most significant hazard to evaluate. For more than three decades, Woodward-Clyde's seismologists and earthquake engineers have been at the forefront in assessing earthquake ground motions. Our ground motion studies are typically oriented toward defining the various levels of earthquake shaking and involve: (1) characterization of potential earthquake sources; (2) the evaluation of ground motion attenuation from source to site; (3) estimation of site-specific effects; and (4) development of design criteria for the safety evaluation of existing facilities and design of new facilities. Depending on the needs of the project, ground motions are characterized for engineering design by peak ground motions, response spectra or time histories. We have the experience and capability to provide whatever characterization you may need, from a rapid assessment of peak ground accelerations for screening sites to site-specific modeling for critical facilities. In addition, Woodward-Clyde has one of the most advanced geotechnical laboratories in the country. It is one of only a few that can conduct strain-controlled dynamic: and cyclic testing; such tests are necessary to characterize the behavior of soil and rock under earthquake loading. Evaluation of Liquefaction Pbtential Liquefaction is the loss of soil strength during ground shaking. Woodward-Clyde has conducted evaluations of liquefaction potential for a wide variety of facilities. Several types of basic data are used to assess the liquefaction characteristics of soils in these studies. These data could include standard penetration test blow counts and cone penetrometer soundings, relative densities measured or inferred from laboratory and field tests, and cyclic triaxial and cyclic simple shear tests in undisturbed and remolded samples. Analytical studies have ranged from application of simplified, empirically-based procedures such as KTROPOSAL\PSK9501.3\9 9 MO 106951604 those relating standard penetration test blow counts to liquefaction potential, to dynamic one- dimensional and finite element analyses. The scope of our services typically includes an assessment of the consequences of liquefaction and development of remedial schemes for those cases where evaluations indicate that liquefaction is likely to occur. Evaluation of Slone Stability and Landslides At Woodward-Clyde, we have applied our geologic, geotechnical, and earthquake engineering skills to evaluate the seismic stability of slopes. We have applied this knowledge to the evaluation of possible remedial actions to improve the stability of marginally stable slopes, existing landslides, ancient landslides, and slopes modified by man. Our evaluations typically include interpretation of aerial photographs and field investigations to identify and characterize previous slope failures, the evaluation of soil properties, selection of appropriate cross-sections, evaluation of potential slope movements, and possible remedial actions to improve the stability of the slope. Probabilistic Seismic Hazard Analysis and Seismic Risk By combining probability theory with our geologic, seismologic, and engineering knowledge, Woodward-Clyde can provide seismic risk evaluations for a site or a structure. We can assess the probability of an earthquake exceeding a range of levels of selected ground motion parameters such as peak acceleration, velocity, displacement, intensity, and response spectra. Combining this probability with a structural engineering estimate of the level of damage for specific ground motion levels, we can estimate the chances of varying levels of financial loss occurring due to earthquakes. We have applied these techniques to power plants, hospitals, shopping centers, and manufacturing facilities. We have used similar techniques to evaluate the likelihoods of loss of life (life safety) and loss of function. H:\PROPOSAL\PSK9501.3\10 10 M0106951604 DOMESTIC OFFICE LOCATIONS Scallk MONTANA NORTH DAKOTA IanJ 0A MINNESOTA4w Helens NE SOUTH DAKOTA WISCONSIN OREGON �1/p• WY NG Minneapolis NH Milwaukee FAP LIF m.,.. I YORK �V �Ca Ma •a.a � MICHIGAN MEW � Fil �1 NE9WISKA IOWA wta Livunia°�l; gYLVPNIA ry A1, pENN NmY,.r► A. `A lohdwklpltia vw 14W Chicago INDIANA (7evelrnd 3s (Titlun/Wayrc A4Vaad SIM COLORADO Oolaha Des Moines We MISSOI" ILLINOIS pE San Jose A,City Deaverlaw OHIO IryV Cau AA A's qw lub Col.Spnags Overland Sl.Lwis a8 I AV Cg Pah VIRGINIA KENTUCKY ARIZ Raleigh'1E✓.s Sarna Barbara ' NEW MEXICO OKLAHOMA Fg"in ozo TEXAS NOKfH CAROLINA Sana Pasadcrla Saa Ana ARKANSAS TENNESSEE SOUTH aa SDiego w aTa CAROLINA vow PM,enis lime Rock MISS. Dallis LOUISIA vw GEORGIA Jftlson ALABAMA a 3 A Austin jay Huustun A..k *40r LORAD ALASKA lake fulleh wallun asuc ChaAu Balun Ikwh a.a Rouge T"qu b Anchuragc 1 _ O Honolulu 9.4 HAWAII 12/29/9 3.0 PROJECT EXPERIENCE Woodward-Clyde has carried out a number of seismic hazard studies for municipalities both in the State of California and throughout the western United States. These include seismic hazard studies in the San Fernando Valley area for the City of Los Angeles; seismic hazard assessments for the Seismic Safety Elements of the General Plans for Contra Costa County and the cities of Newport Beach, Long Beach and Beverly Hills; and a study of liquefaction potential for the City of San Bernardino. Woodward-Clyde has performed numerous studies in northern California including large-scale seismic hazard studies for Pacific Gas & Electric Company at the Humboldt Nuclear Power Plant. A recently completed study was an evaluation of ground shaking for the U.S. Bureau of Reclamation's Spring Creek Dam just west of Redding. The following abstracts are representative projects preformed by Woodward-Clyde and are relevant to this proposed study. The methodologies we propose to utilize on the Seismic Risk Assessment for the City of Redding project are illustrated in these summaries. H:\PR0P0SAL\PSK9501.3\11 l 1 M0106951604 PROJECT: REVISIONS OF Since the adoption of the Seismic Safety element of the PORTIONS OF Contra Costa County General Plan in 1975, a considerable THE CONTRA amount of new information has become available COSTA concerning seismic hazards in the country. Woodward- SEISMIC Clyde carried out extensive review of existing data in order SAFETY to revise and update the Seismic Safety Element. Revision ELEMENT of the plan was directed towards two portions of the Seismic Safety Element: active faulting and seismicity, CLIENT: . CONTRA and liquefaction potential. This effort consisted of review COSTA of existing literature to identify and characterize active COUNTY faults. Fault maps and seismicity maps were revised and COMMUNITY fault activity criteria were updated. DEVELOP- MENT As part of our services incorporating new advances in the DEPARTMENT evaluation of liquefaction potential, we also made revisions to the liquefaction potential map and to the! administrative LOCATION: CONTRA maps of liquefaction potential. COSTA COUNTY, CALIFORNIA Period of Performance: June 1985-July 1986 Project Value: $15,000 H:\PROPOSAL\PSK9501.4\1 M0106951558 PROJECT: SIGNIFICANT The purpose of the project was to characterize the tectonics FAULT AND and seismicity of a 39,000-square-mile area of east-central SEISMICITY IN and northeastern California in which the Pacific Gas and THE Electric Company (PG&E) owns and operates 49 dams. NORTHERN SIERRA A regional aerial reconnaissance examined reportedly late NEVADA Quaternary active faults and compared them with other REGION OF faults in tectonically and seismically similar areas within MWOR PG&E the study area. Woodward-Clyde Consultants (WCC) DAMS identified the locations of the larger and more significant faults in the region and the potential maximum credible CLIENT: PACIFIC GAS earthquakes. For these, estimates were made of the & ELECTRIC relative level of tectonic activity and frequency of COMPANY occurrence of magnitude 6 and larger earthquakes. The characterization of the region was based on available LOCATION: CENTRAD literature, data in WCC's files, and judgments as to fault NORTHERN activity based on data from aerial reconnaissance. SIERRA NEVADA Period of Performance: 1987-1992 Project Value: $500,000 H:TROPOSALTSK9501.412 M0106951558 s � PROJECT: HUMBOLDT The Humboldt Bay Power Plant Unit No. 3, owned and BAY NUCLEAR operated by Pacific Gas and Electric Company (PG&E), POWER was shut down in 1976 for routine refueling. In 1977, the PLANT NRC staff notified PG&E that, because of the lack of sufficient geologic and seismologic data, certain issues CLIENT: PACIFIC GAS concerning reliability of the plant site needed resolution & ELECTRIC before the plant could again be approved for operation. COMPANY The NRC was primarily concerned with: LOCATION: HUMBOLDT, (1) the potential for surface faulting at the plant site and CALIFORNIA the incumbent need to design for fault displacement, and Period of Performance: (2) the basis for defining the vibratory ground motions, 1977-1980 evaluating liquefaction potential and evaluating soil/structure interaction at the plant site. Project Value: >$1,000,000 Woodward-Clyde Consultants was contracted by PG&E to perform regional and site-specific geologic and seismologic investigations and critical data review to evaluate the potential for resolving the technical issues raised by the NRC. The information necessary for this evaluation included: (1) location and characterization of regional faults, (2) location and extent of the Little Salmon and Bay Entrance faults, (3) behavior and capability of specific faults, (4) tectonic setting of the region, (5) age, location, extent, and characterization of regional stratigraphic units, (6) regional and local seismicity, and (7) engineering characteristics of the soils at the plant site. The investigation program was conducted by a team of geologists, seismologists, geophysicists, and earthquake engineers. This program included aerial reconnaissance, geologic mapping; age dating; drilling, sampling and geophysical logging; remote sensory imagery interpretation; exploration trenching; and study of historical earthquakes and recordings of mi.croearthquake activities from two microearthquake networks. KTROPOSALTSK9501.413 M0106951558 e PROJECT: PROPOSED Los Vaqueros, one of the largest dam projects in Northern LOS California, is a multipurpose water storage project designed VAQUEROS to improve the quality and reliability of water distributed DAM by Contra Costa County Water District. Located 50 km SEISMOLOGIC east of San Francisco Bay, plans called for construction of AND one or more dams on Kellogg Creek with a total combined GEOLOGIC storage capacity of 250,000 acre-feet. STUDIES Woodward-Clyde conducted seismic and geotechnical CLIENT: CONTRA evaluations of each of the four Kellogg Creek dam sites as COSTA subcontractor to James M. Montgomery Consulting COUNTY Engineers, Inc. One of the key issues was the potential for WATER surface faulting along any of several Quaternary faults in DISTRICT the area. LOCATION: CONTRA The displacement issue was analyzed first by examining COSTA recent geologic studies identifying three faults that cross COUNTY, the project area: the Brentwood, Kellogg, and Vaqueros CALIFORNIA faults. Although seismicity appears to be associated with these faults, the studies suggest that the faults have not Period of Performance: experienced surface displacement in Holocene time. The 1987-1990 primary objective, therefore, of our seismologic and geologic studies for Los Vaqueros was to: Project Value: $100,000 • Evaluate the activity and potential for surface faulting • Evaluate faults nearby that may be sources of future activity Characterize the ground motions of maximum a�,°t; ,�., _ earthquakes that may be generated on nearby faults. �- ° a,�y,1� *. Our studies included a comprehensive evaluation of the °`~ ' i historical and contemporary seismicity, paleoseismic _ r � *� ' trenching at seven sites across six faults, high-resolution �0 = _so-LJ seismic reflection, and a probabilistic evaluation of the 1. potential for reservoir-induced seismicity. • ! PROJECT: SITE-SPECIFIC Woodward-Clyde provided an estimate of the strong STRONG ground shaking that might result from possible moderate- GROUND to large-magnitude earthquakes for the new State Office MOTION Building in northeast Portland based on a state-of-the-art ESTIMATES ground motion methodology. The earthquakes considered FOR THE were three crustal events of magnitude (M) 5.5, 6, and 6.5 STATE OFFICE and a M 8'/2 Cascadia subduction zone event. Region- BUILDING specific information on crustal structure and seismic attenuation and a site-specific geologic profile were used CLIENT: OREGON in the ground motion estimates. Acceleration response DEPARTMENT spectra estimated for the site for these events were OF GEOLOGY . compared with Uniform Building Code (UBC) design AND NIINERAL spectra. INDUSTRIES (DOGAMI) As a follow-on study, Woodward-Clyde received a research grant from DOGAMI to estimate site-specific LOCATION: PORTLAND, ground motions at selected sites in the Portland OREGON metropolitan area including the east side of the Marquam Bridge, the Portland airport, and downtown Portland. Period of Performance: Downhole shear-wave velocity measurements were 1990-1992 performed at these sites by DOGAIG which provided the basis for developing the site-specific shear-wave velocity Project Value: models. Earthquakes from both the Cascadia subduction $8,000 zone and crustal faults were used as seismic sources for 101 the strong ground motion modeling. Old State Orrice 100 New Stab ButlCing\ Office Building \'� 10-, ��► ar�tl �t 1\ &dam 10-2 10'2 10•' 106 101 PERIOD(seow4e) PROJECT: SITE-SPECIFIC Woodward-Clyde performed a site-specific characterization STRONG of potential strong ground motions in the Salt Lake Valley GROUND based upon ,a state-of-the-art stochastic ground motion MOTION methodology. The objective was to assess the strong ESTIMATES ground motions that could be generated assuming a FOR SALT magnitude (M) 7.0 earthquake occurring on the Salt Lake LAKE VALLEY City segment of the Wasatch fault. CLIENT: UTAH GEO- Strong ground motions were estimated for three sites LOGICAL located within the Salt Lake Valley. These sites were SURVEY selected to represent the range of near-surface conditions in the valley based on the Uniform Building Code (UBC) soil LOCATION: SALT LAKE classifications S,, S,, and S,. Geologic and shear-wave VALLEY, velocity profiles were developed for each site based on UTAH borehole logs and shear-wave velocity measurements and other subsurface information. Period of Performance: 1991-1993 Project Value: $10,000 WEBER SEGMENT ' WARM SPRINGS FAULT Strrnp Mohan F�aadv EM SO Lake,%Man SALT �LrN ! _ . w LAKE _ WEST CITY CEAffr FAULT ZONE l •'� TUmr�N'ate" BENCH FAULT QUAKE 1 SALT LAK CITY ENT PROVO •- SEOYi1/T -1 ..• PROJECT: SEISMIC Woodward-Clyde provided seismic and civil engineering HAZARD services to support the City of Seattle's relicensing effort EVALUATION for the South Fork Tolt River project. OF THE SOUTH The seismic hazard evaluation included an evaluation of the FORK TOLT historical and contemporary seismicity, identification and RIVER characterization of seismic sources, evaluation of their PROJECT maximum credible earthquakes, and analysis of ground motions and selection of the design earthquake. The CLIENT: CITY OF potential sources of earthquakes which may affect the SEATTLE seismic stability of the Tolt Project included the Cascadia WATER subduction zone, shallow crustal faults, and sources which DEPARTMENT cannot be associated with an identified tectonic structure (random earthquake). Woodward-Clyde also evaluated the LOCATION: SEATTLE, potential for active crustal faults in the vicinity of the dam. WASHINGTON The geologic characterization of seismic sources was based Period of Performance: on a review of geologic literature and discussions with 1992-1993 other researchers, a review of available aerial photographs and LANDSAT imagery, an aerial overflight to verify and Project Value: check features identified in the air-photo and LANDSAT $50,000 imagery analysis, and ground reconnaissance of selected geologic features. [V —�� We evaluated the historical and contemporary seismicity in V _ � the region and compiled the historic seismicity in the vicinity of the project. We also examined the seismicity V, data for spatial trends and possible associations with geologic structures and determined the rate of historical earthquake recurrence for the region. 'vu A v, I t Two approaches were used to estimate potential ground spokam s. . .,_,r �/ MON- motions resulting from the sources identified above for the —= "' project: (1) a deterministic analysis using empirical ground • WASHINGTON V °ymp1 motion attenuation relationships, and (2) a probabilistic N. ground motion analysis. The potential earthquake motions p,ro,,,, / were characterized in terms of peak acceleration, response „I spectra, and duration of strong motion. OREGON .Eup�rr IDAHO .ea.. PROJECT: REGIONAL Woodward-Clyde is part of a three-firm team in a three- SEISMOTEC- year project; for the U.S. Bureau of Reclamation which TONIC involves a series of state-of-the-art seismotectonic EVALUATIONS evaluations for selected regions throughout the western OF USBR United States. These evaluations characterize known and DAMS potential earthquake activity in specific geologic provinces and provide deterministic assessments of expected ground CLIENT: U.S. BUREAU motions at project facilities, incorporating data on site OF RECLAMA- conditions and random seismic sources. Results of these TION studies are being used by the Bureau to re-evaluate the structural and hydraulic integrity of their dams in the west- LOCATION: WESTERN ern United States. UNITED Our primary activities are to: STATES (1) Evaluate the nature, distribution, and rate of historic Period of Performance: and contemporary seismicity 1991-present (2) Define the expected nature, distribution, magnitude, and rate of future seismicity based on the tectonic, Project Value: geologic, and seismologic setting $300,000 (3) Define and characterize the occurrence of random earthquakes ,2V 12r (4) Estimate deterministic, or probabilistic ground motions at the Bureau dam sites from the known, ws"INGTO cn.nN potential, and random earthquake sources. r�.• '� f We also assist in characterizing the contemporary tectonic K setting and identify and characterize known and potential .may' seismic sources including both source zones and specific . '4 geologic structures. To date, we have evaluated the Afollowing dams: s�ogcl,. ` ye a,'., TdVrti0ooamk J • f Cc COD TM 0"" a 2 Parker Dam, Arizona MCMifflWft• .� Tucson Terminal Storage Reservoir, Arizona Mormon Island Auxiliary Dam, California Spring Creek Dam, California Flat Iron Dam, Colorado COnIrl.q' Green Mountain Dam, Colorado �.� OREGON ;� Pueblo Dam, Colorado Rattlesnake Dam, Colorado aZ Rifle Gap Dam, Colorado Eugene Bend• Ruedi Dam, Colorado Boise River Diversion Dam, Idaho Hubbard Dam, Idaho Reservoir A Dam, Idaho Agency Valley Dam, Oregon Bully Creek Dam, Oregon Fish Lake Dam, Oregon Scoggins Dam, Oregon Thief Valley Dam, Oregon Unity Dam, Oregon Deer Creek Dam, Utah Echo Dam, Utah Cle Elum Dam, Washington PROJECT: GEOTECH- Woodward-Clyde Consultants (WCC) was retained by the NICAL Alyeska Pipeline Service Company to work on the ENGINEERING extensive geotechnical engineering effort associated with AND SEISNIIC the Trans-Alaska pipeline project. Our work on the HAZARD project included: STUDIES OF THE TRANS- Data Collection and Laboratory Testing - WCC planned, ALASKA located, and supervised sampling of more than 3,000 PIPELINE exploratory borings. Permafrost and thawed soils were extensively investigated. For some of these tests, we CLIENT: ALYESKA developed new testing and interpretation techniques. PIPELINE SERVICE Active Surface Faultine - This study involved geologic COMPANY photo interpretation using side-looking airborne radar, Earth Resources Technology Satellite, infrared, and low- LOCATION: PRUDHOE BAY sun-angle photography, and covered a 240,000-square-mile TO VALDEZ, area along the route. WCC's study generated significant ALASKA new data on fault activity on the surface and provided design criteria to Alyeska for active fault crossings. Period of Performance: 1979-1984 Selection of Construction Modes - Geotechnical and environmental considerations have led Alyeska to designate Project Value: three basic construction modes for the pipeline; $25,000,000 conventional burial; elevated construction; and insulated, refrigerated burial. Our staff participated in establishing criteria for the selection; of proper construction modes and - in designating modes for the entire alignment. An important aspect of this work was the assessment of potential ground movements that might effect the line. Pipgline SuM= - WCC identified the limits of direct soil support in buried construction and developed design criteria for bend supports and block valve installations. We participated in developed adfreeze and end-bearing pile ip systems and several alternative types of thermal piles. In addition to establishing design criteria, we provided specific recommendations for the mile-by-mile design. Special Assignments - An extensive pile and anchor installation and load test program was conducted for Alyeska. This involved analyses of installation methods and types of piles at sites representative of the full range of conditions anticipated from nearly solid ice to dry, frozen gravel. This program was fundamental to the establishment of design criteria for the elevated sections of the pipeline. Another special assignment was the preliminary soil investigation of eight pump station sites along the southern two-thirds of the route. OTHER PROJECT EXPERIENCE Location Client Services POWER PLANTS Mt. Poso Cogeneration Plant, R.W. Beck & Associates Seismic Hazard Evaluation CA Stockton Cogeneration Plant, R.W. Beck & Associates Seismic Hazard Evaluation CA Mecca Cogeneration Plant, Reese Chambers Seismic Hazard Evaluation CA Palo Verde Nuclear Power Risk Engineering Input for Probabilistic Plant, AZ Seismic Hazard Analysis San Onofre Nuclear Power Southern California Edison Seismicity Evaluation Plant, CA Stanislaus Nuclear Power Pacific Gas & Electric Microearthquake Monitoring Plant, Modesto, CA Company Shivta Nuclear Power Plant, Israel Electric Company Historical Seismicity Israel Evaluation Proposed Nuclear Power Public Service Company of Seismicity Evaluation Plant, Grants, NM New Mexico Hanford Nuclear Power Washington Power Public Microearthquake Monitoring Plants, WA Systems and Service Malt Plant, Idaho Falls, ID Anheuser Busch Seismic Hazard Evaluation San Juan County Coal Fire Public Service Company of Seismic Hazard Evaluation Power Plant, NM New Mexico Dixie Valley Geothermal Sun Company IIS-Seismicity Section Field, NV Soda Lake Geothermal Field, Union Oil Company of IIS-Seismicity Section NV California DAMS AND Petersburg Dam, Petersburg, City of Petersburg Seismic Hazard Evaluation AK Sheep Creek Dam, AK Echo Bay Mining Company Seismic Hazard Evaluation Monticello Dam, CA Solano County Water District Seismic Hazard Evaluation New Bullards Bar Dam, CA ' Yuba County Water Agency Seismic Hazard Evaluation H:TROPOSALTSK9501.441 M0106951600 OTHER PROJECT EXPERIENCE (Continued) Location Client Services Pit 1 Forebay Dam, CA Pacific Gas & Electric Seismicity Evaluation Company Salinas Dam, CA City of San Luis Obispo Seismic Hazard Evaluation Bear Creek Dam, Denver, U.S. Army Corps of Microearthquake Monitoring CO Engineers Aswan Dam, Egypt U.S. Agency for International Seismicity and Reservoir- Development Induced Seismicity Evaluations Ashton Dam, ID Utah Power and Light Seismic Hazard Evaluation Company Jessup Hill Pond Dam, MT U.S. Fish and Wildlife Seismic Hazard Evaluation Service Bodie Dam, NV Carson Valley Seismic Hazard Evaluation Subconservancy District McKinney Lake Dam, NC U.S. Fish and Wildlife Ground Motion Evaluation Service Alto Piura Dam, Peru Tahal Consulting Engineers, Seismicity Evaluation Ltd. Orangeburg Substation and U.S. Fish and Wildlife Ground Motion Evaluation Lake Bee Dams, SC Service Logan Canyon Dam, UT Utah State University Seismic Hazard Evaluation Piute Dam, UT Piute Dam Irrigation Seismic Hazard Evaluation Company Kemmerer City Dam, WY City of Kemmerer Seismic Hazard Evaluation Skagit River Dams, WA City of Seattle Water Seismic Hazard Evaluation Department Chino Tailings Dam, NM Phelps-Dodge Mining Seismic Design Review Corporation Stillwater Tailings Stillwater Mining Company Seismic Design Review Impoundment, MT Magna Tailings Expansion, Kennecott Copper Seismic Hazard Evaluation UT Corporation H:\PROPOSAL\PSK9501.4\5 M0106951600 OTHER PROJECT EXPERIENCE (Continued) Location Client Services WASTE FACILITIES Uranium Mill 'Failings, Atlas Corporation Fault Evaluation Moab, UT Yucca Mountain Nuclear Electric Power Research Expert Opinion for Waste Repository, NV Institute Probabilistic Seismic Hazards Analysis Exploratory Shaft Facility, U.S. Department of Energy Seismicity Evaluation Proposed Nuclear Waste Repository, Permian Basin, TX LANDFELLS Cinder Lake Landfill, City of Flagstaff Seismic Hazard Evaluation Flagstaff, AZ Sonoma County Landfills, Sonoma County Department Seismic Hazard Evaluation CA of Public Works Landfill, Longview, WA Sweet Edwards/EMCON Seismic Hazard Evaluation PIPELINES Gas Pipeline, Albany, CA Chevron Oil Company Fault Evaluation Parallel East Pipeline, Santa Clara Water District Seismic Hazard Evaluation Fremont, CA Transwestern/Mojave Mojave Pipeline Company Seismicity Evaluation Pipeline, CA SCHOOLS Evergreen College, Fremont, Evergreen/San Jose Fault Evaluation CA Community College District Ohlone College, Fremont, Ohlone College Fault Evaluation CA HOSPITAIS Kaiser Hospitals, San Kaiser Permanente of Feasibility Study for Base- Francisco Bay Area, CA Northern California Isolation Veterans Administration Zeck Butler Architects Seismic Hazard Evaluation Hospital, Walla Walla, WA H:\PROPOSAL\PSK9501.4\6 M0106951600 OTHER PROJECT EXPERIENCE (Continued) Location Client Services OTHER Route 13/24 Interchange, California Department of Ground Motion Evaluation Oakland, CA Transportation Offshore Platforms, AK Consortium of Oil Companies Seismicity Evaluation Central Valley, CA U.S. Geological Survey Seismicity Research Wilson Quarry, Aromas, CA Granite Rock Company Fault Evaluation Pacific Refinery, Hercules, Pacific Refining Company Fault Evaluation CA Irvington TlLnnel No. 2, San Francisco Department Seismic Hazard Evaluation Fremont, CA Utilities Engineering U.S. Embassies Worldwide U.S. State Department Seismicity Evaluation Strong Motion Sites, CA Kajima Research Corporation Microtremor Monitoring Proposed Development Site, Barry Swenson Builders Seismic Hazard Evaluation San Jose, CA H:\PROPOULTSK9501.4\7 M0106951600 4.0 SCOPE OF SERVICES The following section describes our approach to carrying out the Seismic Risk Assessment for the City of Redding. The plan is divided into a number of tasks as described below. TASK 1 GEOLOGIC FRAMEWORK AND SEISMOTECTONIC SETTING The initial studies for the seismic hazard assessment for the City of Redding will involve a synthesis of all available geologic and seismologic data in order to characterize the seismotectonic province(s) in the region around the City of Redding. As part of this task major geologic groups, discontinuities and faults will be identified and characterized. In addition, other potential large-scale geologic hazards such as landslide-prone slopes and regions of liquefiable and/or sensitive soils will be identified. This task will be accomplished by review and evaluation of existing literature, analysis of black and white stereo aerial photographs, evaluation of instrumental seismicity and by input from knowledgeable'experts. TASK 2 SEISNIIC SOURCE CHARACTERIZATION Recent recognition of several seismic sources makes this update of the Seismic Safety Element very timely. These seismic sources include the southern Cascadia subduction zone which may be capable of generating a M 8-9 earthquake; the Coast Ranges-Sierran block boundary zone which is a system of blind folds and faults on the western margin of the Sacramento fault; and several crustal faults including the Hat Creek fault. The initial step in evaluating the potential seismic hazards to the City of Redding is the identification and characterization of potential seismic sources. Such sources will include both faults and areal zones or seismic source zones which will account for unknown sources (e.g., blind faults) which may not have been identified to date. The results of recent research in northern California particularly that performed by the U.S. Bureau of H:TROPOSALTSK9501.3112 12 M0106951604 Reclamation and Pacific Gas & Electric Company will be obtained to insure that the most- up-to-date information on seismic sources is incorporated into the analysis. Four categories of seismic source parameters will be evaluated as part of this phase: (1) source location, orientation, geometry and style of faulting; (2) fault activity; (3) maximum earthquake; and (4) earthquake recurrence and/or fault slip rate. Estimates of the uncertainties of each of these parameters will also be included. These parameters will be defined based on the review of published data and.input from knowledgeable experts. This task will be accomplished by review of existing literature, analysis of stereo aerial photographs, and evaluation of both historical and contemporary seismicity. Ground reconnaissance and mapping of geologic features may also be required. The historical and contemporary seismicity in the project area will be evaluated to characterize earthquake sources. Seismicity data will be examined for spatial trends and possible associations with geologic structures. To evaluate surface faulting hazards, active fault traces on associated zones of deformation will be identified and accurately located in order to recommend appropriate setback distances for engineered structures. From the information gathered for each fault, maximum magnitudes, slip rates, recurrence intervals and potential activity will be assessed. A map of active and potentially active faults and a map of both historical and contemporary seismicity will be produced. TASK 3 CHARACTERIZA17ION OF EARTHQUAKE GROUND MOTIONS The potential earthquake ground shaking will be characterized by: (1) review and evaluation of past historical earthquakes which have generated ground shaking in Redding and (2) estimation of ground motions assuming the maximum credible earthquake (MCE) incorporating the most recent available information on the near-surface geology and ground motion attenuation. Tb accomplish (1), isoseismal maps developed by Tbppozada et al. (1981) will be reviewed and analyzed to estimate past ground shaking conditions. Based on the distribution of surficial geologic units, an assessment of the relative levels of ground H:TROPOSALTSK9501.3\13 13 M0106951604 shaking from the MCE can be made using empirical attenuation relationships. A map depicting the potential ground shaking conditions in the planning area will be developed. TASK 4 GROUND FAII.URE AND SLOPE STABILITY Several types of ground failure are known to occur during strong seismic shaking. Liquefaction, the loss of bearing strength of weak, non-cohesive soils is the most common. Analysis of existing geologic and soil survey maps, as well as existing literature, will aid determination of areas that are likely to be subject to liquefaction during a strong earthquake. Areas deemed likely to undergo liquefaction during seismic shaking will be highlighted on a map. Landsliding commonly occurs during strong earthquakes. Mechanically weak slopes however, may also fail due to the effects of heavy rainfall, water table changes or erosion at the base of oversteepened slopes. Analysis of geologic maps and stereo aerial photographs will be utilized to determine regions that are susceptible to landsliding, both seismically- induced and triggered by non-seismic means. A map will be produced showing areas that are susceptible to landsliding. TASK 5 SEICHE, TSUNAMI AND SEISMICALLY INDUCED DAM FAILURE HAZARD EVALUATION Due to the distance of the planning area from the Pacific Ocean, there is not expected to be any hazard from tsunamis. Seiches generated in the lakes surrounding the City of Redding are a potential hazard. The magnitude of a seiche is dependent on the strength of the seiche- generating agent. The potential contributions of seismic shaking and landsliding into a lake will be analyzed with regard to seiche generation. As with potential seismically-induced dam collapse, the area of inundation will be analyzed and maps of areas likely to be flooded under these circumstances will be prepared. TASK 6 LAND SUBSIDENCE AND OTHER GEOLOGIC HAZARDS Land subsidence often results from extraction of groundwater or hydrocarbon resources form porous media. Additionally, compaction arising from dewatering following liquefaction also H:\PR0P0SAL\PSK9501.3\14 14 M0106951604 gives rise to localized subsidence. Analysis of geologic maps and existing literature will be used to identify areas that have undergone or have the potential to undergo significant subsidence. Other geologic hazards, namely those related to volcanic activity, will be assessed by analysis of geologic maps. The proximity of the City to Lassen Peak and Mt. Shasta makes volcanism a potentially significant hazard. In addition the effects of erosion and avalanche/debris flow activity will also be assessed, primarily by analysis of stereo aerial photographs. TASK 7 FINAL REPORT A draft final report, which describes and summarizes the project and its results, will be submitted to the City of Redding for review and envisions. Comments will be addressed and incorporated as appropriate into the final report and transmitted to the City of Redding. H.TROPOSALTSK9501.3\13 15 MO 106951604 5.0 SCHEDULE The following section details of the scheduling of the tasks described in Section 4.0. H:\PROPOSAL\PSK9501.3\16 16 M0106951604 PROJECT SCHEDULE: SEISMIC RISK ASSESSMENT, CITY OF REDDING Week 1 Week 2 1 Week 3 Week 4 1 Week 5 Week 6 Week 7 Week 8 Week 9 Week 10 ' Notice to Proceed (Feb.219 1"5) Scoping Meeting TASK 1 TASK 2 TASK 3 _ TASK 4 _ TASK 5 - TASK 6 TASK 7 ' Submittion of Draft Report (April 10, 1995) ' Final Report (May 1, 1995) 6.0 CURRENT RATE SCALE AND FEE ESTBIATE TSme Rate Total (hours) (per hour) TASK 1 Personnel Assistant Project Geologist 16 $67 $1,072 Senior Staff Seismologist 16 $58 928 $2,000 aerial photographs 50 plates $10/plate 500 $500 TASK 2 Personnel Assistant Project Geologist 32 $67 $1,608 Senior Staff Seismologist 24 $58 $1,392 $3,000 ODC Auto Rental 4 days $50/day $200 Meals/Lodging 4 days $100/day $400 Gas $75 $75 15% G&A 101 $776 TASK 3 Personnel Senior Staff Seismologist 24 $58 $1,492 Project Manager 8 $125 $1.000 $2,492 H:\PROPOSAL\PSK9501.3\17 17 M0106951604 Time Rate Total ours (per hour TASK 4 Personnel Assistant Project Geologist 8 $67 $536 Project Engineer 24 $85 $2.040 $2,576 TASK 5 Personnel Assistant Project Geologist 16 $67 $1,072 Project Engineer 16 $85 $1.3 $2,432 TASK 6 Personnel Assistant Project Geologist 10 $67 670 $670 TASK 7 Personnel Project Engineer 8 $85 $680 Assistant Project Geologist 32 $67 $2,144 Senior Staff Seismologist 16 $58 $928 Word Processor 20 $50 $1,000 Graphics 60 $50 $3, $7,752 MEETINGS Personnel Project Manager 16 $125 $2,000 Assistant Project Geologist 8 $67 53 $2,536 TOTAL $24,136 H:\PR0P03AL\P9K9301.3\18 18 M0106951604 ADDITIONAL MEETINGS Additional public meetings and/or hearings will incur the following charges: Per Diem: $75/day (including lodging) Travel: $50/day (auto rental) Staff Time: charged at rates outlined in Section 6.0. e.g., Project Manager $125/hr H;TROPOSAL\PSK9501.3\19 19 M0106951609 7.0 INSURANCE COVERAGE Insurance coverage for Woodward-Clyde is provided by Marsh & McLennan Incorporated, 1166 Avenue of the Americas, New York, NY 10036. Coverage includes General Liability cover of up to $1,000,000 per occurrence. A specimen Certificate of insurance is provided giving details of coverage. H:\P1tOPOSAL\PSK9501.3VO 20 M0106951604 gEorc 55UE OATc;MMiDO/YY) 1—?6—q5 PRODUCER THIS CERTIFICATE IS ISSUED AS A MATTER OF INFORMATION ONLY AND CONFERS MARSH & MCLENNAN INCORPORATED NO RIGHTS UPON THE CEATIFICATI-HOLDER.THIS CERTIFICATE DOES NOT AMEND, 1166 AVENUE OF THE AMERICAS EXTEND OR ALTER THE COVERAGE AFFORDED BY THE POLICIES BELOW. NEW YORt::. NY 100-16 COMPANIES AFFORDING COVERAGE COlmPANY A LETTER RELIANCE NATIONAL INDEMNITY COMFAN COMPANY INSURED Lc i ER B WOODWARD—CLYDE CONSULTANTS COMPANY 4582 S. ULSTER ST. PARK:WAY LETTER C SUITE 606 CCMPANY p DENVER. CO 0 02'7 LETTER COMPANY E LETTER •• 1'r Te THIS IS TO CERTIFY THAT POLICIES OF INSURANCE LISTED BELOW HAVE BEEN ISSUED TO THE INSURED NAMED ABOVE FOR THE POLICY PERIOD INDICATED. NOTWITHSTANDING ANY REQUIREMENT,TERM OR CONDITION OF ANY CONTRACT OR OTHER DOCUMENT WITH RESPECT TO WHICH THIS CERTIFICATE MAY BE ISSUED OR MAY PERTAIN, THE INSURANCE AFFORDED BY THE POLICIES DESCRIBED HEREIN IS SUBJECT TO ALL THE TERMS,EXCLUSIONS, AND CON01- TIONS OF SUCH POLICIES. COI TYPE OF INSURANCE POLICY NUMBER POL;CY EFFECTIVE POGCY EXP AAT;ON LIABILITY U:,MITj IN THOUSANDS LTA OAT E IMMC4NYI GAT'.:IMM,pO YY .c'. GENERAL LIABILITY CvDiLY A X COMPREHENSIVE FORM NGA1496114 01-01-95 01-01-96 IN..uRY is s X PREMISESIOPERATIONS CONTRACTUAL LIAR. PROPE27Y UNDERGROUND INCLUDED AS DAMAGE � g EXPLOSION &COLLAPSE HAZARD �. PROOUCTS/COMPLETEO OPERATIONS RESPECTS THOSE X CONTRACTUAL ACTS COVERED BYFla-lokleINE0 $ Ss Po 1001? X INDEPENDENT CONTRACTORS GENERAL L I AB. INS. X BROAD FORM PROPERTY DAMAGE X PERSONAL INJURY PERSONAL INJURY S $100.000 SIF! � AUTOMOBILE LIABILITY i A X ANY AUTO NKA0101624-3 I01-01-95 O1-01-96 ;P�4 Is ALL OWNED AUTOS(PRN PASS.) N �tPY ALL OWNED AUTOS(OTHER PRN OTHER THAN) HIRED AUTOS PROPERTY ' NON-OWNED AUTOS DAMAGE $ GARAGE LIABILITY eI a PO CCMB;NED $ 1000 I EXCESS LIABIUTY UMBRELLA FORM ` BI 3 PO COMBINED $ S OTHER THAN UMBRELLA FORM NWA0101623-3 01-01-95 01-01-96 STATUTORY WORKERS'COMPENSATION A $1 G!►V(EACH ACCIDENT) AND EMPLOYERS' UAB JTY $1000(OISEASE•POLICY LIMIT) IS 1000(OISEASE EACH EMPLOY! OTHER i DESCRIPTION OF OPERATIONSILOCATIONSIVEHICLESISPECLAL ITEMS • �' •3 • SPECIMEN COPY SHOULD ANY OF THE ABOVE DESCRIBED POLICIES BE CANCELLED BEFORE THE EX- PIRATjQN DATE THEREOF, THE ISSUING COMPANY WILL ENDEAVOR TO 1995 MAIL -u DAYS WRITTEN NOTICE TO THE CERTIFICATE HOLDER NAMED TO THE LEFT.BUT FAILURE TO MAIL SUCH INOTICE SHALL IMPOSE NO OBLIGATION OR LIABILITY TOF ANY KIND UPON THE COMPANY. ITS AGENTS OR REPRESENTATIVES. AUTHORIZED REPRESENTATIVE • i 8.0 CONFLICT OF INTEREST STATEMENT ORGANIZATION CONFLICTS OF T CERTIFICATION Subject: Request for Proposals for Seismic Risk Assessment, City of Redding Certification: Woodward-Clyde Federal Services hereby certifies that to the best of its knowledge and belief, no facts exist relevant to possible Organization Conflict of Interest (OCI). Sincerely, ""M I JJ CvotA., Ivan G. Wong 9 Vice-President and Manager Seismic Hazards Branch January 6, 1995 H:TROPOSALTSK9501.3\21 21 M0106951615 v� v► 9.0 KEY PERSONNEL This section describes the experience and qualifications of the key Project Team members. We have assembled an outstanding group of professionals with experience that directly meets the requirements of the project. The Project Team members have many years of experience in the evaluation of seismic hazards for critical facilities. The contact person for this proposal is: Ivan G. Wong Vice-President and Manager Seismic Hazards Branch Woodward-Clyde Federal Services 500 12th Street, Suite 100 Oakland, CA 94607-4014 tel. (510) 874 3014 fax. (510) 874 3268 H:\PROPOSALIPSK9501.3U2 22 M0106951604 CLARK H. FENTON paleoseismology seismotectonics structural geology EDUCATION University of Glasgow, Glasgow, Scotland: Ph.D., Neotectonics and Paleoseismicity, 1991 University of Strathclyde, Glasgow, Scotland: Doctoral research in neotectonics, 1987-1989 University of Glasgow, Glasgow, Scotland: &Se. (Honors), Geology, 1987 PROFESSIONAL HISTORY Woodward-Clyde Federal Services, Assistant Project Seismic Geologist, 1993-date Geological Survey of Canada, Postdoctoral Research Fellow, 1992=1993 UK Seismic Hazard Working Party, Paleoseismology Consultant, 1992 Soil Mechanics Ltd., Paleoseismology Consultant, 1992 Sir William Halcrow & Partners, Neotectonics Consultant, 1991-1992 SKB AB, Sweden, Consultant, Member of Expert Panel on Postglacial Faulting, 1991 REPRESENTATIVE EXPERJEENCE Dr. Fenton has 5 years of experience in the field of paleoseismology and seismic geology. He has participated in both geological and seismological investigations for seismic hazard assessments of a number of critical facilities, principally in the United Kingdom, Scandinavia, eastern Canada, South America and the western United States. Dr. Fenton's experience includes: • Detailed fault studies and paleoseismic investigations on the Evergreen and Antioch faults in the San Francisco Bay area. • Regional fault studies and detailed paleoseismic investigation in the Tacna and Ilo regions of southern Peru • Regional fault studies and seismotectonic investigations for a number of sites in New Mexico, Arizona and Utah; including studies of fault geometries, rupture dynamics, and recurrence intervals. • Regional fault studies for the Los Alamos National Laboratory, New Mexico, including air photo interpretation and field investigation. • Paleoseismicity and seismotectonic studies for Atomic Energy Canada Limited in eastern Canada including air photo interpretation, trenching studies of Holocene faults, analysis of instrumental seismicity and mapping of seismically-induced soft sediment deformation. • Seismicity analysis and risk assessment for Ontario Hydro, Canada involving field investigation of postglacial faults, seismically-induced soft sediment deformation and shallow stress-relief features. • Research into the occurrence of pop-ups and other shallow stress-relief features in regions of high horizontal stress, particularly in eastern Ontario, Canada. • Research on recurrence rates and seismic risk assessment for areas of low to moderate seismic activity, particularly continental shield regions and passive margin environments including the causes of postglacial surface rupturing faulting in formerly glaciated regions and surface faulting in "stable" continental interior regions. H:\PR0P0SAL\PSK9501.3\1 M0106951604 CLARK H. FENTON page 2 • Paleoseismology and regional fault studies for the Nuclear Electric UK Seismic Hazard Working Party. This involved air photo interpretation, reconnaissance fault studies and paleoseismic investigation in the Lake District and area surrounding the Sellafield nuclear power and reprocessing plant, northern England. • Regional fault studies and paleoseismic field investigation for the Chapelcross nuclear power plant, southern Scotland. This effort involved fault mapping and investigattion of soft sediment deformation features. AFFILIATIONS American Geophysical Union Geological Society of America International Quaternary Association Neotectonics Commission Quaternary Research Association Seismological Society of America SELECTED PUBLICATIONS Fenton, C. (1992). Late Quaternary fault activity in North West Scotland (abs.), in Neotectonics- Recent Advances: Abstract Volume, N.A. Mother, L.A. Owen, I. Stewart, and C. Vita-Finzi (eds.), Quaternary Research Association, Cambridge, p. 21. Fenton, C. (1992). Holocene seismic activity in the UK: A comparison of instrumental, historical and paleoseismic data from North - West Scotland (abs.), EOS Transactions, American Geophysical Union, v. 73, p. 399. Fenton, C.H. (1992). Neotectonics in Scotland: A field Guide, Department of Geology & Applied Geology, University of Glasgow, Glasgow, 81 p. Fenton, C., L Adams, A. Brown, S. Halchuck, and M. Cajka (1993). How often have earthquakes broken the surface of the Canadian Shield? (abs.), Abstracts with Programs, Geological Survey of Canada Current Activities Forum '93, Ottawa, January 1993, 29. Fenton, C. (1993). Pbstglacial faulting in eastern Canada: Recently discovered examples from Northern Ontario and Southern Labrador (abs.), MAGNEC Annual Meeting, Ottawa, October 1993. Fenton, C., J Adams, A. Brown, M. Cajka, and S. Halchuck (1993). Surface rupture in eastern Canada: Searching for evidence and assessing the risk (abs.), EOS Transactions, American Geophysical Union, v. 74, p. 438. Adams, J., L. Dredge, C. Fenton, D.R. Grant, and W.W. Shilts (1993). Late Quaternary faulting in the Rouge River Valley, southern Ontario: Seismogenic or glaciotectonic? Geological Survey of Canada Open File Report 2653, 60 p. Adams, J., L. Dredge, C. Fenton, D.R. Grant, and W.W. Shilts (1993). Comment on Neotectonic faulting in metropolitan Toronto: Implications for earthquake hazard assessment in the Lake Ontario region, Geology, v. 21, p. 863. Fenton, C.H. (1994). Postglacial faulting in Eastern Canada, Geological Survey of Canada Open File Report 2774, 94 p. H:\PR0P0SAL\PSK9501.3V M0106951604 CLARK H. FENTON page 3 Adams, J., and C. Fenton (1994). Stress relief and incidental geological observations in and around Ottawa, Ontario, Current Research, Geological Survey of Canada Paper 1994-IIS p. 155-160. Fenton, C.H., J.E. Sawyer, I.G. Wong, T.L. Sawyer, and D.T. Simpson (1994), The Evergreen fault: an example of Late Quaternary oblique-thrust faulting in the southeastern San Francisco Bay area, California (abs.), EOS, Transactions of the American Geophysical Union, 75, 683. Fenton, C.H. and J. Adams (1995). Seismicity rates for northern Ontario: estimates using analogous worldwide stable cratons, Geological Survey of Canada Open File Report (in press). H:\PA0P05AL\PSK9501.3\3 M0106951604 JOSEPH I-HUNG SUN dam design earthquake engineering seismic hazard studies foundation design EDUCATION University of California, Berkeley: Ph.D., Geotechnical Engineering, 1989 University of California, Berkeley: M.S., Geotechnical Engineering, 1984 National Taiwan University, Taiwan, R.QC.: B.S., Civil Engineering, 1981. PROFESSIONAL HISTORY Woodward-Clyde Consultants, Senior Staff Engineer to Assistant Project Engineer, 1990-1993 Kleinfelder and Associates, Staff Engineer, 1989-1990 University of California, Berkeley, Research Assistant, 1985-1989 Mon and Associates International, Taiwan, Staff Engineer, 1984-1985 Registrations 1991/Civil Engineer/CA Chinese Army Corps of Engineers, Second Lieutenant, 1981-1983 REPRESENTATIVE EXPERIENCE Dr. Sun has a strong background in geotechnical design and analysis, particularly in the area of earthquake engineering and soil dynamics. Dr. Sun obtained his Ph.D. degree with emphasis on earthquake engineering and dynamic soil response from U.C. Berkeley under the direction of late Professor H. Bolton Seed. Dr. Sun assisted Professor Seed on several consulting projects while he was studying at U.C. Berkeley. In addition to his 5-year post-graduate study, Dr. Sun has over 7 years of practical experience on a wide range of geotechnical and engineering projects. His project assignments include dam engineering analyses and design; foundation design and seismic upgrade; probabilistic ground motion assessments; soil-structure interaction studies; liquefaction studies and remediation measure evaluations and cost estimate. The following are some of the projects that Dr. Sun has worked or in the pest 2 years related to embankment dams and other seismic issues. •. Analysis and design of the 200-ft high Los Vaqueros Dam to be built in Brentwood, California in 1996. Dr. Sun conducted the following tasks: probabilistic seismic ground motions assessment, material characterization, slope stability analysis of various loading conditions, static finite element stress analysis, dynamic finite element response analysis, and deformation analysis. Dr. Sun also participated in the preparation of plans and specifications for the project. • Seismic safety evaluation of Tolt Dam and regulating basin. Dr. Sun reviewed the instrumentation records from this 200-ft-high earth dam located in Washington State, evaluated the static stability of the main dam based on monitoring records, evaluated material properties, performed static and dynamic finite element analyses for the potential subduction zone earthgtuLkes, and provided input to the installation of an automated alarm and surveillance system based these results. • Feasibility assessment of Noonan Reservoir located in Vacaville, California. This reservoir is formed by building a 12,000 fleet long of embankment over a difficult foundation. Dr. Sun conducted the stability evaluation of the embankment sections, evaluated liquefaction potentials, assessed various ground improvement techniques, and developed treatment alternatives and associated cost estimates for the project. • California Division of Mines and Geology (CDMG) sponsored research on the dynamic response evaluation of Lexington Dam during the Loma Prieta earthquake. Lexington Dam is located 5 miles from the epicenter of the 1989 Loma Prieta earthquake and the strong ground motion instruments H:\PROPOSAL\PSK9501.3\1 M0106951604 JOSEPH I-HUNG SUN page 2 located at the crest and on the abutment recorded the event. Woodward-Clyde Consultants was granted the research by CDMG for its leading role in the industry to evaluate the adequacy of our current design practice and analytical procedures. Dr. Sun performed dynamic finite element analysis of the dam using motions recorded at the abutment and was able to reproduce the response at the crest in excellent agreement with the recorded response. • In the past 2 years, Dr. Sun was involved in several large-scale probabilistic ground motion assessment projects. These included: development of a statewide ground motion intensity map for the State of Illinois and probabilistic assessment for the area near Salt Lake City, Utah. Dr. Sun also conducts probabilistic ground motion assessments within the State of California on a routine basis. These studies have included: Shriner's Hospital (Sacramento), Imperial West Chemical refineries (Contra Costa County), Ohlone College (Fremont), Kaiser Hospital (Oakland), and Los Vaqueros Dam (Brentwood), Shell refinery (EI Segundo). • Dr. Sun conducted several soil-structute-interaction (SSI) analyses recently for several critical facilities located in California. These included the V.A. Palo Alto Hospital and Pacific Bell Pacific Headquarter building which were damaged in the 1989 Loma Prieta earthquake. WCC was also awarded a research grant by CDMG to study the effects of SSI and its potential impact on seismic design of buildings based on ground motions recorded in instrumented buildings from recent earthquakes. WCC was able to win this project against steep competition because of its leading role in this area and its past performance. AFFQ,IATIONS American Society of Civil Engineers Chinese Society of Civil and Hydraulic Engineers Chinese Society of Road and Highway Engineers Earthquake Engineering Research Institute (SERI) PUBLICATIONS Dynamic moduli and damping ratios for cohesive soils, (with H.B. Seed, et al.), Earthquake Engineering Research Center Report No. UCB/EERC 88/15, University of California, Berkeley, August 1988, 42 pp. Implications of site effects in the Mexico City earthquake of September 19, 1985, for earthquake resistant design criteria in San Francisco Bay Area of California, (with H.B. Seed), Earthquake Engineering Research Center Report No. UCB/EERC 89/103, University of California, Berkeley, March 1987, 124 pp- Relationships between soil conditions and earthquake ground motions in Mexico City in the earthquake of September 19, 1985, (with H.B. Seed et al.), Earthquake Spectra, EERI, Vol. 4 No. 4, November 1987, pp. 687-730. Relationships between soil conditions and earthquake ground motions in Mexico City in the earthquake of September 19, 1985, (with H.B. Seed et al.), Earthquake Engineering Research Center Report No. UCB/ESRC 87/15, University of California, Berkeley, October 1987, 112 pp. The application of in-situ soil vitrification process in geotechnical engineering, CE299 Report. Submitted for completion of requirements for the degree of Master of Science in Engineering in Geotechnical Engineering, University of California, Berkeley, May 1984, 34 pp. H:\PROPOSAL\PSX9501.3U MO 106951604 IVAN G. WONG seismology tectonics geophysics EDUCATION University of California, Berkeley: Doctoral Studies in Geophysics, 1975-1976 University of Utah: M.S., Geophysics, 1976 Portland State University: B.S., Geology, 1972 Oregon State University: B.S., Physics, 1970 PROFESSIONAL HISTORY Woodward-Clyde Federal Services, Vice-President and Seismic Hazards Branch Manager, 1993-date Woodward-Clyde Consultants, Staff to Senior Project Seismologist, 1976-1990; Associate, 1990-1992 Arizona Earthquake Information Center, Northern Arizona University, Research Associate, 1986-date California Academy of Sciences, Seismology Instructor, 1989-1991, 1993-date University of California, Berkeley, Seismological Research Assistant, 1975-1976 University of Utah, Seismological Research Assistant, 1974-1975 U.S. Geological Survey, Denver, Seismological Field Assistant, 1974-1975 U.S. Army Corps of Engineers, Portland, Physical Science Technician and Geologist, Summers 1967-1969, 1971-1972 REPRESENTATIVE EXPERIENCE Mr. Wong is the manager of the Seismic Hazards Branch which consists of 11 seismic geologists and seismologists specializing in seismic hazard evaluations. He has more than 20 years of experience in the field of seismology and is nationally known for his research in seismicity, seismotectonics, earthquake ground motions, and seismic hazards. For the past 17 years at Woodward-Clyde, Mr. Wong has directed and participated in seismological and geological studies and research for the seismic hazard assessment of numerous critical facilities principally in the western United States, Alaska, and Central America. His experience includes: • Principal seismologist for seismic hazard evaluations of numerous dams including, for example, Monticello, Salinas, Pit 1 Forebay, North Fork Stanislaus, New Bullards .Bar and the proposed Los Vaqueros Dam in California, Kemmerer City Dam, Wyoming, Ashton Dam, Idaho, Kennecott Tailings Dam, Utah, and Sheep Creek Dam, Alaska; cogeneration plants near Mt. Poso, Stockton and Mecca, California; hazardous waste facility near Casmalia, California; geothermal developments in Nevada; and an exploratory shaft facility for a proposed DOE nuclear waste repository in west Texas. Mr. Wong has also participated in earthquake studies for offshore platforms, Alaska; Aswan Dam, Egypt; Shivta nuclear power plant, Israel; San Onofre nuclear power plant, California; and a proposed nuclear power plant in New Mexico. • Supervised or advised on the design, installation, and/or operation of several seismographic networks and the subsequent analysis and interpretation of data. Networks included those for the Idaho National Engineering Laboratory, Stanislaus Nuclear Project in central California, the proposed DOE Paradox Basin nuclear waste repository in southeastern Utah, the Bear Creek Dam in Deaver, Colorado, coal mines in the eastern Wasatch Plateau, Utah, a potash mine in southeastern Utah, and the Chulac and Xalala Hydroelectric Projects in central and eastern Guatemala. • Project Seismologist from 1979 to 1987 for DOE's Nuclear Waste Isolation Program in the Paradox Basin, Utah. Mr. Wong developed and managed a program to evaluate the seismic hazard to a potential nuclear waste repository. The program included studies in historical seismicity, seismotectonics, crustal structure, earthquake source characterization, and strong-ground motion; extensive microearthquake monitoring;deep borehole seismic monitoring;and in-situstress measurements. H:TROPOSALTSK9501.311 M0106951604 IVAN G. WONG page 2 • Principal Investigator for an evaluation of the seismicity along the Coast Ranges - Great Valley boundary in California. The study was supported by the U.S. Geological Survey under the National Earthquake Hazards Reduction Program from 1985-1987. • Supervised and performed research on rockbursts and mine seismicity including the operation of two mine microseismic networks. He is internationally known for his studies which have focussed on source processes, the effects of geology and tectonic stresses, and the implications of mine seismicity to the underground storage of nuclear waste. • Since 1988, Mr. Wong has been directing seismic hazard studies at DOE's Idaho National Engineering Laboratory including paleoseismic fault studies and strong ground motion evaluations. He also served on the Strong Motion Expert Panel for Lawrence Livermore National Laboratory in its probabilistic seismic hazard evaluation of the New Production Reactor at the INEL. • Mr. Wong served on the Earthquakes and Tectonics Expert Panel convened by the Electric Power Research Institut for the High-Level Waste Project Performance Assessment for Yucca Mountain, and has provided review for several seismic hazard activities being performed as part of site characterization studies. • Through research grants from the States of Utah and Oregon in 1991 through 1993, Mr. Wong evaluated potential earthquake strong ground motions in the metropolitan areas of Salt Lake City, and Portland. • Currently Mr. Wong is the Project Manager for a seismic hazards evaluation of the Los Alamos National Laboratory. Activities include air photo interpretation,Quaternary mapping, paleoseismic fault studies, seismicity evaluation, drilling, downhole velocity measurements, geotechnical lab testing, and deterministic and probabilistic ground motion analyses. • Serves as WCFS Project Manager for a project team which performs seismotectonic evaluations of U.S. Bureau of Reclamation dams in the western U.S. Mr. Wong has evaluated to date 16 USBR dams in Colorado, Arizona, Oregon, Washington, Idaho, Utah, and California. Mr. Wong is actively involved in the activities of several professional organizations. He has been meeting, symposium, and session chair, organizer, and invited speaker at numerous conferences and meetings of the American Geophysical Union, Seismological Society of America, Geological Society of America and Earthquake Engineering Research Institult Mr. Wong has served on review panels for proposals submitted to the U.S. Geological Survey's National Earthquake Hazards Reduction Program, reviewed proposals for the National Science Foundation,and has been a reviewer for several professional journal& He has been an invited lecturer at Northers Arizona University, an invited speaker at several federal and state agencies, and for several seismic hazard workshops sponsored by the U.S. Geological Survey. A list.of significant professional and scientific assignments is available upon request. AFFILIATIONS American Geophysical Union Earthquake Engineering Research Institute Geological Society of America International Society of Rock Mechanics Seismological Society of America PUBLICATIONS K\PROPOSAL\PSK9501.3\2 M0106951604 IVAN G. WONG page 3 Mr. Wong has presented numerous papers at professional meetings and conferences and has authored or coauthored more than 100 papers and abstracts published in professional journals and conference proceedings. SELECTED PUBLICATIONS Wong, I.G., Swan III, F, and Cluff, L.S. (1982). Seismicity and tectonics of the Basin and Range and Colorado Plateau provinces: Implications to microzonation, in Third International Earthquake Microzonation Conference Proceedings, v. 1, p. 53-69. Humphrey, J.R. and Wong, I.G. (1983). Recent seismicity near Capitol Reef National Park, Utah and its tectonic implications, Geology, v. 11, p. 447-451. Wong, I.G. and W.U. Savage (1983). Deep intraplate seismicity in the western Sierra Nevada, central California, Bulletin of the Seismological Society of America, v. 73, p. 797-812. Wong, I.G. (1983). Comment on seismicity of the Colorado Lineament, Geology, v. 11, p. 558-559. Wong, I.G. and Ely, R. (1983). Historical seismicity and tectonics of the Coast Ranges-Sierran Block boundary: Implications to the 1983 Coalinga, California earthquakes, in The 1983 Coalinga Earthquakes, J. Bennett and R. Sherburne (eds.), California Division of Mines and Geology Special Publication 66, p. 89-104. Wong, I.G., D. Cash, and L. Jaksha (1984). The Crownpoint, New Mexico earthquakes of 1976 and 1977, Bulletin of the Seismological Society of America, v. 74, p. 2435-2449. Wong, I.G. (1985). Mining-induced earthquakes in the Book Cliffs and eastern Wasatch Plateau, Utah, U.S.A., International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts, v. 22, p. 263-270. Wong, I.G. (1986). Tectonic stresses in Colorado and their implications to seismicity, in Contributions to Colorado Seismicity and Tectonics - A 1986 Update, W. Rogers and R. Kirkham (eds.), Colorado Geological Survey Special Publication 28, p. 17-27. Zoback, M.Et, Zoback, M.G., Mount, V., Suppe, J, Eaton, J.P., Healy, J.H., Oppenheimer, D., Jones, L., Raleigh, C.B., Wong, I.G., Scotti, Q, and Wentworth, C. (1987). New evidence on the state of stress of the San Andreas fault system, Science, v 238, p. 1105-1111. Wong, I.G., R.W. Ely, and A.C. Kollmann (1988). Contemporary seismicity and tectonics of the northern and central Coast Ranges-Sierran block boundary zone, California,Journal of Geophysical Research, v. 93, p. 7813-7833. Wong, I.G., J.R. Humphrey, J.A. Adams, and W.J. Silva (1989). Observations of mine seismicity in the eastern Wasatch Plateau, Utah, U.S.A.: A possible case of implosional failure, Journal of Pure and Applied Geophysics, v. 129, p. 369-405. Wong, I.G. and N. Biggar (1989). Seismicity of eastern Contra Costa County, San Francisco Bay region, California, Bulletin of the Seismological Society of America, v. 79, p. 1270-1278. Wong, I.G. and J.R. Humphrey (1989). Contemporary seismicity, faulting and the state of stress in the Colorado Plateau, Geological Society of America Bulletin, v 101, p. 1127-1146. Wong, I.G. and D.S. Chapman (1990). Deep intnaplate earthquakes in the western U.S. and their relationship to lithospheric temperatures, Bulletin of the Seismological Society of America, v. 80, p. 589-599. H:\PR0P0SAL\PSK9501.3\3 M0106951604 IVAN G. WONG page 4 Wong, I., Silva, W., Darragh, R., Stark, C., Wright, D., Jackson, S., Carpenter, G., and Smith, R. (1990). Site-specific strong ground motion predictions of a M 7 Basin and Range normal faulting earthquake in southeastern Idaho, in Proceedings of the Fourth U.S. National Conference on Earthquake Engineering, v. 1, p. 617-626. Wong, I.G. (1990). Seismotectonics of the Coast Ranges in the vicinity of Lake Berryessa, northern California, Bulletin of the Seismological Society of America, v. 80, p. 935-950. Wong, I.G. (1991). Contemporary seismicity, active faulting and seismic hazards of the Coast Ranges between San Francisco Bay and Healdsburg, California, Journal of Geophysical Research, v. 96, p. 19891-19904. Wong, I.G., Silva, W.J., Darragh, R.B., Stark, C., and Wright, D (1991). Application of the Band-Limited- White-Noise source model for predicting site-specific strong ground motions in Proceedings of the Second International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. S. Prakash (ed.), v. 2, p. 1323-1331. Oppenheimer, D.H., I.G. Wong, and F.W. Klein (1992). Seismicity of the Hayward fault, in Proceedings of the Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area, G. Borchardt, S. Hirschfeld, J. Lienkaemper, P. McClellan, P. Williams, and I. Wong (eds.), California Division of Mines and Geology Special Publication 113, p. 91-100. Wong, I.G. (1992). Earthquake activity in the Sacramento Valley, California and its implications to active geologic structures and contemporary tectonic stresses, b Structural Geology of the Sacramento Basin, V.B. Cherven and W.F. Edmonson(eds.), Pacific Section, American Association of Petroleum Geologists, p. 5-14. Silva, W.J. and Wong, I.G. (1992). Assessment of strong near-field earthquake ground shaking adjacent to the Hayward fault, California, b Proceedings of the Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area, G. Borchardt, S. Hirschfeld, J. Lienkaemper, P. McClellan, P. Williams, and I. Wong (eds.), California Division of Mines and Geology Special Publication 113, p. 503-510. Wong, I.G. and Hemphill-Haley, M.A. (1992). Seismicity and faulting near the Hayward and Mission faults, in Proceedings of the Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area, G. Borchardt, S. Hirschfeld, J Lienkaemper, P. McClellan, P. Williams, and I. Wong (eds.), California Division of Mines and Geology Special Publication 113, p. 207-215. Jackson, S.M., I.G. Wong, G.S. Carpenter, D.M. Anderson, and S.M. Martin (1993). Contemporary seismicity of the eastern Snake River Plain, Idaho based on microearthquake monitoring, Bulletin of the Seismological Society of America, v. 83, p. 680-695. Wong, I.G., W.J. Silva, and I.P. Madin (1993). Strong ground shaking in the Portland, Oregon, metropolitan area: Evaluating the effects of local crustal and Cascadia subduction zone earthquakes and near-surface geology, Oregon Geology, v. 55, p. 137-143. Bott, J.D.J. and Wong, I.G. (1993). Historical earthquakes in and around Portland, Oregon, Oregon Geology, v. 55, p. 116-122. Wong, I.G. and W.J. Silva (1993). Site-specific strong ground motion estimates for the Salt Lake Valley, Utah, Utah Geological Survey Miscellaneous Publication 93-9, 34 p. Wong, I.G. and Silva, W-J. (1994). Near-field ground motions on soil sites: Augmenting the empirical database through stochastic modeling, b Proceedings, Fifth U.S. National Conference on Earthquake Engineering (in press). H:Tft0P0SAL\PSK9501.344 M0106951604 O DOUGLAS H. WRIGHT geophysics seismology EDUCATION University of California, Berkeley: B.A., Geology, 1981 PROFESSIONAL HISTORY Woodward-Clyde Federal Services, Senior Staff Seismologist, 1991 - present Consulting Technical Assistant/Seismologist: - Woodward-Clyde Consultants, 1988 - 1991 - Pacific Engineering and Analysis, 1991 - 1993 Woodward-Clyde Consultants, Staff Seismologist, 1986 - 1988 University of California, Berkeley, Seismographic Station, Research Assistant, 1981 - 1986 REPRESENTATIVE EXPERIENCE Mr. Wright has more than 12 years of experience-in seismology and earthquake engineering. His project experience includes strong-motion studies, aftershock monitoring and processing, and probabilisitic seismic hazard estimates. Mr. Wright has developed many computer programs and databases to process and analyze earthquake data Selected project experience includes: • Ground Motion Modeling and Site-Response Evaluations. Conducted strong-motion studies for the Idaho National Engineering Laboratory and the Parkfield Turkey Flat Experiment, western and eastern North America soil and rock parameter characterizations for the Electrical Power Research Institute, site response evaluations for the Los Alamos National Laboratory, and dams and proposed critical facilities in the western U.S. Used and improved time-domain and frequency-domain procedures, including FORTRAN and REXX programs, to create synthetic earthquake time histories compatible with design spectra at single and multiple dampings according to NRC standards. • Seismological Studies. Analysis included the generation and use of computer programs to determine and refine earthquake locations, application of earthquake recurrence relations, probabilistic seismic hazard estimates, earthquake catalog construction,and computer graphics. Facilities included dams in the western United States, such as the proposed Los Vaqueros Dam in California, cogeneration plants, and buildings. Participated in the analysis of seismicity near the Green Valley, Rodgers Creek, Bennett Valley, Tolay, and Hayward faults in northern California • Data Analysis and Processing. Participated in the monitoring and processing of aftershock activity of the 1989 Loma Prieta earthquake at critical facilities in the region, and of aftershock activity at free-field sites for the 1992 Petrolia, California, earthquake. Assisted in deployment of instrumentation. Processed and analyzed microearthquake data and participated in field operations of a local seismographic network for the Paradox Basin Nuclear Waste Repository Siting Study, Utah. • Computer Programming. Wide experience in FORTRAN programming for numerical modeling, graphics, and analysis and processing of data on the PC Familiar with C. Managed the running and functioning of programs. Devised programs in REXX to structure and automate input-streams for a range of programs. Verified, validated, and documented programs. Managed the software and operation of a 9-track tape drive. • Database Management. Assisted in the compilation and management of a site-profile database with PARADOX database software. H:UDM@h90QV 8996.1\I C0I005I M/ DOUGLAS H. WRIGHT page 2 PUBLICATIONS Wright, D.H. I.G. Wong, and J.R. Humphrey (1987). Earthquake activity near Glen Canyon, Utah: Evidence for normal faulting and extnsional tectonic stresses in the Colorado Plateau interior(absract), Abstracts with Programs, Geological Society of America, v. 19, p. 898. Wong, I.G., J.R. Humphrey, A.C. Kollmann, B.B. Munden, and D.H. Wright (1987). Earthquake activity in and around Canyonlands National Park, Utah in Geology of Cataract Canyon and Vicinity, J. Campbell (ed.), Four Corners Geological Society Guidebook, p. 51-58. Wong, I.G. and D.H. Wright(1989). Seismicity and strike-slip faulting along the Green Valley-Cedar Roughs fault trend, central California (abstract), Seismological Research Letters, v. 60, p. 24. Wong, I.G., D.H. Wright, A.P. Ridley, and D.H. Oppenheimer (1990). Seismicity in the vicinity of the Rodgers Creek, Bennett Valley and Tolay faults, northern California (abs.), Seismological Research Letters, v. 61, p. 42. Wong, I., W. Silva, R. Darragh, C Stark, ,D. Wright, S. Jackson, G. Carpenter, and R. Smith (1990). Site-specific strong ground motion predictions of a M 7 Basin and Range normal faulting earthquake in southeastern Idaho, in Proceedings of the Fourth U.S. National Conference on Earthquake Engineering, v. 1, p. 617-626. Wong, I.G., D.H. Wright, J.F. Strandberg, D.I. Gross, and T.F. Hauk (1991). An evaluation of reservoir-induced seismicity in the eastern San Francisco Bay Region, California (abs.), Seismological Research Letters, v 62, p. 52. Wong, I.G., M.A. Hemphill-Haley, and AH. Wright (1991). What and where is the Mission fault in the eastern San Francisco Bay area, California? (abs.), Seismological Research Letters, v. 62, p. 51-52. Wong, I.G., W.J. Silva, R.B. Darragh, C. Stark, and D. Wright (1991). Application of the Band-Limited-White Noise source model for predicting site-specific strong ground motions in Proceedings of the Second International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, edited by S. Prakash, v. 2, p. 1323-1331. Wong, I.G., W.J. Silva, D.H. Wright, and S.S. Olig (1991). Preliminary site-specific strong ground motion estimates for the Salt Latae Valley, Utah, ig Proceedings of the Fourth International Conference on Seismic Zonation, v. 2, p. 203-210. Wong, I.G., W.J. Silva, S. Chiou, C.L. Stark, D.H. Wright, S.M. Jackson, and R.P. Smith (1992). Modeling strong ground motions in the near-field of a Basin and Range normal fault(abs.), Seismological Research Letters, v 63, p. 33. H:uD.+n+�voc�iesv6.��2 croio�sica APPENDIX A SELECTED PUBLICATIONS Selected publications on the geology and seismicity of northern California by Woodward- Clyde personnel. H.IPROPOSALTSK9501AU M0106951623 EARTHQUAKE ACTIVITY IN THE SACRAMENTO VALLEY,CALIFORNIA AND ITS IMPLICATIONS TO ACTIVE GEOLOGIC STRUCTURES AND CONTEMPORARY TECTONIC STRESSES Ivan G.Wong Woodward-Clyde Consultants 500 12th Street,Suite 100 Oakland,California 94607 ABSTRACT relatively rigid and coherent crustal block with relatively little signifi- cant deformation occurring in its interior (Wong and Ely, 1983) The Sacramento Valley,which occupies the northwestern portion of (Figure 1). Instead:deformation as manifested by active faultine and/ the Sierran block, appears to have undergone a moderate level of or folding and seismicity is generally concentrated along the block crustal deformation, at least in Quaternary times. Seismicity is boundaries: the Coast Ranges-Sierran block(CRSB)boundary zone broadly distributed throughout the valley and along its margins. on the west(Wong and Ely,1983;Wong et al.,1988:Wentworth and Areas which have exhibited a moderate level of earthquake activity Zoback, 1989;Unruh and Moores, 1992)and the Great Basin-Sierra include: along the southwestern margin in the Coast Ranges near Nevada boundary zone on the east (Figure 1). In the Sacramento Lake Berryessa and within the Coast Ranges-Sierran block(CRSB) Valley in the interior of the Sierran block,any ongoing tectonism is boundary zone, source of the 1892 M > 6-1R Vacaville-Winters partially masked by several kilometers of Jurassic to Recent sedi- earthquakes;near Williams where three earthquake swarms occurred ments. The Foothills fault system on the eastern boundary of the from 1980 to 1985; in the vicinity of Willows and northward to valley,also within the Sierran block,appears to be undergoing some Coming; near Oroville in the Sierran foothills, site of a ML 5.7 minor reactivation. In this paper, I will describe the historical and earthquake and numerous aftershocks in 1975; in the foothills near contemporary seismicity within and along the margins of the Sacra- Chico;in the stretch of the foothills east of Red Bluff to Redding;and mento Valley and discuss its implications in terms of active geologic in the Coast Ranges west and northwest of Black Butte Reservoir. An structures and the tectonic state of stress. Much of the following area of particular seismic quiescence is in the valley around and south discussion of structures in the Sacramento Valley has relied on the of Sacramento. work of Harwood and Helley(1987)and I would refer the reader to their excellent paper. Detailed analyses of this seismicity and focal mechanisms indicate that active geologic structures include blind thrust and reverse faults and associated folds(e.g.,Dunnigan Hills)within the CRSB bound- GEOLOGIC AND TECTONIC SETTING ary zone on the western margin of the Sacramento Valley, the Willows and Coming faults in the valley interior, and reactivated The Sacramento Valley has been interpreted to be a late-Mesozoic to portions of the Foothill fault system. Other possibly seismogenic Tertiary forearc basin that formed contemporaneously with and faults include the Chico monocline fault in the Sierran foothills and between the accretionary trench deposits of the Franciscan Complex the Paskenta.Elder Creek and Cold Fork faults on the northwestern to the west and an eastern magmatic arc complex (Dickinson and margin of the Sacramento Valley. Seely, 1979). Filling of the forearc basin began with north to south progradation of Upper Jurassic to Upper Cretaceous marine deposits The contemporary state of tectonic stress within the Sacramento which are now exposed in the Coast Ranges to the west. These deep- Valley appears to be transitional,based on a limited number of focal marine deposits were succeeded by shallower-marine and marginal- mechanisms.East-west compressive stresses along the CRS Bbound- marine deposits of latest Cretaceous to early Miocene age that ary zone accommodated by thrust and reverse faulting extend into the prograded into the basin from the east and are preserved in the valley interior where a transition occurs to an extensional or possibly subsurface of the Sacramento Valley. Numerous unconformities are strike-slip stress field characterized by an approximate north-south present in this sequence,and a major unconformity separates it from maximum principal stress and/or an east-west minimum principal a thinner cover of alluvial deposits and locally prominent volcanic stress. In the Sierran foothills,this stress field is manifested by both rocks of early Miocene to Holocene age. normal faulting on northerly-striking faults, as exemplified by the 1975 Oroville earthquakes, and strike-slip faulting on northwest- A large number of folds and faults of varied orientation,many which trending faulm as observed in the 1966 ML 5.7 Chico earthquake. have exhibited late-Cenozoic deformation, occur throughout the Sacramento Valley(Harwood and Helley, 1987). Major late-Ceno- zoic faults include (Figure 2): (1) the Willows fault, which may extend from the northern San Joaquin Valley north to the Orland INTRODUCTION Buttes west of Orland where it may branch off into several splays;(2) the Coming fault,which appears to splay off the Willows fault near In sharp contrast to the significant crustal deformation occurring the town of Willows and extends as far north as Red Bluff;and(3)the along the Pacific-North American plate boundary,as defined by the Chico monocline fault, which extends from near Oroville San Andreas fault system and associated faults in coastal California, northwestward to Red Bluff.Harwood and Helley(1987)suggest that is the apparent low level of tectonism and earthquake activity in the the Willows and Corning faults and, to a lesser extent, the Chico Sacramento Valley. The Sierran block,which consists of the Great monocline fault,have accommodated much of the deformation in the Valley (the Sacramento Valley in the north and the San Joaquin Sacramento Valley during late-Cenozoic times in response to east- Valley in the south)and the Sierra Nevada,appears to be acting as a west compressive stresses. 5 6 MODOC- *, K BLOCKH� /; I'ROVINDCE willows j NJ. 9 ♦ S.. O arc. 9 _ :I• oar O °< ^ 'n ♦ .Patteson <�_:. /0 WoEpt�0[4cz c \ F ' \ q'•- tp Coalinga t' suR-w.pY�ENTO �I,I f.uLT 20,+( 9iy,•� 'O`/ y't a SANTA cu. 0�+ Wtow, 1° . MOJAVE ♦♦ MARIA a's.° 'f- °c BLOCK ♦� BLOCK ° TEHACHAPI BLOCK :­°... J•+ SAN GABRIEL iiT u, u Ww Ce',t•.Y BLOCK TRANSVERSE RANGES PRO03 •.uw.wyr r•w* EXPLANATION ---BOUNDARY OF PROVINCE OR BLOCK 0 200 km (CASHED WHERE APPROXIMATE) Figure 1. Tectonic provinces and crustal blocks of California from Wong and Ely(1983). The Willows fault appears to be a steeply-dipping reverse fault with east-side-up reverse drag on the fault(Harwood and Helley,1987)or the east side up(Harwood and Helley, 1987). It is probably the most fault-propagation folding (J. Unruh, William Lettis & Associates, extensive fault within the valley and appears to be a major tectonic personal communication, 1992). boundary dividing the Sacramento Valley into two late-Cenozoic structural provinces(Figure 2). North of Willows,the Willows fault The Chico monocline is a northwest-trending southwest-facing flexure changes to a northwest strike and appears to splay into the Paskenta. located on the northeast side of the Sacramento Valley(Figure 2).The Cold Fork and Elder Creek faults. trace of the monocline is characterized by a complex surface pattern of anastomosing fault strands that exhibit both small east and west- The Corning fault,which is not expressed at the surface and whose side-down displacements(Harwood and Helley,1987).Harwood and existence is based principally on well data (Figure 2), appears to Helley(1987)believe the master fault is a late-Cenozoic structure that coincide with a north-trending zone of several microearthquakes is also a major tectonic boundary between the Sierran basement on the located by Marks and Lindh (1978) (Harwood and Helley, 1987). east and an ophiolitic basement on the west.They further suggest that Although the youngest rocks deformed by the Corning fault are late-Cenozoic movement on the Chico monocline fault appears to Pleistocene in age, the possibility of associated microearthquakes have been predominantly reverse with the east side up. In contrast, suggests that the fault may be active. Seismic reflection data suggest Unruh(1990)believes the fault has behaved as a steeply southwest- that the Corning fault also is a steeply east-dipping reverse fault. The dipping normal fault during the late Quaternary. Corning domes and the Greenwood anticline occur just to the east of the Corning fault,suggesting that they may be partially the result of Wong and Ely (1983) first suggested that a 600-km-long zone 7 p RICHTER - MAGNITUDE MM INTENSITY °a° Q `— 2.0 O I I v O D 1904 p 0 3.0 O III p Op p O -- O 4.0 IV 8 5.0 Q V p (D o O _ 1940 6.0 O V1 0 O O 19a2^ 7.0 VII Q 0 - O - 9668 o No Measure _.2 = 1928 O 1945 .. ... . .. Approximate Boundary of p' p"- p p Sacramento Valley 00(j O Q 1968 ® Fault Source: Harwood and Helley(1987) ® Epicenter Sources: Toppozada et at.(1981); 1975 p Real et al.(1978);UCS: O 0 p 1903 USGS O OD Q 77� Q 1; e 0 0: ;t?�* 1906 O O 08 -- ��-- ° - -- _ (D p 1978 S �. - ___ ® '• 1904 —(y}�- :dC'=tT :"-!C.. _N._ 1892 1892 1892 (O r•�I 1 tte!a '- 1902 A 0 10 20 30 40 50 O �~' - 153 kilometers (Do `a 1909© Q Figure 2. Historical seismicity(1881-1990)and late-Cenozoic faults in the Sacramento Valley and margins. 8 characterized by both compressional reverselthrust and strike-slip HISTORICAL SEISMICITY faulting coincides with the boundary between the Coast Ranges and the Sierran block The CRSB boundary zone,which lies along the The historical earthquake record for the Sacramento Valley only western edge of the Great Valley as it meets the Coast Ranges,extends extends back to the mid-1800's,coinciding with the influx of miners from north of Willows in the Sacramento Valley to the White Wolf and settlers during the Gold Rush. Until adequate seismographic fault south of Bakersfield(Figure 1). Based on seismic reflection data, coverage came into existence in northern California in the 1930's, Wentworth and Zoback(1989)characterized this boundary as an area earthquake detection was generally limited to those events which where westward upturned Cenozoic and Cretaceous strata at the produced felt or physical effects. The sizes of such pre-instrumental eastern front of the Coast Ranges abut a major southwest-facing step earthquakes are often given in terms of their estimated maximum in the basement surface beneath the western Great Valley. intensities expressed by the Modified Mercalli(MM)intensity scale. Earthquakes as small as ML 3 were probably not completely observed In the Sacramento Valley, Unruh (William Lettis & Associates, throughout the Sacramento Valley until about 1960. In the 1970's, personal communication, 1992) suggests that the tips of eastward- particularly after the 1975 Oroville earthquake,seismographic cov- tapering tectonic wedges of Franciscan Complex locally occur west of erage of northern California improved significantly with the expan- the step in the basement. Seismically-active blind thrusts may be sion of U.S. Geological Survey (USGS) networks along coastal reactivated structures associated with earlier tectonic wedging(Unruh California and the Sierran foothills. The ability to accurately locate et al., 1991). Like the Coalinga anticline and the underlying blind earthquakes improved with the expanded networks, and so did the ability to determine focal mechanisms, a critical tool in assessing thrust fault which was the source of the 1983 Richter magnitude ML 6.7 Coalinga earthquake (Eaton, 1990; Namson and Davis, 1988; earthquake source processes and the tectonic state of stress.Currently, Stein and King, 1984),Pliocene and Quaternary folding and faulting seismographic coverage by the USGS provides complete detection probably occur along most of the boundary as a result of northeast- probably as low as ML 2.5 for most portions of the valley. Detection southwest compression(Wentworth and Zoback, 1989). Unruh and is best along the eastern and western margins of the valley. Moores(1992)also recognized uplift,tilting,and folding above blind, east-vergent thrust faults as the primary modes of Quaternary defor- The first historical earthquake to have reportedly occurred within the mation along the southwestern margin of the Sacramento Valley.The Sacramento Valley or along its margins(as defined in Figure 2)was 1892 ML>6-1R Vacaville-Winters earthquakes and the 1983 Coalinga an event on 7 January 1881 of estimated MLS, possibly located earthquake may be characteristic events for the CRSB boundaryzone. southeast of Red Bluff at the edge of the Sierran foothills(Toppozada et al., 1981). Since then,approximately 2800 earthquakes of ML 1.5 Wong et al.(1988)suggested that the apparent tectonic compression or larger have occurred up through 1990. Of these,433 events were taking place across the boundary zone may be a consequence of one ML 3.0 or larger. (In this paper,I will refer to the historical record as or a combination of three effects: (1)the westward movement of the including earthquakes prior to 1970 only.) Sierran block against the Coast Ranges due to late Cenozoic crustal extension in the Great Basin;(2)slightly convergent motion between the Pacific and North American plates;and(3)fault-normal crustal Sacramento Valley compression due to the low shear strength of the San Andreas fault (Zoback et al., 1987). Historically the interior of the Sacramento Valley has been relatively quiescent at a ML 3 and greater level. The only active area has been The Sacramento Valley is bordered on the east by the Sierra Nevada east of the town of Willows. Marks and Lindh(1978)recognized this (Sierran)foothills (Figure 1). The foothills consist principally of a seismicity to be a persistent feature in this century. Significant events steeply-dipping belt of late-Paleozoic to mid-Mesozoic metamorphosed near Willows have included a maximum MM intensity VII event on volcanic and sedimentary rocks which have been intruded by basic 24 July 1903,and a ML 4.7 event on 29 April 1968(Figure 2). The and ultrabasic rocks of similar age. Granitic plutons of Jurassic to only other earthquake of approximate ML 4.5 or larger within the Cretaceous age have later intruded the entire sequence. The meta- valley was a maximum MM VI event on 16 April 1904 in the morphic belt is complexly faulted and locally folded.Collectively,the northernmost portion of the valley south of Redding. principal faults are called the Foothills fault system,which extends the full length of the Sacramento Valley and beyond from near Mariposa on the south to Lake Almanor on the north, a distance of 320 km CRSB Boundary Zone (Clark,1960)(Figure 2). Clark(1960)characterized the fault system as consisting of steeply east-dipping to vertical faults that tectonically The largest historical earthquakes within or adjacent to the Sacra- separate distinctive belts of Paleozoic and Mesozoic rocks.The faults mento Valley are thought to be associated with the CRSB boundary are complex zones consisting of sheared,cataclastic,and crumpled zone. These were the 1892 Vacaville-Winters earthquakes on 19 and rocks. The two major faults within the Foothills fault system are the 21 April(approximate ML 6-3/4 and 6-1/2,respectively)and a ML 5- Bear Mountains fault zone on the west and the Melones fault on the 1/2 aftershock on 30 April(Wong and Ely,1983;Eaton,1986;Wong east. et al., 1988;Unruh and Moores, 1992)(Figure 2). The two largest events were felt over a widespread area(exceeding 200,000 km2)that The major tectonic activity of the fault system occurred during the extended into Nevada(Dale,1977)(Figure 3). One death,numerous late-Jurassic(Clark,1960).Priortothe1975Orovilleearthquake,few casualties, and extensive damage (including several collapsed studies of the late-Cenozoic deformational behavior of the Foothills buildings)were sustained in the sparsely populated epicentral area. fault system were performed. Subsequently, trenching studies by Severe ground effects, including ground cracking and landslides, Woodward-Clyde Consultants(1977)revealed evidence of activity were also observed in the epicentral area,most notably along Putah within the Foothills fault system in the past 100,000 years. Creek(Dale, 1977). However,it is unclear whether surface faulting accompanied these events. In addition to the large 30 April after- shock, a number of smaller aftershocks were reported during the sequence (Dale, 1977). Based on the reported intensities, Bennett 9 ' DS q[ ur 27 I \ •oma \ .o aw..' •c_ 'rnw • mow• Tr.ri u •vv^r Ger .i M c.,1 �_ Crwe �,v,�, 4rw•vrry •C r GA \ rwwi S! ` 1! wwrr rww• •I \ �r•� 4 � [ (rrr •rir F .Q" ' •tiMer� re wrrl � .• ' (11`1 Il�re•�rwrr•1� IM Yw I Y�r S�a� r •��� I •w \ •7r•4w• / q�wr1 •Sr�w+ •r.�.�. hrwr A` 37. � i2T e e • r O � .....w rA.[• Figure 3. Isoseismal map of the 19 April 1892 Vacaville-Winters earthquake from Dale(1977). (1987)suggested that the 1892 earthquakes occurred within an area California that occurred a few decades prior to the great 1906 moment of some 9 to 13 km wide centered on the English Hills north of magnitude(Mw)8 San Francisco earthquake. Fairfield(Figure 2). The only other known significant earthquakes possibly associated Sierran Foothills with the northern CRSB boundary zone include(Wong et al.,1988): (1)a MM VII-VIII event on 19 May 1902 near Elmira(estimated ML The fust known significant earthquake in the northern Sierran foot- 5.5; Real et al., 1978); (2) a MM VI event on 30 July 1904 near hills adjacent to the Sacramento Valley during the historical period Winters;(3)a MM V event on 14 February 1909 eastof Antioch in the was the 7 January 1881 earthquake. Historically,the most active area Sacramento Delta;and(4)a ML 4.5 on 15 April 1928 west of Black in the foothills has been around the town of Chico(Figure 2). On 8 Butte Reservoir(Figure 2). It is interesting to note that the majority February 1940.a ML 5.7 earthquake occurred approximately 30 km of historical earthquakes in the Sacramento Valley or along its northeast of Chico. The event was assigned a maximum intensity of western margin within the CRSB boundary zone occurred near the MM VI based on minor damage, including cracked chimneys and turn of the century. This activity may be part of the enhanced broken windows in Chico and Grass Valley. A ML 4.6 event also seismicity observed by Ellsworth et al. (1981) in northern coastal occurred on 24 May 1966 very near Chico. Other historical events 10 The most significant earthquake in the Sacramento Valley or along its CROVILLI °�" f margins since 1970 has been the 1 August 1975 ML 5.7 Oroville C c earthquake(Figure 2). The maximum intensity for the event was,"'IM VII. Ten persons were injured and minor to moderate structural A damage was incurred principally in the form of broken windows, cracked plaster and ceilings, some fallen chimneys and damaged _t a buildings. The sequence included 10 foreshocks and aftershocks of ML 4.5 or greater(Figure 2). -9 The distribution of aftershocks indicates that the mainshock was the result of rupture of the previously unknown Cleveland Hills fault, which strikes north-south,dips 60°to the west and extends to a depth of at least 10 km(Lahr et al., 1976;Morrison et al., 1976)(Figure 4). Surface faulting of the Cleveland Hills fault extended for a distance 3, e of 1.6 km. The focal mechanism of the mainshock and aftershocks exhibited normal faulting(Langston and Butler,1976;1vtorrison et al., 5g 1976)(Figure 5). The proximity of the Cleveland Hills fault to Lake ac a Oroville(a reservoir impounded by Oroville Dam),the occurrence of the event soon after the largest fluctuation in the reservoir level.and the absence of prior significant seismicity in the area suggested that the 1975 earthquake was a case of reservoir-induced seismicity ,2P o (Toppozada and Morrison, 1982). South of Oroville,the contemporary seismicity has been at a low to moderate level and diffusely distributed throughout the Sierran foot- hills, with a few small clusters of events especially near Auburn (Figure 2). North of Oroville, two relatively active areas at the • microearthquake level include the area east of Chico which, as •, previously mentioned, has been historically active, and the area .••;�:'` between and east of Red Bluff and Redding. Although the epicentral uncertainties of earthquakes in this region may be several kilometers or more,the seismicity near Chico appears to exhibit a northwest trend roughly parallel to the structural grain in .•'• this portion of the Sierran foothills(Figure 2). The inferred surface • tot• trace of the similar-striking Chico monocline fault is located about 5 �•' km northeast of the zone of seismicity,which includes the 1966 Chico earthquake. Lomnitz and Bolt(1967)determined a focal mechanism for the 1966 event which exhibits strike-slip faulting with the north- west-striking plane parallel to the Chico monocline fault and dipping Figure 4. Map and cross-sectional views of Oroville aftershocks from 650 to the northeast(Figure 5). Although Harwood and Helley(1987) Lahr et_al.(1976). Epicenters are plotted by depth:A(0- characterize the Chico monocline fault as an east-side-up reverse 4km), B (4-8km), and C (8-12km) (top). Subset of well- fault,it is tempting to suggest that the seismicity near Chico,including located events are shown in the cross-section. the 1966 earthquake,may be associated with this fault and that the fault has been reactivated in a strike-slip sense in the contemporary stress field.The possibility also exists that the fault is southwestward- dipping,as suggested by Unruh(1990),which would be consistent with the majority of microearthquakes being located to the west of the include two earthquakes on 18 November 1942 and one on 20 April fault(Figure 2). 1945;all have been assigned maximum intensities of MM VI. Also The epicenter of the 1881 earthquake, though very poorly located, within the foothills,a maximum MM VI event occurred near Grass Valley on 15 May 1906(Figure 2). also plots near the Chico monocline fault(Figure 2). However,the 1881 event also coincides with an unusual east-west trending zone of seismicity which appears to be oriented across the structural grain of CONTEMPORARY SEISMICITY AND IMPLICATIONS FOR the region and oblique to the Chico monocline. No similarly oriented ACTIVE GEOLOGIC STRUCTURES geologic structure is known in this area although several east-northeast- striking strucrures occur further to the north(see following). Further Most of our seismologic knowledge regarding active geologic struc- analyses will be required toevaluate the nature of this epicentral trend. tures and tectonic stresses in the Sacramento Valley has been attained in the period since the early 1970's. Such knowledge has been gained The apparent north-trending zone of seismicity eastof the Sacramento primarily from the evaluation of microearthquakes (events smaller River between Red Bluff and Redding occurs along the topographic than ML 3.0)and a few larger events. Microearthquakes occur more break between the valley and the Sierran foothills(Figure 2). How- frequently than larger events and have been observed due to the ever, there are no known similarly-trending structures in this area. improved regional seismographic coverage by the USGS. The area is dominated by east-northeast-striking faults and folds such s • _ 11 LEGEND Focal Mechanisms Strike-slip faulting —�- Reverse Normal Notes: Inward and outward arrows represent horizontal projections of P and T axes,respectively. Shaded areas are compressional quadrants. Sources of Focal Mechanisms 5 2 1. S.Walter,USGS 2. Lomniiz and Bolt. 1967 3. Langston and Butler, 1976 4. MCNally et al, 1978 7 5-12. Wong et al., 1988 6 8 3 9 10 4 J • .J -N- 11 J 0 10 20 30 40 50 1 kilometers 12 1 � Figure 5. Focal mechanisms of the Sacramento Valley and margins. 12 as the Battle Creek and Bear Creek faults and the Inks Creek fold beneath the Dunnigan Hills and near the town of:Madison(Figure 2). system. Harwood and Helley(1987)believe these faults have been In particular,microseismicity appears to trend parallel to the axis of active in late-Cenozoic times, with the latest style of deformation the anticlinal Dunnigan Hills(Wong et al., 1988). being normal faulting. Harlan-Miller-Tait Consultants (1984), however,suggested they are reverse faults based on seismic reflection The largest earthquake in the northern CRSB boundary zone was a M` data. Detailed studies of the seismicity in this area will be required to 4.2 event in 1978 near Madison(Wong et al., 1988;Wong, 1990). A evaluate the sources of the activity and their association with geologic detailed analysis of this event and its aftershocks suggests a pattern structure. consistent with a westward shallow-dipping thrust fault and possibly steepiv-dipping reverse faults (Wong, 1990). Such deformation is Microearthquake activity recorded since 1970 within the Sacramento identical to the processes involved in the 1983 Coalinga mainshock Valley is consistent with the distribution of historical seismicity and aftershocks(Eaton, 1986; Wong et al., 1988). (Figure 2). A large concentration of events occurs east and northeast of Willows and, to a lesser extent, near Williams. The latter is All focal mechanisms along the Sacramento Valley portion of the probably associated with the CRSB boundary zone (see following CRSB boundary zone have exhibited either reverse or low-angle discussion). The seismicity near Willows appears somewhat diffuse thrust faulting on north to northwest-striking planes(Figure 5). These although the events cluster in a zone which appears to be elongated in focal mechanisms and the observed seismicity are consistent with the a north-south direction. Northeast of Willows, the north-trending existence of blind thrusts and associated reverse faults in several Corning fault may splay off the northwestward-striking Willows fault locations along the western margin of the valley(e.g.Dunnigan Hills). (Figure 2). Wong et al. (1988) suggested that the Willows and Corning faults were the sources of some of the earthquakes east and northeast of Willows. (Note in Figure 2 the epicenters occur east of CONTEMPORARY STATE OF STRESS the Willows and Corning faults possibly due to location errors and/or the eastward dip of the faults.) They also determined a focal Consistent with the existence of active thrust and reverse faulting,the mechanism for a ML 2.8 earthquake in 1985 which was relocated 10 contemporary state of stress along the western Sacramento Valley km east-southeast of town at a depth of 23 km,very near the mapped margin as far north as the latitude of Willows appears to be character- Willows fault(Figure 5). The mechanism exhibited reverse faulting ized by a northeast-southwest to east-west-trending maximum prin- on northerly-striking planes consistent with the style and orientation cipal stress(Figure 5). Unfortunately,no focal mechanism data exist of the Willows fault(Wong et al.,1988). The focal depths of the 1985 north of Willows along the CRSB boundary zone(Wong et al.,1988). event and two other nearby microearthquakes suggest that the Wil- Within the valley,only two focal mechanisms exist: 1)the mecha- lows fault may extend into the lower crust. nism of the 1985 Willows earthquake, which indicates east-west compression and 2)a mechanism for a 40-km-deep earthquake near Elsewhere within the Sacramento Valley,few microearthquakes are Red Bluff,determined by S.Walter(USGS,written communication, located in the southern half,centered around Sacramento,in contrast 1986),which indicates an east-west minimum principal(orextensional) to scattered activity between Willows and Redding. Southwest of stress(Figure 5). The latter mechanism is probably not reflective of S acramento is the controversial Midland fault.No earthquakes to date the crustal state of stress because the event may have occurred within have been conclusively associated with the fault(Wong et al., 1988; the eastward-dipping subducted Gorda plate beneath northern Cali- Wong and Biggar, 1989) (Figure 2). Although some previous fomia(Walter, 1986). investigators have suggested that the Midland fault may have been the source of the 1892 Vacaville-Winters earthquakes, recent studies In the Sierran foothills to the east, the only focal mechanism data indicate that these events probably had their source in the blind thrust available are for the 1975 Oroville and 1966 Chico earthquakes,and and reverse faults within the CRSB boundary zone to the west(Wong acomposite solution fornine microearthquakes recorded near Auburn et al., 1988;Eaton, 1986;Unruh and Moores, 1992). (Figure 5). The 1975 mechanism exhibited an east-northeast T-axis or minimum principal stress(Langston and Butler,1976)and the 1966 One of the most active areas occurs slightly east of the southwestem event, a maximum principal stress oriented north-northeast and a margin of the valley near Fairfield(Figure 2). Much of this seismicity west-northwest minimum principal stress. The Auburn focal is associated with the Green Valley-Cedar Roughs fault trend and the mechanism exhibited normal faulting with a T-axis oriented ap- Vaca-Montezuma Hills fault(Wong et al.,1988;Wong,1990).These proximately northeast-southwest(McNally et al.,1978)(Figure 5).In faults represent the eastern extent of strike-slip faulting associated the southern Sierran foothills east of the San Joaquin Valley,strike- with the San Andreas fault system. Just to the east lies the CRSB slip,reverse and normal faulting are observed from focal mechanisms boundary zone. (Wong and Savage, 1983). These mechanisms also exhibit an approximate north-south maximum principal stress and east-west The analysis of microearthquakes was the basis for postulating the minimum principal stress. existence of seismogenic blind thrust and reverse faults beneath active folds along the CRSB boundary zone (Wong et al., 1988; Wong, The focal mechanism for the 1985 Willows earthquake indicates that 1990).Petroleum geologists and geophysicists,however,have known east-west compressive stresses appear to extend into the interior of the for many years that the Dunnigan Hills is a major southeast-plunging Sacramento Valley. Unruh (1990)suggests that crustal shortening anticline flanked on its eastern side by a southwest-dipping reverse due to east-west compressive stresses began less than 1 m.y.ago as fault. Unruh and Moores (1992) have recently published seismic indicated by folding and thrusting of the 3.4 to 1.0 m.y.old Tehama reflection and refraction data illustrating this structure. Formation: In comparison,two focal mechanisms for earthquakes near the town of Madera in the interior of the San Joaquin Valley The level of seismicity within the boundary zone has been low at least exhibit strike-slip and reverse faulting in response to a north-south since 1970. Earthquakes have been distributed,relatively diffusely maximum principal stress(Wong and Savage, 1983). Although the with some clusteringof events in both space and time(such sequences in situ stress dam is sparse in this region of California,Zoback and are called earthquake swarms)particularly near the town of Williams, Zoback(1989)defined an approximate boundary along the axis of the 13 Great Valley (and Sacramento Valley) separating the San Andreas along the western edge of the Sacramento Valley: U.S. compressional stress province on the west and the Cordilleran exten- Geological Survey Open-File Report 86-370, 11 p. sional province to the east including the Sierran foothills(Figure 5). Eaton, J.P., 1990, The May 2, 1983 Coalinga earthquake and its Of particular tectonic interest is the nature of this stress boundary. It aftershocks: A detailed study of the hypocenter distribution is likely that such a boundary is transitional although characterizing and of the focal mechanisms of the larger aftershocks: in J. its exact nature will certainly require much more in situ stress data. Rymer and W.L. Ellsworth, eds., Mechanics of the May 2, 1983 Coalinga earthquake: U.S.Geological Survey Profes- sional Paper 1487,p. 113-170. SUMMARY Ellsworth,W.L.,Lindh,W.H.,Prescott,W.H.,and Herd,D.G., 1981, The 1906 San Francisco earthquake and the seismic cycle:in The historical and contemporary seismicity,especially microearth- D.W.Simpson andP.G.Richards.eds.,Earthquake PreLtion: quake activity observed since 1970,indicate that active deformation An International Review,American Geophysical Monograph, along blind thrust and reverse faults beneath associated folds is Maurice Ewing Series No.4,p. 126-140. occurring along the CRSB boundary zone in the western Sacramento Harlan-Miller-Tait Consultants,1984,Supplemental fault evaluation Valley in response to approximate east-west tectonic compressive of the Cottonwood Creek Project:unpublished report prepared stresses. The portion of the boundary zone in the southwestern valley for U.S.Army Corps of Engineers,43 p. appears to be particularly active as evidenced by the occurrence of the Harwood,D.S.and Helley,E.J.,1987,Late Cenozoic tectonism of the 1892 earthquakes. Specifically,the Dunnigan Hills is an area char- Sacramento Valley, California: U.S. Geological Survey acterized by microearthquake activity which may be associated with Professional Paper 1359,46 p. underlying seismogenic blind thrust and/or reverse faults. Lahr, K.M., Lahr,J.C., Lindh, A.G.. Bufe,C.G., and Lester, F.W., 1976,The August 1976 Oroville earthquakes: Bulletin of the In the interior of the Sacramento Valley, the Willows and Coming Seismological Society of America,v.66,p. 1085-1099. faults are reverse faults that appear to be active. Within the Sierran Langston,C.A.and Butler,R., 1976,Focal mechanism of theAugust foothills,segments of the Foothills fault system such as the Cleveland 1, 1975 Oroville earthquake: Bulletin of the Seismological Hills fault, source of the 1975 Oroville earthquake, appear to be Society of America,v.66,p. 1111-1120. undergoing reactivation in the contemporary extensional(or possibly Lomnitz, C. and Bolt, B.A., 1967, Evidence of crustal structure in strike-slip)tectonic stress field.The possibly active Chico monocline California from the Chase 5 explosion and the Chico earth- fault also appears to have associated seismicity due to strike-slip quake of May 24,1966: Bulletin of the Seismological Society deformation. Other similarly-trending unmapped faults within the of America,v.57,p. 1093-1114. foothills may also be seismogenic and,hence,presently active. Marks, S.M. and Lindh. A.G., 1978, Regional seismicity of the Sierran foothills in the vicinity of Oroville,California: Bul- In summary,despite the relative absence of strong surficial geologic letin of the Seismological Society of America,v.68,p. 1103- evidence for active faulting in and adjacent to the Sacramento Valley, 1115. observations based on the historical and contemporary seismicity McNally,K.C.,Simila,G.W.and Von Dollen,F.J., 1978. Microe- attest to at least a moderate level of crustal deformation. This is not arthquake activity adjacent to the Rocklin pluton near A uburn, surprising given that the Sacramento Valley lies between the actively California: Bulletin of the Seismological Society of America, deforming Pacific and North American plate boundary and the v.68,p.239-243. actively extending Basin and Range Province. Morrison,P.W.,Stump,B.W.,and Uhrhammer,R.,1976,The Oroville earthquake sequence of August 1975: Bulletin of the Seis- mological Society of America,v.66,p. 1065-1084. ACKNOWLEDGMENTS Namson,J.S.and Davis,T.L.,1988,Seismically active fold and thrust belt in the San Joaquin Valley,central California: Geological My appreciation to Vic Cherven for his invitation to this symposium- Society of America Bulletin,v. 100,p.257-273. Thanks to Doug Wright, Sue Penn, Fumiko Goss, and Andrea Real, C.R., Toppozada, T.R., and Parke, D.L., 1978, Earthquake Schwartz for their assistance in the preparation of this paper. The catalog of California,January 1, 1900-December 31, 1974: paper benefited greatly from critical reviews by Jeff Unruh and Vic California Division of MinesandGeology Special Publication Chevren. Financial support was provided by the Professional De- 52,39 p. velopment Program of Woodward-Clyde Consultants. Stein, R.S. and King,G.C.P., 1984, Seismic potential revealed by surface folding: 1983 Coalinga,California,earthquake: Sci- ence,v.224,p.869-872. REFERENCES Toppozada, T.R. and Morrison,P.W., 1982, Earthquakes and lake levels at Oroville,California: California Geology,v. 35, p. Bennett,J.H., 1987, Vacaville-Winters earthquake...1892: Califor- 115-118. nia Geology,v.40,p.75-83. Toppozada,T.R.,Real C.R.,and Parke,D.L., 1981, Preparation of Clark. L.D., 1960, Foothill fault system, western Sierra Nevada, isoseismal maps and summaries of reported effects for pre- California:Geological Society of America,v.71,p.483-496. 1900 California earthquakes: California Division of Mines Dale,D.C., 1977,California earthquakes of April 19-29, 1892: in and Geology Open-File Report 81-11, 181 p. Short Contributions to California Geology,California Divi- Unruh,J.R., 1990,Statigraphy and late-Cenozoic deformation in the sion of Mines and Geology Special Report 129,p.9-21. Oroville area, east-central Sacramento Valley, California: Dickinson,W.R.and Seely,D.R.,1979,Structure of forearc regions: Ph.D.Thesis,University of California at Davis,272 p. American Association of Petroleum Geologists Bulletin, v. Unruh,J.R., Ramirez, V.R.,Phipps, S.P. and Moores, E.M., 1991, 63,p.2-31. Tectonic wedging beneath fore-arc basins: Ancient and Eaton, J.P., 1986, Tectonic environment of the 1892 Vacaville/ modern examples from California and the Lesser Antilles: Winters earthquake,and the potential for large earthquakes GSA Today,v. 1,p. 185-190. 14 Unruh,J.R.and Moores,E.M..1992.Quaternary blind thrusting in the southwestern Sacramento Valley, California: Tectonics (in press). Walter, S.R.. 1986, Intermediate-focus earthquakes associated with Gorda plate subduction in northern California: Bulletin of the Seismological Society of America,v 76,p. 583-588. Wentworth,C.M. and Zoback. M.D., 1989,The style of Late Ceno- zoic deformation at the eastern front of the California Coast Ranges: Tectonics,v. 8. p. 237-246. W'onz,LG., 1990.Seismotectonics of the Coast Ranges in the vicinity of Lake Berryessa, nor-them California: Bulletin of the Seismological Society of America,v.80,p.935-950. Wong,I.G.and Biggar.N., 1989,Seismicity of eastem Contra Costa County,San Francisco Bay region,California: Bulletin of the Seismological Society of America,v.79,p. 1270-1278. Wong, I.G.and Ely,R.W., 1983,Historical seismicity and tectonics of the Coast Ranges-Sierran block boundary: Implications to the 1983 Coalinga,California earthquakes: in 1.Bennett and R.Sherbume,eds.,The 1983 Coalinga.California Earthquakes. Cal ifomia Division of Mines and Geology Special Publication 66,p. 89-104. Wong, I.G.. Ely, R.W. and Kollmann, A., 1988, Contemporary seismicity and tectonics of the northern and central Coast Ranges-Sierran block boundary zone,California: Journal of Geophysical Research,v.93,p.7813-7833. Wong,I.G.and Savage.W.U..1983,Deep intraplate seismicity in the western Sierra Nevada. central California: Bulletin of the Seismological Society of America,v.73,p.797-812. Woodward-Clyde Consultants, 1977,Earthquake evaluation studies of the Auburn Darn area: Surface faulting potential: unpub- lished report prepared for U.S. Bureau of Reclamation,v.2, 135p. Zoback. M.L. and Zoback, M.D., 1989,Tectonic stress field of the Continental United States: in L.C.Pakiser and W.D.Mooney, eds.,Geophysical Framework of the Continental United S tates. Geological Society of America Memoir 172,p.523-539. Zoback. M.D., Zoback, M.L., Mount, V.S., Suppe,J., Eaton, J.P.. Healy, 1.H., Oppenheimer,D., Reasenberg, P., Jones, L., Raleigh, C.B., Wong, I.G., Scotti, O. and Wentworth, C., 1987,New evidence on the state of stress of the San Andreas fault system: Science,v.238,p. 1105-1111. JOURNAL OF GEOPHYSICAL RESEARCH.VOL.93, NO. B7. PAGES 7813-7833,JULY 10. 1988 - Contemporary Seismicity and Tectonics of the Northern and Central Coast Ranges—Sierran Block Boundary Zone, California IVAN G. WONG, RICHARD W. ELY, AND AURIEL C. KOLLytANN Woodward-Clyde Consultants. Oakland, California Beneath the physiographic boundary between the Coast Ranges and the Great Valley, a fundamental tectonic boundary exists between the Coast Ranges province and the Sierran block. Recent geophysical studies have revealed the Coast Ranges-Sierran block(CRSB)boundary zone to be a complex region of compressional tectonics wherein wedges of comparatively ductile Franciscan Complex of the Coast Ranges have overridden the competent Sierran block basement and peeled up the overlying sediments of the Great Valley Sequence. The boundary zone was the probable source of the two 1892 Winters earthquakes(M 6-7)and the 1983 Coalinga earthquake(.�fL 6.7). We evaluated the seismicity within the northern and central portions of the zone from Red Bluff south to San Luis reservoir for the period 1969-1985. Seismicity was spatially diffuse: most of the earthquakes occurred in somewhat isolated concentrations within the upper crust. A low activity level. temporal clustering, and episodic behavior also characterized this seismicity.The largest earthquake in the boundary zone was a :NL 4.2 event near Madison: 20 events exceeded :fL 3.0. In a few cases the seismogenic sources appear to be eastward dipping. high-angle reverse faults, although some right-slip. north trending faults also appear to be seismogenic. In comparison,the Coalinga and 1985 Kettleman Hills main shocks in the southern portion of the zone appeared to involve gently westward dipping thrust faults, although aftershocks also oc- curred on moderately to steeply dipping reverse faults. Fault plane solutions along the zone exhibited a tectonic stress field of NE to E trending compression,normal to the boundary.Such compression may be a consequence of one or a combination of several influences:(1) the westward movement of the Sierran block against the Coast Ranges due to late Cenozoic crustal extension in the Great Basin. (2) slightly convergent motion between the Pacific and North American plates,and(3)fault-normal crustal compres- sion due to the low shear strength of the San Andreas fault.The tectonic deformation manifested by the Coalinga and recent moderate-sized earthquakes in the southern zone appears to be occurring along the full extent of the boundary albeit at varying rates for different segments. Thus the potential for large earthquakes may exist along segments of the CRSB boundary and the 1892 main shock may represent a characteristic earthquake for that portion of the zone. INTRODUCTION Coast Ranges and Great Valley (henceforth in this paper The seismicity of California has been dominated to a large called the Coast Ranges-Sierran block boundary zone) coin- extent by earthquakes occurring along the San Andreas fault tides with a fundamental tectonic boundary that separates system and the Sierra Nevada Frontal fault system(Figures 1 regions of differing crustal structure [Wentworth et al., 19831. and 2). Both seismic zones coincide with fundamental tectonic possibly representing a fault zone (or suture zone) [Holbrook boundaries. Although the historical record suggests that mod- and Mooney, 1987](Figure 1). erate to large earthquakes have occurred throughout much of This paper describes an evaluation of the seismicity along the state.the occurrence of local magnitude(ML)5 and greater the northern and central portions of the Coast Ranges-Sierran events elsewhere in California always seems to be surprising. block (CRSB) boundary zone during the period 1969 through The May 2. 1983, ML 6.7 Coalinga earthquake that oc- September 1985. The objectives of the study were to define(1 1) curred in the vicinity of the physiographic boundary between the spatial and temporal characteristics of the earthquakes,(2) the Coast Ranges and Great Valley was one such event. In the style and orientation of faulting, (3) the possible associ- retrospect, two other surprising earthquakes occurred in 1892 ation with specific geologic structures, and (4) the nature of along the Coast Ranges-Great Valley boundary near the the tectonic stresses. Further understanding of the boundary towns of Vacaville and Winters with estimated magnitudes zone will hopefully allow earthquakes such as the 1892 Win- greater than ML 6 [Dale, 1977; Toppo:ada et al., 1981; Wong, ters and the 1983 Coalinga events to be put into a geologic 1984]. It has been suggested that a 600-km-long zone of coin- and tectonic context upon which more realistic seismic hazard plex faulting beneath the Coast Ranges-Great Valley bound- assessments can be made for this large region of California. ary probably has been and is a source for moderate to large In order to meet the objectives of this study we analyzed earthquakes [It'vny and Ely, 1983]. Although based upon and interpreted the available seismographic data recorded by only a few fault plane solutions, this boundary zone may also the U.S. Geological Survey(USGS). the University of Califor- represent a change in tectonic style, exhibited by the oc- nia at Berkeley (UCB), the California Department of Water currence of reverse or thrust faulting,and a possibly change in Resources (DWR), the U.S. Bureau of Reclamation (USBR). the nature and orientation of the tectonic stress field. The and Woodward-Clyde Consultants (WCC) for selected earth- existence of such a tectonic/seismic zone should not be sur- quakes from 1969 through September 1985. This study period prising because the physiographic boundary between the was selected because network coverage was poor during prior years. However. the majority of events studied were recorded after 1975 because of the expansion and improvements in the Copyright 1988 by the American Geophysical Union. USGS central California network. The USGS hypocentral Paper number 7B5034. data files contained 570 earthquakes for this study region 0148-0227,'88/00713-5034505.00 during this time period. A set of 217 earthquakes. generally 7813 7814 WONG ET AL.:COAST RANGES—SIERRAN BLOCK BOUNDARY ZONE CMT ALTURAS \SMASTA D / " s ' MODOC— } KLAMATH�j' CASCADE EUREKA'S BLOCK PROVINCE � rur[ fur( 1 i -� \LASSEN (� 4REDOINa, \iAK trrt sLSANVILLE� REN Willows 1 �•I IJP� (�" UWAN 7. t jQ SACRAMENTO rONOPAN SAN 0 • .`f• .Na.o O 0 �% V y r.:•: 4 'n % + Patterson 'e`"' B - ► `� \ .00 \% ,O �f �` � �,p�"'•lf t] //� o INDEPENDENCE 0 7.A O'� FRESNO c+ V/A MONTEREr �j1� J,,•••­ �r ,06 Coalinga KERN A CANrON A_ I� FAULT ! ; = SUN-NACIMIENTO FAULT ZONE �id WHITEwou \f" :Cliff♦ f SANTA OSAN �C WERSFI LD `� MOJAVE MARIA oesro '�" '+�° BLOCK BLOCK ° TEHACHAPI BLACK SANTA NT J'+@� SAN GABRI EL rAULT ANTASARSARA °+I BLOCK G[ AV TRANSVERSE RANGES PRO*4 QAriciLEs T MAUSU-COAST fAULf EXPLANATION ---BOUNDARY OF PROVINCE OR BLOCK 0 200 km (DASHED WHERE APPROXIMATE) � Fig. I. Tectonic provinces and crustal blocks of California[from Wong and Ely, 1983]. .til, >_ 1.5. that were recorded on at least 15 stations were assure inclusion of any significant geologic features that may selected for analysis(Figure 3). influence the seismicity in the region,given the uncertainties in The study region extends from Red Bluff south to San Luis the location of the boundary (due to lack of surface ex- reservoir and includes the area approximately 20 km on either pression) and its role in the contemporary seismotectonics of side of the CRSB boundary, as we have defined it (Figures I the region. The southern boundary of the study region was and 2).The east-west extent of the study region was defined to chosen because detailed studies have already been conducted WONG ET AL: COAST RANGES-SIERRAN BLOCK BOUNDARY ZONE 7815 , L4 n i � i ' a la'I t \iII II 4 YA 41" i 1 •=•tom• •• •ii. <'..•e f 1. « Study + Area ,,\- s -- 'q&7\yo i " Iii. . ' .i �:•. - 71 31 17 3. 01 3 3 o 0• . . t 32 700 KM j, s ° 31 ' 31 ° � ' 126 ° 125 ° 124 ° 1230 122° 121 ° 120 ° 119° 118 ° 117 ° ll,G ° 115 i4 Fig. 2. Seismicity of California.1980--1984,ML 2 1.5[from Hill and Eaton, 1987]. in the vicinity of San Luis reservoir by the USBR [LaForge distributed stations was relatively small because of the low and Lee. 1982] and are currently being performed by the level of activity the generally small magnitudes, and the com- USGS in the southern portion of the boundary zone as part of paratively weak seismographic coverage of this portion of Cal- the investigations into the 1983 Coalinga and 1985 Kettleman ifornia (weak azimuthal coverage and no close-in stations). Hills sequences[Eaton. 1985a,b•c]. Because of the generally diffuse distribution of epicenters,only Two principal factors were considered in the analysis ap- in a few areas were earthquakes sufficiently concentrated to proach taken in this study: (1) Variations in crustal velocity allow evaluation of their seismogenic sources. Thus to date. structure were expected because of the 400-km length of the the ability to characterize accurately the seismicity of the study area and the presence of a major structural boundary CRSB boundary zone has been limited. that separates regions of differing and complex velocity struc- COAST RANGES—SIERRAN BLOCK BOuNMARY ture. Conflicts also exist in the available information on the velocity structure based upon seismic refraction,seismic reflec- The thick sediments underlying the Great Valley of Califor- tion, and earthquake travel time data. (2) The number of nia (Figure 1) conceal a fundamental tectonic boundary that earthquakes that were recorded by a sufficient number of well- juxtaposes the rigid crystalline basement of the Sierran block 7816 WONG ET AL:COAST RANGES—SIERRAN BLOCK BOUNDARY ZONE 1240 1230 1220 1210 1200 41° A __ A• 40° O O® 8 0. O C D D' 39° EXPLANATION O E A Red Bluff A' Orland 8 C9) B Willows C . Maxwell F D Williams ® D' Dunnigan Hills MAGNITUDE SYMBOL E Madison F Birds Landing S.0 TO e.0- O O G G Antioch 380 H Tracy I Patterson 4.0 TO S.0- O 00® H J Gustine 3.0 TO 4.0- O 1 2.0 TO 3.0• O 1.0 TO 2.9- 0 J LESS THAN 1.0 100 KILOMETERS .0 Fig. 3. Seismicity of the study region. 1969 through September 1985.and boundaries of the subregions.Epicenters from USGS hypoeentral data files. against the comparatively ductile Franciscan Complex base- Holbrook and Mooney [1987] suggest that a steeply dipping ment of the Coast Ranges. The precise nature of this juncture fault or suture zone separates these two provinces. We believe remains one of the great engimas of California geology, al- it is more accurate to refer to this boundary as the Coast though recent seismic refraction and seismic reflection studies Ranges-Sierran block boundary rather than the Coast have produced the first images of the basement boundary zone Ranges-Great Valley boundary, which is a physiographic fea- [Wentivorth et al., 1983, 1984; Holbrook and Mooney, 1987; ture that is the expression of a deep-seated complex tectonic Colburn and Afooney, 1986]. Because of the dissimilarity in boundary. crustal structure between the Coast Ranges and Great Valley, The Sierran block is a large region of competent Paleozoic WONG ET AL: COAST RANGES-SIERRAN BLOCK BOUNDARY ZONE 781 J and Mesozoic metamorphic and plutonic rocks that have been point the Quaternary hinge at the junction between the Coast little deformed in the Cenozoic relative to surrounding regions Ranges and Great Valley homoclinal domains is the most [e.g., Bateman and Wahrhaftig, 1966; Huber, 1981]. The Sierra significant feature, since it approximately coincides with the Nevada forms the eastern portion of the block, whereas the eastern extent of the region of elevated seismicity that western portion underlies the homoclinal sedimentary deposits characterizes the Coast Ranges[Wong and Ely, 1983]. of the Great Valley and extends at least as far west as the western side of the valley [Cady, 1975; Ely and Packer, 1978. HISTORICAL SEISMICITY Harwood and Hellev, 1982]. Late Cenozoic tectonism within The historical earthquake record for California dates back the Sierran block has consisted for the most part of westward only to the late 1700s and for the region along the CRSB tilting about a hinge line that approximates the eastern boundary probably only to the mid-1800s. During the prein- margin of the Great Valley [Christensen, 1966; Bateman and strumental portion of the historical record (prior to about Wahrhaftig, 1966], accompanied by westward translation of 1930),only six earthquakes and one earthquake sequence were the entire block relative to the Great Basin and the Coast observed in the vicinity of the boundary zone [Wong and Ely, Ranges [Wright. 1976]. Pervasive Late Cenozoic compression 1983]. These include(locations and magnitudes generally esti- in the Coast Ranges [Page, 1981] appears to be due, at least mated by Toppozada et al. [1981]) (1) ,NL 5.8 earthquake on in part, to the space problem created by crustal extension in July 15, 1866,with a possible epicenter in the Diablo Range or the Great Basin and the westward translation of the Sierran west side of the northern San Joaquin Valley,(2) :kfL 6.0 earth- block. quake on April 10. 1881, which had a maximum intensity of Sparse borehole data coupled with aeromagnetic and grav- MM VI in Modesto; although this is the largest earthquake ity observations indicate that the crystalline basement beneath previously believed to have occurred in the northern San Joa- the Great Valley is mostly dense mane and ultramafic rock quin Valley, it may have occurred farther west, possibly along that resembles oceanic crust [Cady, 1975]. Seismic refraction the CRSB boundary zone [Wong and Ely, 1983],(3) MM VIII lines oriented parallel to the axis of the San Joaquin Valley event on May 19, 1889, near Antioch with an estimated AL of indicate that the velocity structure of the basement rocks is 6.0; surface faulting along the Antioch fault may have accom- complex,implying the presence of major structures and a vari- panied this event, (4) two large events (ML > 6) on April 19 ety of rock types including metamorphic rock like that found and 21 and an ML 5.5 aftershock on April 30, 1892 near in the Sierra Nevada foothills [Colburn and Mooney, 1986; Vacaville and Winters, (5) !SSM VII to VIII earthquake on Holbrook and Mooney, 1987]. May 18, 1902- east of Vacaville near Elmira, (6) MM VII on Overlying the mafic western part of the Sierran block is an July 24, 1903, near Willows,and(7) MM VI on July 30, 1904, eastward tapering wedge of homoclinal southwest dipping near Winters. sediments of Late Cretaceous to Quaternary age [Bartow, The most significant earthquakes known to have occurred 1985]. Broadly warped and locally faulted Upper Cretaceous in the CRSB boundary zone were the 1892 sequence. The two and Cenozoic deposits extend west of the Sacramento and San largest earthquakes were felt over a widespread area(exceed- Joaquin rivers to where they are upturned into a steeply ing 200,000 km2) that extended into Nevada [Dale, 1977]. northeast dipping homocline along the eastern flank of the One death, numerous casualties, and extensive damage (in- Coast Ranges. These two opposing homoclinal domains meet eluding several collapsed buildings) were sustained in the in a synclinal hinge (a concave upward dip inflection) that is sparsely populated meizoseismal area, which encompassed most prominent in the concealed Cretaceous deposits along Dixon and Vacaville in Solano County, and Winters in Yolo the eastern margin of the Coast Ranges. County [Dale, 1977]. Although severe ground effects, includ- A synclinal hinge is also present in the Pliocene-Quaternary ing ground cracking and landslides,were observed in the mei- sediments nearly along the entire length of the western side of zoseismal area, it is not clear whether surface faulting oc- the Great Valley [Lettis, 1985]; we have previously identified curred. The maximum reported intensities were MM IX for this feature as the near-surface expression of the western both events. Dale [1977] assigned magnitudes of AML 6.7 and boundary of competent basement rocks of the Sierran block 7.0 based on the observed maximum intensities for the April [Ely and Packer, 1978; Wong and Ely, 1983].The Quaternary 19 and 21 events, respectively. Toppozada et al. [1981] esti- hinge is located well to the east of the trough in the Great mated ML 6.4 and 6.2,respectively,based on the size of the felt Valley sequence, lying just west of the Sacramento and San areas. Wong [1984] estimated ML 61-7 and 6}--62, respec- Joaquin rivers.At greater depths,recent seismic studies[Went- tively. based on a comparison of felt areas with the 1983 Coa- worth er al., 1983, 19841 indicate that eastward tapering linga earthquake. wedges) of Franciscan Complex have driven eastward both Three significant earthquakes have occurred in the CRSB within the Great Valley sequence and along its basal contact boundary zone since the establishment of adequate seismo- with Sierran block basement. Based on structural analysis, graphic coverage of the region; all have recently occurred in Namson and Davis [1988] suggest that the Coalinga and Kett- the southern portion of the zone. These are the 1982 ML 5.4 leman Hills anticlines,sites of the 1983 and 1985 earthquakes, New Idria earthquake [Scofield et al., 1985], the 1983 ML 6.7 respectively,are the result of fault-bend folding above a thrust Coalinga earthquake [Eaton. 1985x, c], and the 1985 z%,fL 5.5 fault(s) that step up from a detachment within the Franciscan North Kettleman Hills earthquake[Eaton, 1985b]. Complex to the detachment at the base of the Great Valley sequence. Furthermore, they propose as a result that a fold DATA AND METHODS OF ANALYSIS and thrust belt is actively developing along the west side of the In the data set of 217 earthquakes, 26 events (generally San Joaquin Valley. larger than ML 2.7) were selected as calibration (or master) Competent basement of the Sierran block consequently may events (Table 1). These earthquakes were well recorded extend beneath the Franciscan Complex wedge(s) perhaps as throughout northern and central California, possessed good far as the easternmost strike-slip fault of the San Andreas azimuthal seismographic coverage (gap generally less than system (e.g.. the Antioch fault). From a seismotectonic stand- 901, and were well distributed throughout the length of the J 00 OO TABLE 1. Significant Earthquakes Origin Time, Sub- Calibra- Event Date UT Latitude Longitude Depth No. Gap DMIN rms SE" SEZ M,."sOs M,."`'B Location Intensity Reports' region tion FPS 1 March 13, 1969 0323:23.3 38'NO4.78' 121"W49.49' 9.0 35 189 23.3 0.24 1.2 2.8 3.5t 3.5 Antioch MM V Antioch and G Pittsburg 2 Aug.23, 1972 2203:35.5 37'NS5.98' 121'W46.53' 7.5 26 90 11.7 0.33 0.9 1.1 3.3 3.0 Antioch MM III Antioch G X 3 Aug. 14, 1974 1016:51.0 37'N16.90' 120'W56.86' 2.Ot 66 81 24.4 0.19 0.4 1.0 2.8 3.3 Gustine 1 X X 4 May 25, 1975 0615:49.1 37'NO9.50' 120'W59.87' 2.0t 59 70 12.2 0.19 0.3 1.1 3.0 2.8 San Luis J X X Reservoir 5 June 9, 1975 1207:31.1 3TN58.85' 121'W41.10' 10.1 57 140 6.6 0.19 0.4 0.7 2.9 3.1 Antioch G :X X o S 6 June 18, 1975 1750:20.4 37'N10.07' 120'W59.77' 2.0t 58 67 13.1 0.20 0.3 1.0 3.8t 4.1 San Luis J X X Reservoir 7 Sept.5, 1976 0315:09.7 37'N35.34' 121*W26.95' 4.2 62 93 16.6 0.20 0.3 0.6 3.4t 3.5 Vernalis Felt Tracy H X X 8 Oct.6, 1976 2054:20.8 37'N34.75' 121'W26.75' 2.Ot 77 73 17.0 0.23 0.3 1.2 3.1 3.3 Vernalis Felt Tracy,Stockton II X X r 9 Nov. 15, 1976 0558:54.5 38N12.28' 121'WS4.56' 24.3 53 40 11.0 0.24 0.5 0.7 2.7 2.9 Birds Landing F X X n 10 May 4, 1977 1943:34.1 38'NO9.35' 121'W56.45' 19.1 71 32 12.3 0.24 0.4 0.5 3.1 3.2 Birds Landing Fell Fairfield, Vacaville F X X 11 May 5, 1977 2240:32.0 38'N10.28' 121'W56.89' 20.5 114 37 13.1 0.23 0.3 0.4 3.2 3.3 Birds Landing Felt Antioch, Pittsburg F X X 12 June 4, 1977 2057:08.1 38'N10.20' 121'WS6.67' 20.5 106 53 12.7 0.22 0.3 0.4 3.6 3.8 Birds Landing Fell Napa, Milpitas, F X X Walnut Creek o 13 Oct. 13, 1977 1610:28.2 3TN28.27' 121*W03.96' 18.4 77 69 37.6 0.23 0.5 0.7 3.6t 3.7 Patterson MM III Modesto I X X 14 Sept. 8, 1978 1659:47.9 38'N37.17' 121'W55.43' 13.Ot 127 46 24.1 0.29 0.3 0.6 4.2t 4.2 Madison Minor damage Winters E X X 15 Sept. 10, 1979 1411:16.2 3TN17.57' 121*W07.28' 2.Ot 47 87 30.6 0.26 0.5 1.6 2.9 2.8 Gustine J X X 16 Nov. 24, 1980 1910:49.3 39°NI2.45' 122'W14.67' 13.Ot 45 67 27.4 0.36 0.8 1.5 3.6 3.6 Maxwell Felt Willows C X X 17 Dec. 12, 1980 1313:21.5 39°N12.75' 122'W14.96' 17.Ot 47 85 27.5 0.27 0.5 0.9 3.3 3.4 Maxwell Felt Clear Lake, C X X z Williams,Colusa 18 July 25, 1981 0212.19.6 38'N49.76' 121'W58.66' 6.4 17 73 9.1 0.21 0.9 1.3 2.2 - Dunnigan D' X R 19 Sept.3, 1982 1858:24.6 39°N36.53' 122'W31.98' 2.Ot 55 52 16.4 0.24 0.5 1.6 4.2 4.0 Stony Gorge MM 111 Princeton, A' X >S Ilamilton City 20 Dec. 4, 1982 1511:25.6 39°NO9.14' 122'W14.05' 10.0 49 79 21.9 0.24 0.6 0.8 3.0 - Williams Event on December 2, C X X z 1982, 16112 M,. 3.0 d (part of sequence)felt °0c Lake Berryessa, Clear "kc21 Feb. 19, 1983 1213:42.4 39N47.26' 122'W26.93' I I.IIt 33 87 23.7 0.29 0.7 1.5 3.1 - Black Butte I A' X X Lake 22 lune 5, 1983 1122:44.1 38'NO2.07' 121'W54.30' 19.7 94 31 8.4 0.21 0.3 0.4 3.6 3.5 Pittsburg MM V Pittsburg, F X Martinez 23 April 18, 1985 1629:50.1 39'N05.95' 122'W03.50' 13.Ot 66 75 23.2 0.24 0.5 0.8 3.8 3.6 SE of Williams MM V Arbuckle D X X 24 May 21, 1985 0121:17.5 39°NO6.49' 122W113.41' 14.Ot 37 70 24.0 0.15 0-4 0.7 3.3 3.2 SE of Williams 1) X X 25 May 21, 1985 1034:46.9 39°NO6.1I' 122'WO3.46' 8.Ot 42 79 23.4 0.20 0.4 0.7 3.0 2.7 SE of Williams D X X 26 Sept. 8, 1985 0513:31.7 39°N29.51' 122'WO5.30' 22-9 45 95 31.9 0.22 0.5 09 2.9 2.8 Willows It X X *As reported by UCB. tFixed depth. $Wiwwl-Anderson determined magnitudes. WONG ET AL:COAST RA_NGE3-SIEA1kAN BLOCK BOLNDARY ZONE 7819 TABLE 2. P Wave Velocity Models for California USGS Central California Coalinga[Eaton. 1985a] UCB Coast Range UCB Sierra Nevada Velocity, km/s Depth.' km Velocity, km/s Depth.' km Velocity, km/s Depth.' km Velocity, kms Depth.' km 4.0 0.0 2.5 0.0 t 0.0 5.9 3.5 4.3 LS 6.8 15.0 4.7 3.5 7.70 25.0 8.05 25.0 5.6 7.0 5.8 9.0 7.85 45.0 6.3 14.0 6.6 15.5 7.95 28.0 'Depths to top of layers. tVo = 5.28 + 0.075 Z. $Vo = 6.00 + 0.024 Z. study region. Based on the locations of the calibration events pendent of any errors in the calibration event locations (see and concentrations of events, the study region was divided following discussion). into 12 subregions that were approximately 45 km by 45 km The trial depth used in the location was 5.0 km. Elevation (Figure 3). This is slightly larger than is desirable for relocat- corrections were calculated assuming a velocity equal to the ing events using station corrections due to the variations in velocity of the top layer of the appropriate crustal model. ray paths to a given station. It was assumed that the correc. Shear wave velocities were calculated from the P wave veloci- tions would be due principally to local geologic effects un- ties assuming the standard PIS wave ratio of 1.78. derlying the stations and that the ray path contribution to the corrections would not be significantly different throughout eVelocity Models each subregion. The calibration events were relocated employing the com- In the USGS's routine determination of hypocenters a gen- puter program HYPOELLIPSE [Lahr, 1984]. Arrival times eralized velocity modell for central California is employed that from stations within 200 km were used in the locations of the was developed by Wesson et al. [1973] (Table 2). Station cor- calibration events; arrivals beyond 100 km were downweigh- rection were later developed and are now used in the routine ted due to their generally emergent character. A distance location. This procedure provides an epicentral accuracy of cutoff of 100 km or less for northern and central California probably 1-2 km within the densest portion of the USGS would probably have yielded more precise locations because network along the San Andreas fault system in coastal Cali- direct and midcrustal refracted arrivals from the closer sta- fornia[Ellsworth er al., 1982].That level of accuracy,however. tions would have had a greater weight in the determination of degrades rapidly for regions outside coastal California. The focal depths. A greater cutoff distance was required, however, study region is located just to the east of the main Ion- to gain the needed northern and eastern azimuthal station centration of USGS stations. Station to the east of the study coverage provided by the Sierran foothill station beyond 100 region have operated in the Sierran foothills since 1975: these km. Improved epicentral accuracy may thus may been traded provide valuable azimuthal station coverage. This advantage off for some loss in focal depth resolution (see further dis- is offset however, by the complex velocity structure beneath cussion). S arrivals were used wherever available; however, the CRSB boundary zone and the drastic changes in both since the calibration earthquakes were relatively large events, geologic and velocity structure from west to east. For instance. S waves were generally not readable because of record satu- in routine locations of earthquakes within the study region by ration. the USGS,large arrival time residuals of approximately -0.5 The remaining 191 events in the data set were relocated to -1.0 s have been observed for the foothill stations. To using average station correction (only one station used in compensate for these large residuals and rather than employ a these relocations was beyond 100 km) calculated from the single generalized velocity model for the region, we believe appropriate calibration events in each subregion. In some that the use of two models approximating the P wave velocity cases, only one calibration event was available per subregion; structure west and east of the study region is more realistic. in others, as many as four were available. An examination of Thus a Coast Ranges model was assigned to all seismographic station corrections shows a good agreement within subregions stations located west of the CRSB boundary, and a Great for multiple calibration events. Weighted averages were re- Valley-Sierran foothills model was assigned to all stations east quired for some station corrections when the residuals were of the boundary. Both models (Table 3) are based on the not internally consistent from event to event due to poor ar- results of seismic refraction studies performed by the USGS in rivals. The 191 events were relocated based on the arrival the northern San Joaquin Valley [Whitman et al., 1985]. The times provided by the USGS.No additional arrival times were Great Valley-Sierran foothills model contains no near-surface. added nor were times reread. For a few of the subregional low-velocity layer because the ray paths between earthquakes data sets the azimuthal gap was undesirably large because of along the boundary zone to the foothills stations do not pen- the lack of arrival time from stations in the Sierran foothills. etrate the Great Valley sedimentary deposits. Average depths We believe that the use of station corrections partially com- to velocity boundaries were also required in the Great Valley- pensates for the incomplete station coverage.The relative epi- Sierran foothills model because of the east dipping nature of central and focal depth uncertainties of the relocated earth- these boundaries (due to thickening of the crust eastward to quakes are estimated to be ±1 and ±3 km,respectively.inde- the roots of the Sierra Nevada). 7820 WONG ET AL:COAST RANGES-SIERRAN BLOCK BOUNDARY ZONE TABLE 3. Velocity Models Used in Relocations trot,the use of two models resulted in focal depths of 20 km or ,Model I Model 2 more, probably too deep for typical coastal California earth- Coast Ranges Great Valley-Sierran Foothills quakes and deeper than those computed using the central California model. Some of the close-in stations recording these Velocity. km/s Depth.' kmVelocity, km/s Depth,' km five earthquakes exhibited (1) large negative residuals (greater 5.0 than approximately 0.50 s) despite the relatively small overall 5.6 00.0 6.1 0.0 rms errors and(2) inconsistent first motions in their respective 2.0 6.6 7.0 6.7 11.0 fault plane solutions because the arrivals were treated as up- 21.0 7.3 18.0 going (direct) rays. Several earthquakes (Table 1) were reloca- 7.9 28.0 7.9 27.0 ted by fixing the events at shallower depths (a change of 2-8 km; Figure 4),which minimized the large negative residuals at 'Depth to top of layer. the closest stations and made inconsistent first motions consis- tent by treating them as downgoing rays (head waves). This always resulted in a larger rms error (Figure 4); however, the Verification of Velocity Models and Hypocentra! Uncertainty depths were more consistent with typical California earth- To test the validity of the two-velocity model approach, the quakes (generally upper crustal in origin, less than 15 km). 12 calibration events(events 12-14, 16, 17,and 19 to 25;Table Given the aforementioned conditions, the uncertainty of the 1) that had the best station coverage were relocated employing focal depths of the calibration earthquakes is judged to be 4 several different velocity models, including two velocity- km. The standard error of the focal depths of 24 of the 26 gradient-over-half-space models used by UCB (Table 2). The calibration events is less than 4.0 km(Table 1). average rms errors of the residuals of these relocations are Because of the uncertainties in focal depths of the calibra- shown in Table 4. Of the UCB models the Coast Ranges tion events the epicentral locations and their rms errors were model was assigned to all stations west of the CRSB bound- examined as a function of depth (Figure 5). For a well- ary, and the Sierra Nevada model was assigned to all stations constrained location (having a station within a focal depth east of the boundary. For the last models cited in Table 4 a distance of the epicenter), the epicentral change was less than delay of -0.66 s was assigned to all foothills stations based on 1-2 km for the range of typical upper crustal depths(e.g., May an average residual observed during routine USGS locations 5. 1977 on Figure 5). The epicenters of most of the calibration (1. Eaton. USGS, personal communication, 1986). The two- earthquakes that were not recorded by any close-in stations model approach appears to best fit the arrival times compared moved less than 1 km as the focal depth was varied (October to the other velocity models(Figure 4). A decrease in rms was 6, 1976, on Figure 5). In a very few cases where the depth also observed for the majority of the 191 relocated events appears to be poorly constrained by close-in stations, the when the two-model approach was used rather than the change in epicentral location was as much as 3 km(September USGS central California model with station corrections. 8, 1978, on Figure 5). In general, however, the epicentral lo- One particular issue of concern in the computation of hypo- cations for most of the calibration earthquakes including centers within the boundary zone were accurate focal depths. those with fixed depths were well constrained by the strong Focal depth control for earthquakes in the study region has azimuthal station coverage,and so their epicentral uncertainty always been poor due to the absence of close-in seismographic is estimated to be less than 2 km. The epicentral standard stations on the east side of the Coast Ranges and within the error for 25 of the 26 calibration events is less than 1.0 km Great Valley. Only six of the 26 calibration earthquakes were (Table 1). located with the closest station within one focal depth of the We recognized that the two velocity models used in this epicentral location. The nearest station for half of the events study were only first-order approximations to the actual ve- was at least 20 km away. The computed focal depths were locity structure across and along the CRSB boundary. Vari- shallow, less than 2 km, for several of the calibration events. ations in velocity structure,especially depths to the midcrustal For these events, the rms minima extended from 0.0 to 2.0 km and upper mantle boundaries,have been observed by J. Eaton (e.g.. September 3, 1982, on Figure 4); therefore the events (USGS. personal communication, 1986) based on earthquake were fixed at a more realistic 2.0-km depth for their final travel times. These variations probably exist along the length locations(Table 4 of the CRSB boundary. Based on travel times,the depth to the For five earthquakes with especially poor focal depth con- 6.7 km/s layer may be too shallow and the Moho too deep in TABLE 4. Average rms for Selected Calibration Events Average Rms, Model Source (s) Coast Ranges and Great Valley Whitman et al.[1985] 0.209 (this study) Central California Wesson et al. [1973] 0.229 Velocity gradients' UCB 0.340 Western Great Valley Whitman et al.[1985] 0.244 Coalinga Eaton[1985a] 0.262 Coast Ranges and Great Valley . . . 0.243 with -0.66-s delay for foothill stations *Without station corrections. to L0 LO 1.0 1.0 1.0 4 Jun 77 13 Oct 77 8 Sep 78 24 Nov 80 12 Dec 80 3 Sep 82 r It - FL FL FL FL FL FL r 0 0 10 20 30 40 50 0 0 10 20 30 40 50 00 10 20 30 40 50 00 10 20 30 40 50 00 10 20 30 40 60 00 10 20 30 40 50 On DEPTH Ikml DEPTH Ikml DEPTH Ilkm) DEPTH Mail DEPTH Ikml DEPTH(km) 70 Z n 10 1.0 1.0 1.0 TO 1.0 4 Dec 82 19 Feb 83 5 Jun 83 18 Apr 85 21 May 85 21 May 85 0121 GMT 1034 GMT ;^ c - - R x a W K \ 1 I \ t O FL FL � FL FL - f FL FL 00 10 20 30 40 ti0 00 10 20 30 40 60 �0 10 20 30 40 50 O 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 DEPTH(kml DEPTH(kml DEPTH(kml DEPTH(kml DEPTH(kml DEPTH ikml ——Central California model with station delays —Two models(this study) F L Finel IOCd Ii Un I:ig. 4. l llc ruts error verstis focal dclllh for lClcl tcd calibraiion events. 00 7822 WONG ET AL: COAST RANGES-SIERRAN BLOCK BOUNDARY ZONE 11" 5 May 77 6.0 8 0 10.0 12-1 FL 14,0 10 39' 30,0 24,0 22.0 20.5 0.1 2A 8 Sep 78 2 za-0 26.0 eon 18.016A w 10' o 28 0 304 H 26.0 ~ 24.0 J DMIN -13 km 38 224 FL-Final location 0 t km 20.0 9 Films Minimum 58' 57' 56' 55' 18.0 160 LONGITUDE (Minutes) 14.0 c 13.0 FL(Fixed) 36' w37, 12.0 30.0 6 Oct 76 0 104 28.0 24.0 22.0 26.0 ~ 14.0 12.0 Q J 8D 20.0 10.0 6.0 7 35' 18.0 16.0 8.0 3.0 6.0 4.0 36 c 24 FL 24 RMS Minimum (Fixed) I W 10 0.1 O 0.1 F- DMIN-24 km 0 1 km Q F L•Final location J 34' 35' 57' 56' 55' 54' LONGITUDE (Minutes) DMIN-17 km F L-Final location 0 1 km i 33' 30' 29' 28' 27' 26' LONGITUDE (Minutes) Fig. 5. Epicentral variation versus focal depths. the Coast Ranges model north of San Francisco Bay(Table 3). nuclear explosions(M.>_ 5.6) were played out from magnetic The 7.2 km/s layer is also not apparent. Beneath the Great tape and examined to verify the polarities for the USGS, Valley-Sierran foothills, travel times suggest that the upper- DWR, and USBR stations for the period 1969-1983. In con- most crustal layer should have a velocity of 6.3 km/s north of trast to the velocity models used in the hypocentral locations Sacramento with no 7.3 km/s layer. Despite these possible a single model approximating the velocity structure within the variations, the USGS seismic refraction results for the north- study region was used in the fault plane solutions, since the ern San Joaquin Valley are considered to be the best available local velocity structure should have the greatest impact on information and a rational basis for constructing generalized takeoff angles. Also, unlike the plane layer models used in the models for the large portion of California that was being con- locations, a linear velocity gradient over a uniform half-space sidered. was employed to overcome the difficulties encountered when Thicknesses and velocities of individual layers were varied an earthquake is located near a boundary in the velocity by 51/u, and the same set of 12 calibration events were located model.The gradient-velocity model used was an adaptation of to evaluate the effect of uncertainties in the two velocity the UCB Coast Ranges model, modified by increasing the models used in the relocation. In terms of the effects of these upper mantle velocity to 7.9 km/s and the depth to the upper variations and hence possible uncertainties in the velocity mantle to 27 km. Preliminary fault plane solutions based on a models, it appears that the effect is small.an average increase plane layer model differed very little with the solutions deter- in rms error of only 0.01 s and hypocentral changes of gener- mined using the gradient model except in the cases where the ally less than 1 km. earthquake occurred near a velocity boundary. Fault Plane Solutions Magnitudes and Intensities Fault plane solutions of the calibration events were deter- Local magnitudes cited in this study were determined by the mined employing HYPOELLIPSE. Extensive rereading of USGS generally based on a coda duration formula developed first motions were performed. Several large Nevada Test Site for central California[Lee et al., 1972]. Table 1 contains mag- WONG ET AL.:COAST RANGES-SIERRAN BLOCK BOUNDARY ZONE 7823 nitudes as determined by the USGS and UCB for the calibra- calibration event suggests the possibility that the Willows fault tion events. In general, the coda duration magnitudes agree may extend into the lower crust. well with the UCB Wood-Anderson amplitude-based mag- Examples of bursts of seismicity occurred northwest.south- nitudes.The average difference in magnitudes is only 0.17 unit. west,and southeast of Williams in November-December 1980, MM intensities cited in Table 1 are as reported by UCB. December 1982, and April-September 1985, respectively (Figure 10). The highest level of activity observed within the RESULTS boundary zone during this period was the 1985 swarm of at The relocation of 217 earthquakes within the northern and least 71 earthquakes (31 relocated). Fault plane solutions sug- central portions of the CRSB boundary zone revealed a pat- gest reverse or thrust faulting on north to northwest trending tern of seismicity that was spatially diffuse with many earth- faults for all three sequences(Figures 7 and 10).The relocated quakes occurring in isolated concentrations (Figure 6). The hypocenters are consistent,however. with near-vertical reverse level of activity was relatively low,especially in comparison to faults as being the sources of these events (Figure 6). Activity more active areas to the west along the San Andreas fault concentrated beneath the Dunnigan Hills appears to trend system. These concentrations of events occurred generally as parallel to and between the two faults that underlie the flanks bursts of activity with several sequences exhibiting swarmlike of the hills(Figures 6 and 11). None of these earthquakes were behavior. In only a few cases did earthquakes appear to be large enough to produce a well-constrained single-event fault associated with known faults.The majority of the earthquakes plane solution, and attempts at a composite solution resulted occurred within the upper crust at focal depths less than 15 in an indeterminable double-couple solution. km (Figure 6). Fault plane solutions exhibited predominantly The largest event during the study period within the bound- reverse;thrust and strike-slip faulting(Figures 7-9). ary zone was the September 8, 1978, ML 4.2 Madison earth- The only earthquake relocated in the northernmost portion quake. which occurred northeast of the probable source area of the study region was an event (ML 2.9) located west of Red of the 1892 Winters earthquakes(Figure I1). Three foreshocks Bluff at the unusual but well-determined depth of 39 km.This and three aftershocks occurring within a 5-day period, and event occurred in the vicinity of seven recently observed,inter- five other events that occurred in the ensuing 2 years were mediate depth (52-87 km) earthquakes that appear to define relocated. A fault plane solution of the Madison main shock the eastward dipping Wadati-Benioff zone of the Gorda plate exhibits reverse or thrust faulting on a nearly north trending [Walter, 1986]. A fault plane solution for this earthquake(S. fault(Figure 7),although a cross-sectional view of the seismic- Walter, USGS, written communication, 1986)exhibits normal ity between the depths of 10 and 15 km reveals a rather diffuse faulting on north trending planes (Figure 10), which may re- distribution with no obvious hypocentral alignments. The flect deformation within the subducted plate. The earthquake Madison activity is located 2-5 km east of two faults that does not appear to be associated with upper crustal defor- extend southward from both sides of Capay Valley into the mation along the CRSB boundary zone, and although it 10-' Sacramento Valley (Figure 11). Harwood and Helley [1987] cafes epicentrally along the ENE trending Red Bluff fault, its suggest that the Capay Valley faults may have been active depth and the fault plane solution preclude any association. within the past 3.4 m.y. Also in the northern portion of the boundary zone, several One of the hopes of this study was that the results would events were located in the vicinity of the Willows and Pas- provide some insight on the source of the 1892 earthquakes. kenta faults (Figure 10). A fault plane solution for an event Unfortunately, no microearthquakes of sufficient size to be near Black Butte Lake exhibits reverse or thrust faulting on evaluated occurred in the proposed epicentral area between nodal planes trending N70°E (Figure % although no north- Winters and Vacaville(Figure 11). Microearthquake monitor- east trending faults are known in the area. A fault plane solu- ing by the University of California, Davis(UCD), recorded no tion for a earthquake near Stony Gorge reservoir west of the earthquakes in the proposed epicentral area from January study region (USGS location was within study region)exhib- 1986 through January 1987 (M. Merriam. UCD, personal ited oblique strike-slip faulting in response to north-northeast communication, 1987). A possible explanation is that the compression and west-northwest extension similar to other causative fault may be in a stage of quiescence analogous to coastal California earthquakes(Figures 7 and 1% the seismically quiescent period on the San Andreas fault after Activity near the Willows fault and possibly northward the 1906 San Francisco earthquake, as proposed by Ellsworth along the Corning fault was also observed by Marks and et al.[1981] in their seismic cycle model. Lindh [1978], who concluded the seismicity near the town of Farther south in the Sacramento Delta, seismicity during Willows (including earthquakes approaching My 5 in 1903 the study period was dominated by events spatially associated and 1968) has been a persistent feature in this century. Har- with the Vaca fault which is probably part of the San Andreas wood and Helley [1982] describe the Willows fault in this system of strike-slip faults rather than the CRSB boundary locale as a reverse fault,east-side up and dipping 74° or steep- (Figure 11). Fault plane solutions of the four largest earth- er to the east (Figure 10). A fault plane solution for the cali- quakes northwest of Birds Landing(Figures 8 and 11) exhib- bration event located 2 km west of the Willows fault exhibits ited right-slip faulting on a north-northwest trending fault reverse faulting on nodal planes parallel to the fault (Figure consistent with the Vaca fault. A fault plane solution for a ML 10). Despite the uncertainties in the epicentral location and 3.6 earthquake that occurred in 1983 west of Antioch near fault plane solution of the calibration event,these data suggest Pittsburg (at the unusual depth of 19 km) also exhibits right- that the Willows fault may be the source of the event and is slip faulting on a north-northwest trending fault but with a thus seismogenic. The north-south trend of small events minor component of oblique slip(Figures 8 and 11). This fault (,11L < 2.0) shown in Figure 3 seems to support this sugges- plane solution is similar to the solution for the 1965 }11L 4.9 tion. This is fairly consistent with the north trending nodal Antioch earthquake which may have occurred on the Antioch plane of the fault plane solution(Figure 7).Three of the earth- fault [lNcErilly and Casaday, 19671. The 1983 event occurred quakes near Willows were also relatively deep for typical 3 km west of a possible southward extension of the Vaca fault coastal California events. 18-23 km. The 23-km depth of the (beneath the delta) and 5 km west of a possible northward MAXWELL-REGION C BIRDS LANDING - REGION F J 00 Ts' P �. ' M..w.0 70 + IS' + -lo + *Z _1p +++ to, WIIIIEmE + C + + n 44+ -30 +� _70 ..1- + lo' F �R+fir F i e.'a L.OaI E -3 -� o ,0 70 70 C DISTANCE DCVI DISTANCE IKYI n' 70' Is, to, E' + o .. >� z ES' w' .En WILLIAMS - REGION D IE• D D' TRACY-REGION o SS ^ D. 7o' WiDisim + • I Eo H H' + Y + + +. X C +f * T. V -10 ++ 1- _10 LiN'mor. + N ArOuckU40 - + * x m + o -70 70 7s ++ 'L SS' DISTANCE IKYI to, S' 177° EE' o I0 70 w .0 50 9t 00* H Am[ L..riT DnrANCE MW C DUNNIGAN HILLS - REGION D' 76' .5 a" is' 70 75 70' p K N O t D.. 0 D'. D•.• GUSTINE - REGION J 56 + t J + + g -10 + Is _2 + + s 10 ID It .5 R W -10 Loabu,°t E 1prto 0 10 70 30 40 ' DISTANCE IKYI f�.' JO ° 0 10 10 711 40 W b' 70' Is .0' s' 111° s5' w 70' 15' 10' 5' 177° DISIANC!IKN1. Fig 6. Ily1)oCCrll Crs 111 sCICCICII sDhregio Ds,8181),BOCI Cross-sCC11o11A)Mews.Arrows INCIIC8IC IUC8I,OIIs OI Cross sCCllolls. WONG ET AL:COAST RANGES-SIERRAN BLACK BOUNDARY ZONE HZS N N N244W N Q N a6°E 7o°s ► ° ° NfiO•t � sa°Nw ♦ e 0 N70°t • •►. . o • 70°t•w • �° i200M j •0 T♦ T p • • •o— • •o • 8� - ° e 19 Fab 83 8 Seo 82 8 Seo 85 Black Butte Lake Stony Gorge +Viiiows N N N04oN N tat°0s•sN•e°••S• • oe 8o 0° Nae•s•_ _•�` `� 1 `° a o90o ° 10 ^ 0°E N64°w ° Po e o o P % ° • oe ° P o T •• ° ♦ ( 04, T • • •`#T A ° clove • • • 24 Nov 80 120 80 4 Ole 82 Maxwell Maxwell Williams NNoel N Non" 12el 120w 7e•! f241 N Nls°e 7a°! 711°e • o o e° 0 0 0 • • ;fi 8 e • • aHge • • °08 0 0 0 0 0 o ° • o °o1) T 00. T e e T ° ►00 • OP °o •P • 0 9t° e o o 4101 % • ° e o • 00 18 Apr 85 21 May 85.0121 GMT 21 May 85,1034 GMT SE of WilliamsSE of William SE of William Nts°w M ta•w ao'e 0 om o • • OW 0 ° �e • T ° o . • e s • • ° &a • .8.0 8 Seo 78 Madison Fig. 7. Fault plane solutions of the boundary zone in the northern Sacramento Valley. Solutions are equal-area projections of the lower hemisphere. Solid dots are compressions,and open circles are dilatations. Plus and minus signs are compressions and dilatations of leu certainty.respectively. P and T represent compression and tension axes. respec- tively. • s • 7828 WONG ET AL:COAST RA.YGES-SLERRAN BLACK BOUNDARY ZONE / � I MAGNtTUptc3 Rod a c krN ore ufF ; 0.0+ f0Z0 0 O' + 1.0+ 'N' I \ o �- i 2.0+ ..am + 4.0+ A 4 /Cornu/ i o lokm 1 i � 1 n z 1\ 1 q 2 y Fyr tu• `' c 1 ` - i \`\ oft.fltJ rl a 1 Z to \M oy sr•q_; _ 9 1 \ + � •wows c IPA t \fads Pok ( • It `.L\ i� w..w t `, • k� � Q wssrns It QL16- It �1 Cl—tw ,aw. r,•r a,s ,am r,••.' Fig 10. Relocated epicenters and fault plane solutions of the boundary zone in the northern Sacramento Valley. Heavy annotated faults are from California Division of Mines and Geology [1982]. Shaded faults are from Harwood and Helley[1982].The lightly dashed line with large dots represents the boundaries of the study region.Note that some of the earthquakes that were within the study region.based on the original USGS locations,have moved outside after relocation. The heavy line (dashed where inferred) is the CRSB boundary as we have defined it. The dashed-dotted line is the approximate western extent of Quaternary alluvial deposits that topographically separate the Coast Ranges and the Great Valley. The arrows on the fault plane solutions approximate the direction of the horizontal projections of the P axis (inward directed)and T axis(outward directed).Shaded areas are compressional quadrants.The fault plane solution for the 40-km-deep earthquake near Red Bluff was determined by S.Walter(USGS.written communication, 1986). WONG E-r AL:COAST RANGES—SIERRAS BLOCK BOUNDARY ZONE t••or 1 MAGNITUDES I Lo \ \ a- + 0.0+ 4 i 2.0+ 1 Z,"' 3.0+ • I ``\`-k:\• ` \ �\`; •• \\ \ Davis • \f j ` ,.�` `� �wim•.s � \ \ • \04 `•``,�,�:-�; 1892?' � .� sano,na • ail i is �`•. i' ' � ��\ .:1 �►` \ �''• \ ' •eta Lanaine �. � � 4lo / S a JS. ��`�• '1 AMieeh �xTt rpiv X774 tlw• 7�•7a' n°". Fig. 11. Relocated epicenters and fault plane solutions of the boundary zone in the southern Sacramento Valley.Also shown is the su8gested source area of the 1892 Winters earthquakes [Wong, 1984]. Symbol explanation is the same as Figure 10. thrust faulting have occurred infrequently in northern and Ranges [Gawthrop, 1978; Eaton, 1984]. In retrospect, these central California north of the Transverse Ranges. Recent observations are consistent with the geologic observations of studies focused on areas away from the major strike-slip faults more than half a century that northwest trending mountain of the San Andreas system are revealing,however,seismogenic ranges and basins in the southern Coast Ranges indicate reverse faulting to a much greater extent. Fault plane solu- severe compression and crustal shortening in a direction tions near the Verona fault in the Livermore area show a normal to the trend of the San Andreas fault [Crouch et al., progressive spatial change from strike-slip to thrust faulting in 1984]. Thus, although moderate-sized earthquakes have oc- response to a north-northeast oriented compressive stress field curred on reverse or thrust faults,such as the 1982 New Idria [Ellsworth and Marks, 1980]. Thrust and oblique-thrust fault earthquake, it was the occurrence of the large 1983 Coalinga plane solutions with P axes that vary over a 90•azimuth have earthquake that suddenly focused attention on this infrequent- been observed for small earthquakes in the Santa Cruz Moun- ly observed mode of seismic deformation in northern and cen- tains [Olson et al, 1980]. Reverse or thrust fault plane solu- tral California. tions have also been observed for small-magnitude earth- Minster and Jordan[1978] proposed that zones of thrusting quakes occurring along the coastal region west of the San along both flanks of the southern Coast Ranges may be due to Andreas fault from Monterey south to the western Transverse a component of convergent movement caused by misalign- 7830 WONG ET AL:COAST RANGES-SIERRAN BLOCK BouNOARY ZONE :moo- MAGNITUDES \ sroekton + 0.0+ -�1• -- �' i•�l ` + `.�;f`Y{``` gyp? �- 1.0+41, n \ 3.0+ Trwy4.0+ 1 ' N ` Liver"we-,,,44 i/.T •,� 0 t0 km �` vatterson .. + + + see Jose, ` <10 Q.-\r -�,`,\\ '.,`�`•-.ate. �\ .y t -1 •'Y 1 Los Buw ,>oo- t7Pm' t7t�y' t7tgC t7PtS' gtapp xP�S' Fig. 12 Relocated epicenters and fault plane solutions of the boundary zone in the northern San Joaquin Valley. Symbol explanation is the same as Figure 10. ment of the San Andreas fault with respect to the inferred slip strength along the San Andreas which relieves shear stresses direction along the transform between the Pacific and North parallel to the fault and thereby reorients the far-field stresses American plates. This convergence results in 4-13 mm/yr of and the slightly convergent relative plate motion. compression normal to and across the San Andreas fault Either model might explain the active folding and re- system [Minster and Jordan. 1984]. Gawthrop [1978] and verse/thrust faulting in the compressed sediments above the Eaton [1985c] have both evoked this model to explain the advancing tectonic wedge of Wentworth er al. [1983, 1984] occurrence of seismicity due to reverse and thrust faulting on along the boundary between the Coast Ranges and the south- both sides of the Coast Ranges. Recently,Zoback er al. [1987] ern San Joaquin Valley. However, folding and faulting also have proposed that northeast directed horizontal compression appear to be proceeding along the western margins of the characterizes the state of stress along the San Andreas fault Sacramento Valley albeit at a possibly lower rate than in the system in central California in contrast to the long-standing San Joaquin Valley. In the northern Sacramento Valley, re- view of north-south compression which was consistent with verse and/or thrust faulting appears to be occurring on north- frictional faulting theory. They suggest that this fault-normal erly trending faults that are parallel to the CRSB boundary crustal compression is the result of the extremely low shear and not parallel to the northwest trending San Andreas fault WONG ET AL.:COAST RANGES-SIERRAN BLOCK BOUNDARY ZONE 7831 .. as in the southern San Joaquin Valley (Figures 10-12). Also the northern and central CRSB boundary zone, such as the the direction of maximum compression in the Sacramento 1892 earthquakes, seismic slip on a thrust fault may well be Valley based on the fault plane solutions appears to trend the source. Thus both reverse and thrust faults probably play more east-west than a fault normal northeast direction. Har- an active role in the seismic deformation within and along the wood and Helley [1987] also infer an east-west compressive CRSB boundary zone. stress regime for the Sacramento Valley based on the orienta- To a possibly lesser degree, strike-slip faulting on northerly tion and kinematic patterns of structural features formed in trending faults also appears to be involved in such defor- the last 2.5 m.y. These observations seem equally if not more mation,based on the fault plane solutions.The question arises compatible with our model that the boundary zone reflects the as to what factors dictate the style of faulting along the kinematic interaction between two crustal blocks, the Coast boundary zone: local variations in the stress field, the control Ranges and the Sierran block [Wong and Ely, 1983]. Hill by preexisting structure, or both. Of the 24 fault plane solu- [1982] previously suggested that the Late Cenozoic defor- tions determined, 13 exhibited predominantly strike-slip fault- mation in the California-Nevada region reflects the response ing(Figures 7-9). Many of these solutions, however, occurred of a cluster of fault-bounded crustal blocks to a regional stress on the western margins of the study area and were probably field generated by the interaction between the Pacific and not associated with the CRSB boundary zone but instead may North American plates. Local deviations from regional kin- reflect the influence of the San Andreas fault system and its ematic trends will also tend to develop at the boundaries be- associated shear stress field (Figures 10 and 12). Based on the tween regimes as deformation progresses[Hill, 1982]. predominance of reverse/thrust fault plane solutions in the We further suggest that this maximum compression normal vicinity of the CRSB boundary, we suggest that reverse and to the boundary zone may be caused by a westward move- thrust faulting is the dominant mode of seismic deformation ment of the Sierran block against the Coast Ranges(as postu- and that strike-slip faulting probably only occurs under cer- lated by Wright [1976]) as a consequence of Late Cenozoic tain localized stress conditions. crustal extension in the Great Basin to the east [Wong and In terms of individual structures within the CRSB boundary Ely, 1983]. Hill [1982] also observed that his block model zone the Midland fault, possibly the only observed fault that required the westward displacement of the Sierran block with may form part of the boundary,does not appear to be seismi- respect to the stable interior of the North American plate. tally active,at least during this time period. This is consistent Alternatively, the compression along the boundary zone may with the geologic data that suggest no offsets of deposits in fact be the result of the combined influences of block inter- younger than early Oligocene [Harwood and Helley, 1982]. action along the boundary, plate convergence, and fault- The Capay Valley and Dunnigan Hills faults, the latter of normal compression. which may be similar to the faults beneath the anticlines in the Based on the fault plane solutions determined in this study, southern San Joaquin Valley,may be seismogenic based upon the direction of maximum compression appears to trend the observed seismicity. Faults not associated with the bound- northeast to east in the vicinity of the CRSB boundary(Fig- ary that appear to be seismogenic include the Tesla-Ortigalita ures 10-12).Thus a stress field for much of the CRSB bound- fault system(previously observed by LaForge and Lee[1982]), ary zone (and possibly portions of coastal California as pro- possibly the Willows fault, and the Vaca fault. For the Wil- posed by Zoback et al. [1987])may take the form lows and Vaca faults the occurrence of associated(?) earth- quakes down to lower crustal depths has important geologic SNE-E 1 SNw-N= >SV 3 and seismic hazard implications. These deep events and their or possibly possible correlation with the near-surface expression of these faults suggest the existence of faults extending down to 20-25 SNE-EI > SNw-N2 -SVS km. Future studies will need to address (1) the rheological where SL,S2,and S3 are the maximum,intermediate and mini- nature of the crust at such depths in these locales, which may mum principal stresses. An interchange between S' and S3 differ from other coastal California areas where only upper allows both reverse and strike-slip faulting crustal faulting typically occurs, and(2) the possibility of seis- Consistent with the geologic evidence, the CRSB boundary orogenic faults much deeper in extent than is normally ob- does not appear to consist of a single fault but rather a com- served for coastal California and the potential impact on as- plex zone of faulting based on the variations in the fault plane sumptions of rupture areas for seismic hazard assessments. solutions. The initial controversy surrounding the nature of faulting that was the source of the 1983 Coalinga main shock. CONCLUSIONS high-angle reverse or low-angle thrust [Eaton, 1985c; Stein, The region enclosing the northern and antral CRSB 1985], underscores the uncertainty concerning the nature of boundary zone has exhibited a relatively low level of seismici- the CRSB boundary. Although the spatial pattern of the Coa- ty compared to the recently active southern portion centered linga aftershocks suggests a very complex zone of seismogenic on Coalinga. at least since adequate seismographic coverage faulting, Eaton [1985c] proposed that the main shock, as well began around 1969. This is consistent with the lower rate of as the 1985 North Kettleman Hills earthquake [Eaton, deformation expressed in.the less well developed folding along 1985b], occurred on a shallow westward dipping thrust fault the western margins of the Sacramento Valley [Wentworth In response to movement along the thrust fault, Eaton and Zoback, 1986]. Although the boundary zone has been the [1985b] further suggests that slip is induced on reverse faults possible source of moderate to large earthquakes in the past. of both northeast and southwest dips in the overlying plate. only since the recent 1983 Coalinga earthquake has scientific The hypocentral distribution and fault plane solutions of the attention focused on the seismicity of this region. Based on earthquake concentrations near Williams and Maxwell sug- refined earthquake locations and fault plane solutions. seis- gest that at least in these cases, eastward dipping high-angle micity within the CRSB boundary zone north of San Luis reverse faults are the seismogenic sources. For large events in reservoir appears to be unevenly distributed, with most of the 7832 WONG Er AL: COAST RANGES-SIERRAN BLOCK BOUNDARY ZONE activity occurring in somewhat isolated concentrations. Tem- California Division of;dines and Geology, Geologic .Naps Of Califor. poral clustering and episodic behavior also characterize this nia.Olaf P.Jenkins ed.,scale I:250.000,Sacramento, 1982. Christensen. M. N., Late Cenozoic crustal movements in the Sierra seismicity. The largest earthquake in the zone during the Nevada of California.Geol.Soc.Am.Bull.,77, 161-182, 1966. period 1969 to September 1985 was a ML 4.2 event near Colburn. R. H.. and W. D. Mooney, Two-dimensional velocity struc- '10adison. Approximately only 20-.earthquakes have exceeded ture along the synclinal axis of the Great Valley, California, Bull. ML 3.0. In a few cases,seismogenic sources along the northern Seismol.Soc.Am.,76, 1305-1322, 1986. and central CRSB boundary zone appear to be generally east- Corbett. E. 1.,and T. M. Hearn,The depth of the seismic zone in the Transverse Ranges of southern California (abstract), Earthquake ward dipping, hi¢h-angle reverse faults, although some right- Notes.55.23. 1984. slip. north trending vertical faults also appear to be seismically Crouch.1. K.,S. B. Bachman,and J.T. Shay, Post-Miocene compres- active. By comparison, several studies suggest that both re- sional tectonics along the central California margin, in Tectonics verse faults and a westward, gently dipping thrust fault (that and Sedimentation Along the California margin, edited by J. K. may be a major tectonic element in the eastward wedging of Crouch and S. B. Bachman, pp. 37-54, Pacific Section, Society of Economic Paleontologists and Mineralogists, Bakersfield, Calif., Franciscan rocks) are involved in seismic deformation in the 1984 southern portion of the boundary zone [Eaton, 1985a, b, c; Dale. D. C.. California earthquakes of April 19-29, 1892, Spec. Rep. Wentworth et al., 1983; Namson and Davis, 1988].The seismic- Calif.Div. Mines Geol.,129,9-21. 1977. ity to date in the northern and central portions has been too Eaton. I. P., Focal mechanisms of near-shore earthquakes between Santa Barbara and Monterey,California, U.S. Geol.Surv.Open File low level and possibly too small in magnitude to allow the Rep..84-477. 1984. delineation of active thrust faulting. Eaton, J. P., The May 2. 1983 Coalinga earthquake and its after- The tectonic stress field along the CRSB boundary zone shocks: A detailed study of the hypocenter distribution and of the exhibits northeast to east trending maximum compressive focal mechanisms of the larger aftershocks, Mechanics of the May 1983 Coalinga earthquake, edited by 1. Rymer and W. L. stress normal to the CRSB boundary and a generally vertical Ellsworth.U.S.Geol.Surv.Open File Rep.,85-44,132-201,1985a. minimum compressive stress. A model in which the tectonic Eaton.J. P.,The North Kettleman Hills earthquake of August 4, 1985 compression in the region is due to westward movement of the and its first week of aftershocks-A preliminary report, adminis- Sierran block against the Coast Ranges as a consequence of trative report U.S.Geol.Surv,Menlo Park,Calif. 1985b. Late Cenozoic crustal extension in the Great Basin is favored Eaton, J. P., The regional seismic background of the May 2, 1983 Coalinga earthquake. Mechanics of the May 2. 1983 Coalinga here, although plate convergence may also contribute to this Earthquake, edited by J. Rymer and W. L. Ellsworth, U.S. Geol. observed tectonic compression. Surv.Open File Rep.,85-44,44-60, 1985c. Based on this study, it appears that the tectonic defor- Ellsworth, W. L., and S. M. Marks, Seismicity of the Livermore mational processes observed in the Coalinga earthquake (i.e, Valley, California region 1969-1979, U.S. Geol. Surv. Open File thrust and reverse faulting), and several recent moderate-sized Rep_80-515,41 pp., 1980. Ellsworth. W. L., A.G. Lindh, W. H. Prescott, and D. G. Herd, The earthquakes in the southern portion of the zone are operative 1906 San Francisco earthquake and the seismic cycle, in Earth- albeit at varying rates along the full extent of the CRSB quake Prediction: An International Review,Maurice Ewing Ser.,vol. boundary north to Willows and possibly farther. Thus in 4,edited by D.W.Simpson and P.G.Richards,pp. 126-140,AGU, terms of seismic hazard along the 600-km-long boundary zone Washington,D.C.,1981. the potential for large earthquakes such as the ML, 6.7 Coa- Ellsworth,W. L..J.A.Olson,L.N.Shijo,and S. M. Marks.Seismici- ty and active faults in the eastern San Francisco Bay region, Pro- linga earthquake may exist along segments,if not much of the ceedings. Conference on Earthquake Hazards in the Eastern San boundary: that is, the largest 1892 Winters earthquake may Francisco Bay Area,edited by E.W. Hart,S. E. Hirschfield,and S. represent a characteristic earthquake for that portion of the S.Schulz Spec.Publ.Calif.Div.Mines Geol.,62,83-92, 1982. zone. Further seismological and geophysical studies will be Ely. R. W., and D. R. Packer,The boundaries of the Sierrian block. California(abstractl,Earthquake Notes,49,85-86,1978. required to characterize the nature of the CRSB boundary and FoilowilL F. E.,and 1. M. Mills, Locations and focal mechanisms of to assess fully its seismogenic potentiaL recent earthquakes and tectonics of Livermore Valley, California, Bull.Seismol.Soc.Am,72,821-840, 1982. Gawthrop, W. H., Seismicity and tectonics of the central California Acknowledgments. This research was supported by the USGS Na- coastal region. San Gregorio-Hosgri Fault Zone,California,edited tional Earthquake Hazards Reduction Program under contract 14- by E. A. Silver and W. R. Nor-mark, Spec. Rep. Calif. Div. Mines 08-0001-22019. We would like to acknowledge the cooperation and Geol-137,45-56, 1978. assistance provided to us by many scientists of the USGS.in particu- Harwood. D.S..and E.J. Helley, Preliminary structure contour map lar, Chris Stephens. Steve Walter, Shirley Marks, Bill Ellsworth, of the Sacramento Valley,California showing major late Cenozoic Jeannie Taylor,Bob Colburn,Al Walter,and Walter Mooney.Special structural features and depth to basement. U.S. Geol. Surv. Open thanks to Rick Lester,who was always willing to answer our numer- File Rep.,82-737,19 pp.,1982. ous questions. Our gratitude to Jerry Eaton for his guidance and Harwood. D. S.. and E. J. Helley, Late Cenozoic tectonism of the insights throughout the course of this study.Our appreciation also to Sacramento Valley,California, U.S. Geol.Surv. Prof. Pap., 1359,46 Bob Uhrhammer, UCB, and Roland LaForge, USBR, for providing pp,. 1987• data and to Doug Wright for his assistance. Graphics are by David Hill, D. P.,Contemporary block tectonics:California and Nevada,J. Hering and word processing by Joyce Woods. This report greatly Geophvs.Res..87,5433-5450, 1982. benefited from critical reviews by Carl Wentworth,Jerry Eaton,Tom Hill. D. P.. and 1. P. Eaton,Seismicity and the seismotectonic fabric Rogers.Norma Biggar,and an anonymous reviewer. of California and western Nevada 1980-1985,National Earthquake Hazards Reduction Program.Summaries of Technical Reports,vol. REFERENCES Holbrook. U.S.Geol.Surv.Open File Rep.,87-374,246-250,1987. Holbrook.W.S.,and W. D. Mooney,The crustal structure of the axis Bartow, J. A- Map showing configuration of the basement surface. of the Great Valley, California from seismic refraction measure- northern San Joaquin Valley, California. U.S. Geol. Surv. Misc. ments. Tectonophysics,140.49-63, 1987. Field Stud.,flap,MF-1430, 1983. Huber. N. K_ Amount and timing of late Cenozoic uplift and tilt of Bateman. P. C_ and C. Wahrhaftig. Geology of the Sierra Nevada, the central Sierra Nevada.California.Evidence from the upper San Bull.Calif.Div.Mines Geol..90, 107-172, 1966. Joaquin River Basin.U.S.Geol.Surv.Prof.Pap.,1197,28 pp.. 1981. Cady.J. W., Magnetic and gravity anomalies in the Great Valley and LaForge. R.,and W. H. K. Lee. Seismicity and tectonics of the Orti- western Sierra Nevada metamorphic belt. California, Spec. Pap- galita fault and southeast Diablo Range, California. Proceedings. Geol.Soc.Am. 168.56 pp.. 1975. Conference on Earthquake Hazards in the Eastern San Francisco WONG ET AL:COAST RANGES—SIERRAN BLOCX BOUNDARY ZONE 7233 Bay Area.edited by E. W. Hart,S. E. Hirschfield,and S.S.Schulz, plate subduction in northern California. Bull. Seismal. Soc. Am., 76, Spec.Publ.Calif.Diu.;Nines Geol.,61,93-101, 1982. 583-588, 1986. Lahr. J. C., HYPOELLIPSE/VAX. A computer program for deter- Wentworth. C. M.. and M. D. Zoback, An integrated faulting model mining local earthquake hypocentral parameters, magnitude and for the Coalinga earthquakes: A guide to thrust deformation along first motion patterns, U.S. Geol. Suru. Open File Rep., 84-519, 66 the Coast Ranges-Great Valley boundary in central California(ab- pp.. 1984. stract).Eos. Trans.AG.U,67, 1222, 1986. Lee. W. H. K.. R. E. Bennett, and K. L. Meagher, A method of Wentworth, C. M., A. W. Walter, J. A. Bartow, and M. D. Zoback, estimating magnitude of local earthquakes from signal duration. Evidence on the tectonic setting of the 1983 Coalinga earthquakes U.S.Geol.Surv.Open File Rep_ 18 pp., 1972. from deep reflection and refraction profiles across the southeastern Lettis. W. R., Late Cenozoic stratigraphy and structure of the west end of Kettleman Hills,The 1983 Coalinga.California Earthquake, margin of the central San Joaquin Valley, California. Spec. Pap. edited by J. H. Bennett and R. W.Sherburne,Spec. Publ. Calif. Diu. Geral.Soc.Am.,103,97-114, 1985. :Nines Geol.,66, 113-126. 1983. Marks, S. M:. and A. G. Lindh. Regional seismicity of the Sierran Wentworth, C. M., M. C. Blake, Jr., D. L. Jones, A. W. Walter. and foothills in the vicinity of Oroville, California. Bull. Seismol. Soc. M. D. Zoback, Tectonic wedging associated with emplacement of Am..68. 1103-1115, 1978. the Franciscan assemblage,California Coast Ranges,in Franciscan McEvilly, T. V_ and K. B. Casaday, The earthquake sequence of Geology of Northern California,edited by M.C. Blake Jr., pp. 163- September. 1965 near Antioch, California, Bull. Seismol. Soc. Am, 173, Pacific Section,Society of Economic Paleontologists and Min. 57, 113-124. 1967. eralogists,Bakersfield,Calif 1984. Minster, J. B.. and T. H. Jordan Present-day plate motions, J. Geo- Wesson,R.L.,J.C.Roller,and W.H. K. Lee,Time-term analysis and phys.Res.,83.5331-5356, 1978. geologic interpretations of seismic travel time data from the Coast Minster. J. B., and T. H. Jordan, Vector constraints on Quaternary Ranges of central California,Bull.Seismol.Soc. Am.,63, 1447-1471. deformation of the western United States east and west of the San 1973. Andreas fault, in Tectonics and Sedimentation Along the California Whitman, D.,A. W. Walter,and W. D. Mooney,Crustal structure of Alaryin, edited by J. K. Crouch and S. B. Bachman, pp. 1-16, the Great Valley, California, cross profile (abstract), Eos Trans. Pacific Section. Society of Economic Paleontologists and Mineral- AGU,66,973, 1985. ogists.Bakersfield.Calif., 1984. Wong, 1. G.. Reevaluation of the 1892 Winters, California earth- Namson.J. S.,and T. L. Davis.Seismically active fold and thrust belt quakes based upon a comparison with the 1983 Coalinga earth- in the San Joaquin Valley, central California. Geol. Soc. Am. Bull., quake(abstract►,Eos Trans.AGU,65,996-997, 1984. 100.257-273. 1988. Wong, I.G,and R. W. Ely, Historical seismicity and tectonics of the Olson.J. A..A.G. Lindh,and W. L. Ellsworth.Seismicity and crustal Coast Ranges-Sierran block boundary: Implications to the 1983 structure of the Santa Cruz Mountains. Califomia (abstract►, Eos Coalinga, California earthquakes, The 1983 Coalinga, California Trans.AGU.61, 1042, 1980. Earthquake, edited by J. H. Bennett and R. W. Sherburne, Spec. Page. B. M.. The southern Coast Ranges, in The Geotectordc Devel- Publ.Calif.Din.Mines Geol.,66,89-104, 1983. opment of California, Rubey voL 1, edited by W. G. Ernst, pp. Wong, 1. G., and W. U. Savage, Deep intraplate seismicity in the 329-417,Prentice-Hall.Englewood Cliffs.N.J_ 1981. western Sierra Nevada,Central California, Bull. Seismol. Soc. Am., Scofield.C. P., W. H. Bakun, and A.G. Lindh,The 1982 New ldria, 73,797-812,1983. California, earthquake sequence. Mechanics of the May 2, 1983 Wright,L,Late Cenozoic fault patterns and stress fields in the Great Coalinga Earthquake, edited by J. Rymer and W. L, Ellsworth, Basin and westward displacement of the Sierra Nevada block. Ge- U.S.Geol.Suro.Open File Rep,85-44,403-429,1985. ology,4,489-494,1976. Stein,R.S_Evidence for surface folding and subsurface fault slip from Zoback. M. D_et al, New evidence on the state of stress of the San geodetic elevation changes associated with the 1983 Coalinga,Cali- Andreas fault system,Science,138;1105-1111, 1987. fornia earthquake, Mechanics of the May 2, 1983 Coalinga Earth- quake, edited by J. Rymer and W. L- Ellsworth, US. Geol. Suro. R. W. Ely, A. C. Kollmann, and I. G. Wong, Woodward-Clyde Open File Rep_85-44.225-253,1985. Consultants,500 12th Street,Suite 100,Oakland,CA 94607. Toppozada,T. R.,C. R.Real.and D.L.Parke,Preparation of isoseis- mal maps and summaries of reported effects of pre-1900 California earthquakes, Calif. Din. Mines Geol. Open File Rep,81-11, 78 pp, (Received March 27, 1987; 1981. revised March 24, 1988; Walter. S. R.. Intermediate-focus earthquakes associated with Gorda accepted March 10, 1988.) - JOURNAL OF GEOPHYSICAL RESEARCH, VOL. %, NO. B12, PAGES 19,891-19,904, NOVEMBER 10. 1991 Contemporary Seismicity, Active Faulting and Seismic Hazards of the Coast Ranges Between San Francisco Bay and Healdsburg, California IVAN G. WONG Woodward-Clyde Consultants, Oakland. California Contemporary seismicity in the northern California Coast Ranges from San Francisco Bay to the town of Healdsburg and east of the seismically quiescent North Coast segment of the San Andreas fault is generally confined to the intensely deformed Santa Rosa block relative to the adjacent Sebastopol block. Much of this activity is concentrated along the Rodgers Creek.Healdsburg,Bennett Valley, and Maacama faults. A prominent gap in microseismicity exists along much of the 43+ km-long Rodgers Creek fault, although paleoseismological evidence suggests that the fault has generated at least three palecearthquakes of moment magnitude (M..) 7 or greater during the late Holocene (Budding et al.. 1991). Earthquakes in the region are generally confined to upper crustal depths of less than 10-12 km. Right-lateral strike-slip faulting on both northwest and north sinking faults is currently the primary mode of regional crustal deformation based on observed focal mechanisms.although both reverse faulting,especially in the vicinity of the major Quaternary faults, and normal faulting occur within the region. The tectonic stress field in the region is dominated by north-northeast to northeast directed compressive stresses. Although the Rodgers Creek fault may pose the highest known level of seismic hazard in the region in the next few decades, abundant geological evidence and the contemporary seismicity suggest that faults such as the Healdsburg, Bennett Valley.and Maacama faults also pose significant hazards because of their potential to generate Mw 6-7± earthquakes. INTRODUCTION region-specific crustal velocity model (with station delays), and to determine focal mechanisms for all well-recorded The portion of the California Coast Ranges north of San earthquakes. From these analyses and a review of the Francisco Bay to the town of Healdsburg(hereafter referred available geologic data on Quaternary faulting, more accu- to as the study region)(Figure 1) is very tectonically active. rate assessments were made regarding(1) the spatial distri- The region is bordered on the west by a portion of the North bution of earthquakes in the study region; (2) the style and Coast segment of the San Andreas fault and traversed by orientation of seismogenic faulting;(3) the possible associa- several faults that form the San Andreas fault system. tion of earthquakes with specific structures, in particular the Although this segment of the San Andreas fault has been Rodgers Creek, Healdsburg, Bennett Valley, Maacama,and seismically quiescent since the cessation of aftershocks of Tolay faults; and (4) the nature and orientation of tectonic the 1906 San Francisco moment magnitude (M,,.) 8 earth- stresses active in the region. The study described herein quake, the region to the east has been characterized by a represents the first comprehensive and detailed analysis of relatively high level of seismicity.Several investigators have the contemporary seismicity and active faulting in this recognized that the contemporary seismicity between the portion of the northern Coast Ranges. On the basis of this San Andreas fault and the western margin of the Great evaluation an improved understanding of the level of seismic Valley north of San Francisco Bay has been concentrated hazard in the region has resulted and is discussed below. along two major trends: the Healdsburg—Rodgers Creek— Maacatna faults and the Green Valley—Bartlett Springs faults GEOLOGICAL AND TECTONIC SETTING [Bufe et al., 1981;Cockerham, 1986;Eberhart-Phillips, 1988; The study region is located in the Coast Ranges,which are Wong, 19901.The dominant fault within the study region,the composed of rocks of the Franciscan Complex that were Rodgers Creek fault,however,has been essentially aseismic severely deformed during underthrusting of oceanic plate(s) ' along most of its length. This observation, together with beneath the western margin of North America from Late recent paleoseismological investigations (Budding et al., Jurassic to early Tertiary times [Page, 1981] (Figure 1). 19911, suggests that the Rodger Creek fault is a seismic gap Other assemblages within the Coast Ranges include the and capable of generating a Mw 7 or larger earthquake. forearc-basin sediments of the late Mesozoic Great Valley From October 1970, when adequate microearthquake sequence and plutonic and metamorphic rocks of the Salin- monitoring by the U.S.Geological Survey(USGS)came into ian Block [Page, 19811. existence, through August 1989, approximately 1000 earth- The Coast Ranges tectonic province is bounded on the quakes generally greater than Richter magnitude (ML) 1.0 west by the northwest trending San Andreas fault, the reportedly occurred within the study region. The specific principal element of the plate boundary(Figure 1). A 100 to objectives of this study were to refine the hypocentral 200-km-wide region centered on the plate boundary, which locations of these events, based on a more appropriate includes much of the Coast Ranges, is tectonically domi- Copyright 1991 by the American Geophysical Union. nated at present by the dextral shear resulting from the Paper number 91JB02201. relative motion of the Pacific and North American plates. 0148-0227/91/91JB-02201505.00 During the Neogene, en echelon compressional basins of 19.891 19,892 WONG: COAST RANGES SEISMICITY, FAULTING. AND SEISMIC HAZARDS ,tr im !r VAINU FAMT t Clear Luka N �*. Mount �7 Point ✓\' Konoai Arena i Z.1 - iN �Z r. Blount 7 OG st Helena \ C\ !ab 7 Z `P �� is •, O FAULT , 11"P1 r;J, r to EXPLANATION ` d Heed ♦ i�`lr `(,\ Pleistocene, Pliocene, and Miocene 7 d �WEST NAPA FALlLT f� sedimentary and volcanic rocksviuir Melange and broken formation of 9 Franciscan Complex Q� Q 7e' ^rOk�tt Mount CoasW belt of Franciscan Complex Study AfM Sean.a O � ��; •.Die010 Contac �q\\ SUNOL.,CALAVERAS Que"W when uncerreb •:f,R,\ C FAULT- FAULT \ Fault... Dashed whom approxiwaMy kimhd.dot- d Ptearnbn ted where canasaled .. "0 '... o 54U rp C, Boundary between structural blocks 0 10 10 b 40 SO IMOMETEAS 7G Waedaa!o 1 l l l l lPalo All. Fig. 1. Regional geology of the northern Coast Ranges north of San Francisco Bay (modified after Fax (19831). Outline of study region is also shown. deposition, en echelon folds, northwest trending strike-slip of the San Andreas fault and lies beneath the Hayward- faults, and lesser east-west trending thrust faults were Calaveras faults and associated faults(including the Rodgers formed [Page, 19811. Creek and Healdsburg faults). These latter faults, which The San Andreas fault was formed by the northward have developed relatively recently(since 2-4 Ma), appear to migration of the Mendocino triple junction. Furlong et al. have accommodated only a fraction of the plate motion [1989] have proposed that the evolution of the San Andreas where the San Andreas fault has served as the principal fault system is largely controlled by the thermal-mechanical source of long-term strain release since the latter was formed behavior of the Pacific and North American lithosphere in 7-10 m.y. ago [Furlong et al.. 1989]. Eventually, the faults the vicinity of the fault system and the development of a east of the San Andreas fault will evolve into the new plate '•slabless" window beneath the western edge of the North boundary in the brittle upper crust. American plate. The window was formed by the northerly On the basis of a contrast in deformation, Fox (1983] has movement and removal of the subducting Juan de Fuca defined two structural blocks in the Coast Ranges north of (Gorda) plate from beneath North America. Furlong et al. San Francisco Bay: the Sebastopol block on the west and the [1989]also suggest that between the approximate latitudes of relatively intensely deformed (faulted and folded) Santa 37° and 39aN, the plate boundary within the mantle has Rosa block to the east (Figure 1). The average dip of late developed approximately 40-60 km east of the surface trace Miocene, Pliocene, and Pleistocene strata within the Sebas- WONG: COAST RANGES SEISMICITY, FAULTING, AND SEISMIC HAZARDS 19.893 123'00' 45' 30' 'INNS T � O � ''•� MM INTENSITY F9lO ��'• `999 \' ■calistoga Felt, Healdsburg O ` 0 No Intensity 30' 0 IV ` � \ St.Helena 19--Sequence .1 oc ` O 119VI Sebastopol 93 p�Q . ` tt Santa R9F `` BENNETT osa i VALLEY FAULT MAGNITUDE(ML) \,CO h4 Q ft, �2,4" , j. I (D3.0 ARIERICANO C� tI q\ Q \ � by0`��.J ,4 \Ks G(T� \ ► \\4. 1891 i O 4.0 \ ��S// �GCl �4G( �'•.., `� h �OG Sonoma N' 15' �, `�.� ��� `, q 15' O 5.0 ti ®� r0(4 A` �Z ` Petaluma a �O 6.0 eJ9�F( r yF 1898 09� a Faults; dashed when 9s, +�. •—^-� appmtmately located. .c Novato dotted when concealed 9G� Q •'© sou": _NW sou":Banugno 09M F 0 10 3g° kilometer 123'4D' 45' 30' Fig. 2. Historical seismicity(ML i 2.5) in the study region from 1855 to 1%9 and significant Quaternary faults. Epicentral data sources are Toppozada et al. 11981], Real et al. (1978], and the University of California earthquake catalogs. topol block is 5.8°in contrast to 34.51'within the Santa Rosa only complete for very large earthquakes. The first earth- block. quake documented in the study region occurred in 1855 The Santa Rosa block. is cut by eight major north- (Figure 2). Although the first seismographic stations in northwest trending, right-lateral, strike-slip faults or fault central coastal California were established by the University zones including the Tolay, Rodgers Creek, Healdsburg, of California at Berkeley(UCB)and atop Mount Hamilton in Maacama,Bennett Valley,Cameros,West Napa,and Green 1887, earthquakes were not instrumentally located until Valley faults (Figure 1). These faults appear to constitute a additional UCB stations were installed in Palo Alto in 1927, N30°W trending wrench system that has been displaced by San Francisco in 1931,Ferndale in 1933,and Fresno in 1935. an aggregate of 85 t 25 km in a right-lateral sense since Prior to the 1930s, earthquake locations were based princi- about 8 Ma [Fox, 19831. The first five listed faults are the pally on felt reports. After 1930, seismographic coverage, subject of this paper.The seismicity and faulting character- though still quite regional in extent,improved sufficiently for istics of the Green Valley fault have been evaluated previ- UCB to locate earthquakes instrumentally. ously by Wong (19901. Only two UCB stations, however, have operated in the No major faults occur within the Sebastopol block. Pos- study region: in Calistoga and Point Reyes from 1%1 to sible Quaternary faults include the Burdell Mountain,Amer- 1964. After the occurrences of the October 1, 1969, Santa icano Creek, Dunham, Bloomfield, and Wallace Creek Rosa earthquakes, seismographic coverage improved signif- faults, and a possible northern extension of the Tolay fault icantly when the USGS expanded their central California [Wagner and Bortugno, 1982](Figures 2 and 3).These faults network north of San Francisco in 1970. Thus adequate all appear to be generally less than 20 km in length. seismographic coverage of the region for the detection and location of earthquakes smaller than ML 3 came into exist- HISTORICAL SEISMICITY ence between 1970 and 1973.The current epicentral location The historical earthquake record for California dates back accuracy is estimated to be of the order of 2 km or possibly only to the late 1700s (primarily from the initial establish- better and the level of detection is approximately ML 1.5. ment of Franciscan Missions along the coast)and is probably A total of 126 earthquakes of approximate ML 2.5 and 19.894 WONG: COAST RANGES SEISMIcrrY, FAULTING, AND SEISMIC HAZARDS greater are thought to have occurred in the study region from TABLE 1. P Wave Velocity Model Used in This Study 1855 to 1969. Only one earthquake is thought to have exceeded ML 6, and four additional earthquakes have ex- Depth to ceeded ''VfL 5 in the region (Figure 2). The March 31, 1898, Layer Velocity, km/s Top of Layer, km earthquake of M 6.5 (Ellsworth, 19911 partially or totally 1 4.45 0.0 collapsed several buildings(modified Mercalli(MM)VIII)on 2 5.10 1.5 Mare and Tubb islands (Toppozada et al., 19811. Houses 3 5.50 3.0 were knocked from their foundations in neighboring towns, 4 5'90 425 5 5.90 5.5 and extensive ground cracking was observed. Although this 6 6.80 14.0 earthquake has been assigned a location just east of the 7 8.00 1-S.0 southern end of the Rodgers Creek fault based on its isoseismal pattern(Figure 2),the epicentral uncertainty does not permit an association with a specific fault. The four ML 5 earthquakes include events on October 12, Station delays based on the 31 calibration events were 1891, of estimated ML 5.5, August 9, 1893(ML 5.1), and the determined by iteratively incorporating the average station two largest events of the 1969 Santa Rosa sequence(ML 5.6 residuals.A final set of station delays was obtained when the and 5.7) (Figure 2). In the 1891 earthquake, several brick changes in rms errors became minimal. (The use of station buildings were cracked and moved off their foundations in delays improves the relative locations of the earthquakes but Napa and Sonoma. This ground shaking corresponds to a may not remove absolute location errors.) maximum MM intensity of VIII (Toppozada et al., 19811. In All P wave arrival times from the USGS stations within an the somewhat slightly smaller 1893 event, chimneys were epicentral distance 100 km were used in the earthquake knocked down and plaster fell in Santa Rosa(MM VII). locations. Stations beyond this distance were disregarded in Recent seismicity in the region has been dominated by the order to minimize departures from the crustal velocity 1969 sequence. At 2156 LT on October 1, the ML 5.6 model. The first motion data from all stations recording the earthquake struck near Santa Rosa, followed by the ML 5.7 event were used in focal mechanisms which were generated event at 2320 LT. Fifteen injuries were reported and no using the computer program FPFIT [Reasenberg and Op- deaths [Steinbrugge et al., 1970]. Structural damage includ- penheimer, 19851. Arrival times as originally read by the ing damage to building contents exceeded$7 million.At least USGS were used, and no rereading was performed except 200 aftershocks were recorded in the sequence, with the for first motions. S waves for the majority of events were largest a ML 4.3 event on October 2. Aftershock recordings seldom read by the USGS due to the difficulty in reading by a temporary network operated by the USGS suggest that such arrivals on develocorder film: thus no S waves were this sequence occurred principally on a southern extension used in the relocations. Station elevation corrections were of the Healdsburg fault (J. D. Unger and J. P. Eaton, calculated assuming a velocity equal to the velocity of the unpublished manuscript, 1970). However, the source of the top layer of the model. two principal events has not been well determined due to A total of 930 earthquakes (including the 31 calibration location uncertainties and the geological complexity of what events) that occurred from October 1970 to August 1989 in appears to be a right step from the Rodgers Creek fault to the the study region were relocated. After unreliable arrival Healdsburg and Maacama faults (I. G. Wong et al., manu- times were deleted from the location solutions, any event script in preparation, 1991). with fewer than generally seven recording stations was removed from the data set. A few events with rms errors DATA ANALYSIS greater than 0.25 s were also deleted.The average rms error The approximately 1000 earthquakes which occurred from of the relocated earthquakes was 0.07 s compared to an error October 1970 to August 1989 in the study region were of 0.13 s for the original USGS locations. The HYPOEL- relocated using the computer program HYPOELLIPSE LIPSE epicentral standard errors (ERHs) of the relocated [Lahr, 19841. Only events which were recorded by seven or events were 1.0 km or less for 73%of the events. more seismographic stations (generally MI. > 1) were ana- An attempt was made to evaluate the validity of the lyzed using the velocity model in Table 1. velocity model and station delays and hence the absolute This velocity model is based on(1)an upper crustal model epicentral accuracy of the relocated events: however, no developed by Eberhart-Phillips (1988) for the Clear Lake known large explosions occurred within the study region. region and modified by Merriam f 1986 for the area between Fifteen blasts at two quarries near the town of Napa and at Clear Lake and Lake Berryessa and (2)a lower crustal and the Warm Springs Dam located just outside the study region upper mantle model appropriate for the Coast Ranges in were relocated generally within 1 km of the actual quarry central California from Wesson et al. (19731. The depths to locations and at depths of 1 km or less. Thus based on the the layer boundaries were systematically varied for a set of low rms errors and ERHs and the relocations of quarry 31 well-recorded and well-distributed calibration earth- blasts, the majority of relocated epicenters are believed to quakes (ML > 2.5) to find the best model which minimized have an accuracy of.1 km or better. Because of the 10-20 the root-mean-square (rms) errors in the travel time residu. km average spacing between USGS stations in this portion als. This final velocity model was tested against the model of the central California network (and hence few close-in used by the USGS in routine locations of central California stations) (Figure 3) and the absence of S waves in the earthquakes[Wesson et al., 1973]and proved superior based hypocentral determinations,computed focal depths have an on the smaller rms errors of the calibration events. A model estimated accuracy of =2 km. Equivalent Richter magni- similar to the final model was used by Wong[1990]in.a study tudes quoted in this study have been determined by the of seismicity near Lake Berryessa. USGS. Menlo Park, generally based on coda durations. WOtT`v: COAST RANGES SEISMICITY, FAULTING, AND SEIS0C HAZARDS 19,895 125"00 49 30' W ACL LLRF AAECCE yF9 �♦ ` X99• CHILES VALLEY % KEE FAULT SSG �`` �i,~ry4• ' ' '■Calistoga o �♦o °o i`Healdsburg •'E` E� ;= o • °`����` a • ` 30' • 4 ° 30. �� ♦ %. s ` �a'�\ •■ St. Heldna 0 0• Q♦ ♦ QA.�` o ••• o - • 11 • S ROSH ., v b�� F ♦ • o. I t ■ i- t to • • ° kv • ° T oo ♦ ■ Sebastopol ♦ ♦� •,A• ♦8 • �Q t �ENNETT .A \ ♦ a ♦11; VALLEY FACA •ryA. F(p tiyq �♦ t• 0 ono • ♦� t� '•, t ♦ 1 AMERICANA C,9 ; � Oy0 Sonorne 15' � ♦ T T• `� '�OGti ■ O( ♦ �� ` ♦ Petaluma 4y~A. 9G♦9�y � qG lr s o g �T �O 0,9 s ♦ A. Vill ■ Oy F 0 to Nibm�tMs 38- 323'00' 4s Nr Fig. 3. Relocated earthquakes,October 1970 through August 1989,denoted by octagons,and significant Quaternary faults in the study region.Triangles represent present-day USGS seismographic stations used in the relocations. RESULTS AND GEOLOGIC IMPLICATIONS Bay.The following is a discussion of the geological implica- Data from the relocated earthquakes indicate that the vast tions of these results as they pertain to the significant majority of events were concentrated in the vicinity of the Quaternary faults within the study region. Rodgers Creek, Healdsburg, Bennett Valley, and Maacama San Andreas Fault faults (Figure 3). With the exception of the Bennett Valley fault, this seismicity is consistent with the geological evi• From October 1970 to August 1989,only 10 well-recorded dence of these faults being active in Holocene and/or late microearthquakes occurred in the vicinity of the 37-km-long Quaternary times.(It should be noted that seismicity alone is portion of the North Coast segment of the San Andreas fault not always sufficient for, or in some cases capable of, within the study region (Figure 3). Of these, possibly only delineating or completely characterizing all active faults in a half actually occurred along the principal traces of the fault. region.) Diffuse but significant seismicity also appears to be None of the microearthquakes near Tomales Bay exceeded occurring outside this principal zone of faulting and defor- ML 3.0(Figure 3). All events were confined to upper crustal mation(Figures 3 and 4). A few scattered microearthquakes depths of 8 km and less(Figure 4h).Three microearthquakes were located in the vicinity of the seismically quiescent were located near the surface probably as a result of inade- North Coast segment of the San Andreas fault in Tomales quare coverage by the USGS network near the coast. 0 19,896 WONG: COAST RANGES SEISMICITY, FAULTING. AND SEISMIC HAZARDS DtM—(km) • MW saM ft" Taox krk sonar Wk _ i'; -%'•,•. E S 10 13 20 25 70 -S 45 so SS 60 65 79.504 :.� ?� - i 2 0 ° °• a o o p . • , 9 w 0 00 • � i a • � 0 0 0 • ' 70.250 ' 310 B 12 • It is 78'-t�e�J.000 -122.750 -122.500 is (a) MW O+stu+w(km) SE 4 10 5 20 O p O p 0 Op O 2 p O p (�p ® pp O� O p O p � ba O O p� pDp� (Do O�O®(Zp 0 O p O(D p03 O (10 � 0 ® O e 0(D O ORO Q O0 Q. =�� �.�'�?. 70.504 119 � ;1r 2 p p O i 12 O O ' - 14 10 74.-BMJ.809 -122.758 -122.See 1e (b) • -ew • • 70.599 ]0.508 r .' 78.548 �' •..tet • yl, •. >tl, 1• 70.258 • • 70.am • • 78.230 •'r 7s.�1'LJ.900 -122.738 -l2a.se� �-17J.848 -122.758 -122.500 U'-1�.J.e99 -122.759 -122.500 sw owa= we sw DMtv"0'(meq we sw DWUm=(k-) HE e199s e • O 2 2 Q 2 p dMA 6D t � B t t O � e a� e e O Ile I19 lie 0 0 1: O o 12 12 14 1. It 0 is 10 1s is is is (c) Fig. 4. Locations of cross sections and views of the relocated seismicity: (a) Healdsburg—Rodgers Creek faults, longitudinal;(b)Bennett Valley fault,longitudinal.(c)Rodgers Creek and Bennett Valley faults,transverse;(d)and(e) Healdsburg fault, transverse; (j) and (g) Maacama fault, longitudinal and transverse; (h) San Andreas fault near Tomales Bay, longitudinal.and(h Rodgers Creek fault to Hayward fault right bend,longitudinal. WONG: COAST RANGES SEISMICITY, FAULTING, AND SEISMIC HAZARDS 19,897 �h J8.000J.000 -122.750 -122.580 79.000J.088 -122.750 -122.500 NW OManv(k#M SE sW Distan=(km) NE 8 5 t0is • S O p 2moa Q Q p z O a p i p m OO (z%- 0 8 0 p �� p 4 O •o 0 p p p s op �Oo p 9 (D ® O O O E a (D e IL g le g is 0 12 12 14 14 1e le l9 18 m c� 79.580 4V ,': � t 78.258 • • 78.250 Xp�08 � ..•� ,• '� .17J.888 -122.758 -122.58(1 38'- .e88 -122.758 -122.Se8 Ohfre�A�*1mw Dhta=(w+q ew s 9 s 10 ts; sE O 2 2 p v 4 4 o 0 O � d1e u O O O O 12 12 O0 14 14 0 O O ie le L 1B 1B N m Fig. 4. (continued) • • f. 19.898 WONG: COAST RANGES SEISMICITY, FAULTING, AND SEISMIC HAZARDS Rodgers Creek Fault coverage came into existence in 1970 through August 1989; The Rodgers Creek fault as mapped extends for a distance hence no focal mechanisms have been determined for the of at least 43 km from near Sears Point near San Pablo Bay Rodgers Creek fault (Figure 6). northwestward across the Sonoma Mountains to a location 4 The fault has also been apparently devoid of significant. km north of Santa Rosa [Wagner and Bortugno, 19821 seismicity in historical times dating back to the mid-1800s(or (Figure 2). Uncertainty regarding the location and character 1808 as suggested by Budding er al. (19911), which supports of large portions of the fault is due to burial by landslides. the observation. that the fault is presently a seismic gap. Although some investigators consider the Rodgers Creek Empirical relationships based on fault rupture length indi- fault to be the southern extension of the Healdsburg fault, rate that if the mapped 43-km or longer fault ruptured in a Herd and Helley [19771 suggest that the Maacama fault zone single event, the fault could generate a M, or Mme, 7 or larger has apparently acted as the northward continuation of the earthquake. This value is consistent with the estimate by Rodgers Creek fault zone during the Quaternary. In con- Budding et al. [19911,based on an estimated average slip per trast, the seismicity(as will be discussed later)suggests that event observed in their paleoseismological trenches. The the Rodgers Creek, Healdsburg, Maacama, and Bennett Working Group on California Earthquake Probabilities Valley faults are probably all part of the same broad zone of (19901 has estimated a 22% probability for a M 7.0 or larger deformation. earthquake occurring on the Rodgers Creek fault in the next Of the faults located within the study region the Rodgers 30 years based primarily on the findings of Budding et al. Creek fault exhibits geologically the greatest degree of (1991]. recent activity as manifested by geomorphic features such as Ellsworth et al. [1982] suggested, on the basis of mi- sag ponds, stream offsets, and small linear rift valleys croseismicity, that the Healdsburg—Rodgers Creek fault is [Pampeyan, 1979]. The fault zone appears to consist of at continuous with the Hayward fault to the south, although least four geometric segments (not rupture segments) with Wagner and Bortugno [1982] show the Rodgers Creek fault each segment showing evidence of recent and systematic unmapped 3 km from San Pablo Bay (Figure 3). The projec- right-lateral slip [Hart, 1982a]. The segments are well de- tions of the mapped faults indicate the two are separated by fined by major right step-overs with the longest segment a 6-km right step-over or fault bend. Aydin [1982] has extending approximately 12 km. suggested that a pull-apart basin may exist beneath San Recent significant paleoseismological trenching studies by Pablo Bay as a result of extension across a right step-over. Budding et al. [1991], 18.5 km northwest of San Pablo Bay, Budding et al. [1991] note that the step-over or bend is have revealed possibly three to four paleoearthquakes on the associated with a 35-mGal negative gravity anomaly in San Rodgers Creek fault. They also estimated a minimum late Pablo Bay and that such areas are often associated with Holocene slip rate of 2.1-5.8 mm/yr for the past 1300 years rupture termination points. On the basis of the broad north and a maximum recurrence interval of 248-679 years for trending zone of epicenters (Figure 3), a bend between the surface-faulting events(M—7).Budding et al. [1991]further two faults appears more likely. The presence of both strike- suggest, based on the absence of fault creep and seismicity, slip and reverse faulting, combined with the focal mecha- that the fault is locked and, given the uncertainties of their nisms (Figure 6), suggests that the bend consists of a recurrence and slip rate estimates,the elapsed time since the complex zone of deformation, possibly last major earthquake on the Rodgers Creek fault(minimum P P Y including multiple of 182 ears) may be approaching the ave faults in San Pablo Bay. Y Y PP g rage recurrence interval. Significant clusters of events have occurred off the Rodg- The relocations supporters Creek fault: in particular, one cluster to the southwest dgeearlier observations rally Buse et and one along a northwest striking splay fault northwest of al., 1981] that the Rodgers Creek fault is generally seismi- tally quiescent. A dramatic absence of microearthquakes Sonoma Mountain (Figure 3). In the former, two focal characterizes the southern 22 km of the fault south of mechanisms (events 10 and ll, Figure 5) exhibit predomi- Sonoma Mountain(Figures 3 and 4a). In the mapped north- nantly reverse faulting along a northwest trending plane. ern 21 km,only a few microearthquakes occur in the vicinity `Which is consistent with a subtle northwest trending zone of of the fault except for a concentration of events at a depth of epicenters(Figure 6). Such semiparallel seismogenic reverse about 8 km near the junction of Taylor Mountain and a faulting located off a major strike-slip fault has been increas- northwest striking splay of the fault considered to have been ingly observed along faults of the San Andreas system, active in the late Quaternary by Wagner and Bortugno(1982] including the Calaveras and Hayward faults [Oppenheimer (Figures 3 and 4a). A cross-sectional view through the et al., 1988; Oppenheimer, 1990; Wonget al., 19911. Taylor Mountain activity suggests that the Rodgers Creek Focal mechanisms 2, 4, and 22 for the cluster of events fault is a near-vertical fault to a depth of about 14 km(Figure along the Sonoma Mountain splay fault(Figures 5 and 6)are 4c). Given the absence of additional observations, however, nearly identical,exhibiting right-lateral strike-slip faulting on this dip may vary slightly along the length of the fault. the northwest trending plane. The area also appears to have In the northernmost portion of the fault east and north of been the site of previous historical activity (Figure 2). Santa Rosa (although there is some question whether the Wagner and Bortugno (1982] show this fault to have been latter is part of the Rodgers Creek fault or the Healdsburg active in late Quaternary times. A focal mechanism for a fault), no microearthquakes have been observed to date single event (event 25, Figure 5), located between the splay (Figure 3). A concentration of activity does occur on the and the Rodgers Creek fault, also exhibits right-lateral parallel, southernmost traces of the Healdsburg fault (see strike-slip faulting. Seismicity in the vicinity of the fault following section). No earthquakes larger than ML 3.0 have appears to be confined to the top 12 km of the crust, with a been observed along the fault since adequate seismographic few events as deep as 15 km (Figures 4a and 40. WONG: COAST RANGES SEISMICITY, FAULTING, AND SEISMIC HAZARDS 19,899 1 761211 1628 8 790110 4s7 15 840310 2148 22 ssigti` 643 Z- 6.00 M. 2.30 Z-10.26 N.2.20 Z. 4.54 N.2.60 Z- 8.29 M- 2.7o o + + $ + +# + 00 +++ + o # ® CM 2 760527 17 1 9 800109 1953 16 841003 1218 23 660116 938 Z- 6.20 M- 3.60 Z- 5.27 N- 3.00 2. 1.57 M- 2.40 Z• 4.16 M- 2.60 + G=P8 0 0 * o T + + $ T ++ + 8 f + +o o 3770213 250 10 811218 1441 17 s4103o 2050 24 880428 2259 2.10.40 M. 1.90 Z- S.20 N.3.M Z. 3.60 M. 2.70 Z-2.01 M- 2.10 t.+°° + + ° T + + + ° 000 o O f o + 0 4 770327 ll2q 11811220 741 18 841030 2344 25 890409 15 7 Z-4.47 M. 2.50 1.5.03 N-3.40 1. 4.07 N.2.90 Z- 1.64 M- 2.10 ®° ° ® ++ 00 o ++ ++T o T t + 0 ++ 0 0 0 +++ 0 +++ °00 5 770831 2339 12 emm 42o 19841208 923 26 8906 t0 172s z-6.60 M. 2.70 z-L 0 N.2.10 Z- 5.61 N-2.30 Z-2.29 N• 2.30 o *Q7D°& + �+ o # 00 0 0 00 ac (D 6 771019 i146 13 aM12 20 W 20 650316 17 9 Z•9.99 NM 5.]0 Z.M.12 M.2.0 Z. 0.01 N-2.40 #+ °® 0 0 0vO6+ + p 7 780527 1822 14 831101 123 21 850712 538 z-5.14 M. 7.50 z-S.13 N-2.20 Z. 8.36 A.2.W 0 + o ++ o ++ + + + t + + + + o 0 + ° �+ Fig. 3. P wave focal mechanisms of largest earthquakes relocated in this study.All are equal-area projections of the lower hemisphere. Focal depths(Z)and magnitudes(D)are also shown. Pluses and circles denote compressional and dilatational first motions.respectively.P and T represent compression and tension axes,respectively. 0 r 19,900 WONG: COAST RANGES SEISMICITY, FAULTING, AND SEISMIC HAZARDS 26 123°00' 1 45' 30' ♦ 7 / CHILES VALLEY'% WALLACE\y�91 `� `� \�9C� 24 ' FAULT %` CREEK O� `�♦ \ ♦`9 ` AULT FBG ��;� `0 t4, 0Calistogg5 I I Healdsburg 9c q( `y\�`� Al `` �'�G \ "` 1 ♦♦♦�� 12 30' ♦ ■ � 30' St. Helena 17 ANTA� \ �c`� 9 FiOSA • 9 ' 23 19 18 ■ t �p.`�00 t 20 ` 25 Ta" i�'c� \\ ♦ \` ■ Sebastopol 4 mu %sc,\`\ 5 /I 2 9� `� `♦ t _BALL F E n B 22 •'�, 6� V�—� �`� VALLEY FAULT 99 <00 O ♦� e ``� I 6 G ♦ � s Af tE �♦�`� SonoT 1i 21 ;1 9GG 9 \� iL ♦ d+ O feF01 i '4 R1Cgty C FFk �qGt `` MvC `'yt I,1 % �gGIT ♦ 10 11�. I -0 Sonoma �\ Petaluma OtqY gG`9y14 qG !� S , G 8 Novato■ 3 �0 y� o to kibmotas 38' 123°00• 4s• so' Fig. 6. Map of focal mechanisms in the study area. Mechanisms are numbered as shown in Figure S. Inward and outward arrows represent horizontal projections of P and T axes, respectively. Shaded areas are compressional quadrants. Healdsburg Fault however, contend that these faults are part of the southern The Healdsburg fault, north of the Rodgers Creek fault,is Healdsburg fault. only locally well defined (Figure 3) and is characterized by In contrast to the conflicting geological observations, the geomorphic features indicative of right-lateral displacement relocated microseismicity since 1970 is abundant along the along the fault zone [Bryant, 19821. Disagreement exists, Holocene-active Healdsburg fault as delineated by Wagner however, concerning the recency of displacement along the and Bortugno [1982] (Figure 3). Activity appears to be length of the Healdsburg fault. Herd et al. [1977] and Herd greatest on the southern portion of the fault nearest Santa and Helley [1977] did not consider most of the Healdsburg Rosa, as compared to the northern half near Healdsburg. fault to be active in Quaternary time. They stated that the The cluster at the apparent southern termination of the fault recently active faults north of Santa Rosa are part of the northeast of Santa Rosa probably represents late aftershocks Rodgers Creek fault zone. Huffman and Armstrong [19801. of the 1969 sequence. Focal mechanisms 13, 17, and 18.near WONG: COAST RANGES SEISMICITY, FAULTING, AND SEISMIc HAZARDS 19,901 t Santa Rosa, and 26,combined with the abundant microseis- (Oppenheimer, 19861 (Figure 1). However, the Maacama micity,attest to the high level of activity and the right-lateral fault is probably a right-lateral strike-slip fault based on its strike-slip nature of the fault (Figures 5 and 6). geomorphic expression, focal mechanisms determined by According to Wagner and Borrugno(1982]the Healdsburg Eberhart-Phillips (1988] and Castillo and Ellsworth (1991], fault consists of two, sometimes three, parallel traces north and aftershock focal mechanisms by Warren and Scofield of Santa Rosa (Figure 3).. Although seismicity appears to (1985] for the 1977 Willits earthquake (ML 4.8) along the cluster along all traces, cross-sectional views show a single northern portion of the fault. Given the complex nature of well-defined active planar zone dipping steeply (approxi- the fault as it is expressed geologically at the surface, a mately 75') to the east (Figure 4d and to a lesser extent, varied behavior for its splays and branches would not be Figure 4e). This orientation of the Healdsburg fault is in surprising. Seismicity in the vicinity of the southern Maa- contrast to the near-vertical dip of the Rodgers Creek fault Cama fault is relatively shallow, generally less than 8 km in (Figure 4c). This difference in dip argues for two distinct depth (Figures 4f and 4g). faults acting as independent seismogenic sources in contrast Diffuse seismicity south and southeast of St. Helena to earlier views that the faults were part of the same zone. appears to be a continuation of a broad northwest trending The largest event observed on the Healdsburg fault since zone of activity spatially associated with the Maacama fault 1970 was a ML 3.5. Seismicity along the fault appears to be (Figure 3). A cluster of events occurred in the vicinity of the no deeper than 12 km with the majority of events occurring St. Johns Mountain fault approximately 9 km south of St. in the top 6-8 km of the crust in contrast to the Rodgers Helena, which Wagner and Borrugno(1982] show as a north Creek fault where significant activity occurs down to 9 km dipping pre-Quaternary thrust fault(not shown on Figure 3). (Figures 4a, 4d, and 4e). Focal mechanism 19 (Figures 5 and 6), however, suggests that a north trending, right-lateral strike-slip fault is the source of at least one event within this cluster. Maacama Fault The Maacama fault is approximately 150 km long and Bennett Valley Fault displays discontinuous geomorphic evidence of young dis- placement (Figure 3). The fault extends from near Mark The Bennett Valley fault, suggested to be a southern West Springs northwestward through the Mayacamas Moun- extension of the Maacama fault, runs nearly parallel along tains to the vicinity of the town of Laytonville. Upp [1980] much of its length with the Rodgers Creek fault (Figure 3). has argued that the Maacama fault has ruptured during The fault is very poorly expressed geomorphically especially Holocene time because the fault is coincident with a series of in comparison with the Maacama or the Rodgers Creek sag ponds,linear valleys, side hill trenches,aligned notches faults. The fault displaces Huichica Formation gravel and and saddles, shutter ridges, and scarps. The fault zone is thus has been active during or since the late Pliocene (Fox, composed of several parallel fault strands,locally as wide as 19831, although the geologic evidence gives no clear indica- 800 m,across which the upper part of the Sonoma Volcanics tion whether the fault is active today.Herd and Helley(1977] are downfaulted on the west against Franciscan rocks on the believe that the fault displaces a late Pleistocene terrace east east [Fox, 1983]. Herd [1978] suggests that the Maacama of Santa Rosa. Wagner and Borrugno [1982] consider the fault may connect with the Rodgers Creek and Hayward northernmost portion of the Bennett Valley fault to be late faults to the south and with the Lake Mountain fault to the Quaternary in age. Well data suggest that the fault probably north to form a major plate boundary fault.The pronounced has at least 300 m of down-to-the-east displacement (Fox, discontinuities between these fault zones, however, argue 19831. Fox[1983] suggests that the apparent sinuous nature against a single throughgoing fault zone. To account for a of the Bennett Valley fault as observed in the topography linear trend of microearthquake epicenters, Eberhart- may be due to the possible low-angle nature of the fault. He Phillips [1988] suggested that the Maacama fault may con- further suggests that the difference in the surficial expression nect southward with the Green Valley fault zone. Fault of the fault, if not due to the orientation of the fault, may creep at a rate of 1.8 mm/yr has been documented along the imply that part of the recent movement of the Maacama fault Maacama fault zone at Willits (Harsh et al., 19781. has transferred over to the Rodgers Creek fault rather than The relocations indicate that a rather broad zone of the Bennett Valley fault. epicenters occurs in the vicinity of the southern Maacama Examination of Figure 3 shows a relatively broad zone of fault consistent with the multiple-stranded nature of the fault epicenters concentrated along the mapped multiple northern (Figures 3 and 4g). Only a few of the events actually appear traces of the Bennett Valley fault. A cross-sectional view to be associated with the main traces of the fault.In contrast, (Figure 4c) shows these events to be distributed over a 2 to Castillo and Ellsworth (1991] characterize the northern and 3-km-wide zone,although there also appears to be a sugges- central portions of the Maacama fault as a single well-defined tion of a near-vertical zone that may correspond to the 60°45°eastward dipping fault. Numerous epicenters cluster Bennett Valley fault. No hypocentral trends are apparent along two branch faults 5-10 km west of St. Helena that which would be consistent with a low-angle fault(Figure 4c). Wagner and Bortugno [1982] have characterized as being Focal mechanisms 9 and 12 exhibit right-lateral strike-slip northeastward dipping thrust faults (Figure 3). faulting along a north trending plane, consistent with a Only one focal mechanism,24,has been determined in the possible northward extension of the fault(Figure 6). vicinity of the southern Maacama fault, and this event Focal mechanism 5 of an event 1 km to the west of the anomalously displays predominantly normal displacement mapped trace of the fault is consistent with a northwest along a north or northeast trending fault (Figures 5 and 6). trending,right-lateral strike-slip fault(Figure 6). Mechanism Normal faulting has been observed elsewhere in this portion 20 shows a northeast steeply dipping plane which coincides of northern California, principally in The Geysers region with a short fault parallel to the Bennett Valley fault. 19.902 WONG: COAST RANGES SEISMICITY, FAULTI 4Q, AND SEISMIC HAZARDS y Mechanism 23 may be representative of off-fault seismicity. Santa Rosa block or(2)the unique position of the two blocks Focal mechanisms 6 and 21 suggest a north-northwest trend- relevant to the dynamically interacting Pacific, North Amer- ing, right-lateral strike-slip fault(s) between the Bennett ican, and Juan de Fuca plates [Fox, 1983]. The widespread Valley and Rodgers Creek faults (Figure 6). existence of late Miocene to Pleistocene volcanic rocks and the Geysers geothermal field attests to the higher heat How in Tolav Fault the Santa Rosa block. Furlong et al. [1989] suggest that the Sebastopol block is The Tolay fault extends for a distance of 35 km to the underlain by a subhorizontal shear zone connecting the plate northwest from the vicinity of Sears Point and the southern boundary in the deeper ductile portions of the lithosphere end of the Rodgers Creek fault (Figure 3). The fault is not with the surface trace of the San Andreas fault. This deeper well defined at the surface and may actually consist of a zone plate boundary presently underlies the Santa Rosa block of faults which may or may not be continuous along its resulting in youthful and discontinuous faulting as mani- length [Hart, 1982b]. Both the northwestern and southeast- fested by the Rodgers Creek, Healdsburg, Bennett Valley, ern portions of the fault offset units of Pliocene but not and Maacama faults. Furlong et al. [1989] further suggested younger age [Hart, 1982b]. The fault zone has been charac- that the Sebastopol block is acting as a semirigid crustal terized as a right-lateral strike-slip fault with some reverse block between the Pacific and North American plates. displacement along steeply southwest dipping plane(s). Hart Consistent with either of these causes of deformation (19826] suggests that if the Tolay fault has been active in within the two blocks,the occurrence of Quaternary faulting Holocene times, such activity is minor, distributive, and and the contemporary seismicity east of the relatively qui- restricted to the southern end of the fault near the active escent and locked North Coast segment of the San Andreas Rodgers Creek fault (Figure 3). No relocated epicenters fault is much more prevalent throughout the Santa Rosa during the 1970-1989 period occur along or near the fault block (including the eastern portion of the block [Wong, except for one event adjacent to the southern half. In lieu of 1990]) than in the Sebastopol block (Figure 3). Seismicity more definitive geologic information on the Tolay fault, it within the Santa Rosa block is concentrated along the zone should be considered inactive at this time. consisting of the Rodgers Creek, Healdsburg, Bennett Val- ley,and Maacama faults.These faults also exhibit geological Other Quaternary Faults evidence-for late Quaternary and/or Holocene displacement Wagner and Bortugno (1982] show the Burdell Mountain except for much of the Bennett Valley fault. However, with fault to be a 19-km-long fault that has been active during the the exception of the central portion of the fault near Taylor early Quaternary. Only two epicenters occur in the vicinity Mountain, the Rodgers Creek fault, which is possibly the of the fault,although they locate adjacent to the well-defined dominant fault in the study region east of the San Andreas portion near Burdell Mountain (Figure 3). The fault may be fault, has been devoid of microearthquake activity since active, although neither the seismological nor the geological 1970,especially along its southern half(Figure 3). Consider- data are conclusive. able off-fault activity appears to be occurring on secondary East of the town of Sonoma, several short early Quater- faults adjacent to the Rodgers Creek fault, some showing nary faults occur west of the Cameros fault [Wagner and reverse displacement, although most are right-lateral strike- Bortugno, 19821 (Figure 3). Several events occur in the slip faults. Seismicity is also absent on the southern half of vicinity of these faults and the Cameros fault, which sug- the Bennett Valley fault. gests that they may be active. Focal mechanism 14 is Focal mechanisms indicate that right-lateral strike-slip consistent with such an active north trending, right-lateral faulting is the predominant mode of crustal deformation in strike-slip fault (Figures Sand 6). the study region (Figure 6). Reverse faulting on northwest A diffuse concentration of microearthquakes was located trending faults and normal faulting on a small scale also northeast of St. Helena, southwest of two northwest trend- occurs within the region as is often observed in other ing early Quaternary faults (Figure 3). Focal mechanism IS detailed studies of seismicity in central and northern Cali- exhibits right-lateral strike-slip faulting on a north-northwest fornia [e.g., Oppenheimer et al., 1988; Wong and Biggar, trending fault in the vicinity of the similarly trending Chiles 1989; Wong er al., 19911, including the region to the east Valley fault(Figures S and 6). A cluster of microearthquakes along the Green Valley—Cedar Roughs fault trend (Wong, also occurred in the vicinity of several early Quaternary 19901. Also, as has been increasingly observed, a north- faults west of Healdsburg,one of which is the Wallace Creek northeast to northeast directed maximum principal stress fault (Figure 3). A few small events also were located in the appears to characterize the tectonic stress field in this vicinity of the Ameri r, 3 s WONG: (,,.ST RANGES SEISMICITY, FAULTING. AND SEISMIC ti1ARD5 19.903 deep as 15 km. Miller and Furlong [1988] suggest that REFERENCES seismicity increases approximately 3 km in depth from Aydin, A., The East Bay hills, a compressional domain resulting northern to central California due to a corresponding in- from interaction between the Calaveras and Hayward-Rodgers crease in strain rate and stress. Interestingly, a longitudinal Creek faults. in Proceedings of the Conference on Earthquake cross-sectional view through the region (Figure 4a) is con- Hazards in the Eastern San Francisco Bay Area.edited by E. W. sistent with a deepening of most events from 5 to 9 km. Hart, S. C. Hirschfeld. and S. S. Schulz. Spec. Publ. 62, pp. On the basis of geodolite measurements east of the San 1 ant, Calif. Div.is Mines and Geol., Sacramento, 1982. Bryant, W. A., Chianti, Healdsburg, Alexander. Maacama and Andreas fault, Prescott and Yu [1986] estimated 25 t 6 related faults,California,Fault Eval.Rep.FER-195,23 pp.,Calif. mrtvyr of right-lateral slip distributed over a 60-km-wide Div. of Mines and Geol., Sacramento, 1982. region. A peak shear strain of 0.6 } 0.l u. rad/yr was Budding, K. E.,D. P.Schwartz,and D. H.Oppenheimer,Slip rate. observed near the San Andreas fault,and 0.3 = 0.04µrad/yr earthquake recurrence,and seismogenic potential of the Rodgers was observed for the region to the east. Prescott and Yu Creek fault zone, northern California: Initial results,,Geophys. Res. Lett.. 18, 447-450, 1991. [19861 were unable to detect any localization of deformation Bufe,C. G., S. M. Marks, F. W. Lester, R. S. Ludwin, and M. C. (including aseismic slip or creep)along surface fault traces in Stickney,Seismicity of the Geysers-Clear Lake region: Research the region. Nfore recently, on the basis of repeated trilater- in The Geysers-Clear Lake geothermal area,northern California. ation during the period 1973-1989, Lisowski et al. [1991] U.S. Geol. Surv. Prof. Pap., 1141, 129-137, 1981. observed that approximately half of the 31 t 3 mm/yr of Castillo. D. A., and W. L. Ellsworth, The seismotectonics of the late motion occurs across the faults east of the San San Andreas fault system north of Point Arena along the Coast relative p Ranges of northern California(abstract),Seismol.Res. Lett.,61. Andreas fault.The horizontal velocity field appears to decay 11, 1991, eastward in a generally linear manner, again with no appar- Cockerham,R.S.,Seismotectonics of the northern California Coast ent strain concentrations along any of the faults. However, Ranges from San Francisco to Eureka (abstract), Eos Trans. the presence of fairly high levels of contemporary seismicity AGU,67, 1214, 1986. Eberhart-Phillips,D..Seismicity in the Clear Lake area,California, [Coc•kerham, 1986, Eberhart-Phillips, 19881, the belief of 1975-1983.in Late Quaternary Climate,Tectonism,and Sedimen- several investigators that the Rodgers Creek fault represents cation in Clear Lake,Northern California Coast Ranges,edited by a seismic gap, and the geological evidence for Quaternary J. D. Sims, Spec. Pap. Geol. Soc. Am.,214, 195-206, 1988. displacements are suggestive of concentrated deformation Ellsworth,W. L.,Earthquake history, 1769-1989:The San Andreas along the Rodgers Creek, Bennett Valley. Healdsburg, and fault system, California, U.S. Geol. Surv. Prof. Pap., 1515, Maacama faults and of the occurrence of a significant 152 1991. Ellsworth152-187, ,, W. L., J. A. Olsen, L. N. Shijo, and S. M. Marks. amount of plate boundary motion on these faults east of the Seismicity and active faults in the eastern San Francisco Bay San Andreas fault. region,in Proceedings of the Conference on Earthquake Hazards in the Eastern San Francisco Bay Area,edited by E. W. Hart, S. C. Hirschfeld,and S. S. Schulz,Spec.Publ.62,pp.83-91.Calif. CONCLUSIONS Div.of Mines and Geol., Sacramento, 1982. Fox, K. F., Tectonic setting of late-Miocene, Pliocene and Pleis- Within the Coast Ranges between San Francisco Bay and tocene rocks in part of the Coast Ranges north of San Francisco. the town of Healdsburg the Rodgers Creek fault may pose California, U.S. Geol.Surv. Prof. Pap., 1239, 33 pp., 1983. the highest level of seismic hazard in the next few decades. Furlong,K.P.,W.D.Hugo,and G.Zandt,Geometry and evolution However, despite the relative absence of moderate to large of the San Andreas fault zone in northern California,J.Geophys. historical earthquakes east of the San Andreas fault (the Res.,94, 3 1989. Harsh, P. W.... EE.. HH.. Pampeyan, and J. M. Oakley, Creep on the largest being the 1898 M 6.5 and the 1%9 ML 5.7 and 5.6 Willits fault, California (abstract), Earthquake Notes, 49, 22, earthquakes),abundant geological evidence and the contem- 1978. porary seismicity attest to significant potential hazards from Hart, E. W., Rodgers Creek fault, Sonoma County, California, other faults, especially within the Santa Rosa block. These Fault Eval.Rep.FER-141,20 pp.,Calif.Div.of Mines and Geol., Sacramento, 1982a. H include, most prominently, the Maacama. Healdsburg, and art. E. W.,Tolay fault, Sonoma County, California, Fault Eval. Bennett Valley faults, which based on their lengths, appear Rep. FER-140, 13 pp., Calif. Div. of Mines and Geol., Sacra- capable of generating Mw 6-7+ events. Such earthquakes mento. 1982b. could have a significant impact on a growing urban popula- Herd.D.G., Intracontinental plate boundary east of Cape Mendo- tion expanding northward from San Francisco Bay. Hope- Gino, California,Geology,6, 721-725, 1978. Herd, D. G., and E. J. Helley, Faults with Quaternary displace- fully, future paleoseismological investigations will be per- ment. northwestern San Francisco Bay region, California, scale formed along these faults to accurately characterize their 1:125,000, U.S. Geol. Surv. Misc. Field Stud. Map, MF-818, seismogenic behavior. Such studies will most likely reveal a 1977. greater hazard from these faults, with regard to the size and Herd, D. G., E. J. Helley, and B. W. Rogers, Map of Quaternary recurrence of their maximum or characteristic earthquakes, faulting along the southern Maacama fault zone,California,scale q 1:_4,000, U.S. Geol. Surv. Open File Map, 77453, 1977. than that indicated by the historical record. Huffman, M. E., and L. F. Armstrong, Geology for planning in Sonoma County,Spec.Rep.Calif.Div.Mines Geol.,110,31 pp., 1980. Acknowledgments. I would like to extend my gratitude to the Lahr,J.C.,HYPOELLIPSE/VAX:A computer program for deter- WCC Professional Development Program and the Sonoma County mining local earthquake hypocentml parameters, magnitude and Department of Public Works for their support of these studies. My first motion patterns, U.S.Geol.Surv. Open File Rep.84-519,66 thanks to Doug Wright,Al Ridley,Sam Spencer.and Sue Penn for pp., 1984. their assistance in this study. I would like to give special thanks to Lisowski. M..J. C. Savage,and W. H. Prescott,The velocity field the U.S. Geological Survey, Menlo Park, and. in particular, to along the San Andreas fault in central and southern California,J. David Oppenheimer,Rick Lester,Jerry Eaton.and David Schwartz Geophys.Res., 96, 8369-8389, 1991. for unselfishly providing data and sharing their knowledge.Thought- Merriam, M. K., A microearthquake study of a region east of the ful reviews by Karin Budding and Jean Olson of the USGS are Geysers, northern California: Operation of a network of seismic greatly appreciated. recorders,data processing and interpretations in view of regional a. 19,904 WONG: COAST RANGES SEISMICITY, FAULTIN- AND SEISMIC HAZARDS • and local tectonic regimes, 256 pp., M.S. thesis, Univ, of Calif., California earthquakes,Open File Rep.81-11, 181 pp.,Calif.Div. Davis. 1986. of Mines and Geol., Sacramento, 1981. Miller, C. K., and K. P. Furlong,Thermal-mechanical controls on Upp, R. R., Evidence of Holocene activity on the Maacama fault seismicity depth distributions in the San Andreas fault zone, zone, Mendocino County, California (abstract), Geol. Soc. Am. Geophvs. Res. Lett., 15, 1429-1432, 1988. Abstr. Programs, 12, 157, 1980. Oppenheimer.D.H.,Extensional tectonics at The Geysers geother- Wagner,D. L..and E.J. Bortugno,Geologic map of the Santa Rosa mal area, California.J. Geophys. Res.. 91, 11,463-11,476, 1986. quadrangle.California,scale 1:250,000,Reg.Geol.,Nap Ser.2A. Oppenheimer. D. H.. Aftershock slip behavior of the 1989 Loma Calif. Div. of Mines and Geol., Sacramento, 1982. Prieta. California earthquake, Geophys. Res. Left., 17, 1199- Warren. D. H., and C. Scofield, Aftershocks of the 22 November 1202, 1990. 1977 earthquake at Willits, California: Activity on the Maacama Oppenheimer. D. H.. P. A. Reasenberg,and R. W. Simpson. Fault fault zone.Bull. Seismol. Soc. Am., 75, 507-518, 1985. plane solutions for the 1984 Morgan Hill, California earthquake Wesson.R. L.,J.C. Roller,and W. H. K. Lee.Time-term analvsis sequence: Evidence for the state,of stress on the Calaveras fault, and geologic implications of seismic travel time data from the J. Geophys. Res., 93, 9007-9026, 1988. Coast Range of central California, Bull. Seismol. Soc. Am., 63, Page, B. M., The southern Coast Ranges, in The Geotecrom.c 1447-1471, 1973. Development of California, vol. 1. edited by W. G. Ernst, pp. Wong, 1. G.,Seismotectonics of the Coast Ranges in the vicinity of 329.417, Prentice-Hall, Englewood Cliffs. N. J., 1981. Lake Berryessa,northern California,Bull.Seismol.Soc.Am..80, 935-950, 1990. Pampeyan. E. H., Preliminary map showing recency of faulting in Wong, 1. G., and N. Biggar, Seismicity of eastern Contra Costa coastal north-central California. U.S. Geol. Surv. Map MF-1070, County,San Francisco Bay region,California,Bull.Seismol.Soc. 1979. Am., 79, 1270-1278, 1989. Prescott, W. H.. and S. Yu.Geodetic measurements of horizontal Wong, 1. G., M. A. Hemphill-Haley, and D. H. Wright, What and deformation in the northern San Francisco Bay region.California, where is the Mission fault in the eastern San Francisco Bay area. J. Geophys. Res.. 91, 7475-7484, 1986. California(abstract), Seismol. Res. Lett., 62, 51, 1991. Real,C. R..T. R.Toppozada.and D. L. Parke. Earthquake catalog Working Group on California Earthquake Probabilities. Probabili- of California.January I. 1900-December 31. 1974,Spec.Publ.52. ties of large earthquakes occurring in the San Francisco Bay 39 pp., Calif. Div, of Mines and Geol.. Sacramento. 1978. region. California, U.S. Geol. Surv. Circ. 1053. 51 pp., 1990. Reasenberg, P. A.,and D. H. Oppenheimer, FPFIT. FPPLOT and Zoback,M.D.,et al.,New evidence on the state of stress of the San FPPAGE: FORTRAN computer programs for calculating and Andreas fault system. Science,238, 1105-1111. 1987. displaying earthquake fault plane solutions, U.S. Geol. 'Surv. Open File Rep.,85-739, 109 pp., 1985. 1. G. Wong, Woodward-Clyde Consultants. 500 l2th St.. Suite Steinbrugge,K.V.,W. K.Cloud,and N.H.Scott.The Santa Rosa, 100,Oakland, CA 94607. California, earthquakes of October 1, 1%9, report, 99 pp., U.S. Coast and Geod. Surv., Rockville, Md., 1970. (Received May 23, 1991: Toppozada, T. R., C. R. Real. and D. L. Parke, Preparation of revised July 29, 1991; isoseismal maps and summaries of reported effects for pre-1900 accepted August 20, 1991.)