ML19254D985

Special Publication 54, Technical Review of Seismic Safety of Auburn Damsite

ML19254D985
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Issue date:	05/31/1979
From:	CALIFORNIA, STATE OF
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& GE TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE

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Prepared by THE CALIFORNIA DIVISION OF MINES AND GEOLOGY 791030o31o

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STATE OF CAliFORNfA EDMUND G. BROWN JR.

GOVERNCR THE RESOURCES AGENCY HUEY D JOHNSON SECRETARY FCR RESCURCES DEPARTMENT OF CONSERVATION P91 SCILLA C. GREW DIRECTCR DIVISION OF MINES AND GEOLOGY JAMES F. DAVIS STA TE GEOLOGIST 1229 20 o

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SPECIAL PUBUCATION 54 A

TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE By California Division of Mines and Geology Staff James F. Davis, State Geologist and C. Forrest Bacon, Senior Geologist in association with John H. Bennett, Glenn A. Borchardt, Chris Cramer, John T. Ragsdale, Salem J. Rice,

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Gary C. Taylor, and Tousson R. Toppozada. \\

Assisted by Quintin A. Aune, Richard T.

Kilbourne, and Lalliana Mualchin.

May 1979

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32l California Division of Mines and Geology 1416 Ninth Street, Room 1341 Socramento, CA 95814

PURPOSE OF THIS REPORT This report sets forth the general conclusions eoched by the Califomio Division of Mines and Geology ( CDMG) as a result of its onc;ysis of the seismic design parameters of the proposed Aubum dom. The CDMG conclusion regarding the amount of the surface fou't displacement is port of the State of Cali'omic position regarding the earthquake design requirements of the Aubum dom which was transmitted by Huey D. Johnson, Secretary for the Resources Agency,in a letter to Cecil Andrus, Secretary of the United States Department of the Interior. A copy of thi: correspondence is presented in the succeeding pojes of this section.

The discussion of the CDMG surface faulting displacement parameter is the most impor-tant segment of this report. Since this conclusion is interrelated with CDMG conclusions regarding the size of the Maximum Credible Earthquake, and the size and proximity of earthquakes which may occur at the dom site, these subjects are treated first.

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CONTENTS PURPOSE OF REPORT iii INTRODUCTION 1

ROLE OF THE CALIFORNIA DIVISION OF MINES AND GEOLOGY PRINCIPAL CDMG CONCLUSIONS REGARDING THE AUBURN DAM EARTHOUAKE DESIGN PARAMETERS 1

1.

THE NATURE OF DEVELOPMENT OF EARTHOUAKE DESIGN PARAMETERS FOR FOR THE PROPOSED AUBURN DAM 2

II.

CDMG DESIGN PARAMETER CONCLUSIONS FOR TH8. PROPOSED AUBURN DAM 2

A.

Maximum Credible Event 2

Evidence for a M 6.5 MCE Based Upon Seismic History Evidence of MCE from Foult Offset of Paleosols Evidence for MCE Derived from Length of Foutting Relationships B.

Proximity of Fault Movement to the Dom Foundation

... 7 Geologic Structures in the Foundation T-zones, and Movement on the Maidu Zone Potential for MCE Associated with Favits in the Foundation Potential for Surface Faulting Within the Dom Foundation Area F-1 Structure F-4 Structure Movement of F-0, F-1 Latvel Line Dato C.

• Ground Motion Design Porometers.

12 D.

Surfoce Faulting Design Parameter for the Do nsite 12 Potential for Sympathetic Movement on F-1 and F-O Fault Gouge Evidence Eridence from Displacemant Curves Geologic Evidence of Displacement in the Sierra Foothills Foult System E.

Significance of the Surface Faulting Porometer in the Design of Aubum Dom

. 14 value Based on Geology Compared with Fault Displacement Curves Significance of the Design Porometer Related to Frequency of Recurrence Rote Historical Displacement Record-Seismic History Comparison of Seismologic and Geologic Records Recurrence in Years for Latitude of Aubum Dom Based on Dougios and Ryall(1977) Method F.

Reservoir Induced Seismioty ( RIS) 15 111.

SUMMARY

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THE RESOURCES AGENCY OF CAllFORNIA SACRAMENTO, Call:C?NIA MAR 51979 Honorable Cecil D. Andrus Secretary of the Interior Interior Building, Room 6151 Washington, DC 20240

Dear Mr. Andrus:

The State of California has completed the review of the seismic loading.paraceters for the Auburn Dansite.

The Department of Water Resources Consulting Board fo:- Iarthquake Analysis for Auburn Dan which was engaged to revieu our work hhs had its final meeting and issued its concluding report; the report is enclosed.

The Board's report considers the work accomplished by the U. S.

Bureau cf Reclamation, Bureau consultants, the review of the Woodward-Clyde Consultants report by the U. S. Geological Survey, and work accomplished by staffs of the Department of Conservation and the Department d' tlater Resources.

The State revieu followed the activities list:og which is shown en page 33 of the Bureau's report entitled " Auburn Damsite Seistic Studies Overview, An Overview Report on the Seismic Investigations Conducted for the Auburn Damsite."

The State Geologist has submitted a cerorandum report (also enclosed) which differs frca the Board's report only in the matter of the amount of fault displacenent which should be con-sidered to occur in the foundation rock'during one earthcuake event.

He recer. ends that the dam te designed to withstand a displacenent of three-quarters of a f Ot rather than the 5 inches presented in the Scard's report.

The State regards the scard's report as establishing minimum crite'la for rn;- dan at the Auburn site.

The State of California will c;ocse cenatruction of any dan at that site which does not 122')

325

I!AR 5 G 79 Honorable Cecil D. Andrus Page 2 neet those criteria.

However, in view of the State Geologist's opinion we encourage development of a design that would perni; the structure to withstand a fault displacecent of three-quarters of a foot.

We appreciate the cooperation provided and the many hcurs intested by your Agency during this seismic safety review uhich have cade the completica of the first step possible.

Sincerely, g

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Huey D. Johnson Secretary for Resources Enclosures cc:

Honorable R. Keith Higginson Concissioner of Reclamation U. 'S. Department of the Interior Interior Building, Roon 7o54 Washingtori, DC 20240 A

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Mr. S. E. Martin, Regional Director Mid-Pa'cific Regional Office U. S. Bureau of Reclamation 2800 Cottage Way

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' Stats of California The Resources Agency Memorandum Priscilla C. Grew, Director Date: February 23, 1979 to Department of Conservatioq

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Auburn Dam This memorandum summarizes my recommendations to the Departments of Conservation and Water Resources regarding earthquake hazard design parameters for the proposed Auburn dam.

I have developed these conclusions together with staff members of the California Division of Mines and Gcology (CDMG) in order to fulfill the role of the Department of Conservation in its participation in the development of a State position on the geologic and seismic design parameters which the U.S. Bureau of Reclamation (USBR) should consider for the proposed dam'.

Other participants in developing the State's position have been the Division of Safety of Dams (DSOD) of the Department of Water Resources (DWR), and the Consulting Board for Earth-quake Analysis for Auburn dam which advises DWR.

The CDMG presented its preliminary conclusions regarding de, sign parameters for Auburn dam to the Consulting Board during the Board's delibtrations in late November. When the Consulting Boa.4's report was presented 4n January, I deter-mined that the CDMG conclusions on cesign parameters were all comparable to those of the Consulting Board, with the single exception of displacement related to surface faulting. Specifically, CDMG's earlier conclusions concurred with the Consulting Board's recommendations that Magnitude 6.5 is a conservative and an appropriate value for the Maximum Credible Earthquake (MCE), that reservoir induced seismicity may sometimes alter the natural earthquake occurrence rate, and that the spectral response acceleration at the 1.0-second period should be about 50 percent gravity.

In its earlier evaluation, CDMG had concluded that a surface faulting displacement of 1 to 2 feet within the dam foundation rock might be associated with the design earthquake if it were to occur in the vicinity of the proposed structure.

The Consulting Board reached the conclusion that an appropriately conservative design requirement is that the dam be able to survive, without uncontrolled release of water from the reservoir, fault slip in the foundation rock of up to 5 inches.

They further concluded that this may or may not be distributed over several faults.

I and my staff have reviewed our earlier position regarding the amount of surface displacement in the foundation rock in the context of the Board's conclusion.

None of the informati0n reviewed in this process is new and all of it has been included in materials considered by other parties. We. have focused upon the following aspects in our review:

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e The propensity for surface faulting in the region in the context of its structural geologic and earthquake history.

e The literature data on the amounts of surface fault displacement associated with earthquakes in the Magnitude 6 to 6.5 rar.ge.

e The recurrence rate of earthquakes in the Magnitude 5.0 to 6.5 range, using the relationship of the log of cumulative number plotted against magnitude, the regional geologic field evidence of surface fault dis-placement rates and the method of evaluating recurrence of surface faulting employed in another area by Douglas and Ryall (Bulletin of the Seismological Society of America,1977).

e The geometry of offsets of paleosols and/or colluvium exposed in trenches made within the Sierra Foothills region in studies conducted en behalf of USBR prior to June 1978 and including specifically the Spenceville, Swain Ravine and Oroville areas.

e The geometry and characteristics of fault structures in and near the proposed Auburn dam foundation, especially F-1, F-0, and several T zones including the Maidu East structure.

e The relationship of fault structures in and near the proposed Auburn dam foundation to the regional structures of the Sierra Foothills fault system.

e The literature sunearizing the world-wide distribution of case histories of reservoir-induced seismicity and evaluation of event correlations with reservoir depth, volume and faulting.

In gur opinicn, the profession generally concurs that the sta'ta-of-the-art in evaluating the propensity for and cxtent of surface faulting ab a specific site requires weighing and weighting of evidence such as that enumerated above, in c decision-making process, and includes value judgments regarding both the signifi-cance of what is known and what remains to be established.

It is my conclusion and my recomendation to DWR that a surface displacement of up to three quarters (3/4) of one foot, or nine (9) inches, should be considered as the design paramater with the possibility of this movement taking place along a single fault surface or distributed among several.

It is my understanding that you support my position.

As you know, I have presented my conclusions, together with the technical rationale for them, to a joint meeting of the Department of Conservation and the Department of Water Resources.

It has been agreed by both the Departments of Conservation and Water Resources that my conclusion regarding surface faulting would be presented to the U.S. Department of the Interior as part of the State position on seismic loading parameters.

Since the process of reaching a surface faulting displacement conclusion is somewhat judgmental, I view the reconmended nine (9) inches as appropriately conservative.

Design for smaller displacements of the foundation rock, become progressively more acceptable, in my opinion, as they approach the reconmended nine (9) inches.

1229 28 K

We will be releasing a special report in early March which will detail the technical rationale for each of our design parameter conclusions, f

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23 December 1978 Mr. James J. Doody, Chief Division of Safety of Dams Post Office Box 388 Sacramento, California 95802 During the past one and one-half years the Consulting Board for Earthquake Analysis for Aubum Dam has been studying the problems posed by the possible occurrence of earthquakes in the vicinity of Auburn Dam site.

'Ihe Board has reviewed reports and heard technical presentations from various agencies, including Woodward-Clyde Censultants, the U.S. Bureau of Reclamation, the U.S. Geological Survey, the State of California Division of Mines and Geology, the State of California Division of Safety of Dams, and individual consultants to the Bureau of Reclamation; and the Board has also reviewed comments and suggestions offered by qualified' members of the public.,The members of the Board have each inspected the d site and its vicinity one or more times. The Board is aware of the importance of the Auburn Dam Project both in providing future benefits to the public and in the necessity for insuring public safety. In its approach to the problem the Board has considered that its primary responsibility is to the public and its reccmmendations are made accordingly.

Auburn Dam site is in a region that has had relatively low historical seismicity. Earthquakes of potentially destructive magnitude have not occurred in this region, and strong ground shaking has not been experienced, during the period covered by historical records. 'Ihe site spans abcut one half of the Foothills Fault System whose tectonic activity was greatest over 65 million years ago. Based on the evidence at hand, it can be concluded xiii 1229 330

that the probability of an earthquake of Richter magnitude 6 or greate:-

occurrir4 close to the das site durirg the projected life of the dam is very sma'i.

In view of the exposure of the public, however, the possibility of an earthquake of engineering significance occurrir4 in the vicinity of the site during the life of the dam can not be ruled out of consideration.

It appears that small to moderate earthquakes may have been produced by fault movement in the general vicinity of the dam site during the past 100,000 years. Utere is also evidence that large reservoirs sometimes alter the natural earthquake occurrence rate nearby. In addition, the occurrence of an earthquake of magnitude 5.7 in the vicinity of Oroville in 1975 raises the possibility that an earthquake of similar magnitude might occur in the vicinity of Auburn Dam Site.

Since the reservoir behind Auburn Dam would contain a large volume of water whose uncontrolled release would be hazardous to the public, the

' design of the dam must be based on very conservative req %irements.

In the opinion of the Board, the earthquake design criteria should be more con-servative than those corresponding to earthquakes that might normally be expected during the lifetime of the dam.

Based on these considerations the Board therefore responds to the questions asked of it, as follows:

Question 1.

Attached is a list of the seismic loading parameters the U.S. Bureau of Reclamation has proposed for use in the design of a major dam at the Auburn site. Does the Board believe the proposed para-meters are appropriate?

Die Board believes that a magnitude 6.5 earthquake is a very conservative event to postulate in the vicinity of the dam.

In the opinion xiv 1229

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of the Board, a very conservative design would result if the dam were able to survive, with-nt uncontrolled release of the water from the reservoir, the following postulated earthquake motions:

a)

A small set of time-histories of accelerations each having a peak ground acceleration of 0.6g, a duration of strong shaking (greater than 0.05g) of about 12 seconds and such that the mean plus one standard deviation spectral shape has at least the' values specified in the following table.

Period (sec)

Ordinate (%g) 0 60 0.1 150 0.2 165 0.3 150 0.4 110 0.6 75 1.0 50 1.4 40 In addition, the time-history of motions should include char-acteristics representative of a ' fling' in the ground motions which has been noted to occur at locations close to a fault in previous earthquakes. he spectrum shape defined by the above table makes allowance for the effects of such a fling in the longer period portion.

In addition to this, however, the

' fling' effect in time-history representations should have motions with a peak acceleration of about 0.35g and a period of about 1 second.

b) he Board is of the opinion that the dam should be capable of withstanding possible fault displacement in the foundation, even though this is a remote possibility. An appropriately conserva-tive requirement is that the dam be able to survive, without XV

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uncontrolled release of water from the reservoir, fault slip in the foundation rock of up *.o 5 inches this may, or may not, be distribute' over several faults.

Question 2.

Does the Board endorse the 100,000 year age criterion for determining fault activity in the area of the Foothills fault system and specifically in the vicinity of the proposed Auburn dam?

he fault activity criterion in terns of a specific numerical age of the last displacement on a fault,has generally proved useful in the geolo-gical investigation for the Auburn dam site. The USBR criterion in this case was 100,000 years and many special studies of faults in the area were directed to this time boundary. Se Board wishes to emphasize, however, that to the extent that the specification of such a precise age limit is arbitrary it sometimes leads to unproductive geological effort due to the absence of appropriate stratigraphic evidence. Se most effective proce-dure is to set fault activity criteria for each site in terms of the local a

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geological conditions and nature of the project.

Question 3.

In your report of June 30, 1977, the Board requested additional surveys of level profiles across the Bear Mountains and Melones fault zones. Does the Board believe the results are definitive for inter-pretation of tectonic strain?

me Board is pleased that the additional surveys were acecmplished as the results have been useful in reaching our conclusions. Although the surveys do not provide specific information on differential ground movements within the dam site, they do confirm the geologic evidence for identification and location of the Bear Mountains fault tone and classify demonstrate that regional deformations are occurring across that zone.

Lacking evidence to the contrary, the observed elevation changes may be 1227 333

attributed to regional tectonics. The observation that the Auburn Dam site lies within the area of deformation in the fault zone is one influencing factor used by the Board in applying conservatism to its judgments on earthquake motions the dam should be able to withstand.

Level profiles of the type performed are useful in identifying changes in rates, or locations, of movement across the Bear Mountains fault zone. Since such information could be useful in the Department's overall dam safety program in the future, the Board reccmends that the line be resurveyed at about five year intervals.

Question 4.

Is the strcng motion accelerogram at Pacoima Dam during the 1971 San Fernando earthquako suitable for inclusion in the data set used to develop response spectra for design of a dam at, Auburn? If so, is the original, or one of the deconvoluted versions, most appropriate and how should it be used?

The Board is of the opinion that the Pacoima Dam record contains a

valuable information about ground shaking on the crest of a hidge, pro-duced by an earthquake generated on an underlying thrust fault. The Board does not believe that it is appropriate to transfer the original Pacoima Dam accelerogram to the different situation pertaining at the Auburn Dam site.

Nor does the Board believe that it is appropriate to give much weight to the spectral characteristics of the Pacoima Dam accelerogram in a set obtained from other accelerograms of more uc.ual type. The Board does believe that it is appropriate to modify a hypothetical ground motion to reflect the information contained in the Pacoima Dam accelerogram.

Question 5.

Does the Board have any additional cements that might bear on the seismic safety of a major dam at the Auburn site?

Ybbih XVII

The Board commends the Bureau of Reclamation, the censultants, the Department of ' dater Resources, the Division of Mines and Geology, and the U.S.

Geological Survey for the extensive investigations made of the das site and surrounding regicn. The infor=ation provided by these investigations has been of great value. These investigative efforts have been exceptionally thorou6h and, in the opinion of the Board, additional infor=ation of significant value to the Auburn Dam Project would not be expected from further invest-igations.

Respectfully submitted, p)f/,s orge CHousner, Chairman Douglas DJ Campbell

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TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE INTRODUCION on Auburn dam and transmitted as an attachment to the March 5.1979,!cttar by Huey D. Johnson, Secretary for the California Resources Agency, to Cecil D. Andrus, Secretary of 'he Dited Role of the Caliform.a Dm...sson of States Department of the Interior.

Mines end Geology ( CDMG)

PRINCIPAL CDMG CONCLUSIONS in proceeding with the independent State review of the safety REGARDING THE AUBURN DAM of the proposed Auburn dam, the Departments of Conservation EARTHQUAKE DESIGN PARAMETERS and Water Resources have developed a State of California posi-tion on the geologic and seismic parameters to be used i. its design. The task of developing and presenting the parameters to CDMG DESIGN CONCLUSIONS INCLUDE THE Follow-fuhill the role of the Department of Conservation was undertak-ING en by that Department's Division of Mines and Geology (CDMG). Other participants in developing the State's position

• The dam should be able to accommodate surface faulting in have been the Division oiSafety of Dams (DOSD) Department the foundation up to three quarters of one foot ( 9 inches) along of Water Resources (DWR), and the Consulting Board for a single surface or currtulatively along several surfaces. This Earthquak.e Analysis for Auburn dam which has advised DWR.

conclusion is comparable to the WCC recommendation of 0.8 The resultsof this effort by CD MG are outlined on the following foot surface displacement. It is less than the three feet of surface pages.

fault displacement the USGS states is conceivable using the available geologic data, and it exceeds the one-inch displacement The CDMG made field investigations and described geologic proposed by the USBR' and.the 5-inch displacement presented structures exposed during the 1977 trenching and mapping ac-by the Consulting Bard in its advisory report to the State DWR.

tivities associated with the consulting services provided by Woodward-Clyde Consultants ( WCC) to '. a United States Bu-

. The surface faulting par's(neter is the pnncipal point of reau of Reclamation (USBR) in order to establish an improved difference between the conclusiogs reached by CD MG and those structural and seismic context for considering Auburn dam de-of the S; ate Consulting Board to DWR. In the State position sign conclusions. Additionally, CDMG has evaluated all of the (the March 5 ! citer). Secretary Johnson stated that California WCC report volumes which detail the conclusions reached by would oppose any USBR design criteria which are less rigorous this consulting group. CDMG has observed exposures developed than those presented by the Consulting Board. Additionally, he during the USBR staff mapping and analysis of the dam founda-encouraged the Department of the Interior to develop a design tion and immediately adjacent areas. CDMG has also coi.sidered which would withstand surface fault displacement of tbree-the conclusions reached by the United S:stes Geological Survey quarters of a foot as recommended by the State Geologist.

(USGS) in its July 1978 review of the WCC studies of the Auburn dam atta. CD MG staff held numerous technics discus-

• The Maximum Credible earthquake Event ( MCE) =hich s;ons with DSOD during the course of developing its conclu-CDMG considers appropriate for the Sierra Foothills fault sys-sions. Tne CD MG staff presented its tentative conclusions to ti e tem is Richter 6.5 magnitude. This conclusion is similar to those Consulting Board for Earthquake Analysis for Auburn dam conclusions reached by WCC, the USGS. the State Consulting during that board's deliberations. This report outlines the final Board, and the USBR. The USGS, however, has stated that the conclusions of the CDMG, which were initially put forward by range for the MCE is 6.5 to 7.0.

James F. Davis, State Geolegist an( J aief of CD MG to Priscilla C. Grew. Director of the Depar en at of Conservation, in a

= Ground motion severity which the Auburn dam rnust be memorandum report dated February 23,1979. That memoran-constructed to withstand is derived from each investigator's per-dum report was incorporated into the State of California position ception of the proximity to the damsite that the MCE can take place, the manner in which the wave form attenuates between its origin and the site, and the general ground response spectrum

• Aaotoms to the my 19'9 t, SBR reprt enutled. Amburn Damsne Ermmm:

associated with the MCE.The CDMG concludes that a response st o.es Summarv.* the LS8R stairconcisded that no dopiacement cuvid take place in tk roundataos. In a tabse summarmag the evaluauuns or the various acceleration of 0.50g in the I second portion of the spectrum is parues.no have

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appropriate for the site. This is similar to the State Consulting con.unnts to tsBa are prewsted as asrer as apon e o piacement dapprou.

Board's recommendation, although the conclusions *ere not maiety one inen. Dr clarence raen. one a these rm consuitanta. iesuried in derived in precisely the same manner. Results differ from the response to a q.c.uo p.ed. tw way n, it's hearms d ik t. SBR in Sacramento on Asburn dam seismic parameters that be would be comfortable USBR value of 0.29g for the same period. Employing the 34th percentile, the WCC value. 0.45g. The USGS. using the Pa:oi-is

.un a de sn inat a.itastand on tw oroer or.ncus or rrace ra is dispiacement.

ma record, obtained a value of 1.lg.

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2 CALIFORNIA DIVISION OF MINES AND GEOLOGY SP54 1.

The Nature of Development of Earthquake 11.

CDMG Design Parameter Condusions Design Parameters for the Proposed Auburn for the Proposed Aubu.n Dom Dom A.

MAXIMUM CREDIBLE EVENT:

An earthquake design parameter for an engineered structure is a requirement for performance which the constructed entity As previously stated, there is general agreement among the must provide and still maintain its prescribed functions. In earth scientists evaluating the seismicity in the Auburn dam area reaching a conclusion agarding carthquake related design re-that the MCE on the Foothills fault system is a M 6.5. This quirernents, earth scientists must distinguish between ihose cita-CDMG conclusion is based upon the scismic history of the area, strophic events which are only remote!y geologically plausible evidence of significant fault offsets of geologically young materi-and those which are less severe but which have sufScient proba-als includmg palcosols, the general length of fault zones in the bility of occurrence to require construction measures that will Serra Foothills (240 km, figure 1), and the relationships accommodate their effects.

between the length of the ground surface rupture pattern as-sociated with the 1975 M 5.7 Oroville carthquake as a context for considering the s'atistical relationships between length of Cntical structures, such as dams, can pose a significant threat faulting and magnitude, sy nthesized from observations in North to offsite populations and property downstream if they are not Amenca' constructed in a fashion which will foreclose the possibility of an uncontrolled release of water as a result of signiGcant future The LSGS has concluded that the MCE for the area is 6.5 to earthquakes occuning in their ir tmediate vicinity.

7.0. The CDMG considers a magnitude 7.0 MCE to be exceed-ingly unlikely and not appropriate for a dam design parameter The surface faulting design parameters for a dam, such as the in this area.

proposed Auburn dam, most include consideration of the MCE for the region in which the structure is ta be situated. The Evidexe /or o M 6.5 MCE Based Upon Seismic History frequency of occurrence of such events and smaller events which are capable of creating ground rupture needs to be established.

The faulting in the dam foundation and its vicinity must be

. Two rr.agnitude 5.5 o,r greater earthquakes have occurred evaluated and the propensity for and amount of earthquake since 1900 along portions of the northern Foothills fault system associated ground rupture assessed. The potential for reservoir (Ggure 2b nis evidence of moderate seismic activity indicates that the MCE _s probably somewhat higher than M 5.5. As i

irduced seismicity must be evaluated and the extent to which it could reduce the natural recurrence rev must be considered. All previously stated, the MCE is not the largest event that can these factors, along with the planned life span of the dam, must c nce vably take place. It is, rather, the largest event the occu -

be carefully considered w hen a judgment rega-ding the potential rence of *hich is sufDciently credible to merit consideration in for surface fault displacement is made.

setsmic safety design.

A Unfortunatelys in some parts of the country, the probability of Figure 3 shows the distributioh of the cumulative number of an earthquake of sufficient size to cause ground rupture affecting earthquakes of various magmtudes during the last 78 years in the a foundation is difncult to determine as a rigorous and unique Sierra Foothills. The largest earthquake was the M 5.7 Oroville conclusion. This,in our opinion,is true of the proposed Auburn carthquake of August 1975. The second largest earthquake was damsite. ne MCE for the Serra Foothills region containing the the M 5.5 Downieville earthquake of June 1909, whose magni-damsiw has been generally accepted to be Magmtude (M) 6.5 tude was estimated from the intensity values usmg the method by most investigators. This region and its fault system are illus-of Toppozada (1975): the maximum reported intensity VI to trated in Figure 1. The proposed Auburn damsite has faults VII yielded M 5.0 to M 5.7; the area of 2400 km shaken at 2

passirig through it. The likelihood or probability that these faults intensity V and greater yielded M 5.5, and the total felt area of might be directly associated with an earthquake of sufficient about 70.000 km: yielded M 5.5. A magnitude of 5.0 was estimat-magmtude ( 5.5 to the MCE of 6.5) to cause significant surface ed fer the March 1909 Downieville earthquake using the same displacement to take place along one or more of them dusing the hfetime of the dam is the entical issue in establishing the surface faulting design parameters. The tectonic functions of the faults in the foundation, the geologic history of these faults, the amount The r tlation tog N = a-bM was 'itted to this data set, using of surface offset which can be anticipated with earthquakes a 'b' slope of unity, which is a common 'b' value for California between M 5.5 and M 6.5. the etTect upon adjacent faults, wben as shown by the earthquake catalogs of both U.C. Berkeley and displacement occurs along one fault, and the potential for sigmfi-Caltech. Extrapolating from a M 5.7 event in 73 years to M 6.5, cant earthquakes betng induced by reservoir impoundment - all we find that the recurrence of the MCE is about 500 years in the are principal factors which must be clarified and weighed during 125 km fault system that was sampled.

the derivation of this deign parameter.The investigators of the Auburn damsite have recommended construction design param-The CDMG recurrence interval is one third that of Dr. Lane eters based upon differing interpretations of the prospects of Johnson, one of the consultants to the USBR. The results difTer these phenomena. At this present stage of development of the because different data sets were used; the CDMG data set in-carth sciences the interpretations are inevitably value judgments cludes the M 5.7 Oroville earthquake, w hereas Dr. Johnson's did and ditTering conclusions result from different manners of weigh-not: CDMG assigns M 5.5 to the June 1909 Downieville earth-ing the available evidence, despite the fact that all of the partici-quake based on all the intensity cata reported, whereas Dr.

pants are proceeding with equally good faith to achieve public Johnson assigned M 5.0 to this event based on the single value safety.

of maximum intensity.

J.z '1

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1979 TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE 3

EXPLANATION FOOTHILLS FAULT SYSTEM

/ revits, dashed enere approaimately located, detted enero conteeled.

g=5 Sheer Zone.

Modified from Surnett and Jennings,19421 Strand and Koenig,1945 Rogers 1944 Hiet e n e n,19736 Jennings,1975; Clare,1976.

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4 CALIFORNIA DIVISION OF MINES AND GEOLOGY SP54 BOUNDARY OF SEISMICITY SEARCH EMPLOYED IN THE RECURRENCE ANALYSIS 12f.00 It'

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Agure 2.

Earthquohes of magnitude 2 4.0, 1900-1977.

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1979 TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE 5

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6 CALIFORNIA DIVISION OF MINES AND GEOLOGY SP54 Evidence of Maximum Credible Event from Fault Offset of to have ofTsets up to 6 cm. The length of the rupture zone p,f,,,,f, expanded during the aftershock sequence to approximately 11 km. The total length was made up of a series of short en echelon The regional investigations conducted by Woodward-Clyde breaks that resemble fault patterns seen elsewhere m the Foot-Consultants and by others, including CDMG, have identified a hills area. A larger event, such as one with M 6.5 takmg place number oflocations w here palcosols and/or colluvium appeared at a comparable depth of 8 km, would be expected to have a to be significantly offset (see table 1). General observations s smficantly longer rupture length. The relationship of rupture throughout North America (Slemmons and others) indicate length to magnitude has &cen examined recently by Stemmons that notable fault displacement is restricted to events generally (1977). The length of rupture reasonably associated with a M exceeding M 5.5. Some investigators have concluded that the 6.5 event ranges from 5 km to 30 km.

masimum age of the palcosols may be between 100.000 to 140,-

000 years. The minimum age has been intetpreted as being ap-dward-Clyde Consultants concluded that, based upon W

proximately 10.000 years. In any case, significant carthquakes fault rupture length, a magnitude 6 to 6.75 event is possible.

larger than about M 5.5 have occurred in the Sierra Foothills However, they also concluded that, because fault lengths in the fault system during relatively recent geologic time. This relation-Sierra Foothills are not well defined, they preferred other meth-ship does not prove the MCE to be M 6.5, but it is compatible ds f r determining the MCE, such as comparison with similar with such a conclusion.

faults elsewhere, seismic source parameters, and shp relation-ships. It should be pointed out that the length relationships yicided the hsghest magnstude numbers.

Evidence for MCE Derived froen length of F.viting Relation-ships The USGS concurs that Cenozoic deposits are insufficient to allow a meaningful estimate of the length oflate Cenozoic fault-Surface rupture alcng the Bear Mountain fault zone has been ing, but also points out that for such an estimate it is appropriate well documented. In the Oroville area, surface faultmg associat-to use the maximum overall length of multiple discontinuous ed with the M 5.7 earthquake of August I,1975 was observed breaks.

Table 1.

Results of Fault Activity Assessment at Sploration

~

localities WCC ( Vol. 2, TaNe 2)

CDMG Poss>ble orTsets. cm Approssmate Level of Onanum Puernot Alavraum Displace.

Exploration Dustance froir Faul Activity CocBdence ment rates. cm/1000yr Locausty Auburn Darn Class Scauon m

Reso-

,Reso-Site Miles tLSBR Cntena) Assewnent'

\\ fin Max lution*

Mm Max 1 toon*

Holocene Pre-Holocene Spear-vale

,19 Active' 8

0 3

20 0

40 20 0.3 4

Smith Property 14 Indeterminate 4

0 0

3 30 60 20 0

6.7

( Active)

The Knolls 9

Indeterminate 4

0 0

20 0

20 20 0

2

( Active)

Lunemen Road 9

Indeterminate 4

0 40 20 0

60 20 44 6.7

( Active)

Hubbard Raad 7

Indeterminate 4

0 20 20 40 60 20 4.4 6.7

( Active)

%du East a/2 Indeterminate 2

0 0

20 0

40 40 2.2 0.3

( Active) 8HT-so ( F-0) 1 Inceterminate' 0

0 20 0

60 20 0

6.7

( Active)

Railroad Tunnel I

Indeterminate' O

O 20 0

60 20 0

6.7 (F-Oi i Active)

' CDMG wacurs was ather=me :narket

' CDMG assessment only.

' Con 6dexe scale 5etween 0 to 10 based on anscasment of certainty of conclusion.

/

• Renoeupon is the comersal warmten in the configuraten of the palmeoUcanlunum interfxe.

1979 TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUPURN DAMSITE 7

B.

VROXIMITY OF FAULT MOVEMENT TO THE DAM 64, individual branches define an anastomosing pattern in both FOUNDA TION plan and section over a zone 100 feet wide.

The anastomosing pattern and vertical displacement along Potential for fault movement in the vicinity of the dam foun-strike is typical of normal faulting that has been documented dation is the determining factor regarding assessments of ground along the western Sierra Foothills (Cleveland Hill and Table motion and surface fault displacement design parameters.

Mountain). Thse examples are incompatible with the advance-CDMG has concluded that it is possibic for the MCE of M 6.5 ment of the idea that the Maidu East has coalesced into a sing!c to take place in the immediate vicinity of the Auburn damsite.

strand with minimum vertical displacement over a short hori-zontal distance. Instead, CDMG considers it possible that the The Auburn damsite is located within the Bear Mountain movement has translated to the east to adjoining or sub parallel Zone, which is a western branch of the Foothills fault system as zones. Because the Maidu East fault lies very close to the eastern illustrated in Figure 1. Width of the Bear Mountain Zon:in the boundary of the Cenozoic Mehrten strata,a complete assessment vicinity of Auburn is approximately 3 km and includes, as major of this possibility has not been feasible. Additionally,in the area

~

elements with regional extent, the Dewitt-Salt Creek Lineament north of the dam foundation there is evidence for post-Mehrten tones on the east and the Pilot Hill-Maidu-Deadman Linea-fau! ting at the Radio Tower trench exposures that can be inte -

ment zones on the west.

preted to indicate translation of Maidu East associated move-ment from T-25 to T-16 or T-14. This evidence was discussed The Cleveland Hill fault, which exhibited rupture during the in the CDMG conclusions presented to the State's Consulting 1975 Oroville carthquake, is on the same trend as the elements Board in November 1978. One of the basic problems in interpret-of the Bear Mountain fault that pass through the Auburn dam-ng the recency of faulting in the foundation area is the general site area, and although there is no historic record of a moderate lack of Quaternary sediments that can be used to date fault or large earthquake in the Auburn vicinity, evidence points to activity.

the probability that faults in and near the dam foundation should be considered active.

T-16 and T-14 can also be interpreted as being associated or interconnected with T-9 and T-10, which cross the dam founda-The Bear Mountain fault zone, viewed in regional context, exhibits a complex pattern: major elements of regional extent tion near mid-channel. Since these faults do not cut young sedi-ments, it has not been possible to assess their recency of serve as bounding zones, but cross-cutting faults extend between the bounding zones. This is the pattern in and near the Auburn movement. However, WCC has observed that each has bedrock characteristics similar to those of late Cenozoic and active damsite where the cross-cutting faults are represented by the F-0 F-1 fault zones (figure 4). The F-1 cross-cutting farit in (USBR criteria) faults in the Sierra Foothills.

the immediate vicinity of the dam foundation may link signifi-cant lengths of NNW trending faulting on the western and east-CDMG judges the Maidu East shear zone to be indeterminate ern margins of the Bear Mountain fault zone,a zone which could (active), and although the' evidence is somewhat ambiguous, be capable of generating a MCE, movement or, the zone as recent as Holocene cannot be preclud-ed. Post Mehrten vertical o'fsit on the Maidu East of 18 feet has been documented. When this n\\mber is combined with a lateral Geologic Struervres in the Foundation component derived from dipping slickensides,it may be conclud-ed that a maximum net slip of approximately 30 feet is possible.

e The geologic structures in the fcundation of Auburn dam are of two principal types: the NNW trending T zones with nearly Hm o # M n h Mim m W W M vertical dips and the WNW trending F zones with widely varia-

, g g;

g g

g ble dips that range from nearly vertical to 40* to the south palcosol deposit, by reason of its geometry, could conceal up to (dow nstream).

40 cm of offset.This means that any movement that has occurred on this strand of the Maidu East Zone in the last 100,000 years, though small. might amount to as much as 40 cm.

T-zones, and Movement on the Maidu East Zone CDMG's investigation of the sessmic safety of the Auburn Potential for MCE Associated with Cavits in the Foundation damsite indicates that the Maidu East fault or shear zone may be a T-zone which has experienced Cenozoic reactivation and As has been mentioned above, the F zone faults, and in par-appears to otTset palcosols. The Pilot Hill lineament, w hich may ticular F-0, appear to represent major oblique cross-cutting be a conticuation of the Maidu East several miles south of the elements in the Bear Mountain fault zone. Additionally, the damsite, may thus represent a significantly long strand in the T-zone faults trend nearly p.rallel to the bounding elements of Bear Mountain fault zone. To the north, for the area in the the fault system, and some could be subject to translation of vicinity of the damsite, evidence has been sited by USBR that the movement from bounding or throughgoing regional elements of Maidu East fault may die out along a single trace a few hundred the Bear Mountam system. Local low level seismic activity in the feet west of the dam. It has not been disproven that the faults vicinity of the NE border of the Rocklin P!uton has been meas-exposed in trench ST-65 may be continuations of the main fault ured in recent months by CDMG and by the USGS. This may zone to the north, perhaps correlating with bedrock fault T-25 indicate an active stress field along the margm of the P!uton.

and extending into the right abutment.

These facts tend to indicate ( !) that there is a major tie of faults that are present in the foundation with regional throughgoing in general, and as shown in plan view by the USBR's l' =

elements that may be associated with the MCE, and ( 2) that 50' scale mapping, the Maidu East shear zone has a complex local seismicity is now occurr:ng. Some of the c points will be geometric expresson. In the area of trenches ST-68 and BHT-elaborated on below.

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8 CALIFORNIA DIVISION OF MINES AND GEOLOGY SP54 I.

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1979 TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE 9

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10 CALIFORNIA DIVISION OF MINES AND GEOLOGY SP54 Potential for Sur/oce Fov/rmg Within the Dom foundation are virtually unaffected by warp. This would indicate that the Area warp may not be the result of post fault folding but that F-1, a subsidiary break of F-0, chose the path ofleast resistance during its f rmation, a path that was controlled by inhomogeneity or F-1 Structure. The geologic mapping of the foundation area wok zones in the rock.

at Auburn damsite has revealed a relatively sinuous pattern for the F-1 fault zone, u it appears in outcrop. in and near the dam F-0 Structure. As has been mentioned, the structure of F-0 foundation (ngure 4). This sinuosity, not controlled solely by topography,is indicative of the general warped condition of the and F-1 can be extended along trend southeastward to smoothly fault plane. The F-1 zone is perhaps the most critical fault Join with the 8,000 ft. long unnamed fault on the same trend to structure for the dam because it crops out directly in or along the southeast. !t is noteworthy that all three faults ( F-1, F4 and the foundation excavation throughout the entire left abutment the 8,000 ft. fault) dip steeply to the northeast as they apprcach from the east end of the dam to a point in 2:left part of the the talcose serpentine and serpentine mass that marks their channel near the ceater of the span. At that point the fault trace USBR mapped terminations at the top of the left abutment.

makes an abrupt change and trends upstream out of the founda.

From USBR mapping, F-1 and F-0 terminate on the northwest side of the serpentine and the 8,000 ft. fault terminates on the tion cut.

southeast side of the serpentine. F4 is 6,600 feet long as mapped The length of the F-1 fault trace exposed within or on the by USBR. When this length is combined with the 8,000 ft, long zone to the southeast, the overall mapped length of the combined margm of the dam foundation is 2,000 feet. The mapped length of the fault is approsimately 4,300 feet as shown on USBR F-0 fault (including the segment within the serpentme) would mapping. The fault splays out on the northwest end in several be 15,000 feet. It is quite conceivable that faults on exactly the small faults which die out in a short distance ( : 250'). On the same trend, with almost exactly parallel dips, could be joined southeast, the fault is shown as terminating in a body of serpen.

within the mass of serpentine that is only a few hundred feet in tine and talcose serpentine at the upper left abutment end of the width. It is possible to extend the mapped length of F-0 still dam foundation. This same bodv of serpentine is also shown by further by adding a 3,000 ft. segment to the northwest end of the USBR mapping as the termination for the F-0 fault zone ( figure USBR mapped portion. The 3,000 ft. addition would carry the 4). However, projection of F-1 and F-0 along their general fault to the railroad yard trench exposure at BHT-86, and on to the Southern Pacific Railroad tunnel, where a fault with identi-strike,in the vicinity of the upper left abutment, shows that they converge at the serpentine body approximately at the mapped cal characteristics,on trend with F-0,is exposed at the north end of the tunnel. The combined additions of the 8.000 ft. fault on northwestern termination of a third fault exactly on trend that the southeast, and the 3,000 ft. cxtension on the northwest, give is considered by CDMG, using USBR mapping data, to extend at least 8,000 feet to the southeast. The pomt of juncture of the F4 a possible length of 18,000 feet. It is possible that the faulting could extend further on both the southeast and northwest ends.

three faults ( F-1, F-0 and the unnamed 3,000 ft. long fault) would lie very close to the contact between the talcose serpentine mass and the adjacent amphibolite (undifferentiated) unit. This The question of the probable junctures of the F-0 tone with implies that the three zones are interconnected within the ser-the throughgoing north-northwest trending elements of the Bear pentine mass and could all be part of the same fault system w hich Mountain fault zone is not yet fujly explored. The F-0 extension bifurcates only to have its southern branch (F-1) eventually that has already been,roposed isbasically on strike with the Salt splay and die out. Total mapped length for F-1, including its Creek lineament (fi, are 5), which suggests that the two zones probable continuation to the southeast, combined with F-0, could merge smooth y. There is some ambiguous data on the would then be 12,300 fect-faulting within the Salt Creek lineament, that is, the Bayley House trench, which was excavated within th-lineament, faded Another very interesting point is the bend or " swing" of the to expose any fault. The trench, which was located on the basis F-l fault toward the north that begmsjust above invert elevation of a vegetation change and break in slope, has a length only about on the left abutment and extends northwestward out into the one tenth the width of the entire Salt Creek lineament. It may channel where F-1 joins and is coincident with T-10. This com-be that the trench location missed the zone of faulting, just as bmed outcrop of the two zones continues upstream for a distance it turned out that the break in slope, that served as the main basis of perhaps 350-400 feet where the T-10 zone becomes ill-de-for trench location, was caused by a facies change in the rock Gned. A simdar abrupt change in direction was noted in the rather than by a fault. Additional work is needed to examine pattern of surface rupture associated with the Oroville carth-fault re!ationships in the Salt Creek lineament.

quakes.

The possibdity of an F-0 tie into the Maidu or Deadman At and near the centerline for the dam, F-1 has a recorded lineament zones, as western margms of the Bear Mountain fault, surface attitude N 38W. dip 43'SW. However, subsurface infor-must also be considered. The northwest extension of the F-0 mation shows that the dip may be more nearly 55-60*, as re-fault tends to line up on a general trend ( N73W) with the faults vealed by drill hole intersections with F-1. This means the dip in the nearby Ophir district. F-0 would not make a smooth is swinging back toward vertical and indicates a probable con-transition to any north northwest trending regional fault ele-tinuation of the warped condition of the F-1 plane at depth. It ment, unless there is a bend or swing to the north in the un-also helps to substantiate the concept that the gross attitude of mapped continuation of F-0 northwest of the railroad tunnel the F-1 fault tone may not be divergent from F-0 in the deeper exposure, or unless there is a bifurcation coupled with a sharp subsurface, and that the two pwne, may join both laterally and bend in F-0 to allow a part of it to continue along a T-zone at depth.

trend,in a manner similar to the merge of F-1 and T-10 at their juncture in the dam foundation. Additional field work could help Observation of the geologic maps V the foundation area to prove whether or not such a bend on F-0 to the north may reveals that in the area where the greatest warp of the F-1 plane exist, but it is probable that trenching would be requbed to occurs, near the lower part of tbc nght abutment, the T-zones confH any findings based only on surface mapping.

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1979 TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THS AUBURN DAMSITE 11 e

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12 CALIFORNIA DIVISION OF MINES AND GEOLOGY SP54 Movement of F-0, F-1. The pattern of oblique angle cross-USBR selected the scaling factor to be spectral intensity and cutting faults within the bounding e!cments of the Bear Moun-compared two period ranges.The two period ranges for spectral tain fault zone is duplicated elsewhere,a good example is present intensity were 0.1 to 2.5 seconds and 0.15 to 1.0 seconds. They in the Bangor quadrangle south of Oroville (1978 mapping by selected the same data set as WCC with the exception of the Q.A. Aune, personal communication). It is apparent that the Pacoima Dam record, which was excluded. They plotted spec-cross-cutting faults form an important interconnecting link in tral intensities for each record against distance and determined the Bear Mountain system, and can be considered as a major a value of 32 inches for the wide period range and 13.0 inches elements that are capable of supporting a major seismic event.

for the narrow period range. From their data set they developed As has been stated above,in the section on the geometry of F-1, only the mean spectrum shape and did not investigate the 84th the F-1 fault is apparently a subsidiary break of the F-0 fault, percentile shape. The final spectrum shape, developed from the and any movement that may occur on F-0 can be expected to period range 0.1 to 2.5 seconds, had a spectrum intensity create movement along F-1.

between 0.15 to 1.0 seconds of 14.1 in. Because the 14.1 in. was quite close to the 13.0 in. they developed from distance relations, Level Une Defa they used the final shape from the wider period range as repre-sentative of the shape from the narrow period range. This final High-order geodetic leveling surveys, dating back to 1912, shape, scaled to the selected spectrum intensities, gave a max-have been run at intervals along the Southern Pacific Railroad imum ground acceleraton of 0.49g as compared tc 0.55g for the where it traverses the western Sierra Nevada Mountains. Surveys WCC approach. USBR values of spectral acceleration for the in recent years ( 1969,1977,1978) have shown on going enstal mean shape were 1.27g at 0.15 sec and 0.29g at 1.0 sec.

deformation within the Bear Mountain Zone (Bennett.778).

The maximum point of inficction is coincident with the north.

USGS recommended that the scaling factor for the spectrum ward projection of the Maidu East, F-1 and F-0 structures.This lue at a period of 1.0 seconds be peak velocity. Bill Joyner, a y

relative change exceeds probable measurement error by about an USGS navestigator, advised CDMG, in a personal communica-order of magnitude. Measurable movement that can be correlat-tien, that short period recommendations have not been present-ed with a known fault feature is conclusive evidence of either ed. The USGS is in general agreement with the records used for displacement along an active fault or of strain accumulation the WCC data set except that full weight would be given to tre along the fault.

peak velocity of the Pacoima Dam record. A pkt of scaling factor against distance was not presented by the USGS. They recommended values of 2 to 3 times the WCC unsmoothed mean C,

GROUND MOTION DESIGN PARAMETERS spectrum at 1.0 seconds. This calculation results in a spectral acceleration between 0.72g and 1.08g at a period of I sec.

In preparing its design ground motion parameter, CD MG first reviewed the WCC and US3R development of design ground The CDMG approach is to use peak acceleration as a scaling motion. CDMG also reviewed the comments prepared by the factor. In general we agree with the statements in Appendix A USGS in their review of the WCC report. The suggested CDMG of the WCC report, Volome'6, pointing out that use of peak design grpund motion for a MCE of magnitude 6.5 at the site was velocity or spectral intensity iould result in similar design then developed. The major steps used in this process included:

ground motions provided that thhPacoima Dam record is down-weighted. Because the peak acceleration at the site is considered

( 1) selection of the type of scaling factor to be used.

by CDMG and because there tre no records available for a 6.5 magnitude at the source, we n.= a project to the site using a plot

( 2) selection of earthquake record acto set for magnstudes of peak acceleration against distance from the source. It is our near 6.5-opinion that the data set presented by WCC is reasonable to use in making such a projection, and we would project a peak accel-( 3) plotting of the scaling foctor for each record against dis-eration of not less than 0.7g at the site. Previous curves published tonce and selection of a scaling factor vo ve for the safe, by Schnable and Seed (1973) and by Seed and others (1976) a and project peak accelerations of 0.66g at 2 miles (1973 reference)

( a) development of a mean or 84th percentile response spec-trum shape froen a record dato set and oppscotion of the Woodward-Clydr's 34th percentile response spectrum shape goi;ng fac,, to this shape.

from volume 8 seems to be reasonable. Considering the uncer-tainty of all approximations, use of the 84th percentile shape WCC selected the scaling factor to be peak acceleration. They seems reasonable. Using this spectral shape and 0.70g peak rock studied the use of peak velocity and spectral intensity and found acceleration, the spectral acceleration at 0.15 seconds is 2.34g.

their results would be changed very little by use of these other and the spectral acceleration at 1.0 seconds ts 0.57.

3 scaling factors. They selected an earthquake record data set with magnitudes from 6.0 to 6.5 and within 30 km of the source.They down-weighted the Pacoima Dam record to give 0.73g peak acceleration. They plotted peak acceleration against distance and DAMSITE projected a value of 0.55g for a distance ess than 0.8 km from the site. From their data set they developed an 34th percentile response spectrum shape and a mean response spectrum shape.

In developing the surface faulting design parameter for the Final values of spectral acceleration for the $4th percentile shape site, particular attention was paid to the potential for sympa-were 1.34g at 0.15 sec and 0.45g at 1.0 sec. Final values of thetic movements on faults in the foundation, condition of fault spectral acceleration for the mean shape were 1.33g at 0.15 sec gouge, use of displacement curves developed for faults through-out the world, and geologic evidence for displacement.

and 0.30g at 1.0 sec.

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1979 TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE 13 Potential for Sympathetic Movement on F-1 and F-0 Geologie Evidence of Displacement in the Sierra Foothills Fault System As has been desenbed in the proximity of fault movement section, F-0 represents a major oblique cross-cutting eleme-t in Geologic evidence for 2 feet of vertical offset within the last the Bear Mountain fault system, and F-l is apparently a subsidi.

19) 000 years is found in threc locetions in the Oroville area and ary break. F-1, which traverses the dam foundation in the left also in one location in the Table Ntountain aret, along faults in abutment, apparently joins F-O in the vicinity of he serpentine the western Serra Foothills. These offsets have been found in t

mass that occurs on the left abutment south of the dam. That the trenche < hat were excavated in locations chosen to ensure a high two zones may join in the deeper subsurface in the Icft abutment probability that offsets in young sediments would be found. In area is suggested by the warped condition of the F-1 plane, the spite of this selective prouss in choosing trench locations, it is general similarity of dip and dip variation for both faults, and the highly probable that the trenching that has been completed has suggestion from drill hole information that the F-l dip may not exposed the regiond maximum offset.

steepen in the deeper subsurface. This would mean that any movement that occurred on F-0 would most likely result in Vertical offset is comparatively easy to document in a trench movement on F-1.

exposure. Not so easily proven is the amount of horizontal offset that may be associated with the vertical component, particularly fault Gouge Evidence where the marker beds are natlying, discontinuous palcosols.

Estimates of net slip have been attempted by Woodward-Clyde Fault gouge in the F-1 zone is variable in width and often Consultants, USGS. and CDNIG. These vary according to the consists of a wider, firm zone of broken rock fragments and clay, dip slip and honzontal slip assumed, and the computed net slip with mineralization and quartz stnngers, and containing a nar.

amounts range from 3 feet ( USGS) to 2.4 f-et ( WCC). The 2.4 row zone of soft plastic clay that squeezes from newly exposed feet figure for net slip is assumed by WCC to have occurred in surfaces in the manner of toothpaste. This has been interpreted 3 distinct events or episodes so that the maximum slip per event as reactivation of an old fault by breakage along a new, narrow is 0.3 feet. The evidence does not preclude the possibility that the surface within the old zone. The condition of the fault gouge has entire amount of 2.4 feet could have occurred in a single event.

also been interpreted as an indication of a shallow depth of burial Smilarly it is possible that the observed 2 feet vertical offset during fault activity and hence indicative of relatively recent associated with Quaternary movements on faults in the Foothills fault movement (Compton,1978, in USBR supplement to area does not represent the maximum displacement.

Project Geology Report).

A number of types of Geld observations can be and were Evidence from Displacement Curves utilized to estimate the amount of vertical displacement along faults in the Serra Foothills. However, primary emphasis, relat-Niagnitude 6.5 carthquakes are known to have surface dis-ing to a single event displacement, mast be placed on the amount placements varying up to several feet. To obtain an idea of the of slip that postdates the formation of the paleo-B soil honzon.

range of displacements that can be expected from a Ni 6.5 event, we examined the relationships of earthquake magnitude to the Selected locations where ver'fpal separaGn of the paleo-B soil log of tl e maximum displacement as presented by Semmons' horizon could be measured along representative faults in the Table 11 (1977).

western Serra Nevada are listed in Table 1. As documented in tn3 table, the maximum urtical cumulative separation of the Normal faulting with some element of strike-slip would be pale -B soil honzon ever observed was 2.0 feet, from which a expected at Auburn. To obtain a range of expected displace-maxii um dip slip of 2.3 feet was calculated and a maximum ments we examined the vanation in the regressions for normal post p leo-B net slip of 2.4 feet was estimated.

only, normal oblique only, and a combination of normal, normal oblique, and stnke slip. This provided for the variations in Otmervations or paleo-B honzons and younger units overlying regt:ssion coefficients a nd standard deviations. For each case the active fault zones indicate that slips are probably cumulative and following table presents the mean and one standard deviation in not related to a single seismic event The multiple bedrock steps maximum displacement for a NI 6.4 event.

observed in the paleo-B-bedrock contact have been interpreted as being produced by a senes of scismic events. The observed Table 2.

Range of maximum displacements for a M 6.4 vertical separations at the Cleveland Hill and Bowie Flat trench earthquake from CDMG regressions of Slemmons loc tions range in size from.4 to 1.0 feet. At three other localities

( 1977) dato.

(Cleveland Hill, Rawhide Flat, and Spenceville), where the mM paleo-B soil honzon has been cut by a slickensided shear planc

'normd' coincident with an underlying bedrock step, the younger overly-Normal ouique, ing collusium is also cut but with a vertical displacement at the Normal oblique & stnke-slip base of the colluvium which is too small to measure. This evi-dence tends to indicate a major seismic event, as recorded in the

+ SD.

34' 3.6' 6.7' paleo-B-bedrock interface step, followed by lesser events which cut but did not measurably olTset the youngest colluvial u iit.

rnean I.y 1.7' 2.4' in our interpretation, the paleo-B soil horizon was an active

-SD.

05

0. 8' O.9' soil horizon dunng the interva' 130.M0 to 9.000 years. As such, this soil honzon was undergoing active pedogenic processes Comparisons between maximum observed displacement and which would destroy or modify tectonically generated shears magnitude data suggest that displacements of more than three and offsets. Thus, where the soil record shows evidence of tecton-feet are possible, but not very likely.

ic activity, no implication as to an absolute time can be made nor 1229 M8

14 CALIFORNIA DIVISION OF MINES AND GEOLOGY SP54 can a number of events be unequivocally stated. CD'C has yielded M 5.5. A magnitude of 5.0 was estimated for the March assumed that the displacement range of between.4 and 1.0 feet 1909 Downieville earthquake using the same technique.

in paleo-B bedrock steps and in the stone line separating"olluvi-al umts ( Woodward-Clyde Consultants, v. 7, p. 24) represents The relation log eN = a-bM was fitted to this data set, using individual scismic events, the occurrence cf w hich is more proba.

a 'b' slope of unity, which is a common 'b' value for California ble than the MCE. With these caveats in mind, CDMG estimates as shown by the carthquake catalogs of both U.C. Berkeley and that a reasonable design parameter can be based on a net slip of Caltech. Extrapolating from a M 5.7 event in 78 years to M 6.5, thrcquarters (.75) of a foot per event.

we Gnd that in the 125 km fault system that wr. sampled, the recurrence of the MCE is about 500 years E.

SIGNIFICANCE OF THE SURFA CE FA UL TING PA RAME-e NPture 1ength of a M 6.5 earthquake is onsidered te be TER IN THE DESIGN OF AUSURN DAM about 25 km, usmg published data (Semmons, 977). The prob.

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The development of a surface faultirg parameter for an area sa t systm ht incMes Aukrn is I n 5, he it such as that at the Auburn damsite, an area without a known and 5 one fifth the 125 km length of the fault sys.em that was well documented carthquake history, involves a distinctly judg-sampled. The width of the fault system near Auburn is such that mental conclusion.

this earthquake would occur within 20 km of Auburn with a probability of I in 5 (20%) in 500 years. If the fault system is considered to consist of 3 fault zones (Scar Mountain Zone, Value Based on Geology Compared with Fou/t Displocement Intermediate Lne, and Melones Zone), then the probability of Curves occurrence in any one zone is further reduced by I in 3. Thus, the MCE of M 6.5 would recur once in about 500 years between Geologic, geomorphic and soils evidence found in the field in acepille and Oroville, with a probability of I in 15 (a recur-the Foothills region, do not tend to support the maximum sur-rence interval of 7500 years) of being located on the Bear Moun-face displacement values that can be obtained through use of tain fault z ne, within which the damsite is located. Although published curves that re!ste earthquake magnitude to length of such an event, with a displacement of about 60 cm (Bonilla and the zone of surface faulting (Semmons,1977) and maximum Buchanan,1970, p.15), could o*ur anyw here,n the 5 km-wide i

surface displacement on the main fault to magnitude (Bonilla Bear Mountain fault zone, sympathetic movement within the I and Buchanan,1970). For instance, three foot Quaternary fault km span of the dam, which is oriented across the fault zone, scarps have not been located by geologic mapping to date. Al-cannot be ruled out in each such occurrence. The maximum though this does not contradict the curve data based on fresh credible displacement of 60 cm should not be confused with the uncroded scarps, such geologic observations have bc<. used by

" cm, r in., rec mmended for design purposes.

CDMG to temper the development of the surface faulting parameter.

Comparison of Seismologic and Geologic Records Significance of the Design Parameter Related to Frequency of Recurrence Rate.

Cenozoic activity along thE. Foothills fault system encom-passes normal faulting during Tgrtiary, Pleistocene, Holocene, CDMG has computed a recurrence interval for a M 6.5 event and historic time. Using known

,gregate displacements, at the Auburn damsite of 7,500-75.000 years based on scismic CDMG has concMded tl.at over the last nine million years, the historv and geologic observations. Subseg tently, the method of rate of vertical offset is low - about I cm/1000 ye trs for the Douglas and Ryall ( 1977) for linear source regions was applied system with a maximum of 0.6 cm/1000 years for any one strand to the Foothills fault system as a check of the earlier CDMG (table 1). There may be some indication that the rate wss great-estimates. Both the earlier recurrence computations based on est in the latter portion of this time span. Palcosol offsets, for seismic history and geology and the appraisal using the method example, imply that during this later period there was a bqther of Douglas and Ryall are presented below.

rate of displacement than the rate derived from the total of Cenozoic displacements measured in the Table Mountain area.

Histoncal Displacement Record - Seismic History A companson of displacement rates derived from the short-The recurrence of the MCE of M 6.5 along the Foothills fault term seismological record with the long-term geologic record system was estimated from the occurrence of earthquakes during provides a useful perspective. Although the results are somewhat the twentieth century (figures 2 and 3). The Serra Nevada problematical, in attempt can be made. Suppose, for example, foothills were sampled from 20 km south of Placerville to 10 km using the recurrence derived from the seismic history, that at north of Oroville and Downieville, for a total length of 125 km intervals af 500 years the M 6.5 MCE produced 60 cm of offset (see accompanying epicenter map).

along a 25 km length of the Foothills fault system considered as a single s; rand. It would take 2500 years to rupture the entire 125 As stated above in the section on design parameter conclu-km length from Oroville to Piacerville. A transect at any place sions, the graph in Figure 3 shows the distnbution of the cumula-across the system would produce a displacement rate of 24 cm/

tive nur*r of earthquakes of var ous magnitudes. The largest 1000 years. Additional displacement produced by smaller carthquake is the M 5.7 0roville carthquake of August 1975. Tlie quakes would produce an additional displaument of 10 cm/

second largest earthquake is the M 5.5 Downieville earthquake 1000 y ears, giving a total of 3> cm/1000 years. This is more than of June 1909, whose magnitude was est: mated from the intensity a magnitude greater than the Cenozoic rate of I cm/1000 years.

values: the maximum reported intensity N I to VII yielded M 5.0 Palcosol data, however, possibly support a higher rate (table 1).

to M S.7, the area of 2400 km'shasen at intensity Vl and greater Palcosols on individual strands of the system appear to have yielded M 5.5, and the total felt area of about 100,000 km:

experienced up to 6 cm/1000 years displacement. Thus, a 5 or h

1979 TUCHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE 15 6 strand segment of the Sierra Foothills fault system could possi-oblique, and ( 3) normal, normal oblique, and strike slip. Thus bly include displacem :nt in the general range suggested by tne the parameters for the above listed types of faulting are, respec-historical scismic rec 3rd.

tively: ( 1) c = -1.138, d = 0.2974; ( 2) c = -0.6072, d =

0.2974: and ( 3) c = 0.319, d = 0.265.

Given the difference (one order of magnitude) between the length of the MCE recurrence interval suggested by the histori-Taking all the possible permutations of the three cumulative cat carthquake record and the length suggested by observations frequency-magnitude and the three rupture length-magnitude c' Cenozoic offsets, it is reasonable to estimate the recurrence relations, nine curves can be derived based on the method of interval as a range of potential spans of time ( rather than as one Douglas and Ryall( 1977) assuming Mmax = 6.5 for the Footh-specific figure), with the upper limit of the range based upon the ills. The results are presented in Table 3, w here a, b, c, and d are historical earthquake record. Thus, the estimated interval for the coefficients defined by the relationships log N = a-bM and log Auburn latitudinal portion of the Sierra Foothills fault system L = c + dM.

(or any segment) ranges between 2,500 and 25,000 years; and the estimated local interval on the Bear Mountain fault zone Toble J.

Recurrence in years for lorirude of Aubum dom would be 7,500 to 75,000 years. Uncertamtics could dictate based on Douglas and Ryoll( 1977) method.

rounding these figures to between 10,000 and 100,000 years, Because of the likelihood of greater seismicity during the latter Mn.ax = 6.5, L r = 100, t = 79 part of the Late Cenozoic (last million years) and the lower degree of modern seismic activity in the southern Sierra Footh-Orovdle included Orovdle mcluded Orovale ncludd ills, which include the Table Mountain area from which the geologic evidence of the occurrence rate is der ~ ed,it is desirable a-17 b - 10 a-4.M b.37 a-4 07 b -3J to consider the recurrence interval to be in the shorter segmmt M

years years years of the range. Perhaps approximat ?y 30,000 years is an appropii-2te Ggure.

c - -0.319 5.5 522 581 887 Douglas and Ryall (1977) express the average number of d=

0.265 6.5 t,740 1,748 2.419 times per year (inverse recurrence penod) that earthquakes cause rupture within a oistance, x, of a site along or near a linear 6.4 12y53 11,774 15.235 source region for a given magnitude M or larger in terms of an integral from M to M/ max, the largest earthquake expected along tne wurce region. The integral takes into account the c - -0 6072 5.5 655 727 1,108 cumulative frequency-magnitude relation for the source.egion, d= 0.2974 6.0 2,124 2,134 2.952 and the probability of rupture within a distance, x, of the site.

The probability of rupture for a site or a linear source region is 6.4 15,067 14.131 18.284 simply the length of rupturc expected for a particular magr3ude, based on a rupture length-magnitude relation, divided by the k

total length of the linear source region being considered. In e - -1.138 5.5 890 986 1.496 applying this approach to the Auburn vicinity, we assumed that the entire Foothills system is one linear fault zone and then 4-0.365 6.0 2,740 2,749 3,799 computed the recurrence of an earthquake of magnitude M or larger for the lat tude of Auburn (or any other latitude along the 6.4 18,745 17.580 22.747 i

system). Due to the uncertaint' a the basic data involved in calculation of frequency-magn tude and rupture length-magni-Because the above recurrence table is for the latitude of Au-tude relations,a rangeof recurrenceintervals was calculated for burn and because there are three major fault zones in the Footh-M 5.5, M 6.0, and M 6.4 events.

ills system at that latitude, the recurrence for the zone containing the damsite should be three times the above values. Hence the CDMG looked at the scismicity for a 160 km segment of the estimated recurrence range for aa M 6.4 event, based on the Foothills fault system between Oroville and the Mokelumne method of Douglas and Ryall ( 1977),is 33,000 to 67,00) years.

River for the period 190ly-1978 (totallength = 160 km; time =

This is in general agreement with the earher recurrence estimate 79 years). To this seismicity data, which includes the M = 5.7 by CDMG.

Oroville earthquake of 1975 and M N 5.5 and M 5.0 earthquakes in 1909 between Grass Valley and Downieville, we fitted three Thus, the recurrence interval for the maximum single-event-related surface fault offset must be regarded as an estimate with cumulative frequency-magnitude relations. For the first we as.

sumed a slope (b) of I and N = 1 at M 5.7 (corresponding to an appreciable range. Nevertheless, CDMG feels that the M 6.5 recurrence interval falls well within the USBR cnteria for fault Oroville) so that a = 5.7. For the second we did a best "eveball-fit to the data, including the Oroville data, and calculated a =

activity ( 100.000 years) and is relatively short in geologic time.

4.95 and b =.87. For the third we ercluded the Oroville data The recurrence interval for potentially ground rupturing events from the best " eyeball" fit to allow for the possibility that Oro-in the range between M 5.5 and the MCE is, of ccurse, even ville might be a reservoir induced event and obtained a = 4.07 shorter. Additionally, the possible influence of Reservoir in-and b =.74. These three cumulative frequency-magnitude fits duced Seismicity must be considered.

represent the uncertainty in the seismicity data. To determine a F.

RESERVOIR INDUCED SE/SMICITY ( #15) range in rupture length magnitude relations we tooked at the relations presented in Slemmons (1977). For faulting at Au-burn, we found the range of uncertainty covered by three rela-There is reason for concern about Reservoir Induced Seismici-tionships: (1) normal oblique only, (2) normal plus normal ty. It is quite possible that the presence of a reservoir can trigger l G {)

"o Gl JJU 1,

(-

16 CALIFORNIA DIVISION OF NIINES AND GEOLOGY SP54 a large earthquake prior to the time when an earthquake might port and recommendations on design parameters were then otherwise be expected. Worldwide RIS studies indicate that res.

transmitted to the Secretary of the Interior as the state's position ervoir induced carthquakes are not larger than the MCE for the on the seismic loading parameters for the Auburn damsite.

region. w hen an \\lCE can be properly determined. Because there is no *ay of reliably predicting where the Auburn segment of the in developing its position on seismic design parameters for the Foothills fault system is in its recurrence cycle a near MCE damsite CDMG considered the evidence for the MCE that induced event ( M 6.0 - 6.5) must be comidered,n nsk evalua-could occur on the Foothills fault system in the vicinity of the i

t;ans at Auburn.

site. The conclusion that a M 6.5 event was an appropriate MCE for the Auburn area was based upon the seismic history of the northern Foothills area (three M 5.5 or greater events since At present, there is little established corcelation of resmoir 1909), the otTsets recorded in palcosois ( 9,000 - 140.000 years, geoloes with RIS, but the conditions known t0 be necessary for with vertical offset of 2 feet at several locations), and the rupture RIS a're ( I) pre-existing faults and Gssures and (2) an existing length to magnitudes relationships for the Oroville earthquake state of stress sufficient for earthquah: activity. These conditions (1975) and for faults m other areas.

are present at the Auburn damsite.

A careful appraisal of the potential for fault movement in the Stuart-Alexander and Mark,s study (1976) of worldwide foundation area revealed that a combination of the F-1 and F-0 cases of possible RIS indicates that RIS occurs at 26 percent of faults provided a fault zone that may form a major interconnect-very deep reservoirs ( m!50m). Auburn, as proposed. will be a ing link in the Bear Mountain segment of the Foothills fault very deep reservoir (N200m). More recent work by W,oodward system. The appraisal also revealed that this fault zone may be

-Clyde Consultants iWCC, oral commanication by R.E.

functionally associated with an MCE. F-1 lies in the foundation 15,1979),ndicates that often evidence of for the ent' ire left abutment and can be expected to move if Harpster, February i

Quaternary movement exists on faults beneath or near reservoirs displacement occurs on the associated larger F-0 fault. Addi-exhibiting RIS. particularly reservoirs with larger RIS events.

tionally, a projection of the Maidu East fault along T-25. T-16 Faults with possible Quaternary offsets exist near and possibly or T-14 would place it in the dam foundation: as much move-beneath the proposed Auburn reservoir. Because of the absence ment as 40 cm may have occurred on that zone in the last of sediments of the appropriate age to serve as a time reference, 100,000 years. High order level lines that have been run along we cannot make an absolute conGrmation of the existence of the southern PaciGc Railroad in recent vears have revealed ongo-Quaternary movement within the found* tion.

ing crustal deformation with a point of maximum inHection c incident with the northward projection of the Maidu East, F-1 There is, therefore, no evidence tc ggest that RIS cannot

• I"# "I***

occur at Auburn. Also, recent work ( foppozada and Cramer, 1978) suggests that reservoirs can trigger carthquakes a signifi-cantly long period of time after the imtial reservoir filling (e.g.,

Design ground motion studies, including a review of the Koyna, Marathon, Menoocino, and possibly Oroville). The WCC, LSBR, and USGS meihods, were ;n. formed with the present lack of knowledge about which reservoirs are likely to result that WCC's 84th percentue response spec ::m shape was mduce earthquakes and which are not, plus the geology of the found to be reasonable. Based onkhis and a M 6.5 event in the Auburn site and the size o,f the proposed reservoir, argue in favor immediate vicmity of the site, the spectral response acceleration of a design sufGcient to withstand offset that appears geologically at the lesecond period should be approximately 50 percent of probable for the Foothills fault system.

gravity.

In devel ping the surface faulting design parameter for the 111'

SUMMARY

site, careful attention was paid to the potential for sympathetic movements on faults in the foundation, condition of fault gouge.

Th CDMG in the Department of Conservation has bes.

displacement curves developed for faults throughout the world, assigned the task of develcping the Department's input to a State and geologic evidence for displacement. Interrelationships of of Califorma position on the seismic and geologic safety of the faults 'n the foundation tend to indicate a potential for sympa.

Auburn damsite. Other participants in developing the state's thetic movement; the development of narrow zones of soft gouge, position have been the Division of Safety of Dams, Department with evidence of cavities, within broader, more firm gouge zones, of Water Resources, and that Department's Consulting Board suggests that reactivaticn of older fault zones has occurred in for Earthquake Analysis.

relatively recent times under conditions of sha!!ow burial. Dis-placement curves (Siemmons,1977) developed for a M 6.4 event The CDMG Ngan its investigations on Auburn dam early in suggest normal, normal oblique and strike-slip displacements of 1976 and presented its recommendations regarding design the order of 2.4 feet. 9ecause geologic, geomorphic and soils parameters for the proposed dam before the Consultmg Board evidence found in the fic!d in the Foothills region do not tend in November 1978. When the Board's report was issued in Janu-to support the maximum surface displacement values that can be ary 1979 it was determined that all the parameters recommended obtained through use of the displacement curves, CDMG has by the Board were in agreement with those developed by CD MG tempered its development of the surface faulting parameter using with the single exception of the potential for fault otTset in the the geologic evidence. Geologic evidence shows 2 feet of vertical foundation, for which the Beard had recommended five inches.

displacement of young ( <100.000 years) palcosols in several CDMG has performed a painstaking i* examination of all the foothills locations, and these can be mterpreted as 2.4 feet of total available dra and concluded that an appropriately conservative displacement. If, as some evidence suggests, this displacement design parameter, as opposed to the matimum displacement that took place in three separate events, and if smgle vertical separa-could occur throughout all time, was nine inche.t of offset in the tions of 0.4 to 1.0 feet, observed in areas of muiupie bedrock foundat.on. This recommendation together with the Board's re-steps, are the result of single events, then a displacement of 0.75 ILL/

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1979 TECHNICAL REVIEW OF THE SEISMIC SAFETY OF THE AUBURN DAMSITE 17 feet or 9 inches is a reasonable design parameter. CD MG does CD MG ( 7.500 to 75,000 years) using the seismic history and the not recommend a surface faulting displacement parameter below geologic evidence of displacement.

0.75 feet.

Reservoir Induced Seismicity is of extreme importance for the Auburn site because a large earthquake could be triggered by the The recurrence rate of an earthquake at the latitude of the presence of the reservoir prio to the time when an earthquake Auburn site was developed by CD MG using nine curves that can might normally occur. Conditions known to be necessary for be derived using the method of Douglas and Ryall(1977) and RIS are, or will be, present at the Auburn site, including pre-assuming M max = 6.5. Because there are three major fault existing faults and fissures, an existing state of stress sufficient zones in the Foothills system at that latitude. '.he recurrence at for earthquake activity, faults with possible Quaternary offsets the dam should be three times the 'igure for th: latitude a ; was beneath the reservoir, and a very deep reservoir. All of these estimated as 33,000 to 67,000 years for a M 6.4 event. These factors argue in favor of a design sufficient to withstand offset numbers are in general agreement with earlier estimates by that appears geologically probabic for the Foothills fault system.

REFERENCES Allen, C.R.,1978, Evaluanon of seesn=c hazard at the Aubum damsde, are6y samno earthquakes. Bdleem of the Sersmo%al Sooety of Cakdom.ai Report to the U.S. Bureau of Reclamanon 10 p.

Amenco, v. 66, no. 4, p.1323-1342.

Bennett, J.H.,1978, Crustal movement on the Footh.Ils fault system near Slemmons, 0.8.,1977,5 tate-of-the-art for assessmg earthquake hazaron Avbum, Califonwa Cakfornea Geology, v. 31, no. 8. p.177-182.

e the Unded States: Report 6, Mesceilaneous Paper S-73-1. MacKay School of Mmes, Unrversdy of Nevado For U.S. Army Corps of Engmeers.

Sonella M.G., and Suchman, J#.,1970, intenm report on worldwide histoe-ic surface laviemg Open-File Report, U.S. Geological Survey.

Stuart-Alexander, DE, and Mark, R.K.,1976,1-~-

Wed sers-nuoty assocated weh large reservoirs: U.S. Geological Survey, Open-Compton, R.C.,1978, Gouge and associated deformanon along fault F-1 File Report No. 7&770.

Aubum damsde: for U.S. Bureau of Reclamanon. t -.--

to Protect Geology Report. Seisnuc evaivanon of Avbum damsde, v. 4.

Toppozada, T.R.,1975, Earth 9,ake magndude as a f weien of intensdy data in Califonna and westem Nevada. Bullenn of the Semmological Socwey Douglas. 8#., and Ryo#, A 1977. Sersm.c nsk in linear source mgeons, wwh of Amenca, v. 65, no. 5, p.1223-1238.

appricanon to the $an Andreas faus: Budets of the Seesmoeog. col Soo-ety of Amenca, v. 67, no.1, Feb.1977.

Toppozada. T.R., W h, C.H,1978, M M@, 25 hh Johnson. L.R.,1978. Sesm.c loodmg cons.deranons for Auburn dom: Report y

k to the U.S. Sureau of Reclamanon,11 p.

Schnabel P 8., and Seed, HT.,1973, Acceleranens in rock for earthquakes U.S. Geological Survey,1978, Ter.hnical Review of earthquake studies of the ei the westem Uruted States, Sudenn of the Wai Soosty of Aubum darn area ( those conducted by WoodwarcK}yde Consultants, 1777) R'Pon to the U.S. Sureau of Reclamanors.

Amenca, v. 63, no. 2, p. 501-516.

Seed. H.S.. and others,1976, Reianonsh.ps of man mum acceleranon, man-woodward-Cyde Consvitcsws,1977, Earthquake evak, anon studees of the enum velocery, distance from source, ed local arte condinons for moder-Avbum dam area, U.S. Sureau of Reclamanan, Open-Ale Report, v.1-4.

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