ML20215N038
| ML20215N038 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Diablo Canyon |
| Issue date: | 01/16/1968 |
| From: | Boyd R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Newmark N ILLINOIS, UNIV. OF, URBANA, IL |
| Shared Package | |
| ML20197J003 | List: |
| References | |
| FOIA-86-371 NUDOCS 8611040198 | |
| Download: ML20215N038 (1) | |
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l W 16 G68 Docket No. 50-275 Ih. Nathan M. Newmark 1114 Civil Engineering Building University of,T111n*4s Urbana, Illinois 61801
Dear Dr. Neinmark:
As you know we are presently preparin6 our Safety Evaluation regarding Pacific Gas and Electric c e ny's Diablo Canyon Nuclear Plant. An attachment to our evaluation will include your report on the Adequacy of the Structural Criteria for the Diablo Canyon Site Nuclear Plant. We have placed your draft report of December 1967 in final form as per our telephone conversations. If the report ic acceptable te jat,.
we would appreciate your signature on one of the enclocc4 O
reports to be inclueef ta ear rosest files.
Sincerely yours, Noger S. Boyd, Assistant Director for Reactor Pro.jects Dtvision of Reac$or Licensing l
Emelosuru Neumark Report dated 12/67 gjlO 8 861023 HOUCH36-371 PDR RPBf 5 DRL,,,,,,,
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JCStepp Docket File RBMcMullen
AGiambusso VAMoore Docket Nos. 50-276 /
N oller RSBoyd and 50-323 FSchroeder DJSkovholt HDenton VHWilson WPGammill LWR 1 & 2 Br. Cfs.
R M ecker Edson G. Case, Acting Director of Licensing THRU: A. Giambusso, Deputy Director for Reactor Projects, L STATUS OF THE GEOLOGY AND SEISMOLOGY PORTION OF THE DIABLO CANYON OPERATING LICENSE SAFETY REVIEW The staff last met with PG&E on this item on July 5,1974. The summary r
of this meeting is attached as Enclosure No.1.
he primary purpose of this
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meeting was to review the progress of the offshore geologicalinvestigations which had recently been initiated by the applicant. At that time, PG&E stated that their final report on offshore faults would be submitted to the staff by September 1,1974. The staff indicated that 30-45 days would be required for staff and USGS review of this report, and that, assuming favorable resolution of this item, a supplement to the safety evaluation on geology and seismology could probably be issued around mid-October of 1974. This date would conform reasonably well with the scheduled ACRS full committee meeting date of November 14-15, 1974.
In late August PG&E verbally informed the staff that their final report would be delayed about three weeks from the September 1 date. hey indicated MWIlld that the report would discuss all field work accomplished to date, would contain some new analysis of earthquake epicenters, and would mention the results of meetings with two oil companies regarding offshore geological data which are considered by these companies to be proprietary. The report will not contain the results of some additional (confirmatory) field work which PG&E is planning for September and October.
This three week slip will delay issuance of the SER supplement on this I
subject to approximately the first week in November, and makes the schedule extremely tight with regard to giving ACRS and their consultants appropriate time to review the report in time for the mid-November full committee I
meeting. An early Diablo Canyon ACRS subcommittee meeting emphasizing geology and seismology is scheduled for September 12,1974. At this meeting PG&E will discuss all work performed to date, although their final written l
report will not be available at this time, his meeting will provide the ACRS and their consultants with an initial presentation on the Diablo Canyon geology and seismology.
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With regard to evaluation of the seismic potential of the offshore faults in the vicinity of Diablo Canyon, the staff and USGS will need to review PG&E's report before a final determination can be made. The stait did conclude after the July 5,1974 meeting that PG&E had undertaken a very comprehensive offshore field program. However, the feeling still prevails that it will be extremely difficult to establish the capability of these faults using conventional dating methods.
Origittal i Ed by 2
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R. C. DeYoung, Assistant Director for Light Water Reactors Group 1 Directorate of Licensing
Enclosure:
1.
Meeting Summary dtd July 11, 1974 r
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' Form AEC.)l3 (Rev. SS)) ABCM 0240 W u. s oovannassar enintime orrects se74.ese.tes
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'MI 5UL.1 i W4 1 DOC!'ET N0S:
50-275 and 50-323 APPLICANT:
PacificGasandElectricCompany(PGSE)
FACILITY:
Diablo Canyon Units 1 and 2 SUMMRY OF MEETING llELD OU JULY 5,1974 REGliRDING CFFSliORE FAULTS A meeting betren representatives of PG&E, their consultant (Earth' Sciences Associates), and the AEC was held at the applicart's offices in San Francisco on July 5,1974. A complcte list of attendees is
- given in Lnclosure No. 1.
The primary l urpose of the meetin? was to '
i revicw the progress of the offshore geological investigations which have been initiated recently by the appliccat.
, Earth Sciences As!,cciates presented a summary of the Diablo Canyun Of fshore Seismic Int.crpretation Program, and the Prospectus on Future.
Data Acquisition and Interpretation Programs. This surnary is~ attached as Enclosure No.-2, and is divided into four parts:
1.
Exjsting data, "i "!!M 2.
State of interpretation, 3.
Future data acquisitions, 4.
Prospectus on future interpretations and final report.
In addition to the offshore work, representatives of Earth Sciences also discussed additional field work to be performed on land. This~ included explorations in the San Luis Range in the vicinity of the Miguelito Fault, work near San Simeon Poi.nt where tertiary faulting has been reported, and some examination of ti.e transverse range structures near-Point Sal.
Finally, PG&E is currently conducting a review of aerial photographs that are available.
The ' subject of availability of oil company geological data was discussed at 'some length. PG&E indicated that they'had contacted several companies and that arrangements could possibly be'made to. examine some of the data.
Ilowever, the oil companies cannot make the <tata available publicly.
In general, the data obtained by these companies gives only deep structure information, and provides lighter coverage than that obtained from some of the recent USGS work.
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v PG&E indicated that all' field work, both on land and offshore, would hopefully be coirpleted by the end of July, and that their final report would be submitted to the staf f by September 1,1974.
Allowing appropriat:
tine for staff and USGS review of ibis report, c ir safety evaluation of geology and seismoiogy would probabiy be published around mid-October of 1974.
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Thomas J. Hirons, Project flanager Light linter ileactors Project i: ranch 1-3 Directorate of Licensing
Enclosures:
1.
Attcwlance Lisi.
2.
Summary of State of Diribio Canyon Of fshore Seismic Interpretation and Prospectus on future Data Acquisition and Interpretation Progrc.s cc:
Pacific Gas and Electric Company fir. H. J. Lindblad Andr ew J. Skaff, Esq.
l1s. Elizabeth E. Apfelberg lis. Sandra A. Silver m
Mr. John Forster lir. Lonnie Valentine Mr. Gordon Silver Mr. William P. Cornwell e
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EilCLOSURE fiO. 1
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,t-ATTEf?DAliCE LIST Pacific Gas and Electric Corrg_any_
Earth Sciences Associetes (PC&E Conr.ul tant)
R. Bettinger V. J. Ghio D. H. flamilton J. B. Iloch R. !!ellinghani F. l'. !iautz*
J. C. Morris: icy AEC - Licensing T. J. Hirons R. B. McMullen J. C. Stepp 6
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Efict05URE ??O. 2 Sumre.try of.Pate c! lb iblo ( ufshore Seismic hierpt et. tion and I'ro3 pectus on Future 1.;att Acquisition and fa'erpretatioa Pro ;rama 1.
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USGS Irelt z cruis. rparker data covering area from Pt. El to Cape S.tn ?.Ltrtin to.m nver: ge dist;uwe of t o railes of f 2hore. Q.ality: y v3 - paor; maximura P2'u t ratio i abatit to, NW f""t.
b.
IIT,GM ILit tiett d tLi ro. erin:, acca trom Pob.t Eat ta Cape m Martin. Tracks appro:o h to within 3 miles of shore.,ad extend npproxilct::h-1 J triles off coa d.
Spacing lx! ween tr:teks is about 5 miles Qaality ;':oj te excellent; ina_xi:num penatraliaa abaut 10,009 fcct.
11HN spa.ter data with high denrity con:rnge ois Diabb Can),n cite and nur;h-c.
wcat to Point Estero. Quality gonj; maxinmct ; tr.att atien 2000 feet.
2.
State of Interprctation.
A prelimmar J interpretation has ines campwied n tin td ua..eie/ cruise nr.d cu BilN data. Tld:, intecpi eu tior. hu conce.J rated upan : tt ucttJc;; existing in th^ Miocene and Pliocene strata in thu effahare Santa !bris Dasin. The interpretation irts also em-g phasized determination of the nature of the congct between the Pliocene strata and the Mesozoic cocks which farm the bedrock and basement complex Icta. din;; the east nide of the Santa $1 aria Basm. A detailed examination also has been made of the junction of the WNW-irending structures of the San Luis range with the eastern inrder of the San Luis range.
3.
Future Data Acquisitions a.
BT3N sparker; maximum penetration 3000 feet.
- 1) 1111N has lieen contracted to shoot 240 miles of sparker line between Cape San Martin and Point Lobos. The purpose of this data is to trace the northern extensien of the offshore structures located by previous sparker surveys.
b.
Atluatronics sparker; maximum pecetration alout 4000 feet.
- 1) Aquatronics has been retained to provide a more detailed assessment of the structural merger of the S'an Luis rarge structures and the structures 1 310 July 3,1974 1
[arth Sciences Associates t
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' bounding.thp castern.'edje;.of the Santa Maria'B'tsin. ' They.will als6 provide..
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recomui!Js(.. hee datr. L'o~be utiliz6d in tracing tr.. southern continuation of.
the offshore structuren f rom Point Sal to Point Arguello.
c.
Oil Company Data.
1)
Plans are now in operation to obtaia any available oil company data in the area of concern. Thent' data will be us_eful in delineating the fornt of the b.tsoment sedimeo! interfpee, but hacause of its mode of collection will not likely aid in interpre!ing the near surface (e... recent) geologic history of the region.
4.
Prospectus on l'uture lutnepreteliom and l'inal Report.
Work to date ha; delia<.dcJ a major Nn'-trendir;,.one of faulting i:nminliately a.
of f the central California coastline. The available Ma have provided a picture of the trends.nd extcut of major folds azul fatdts in this zone. It lus also de-lineated the inajor structural styles along the coast. Areas of particular inter-est whero more interpt.eintive work is necessary include:
1.
Tbc juncture of the trends of the San Luis r:mge with lim eastern edy of the Santa Maria Hauin; The nature er ti e sedimtr.i 1:ascmcut interfac.' along the entire coastal.trca i
in question; and 3.
The determination of the relationsidp of observed structures v<ith the NW-t rending faulting within and south of Aionterey Bay and the EW-trending structures associated with the northwestern Transverse IJanges.
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The final report is to have the following form.
1)
A written report discussing the stratigraphy, structural style, and regional tectonic significance of the offshore fault systems of significance in evalu-ating carthquake hazards at the Diablo Canyon reactor site.
- 2) The written report will be accompanied by maps showing:
a)
The position of surface geologic contacts and position of surface and subsurface faulting and foiding.
b)
The thicimess of Pliocene sediments.
c)
The configuration of the basement surface.
3)
Illustrations will also be included to show examples of the data used in reaching the conclusions presented in the report.
2.
Earth Sciences. Associates e
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Docket Fi1 #
l LWR 1-3 Reading
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LWR 1-3 File Docket Nos.. '50-275 VHWilson and 50-323 40V t,W4 DPA111 son Note to:
- 11. R. Denton W. P. Gammill C. Stepp R. I!offman G. Ilulman E. Itawkins GEOLOGY-SEISM) LOGY REPORT FOR DIABLO CANYON Pacific Gas and Electric submitted the geology-seismology report for Diablo Canyon on November 1, 1974. The tsunami report was submitted on October 22, 1974. Now that this critical information has been received, it is necessary for us to complete the review as quickly as possible in order to support the scheduled February full ACRS meeting. Please note that it will be necessary to identify any problems or issues very early in the review so they may be resolved in time to meet the schedule.
The current Diablo Canyon schedule milestones leading up to the ACRS meeting are listed below for your convenience:
(1) Applicant submit geology, seismology, tsunami 11/1/74 f
(2) Geology, seismology and hydrology input for SER supplement to LPbf 1/3/75 (3) SER supplement issued on geology,. hydrology and seismology 1/10/75 (4) ACRS subcommittee meeting 1/24/75 (5) ACRS full committee meeting 2/7/75 0:tinal SIWd Of Darh D Ol!SG" D. P. Allison Light Water Reactors
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P[. C. DeYoung, Assistant Director for Light Water Reactors, Group 1, RL SUPPLEMENT TO SAFETY EVALUATION REPORT FOR GEOLOGY, SEISMOLOGY AliD FOUNDATION ENGINEERING PLANT NAME: Diablo Canyon LICENSING STAGE: OL DOCKET NUMBER:
50-275/323 RESPONSIBLE BRANCH: LWR l-3 REQUESTED COMPLETION DATE: NA APPLICANTS RESPONSE DATE NECESSARY FOR NEXT ACTION PLANNED ON PROJECT: NA DESCRIPTION OF RESPONSE: NA REVIEU STATUS: Supplement I to SER Complete Enclosed is a supplement to the Diablo Canyon Safety Evaluation Report prepared by W. Gamm111. R. McMullen, R. Hofmann, J. Stepp and L. Heller for your use. The changes were necessitated by our-further review of the offshore geology and seismology.
0%hialsigned by DISTRIBUTION:
TR: DOCKET FILE
_ E.R.Denton TR:SAB Harold R. Denton, Assistant Director TR:RDG for Site Safety i
Division of Technical Review Office of Nuclear Reactor Regulation
Enclosure:
As stated cc w/o encl:
i A. Giambusso W. Mcdonald J. Panzarella ec w/ encl:
S. Hanauer R. McMullen D
F. Schroeder R. Hofmann j
SS Branch Chiefs J. Stopp g
A. Kenneke L. Heller
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16//75 1/3//75 Form ABC 318.(Rev. 9 53) ABCM 0240 W u. s: sovenmuswr rnaN,1NG OFFICE 8 9974 989-104
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2 - 8' 2.5 Geology and Seismology This geology and seismology evaluation reflects our review of investigations conducted since 1969.
These investigations are des-cribed in the Final Safety Analysis Report (FSAR) for the Diablo Canyon ~ Nuclear Plant site and in a report by Wagner (1974). The geology and seismology of the Diablo Canyon site was reviewed by the AEC staff and its geological and seismological advisors, the U. S.
Geological Survey (USGS) and the U. S. Coast and Geodetic Survey, during the construction permit review.
9 The findings of that review were published on November 18, 1969, as part of the SER for Unit 2.
With respect to sefsmic design input, the SER concluded:
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(1)
"There are no identifiable major faults or other geologic structures in the area that could be expected to localize seismicity in the immediate vicinity of the site. The nearest seismically active major fault is the Nacimiento fault, a northwest-trending fault zone that approaches to within about 16-20 miles of the site to the northeast," and (2)
".... the Coast and Geodetic Survey agrees with the applicant's statement of 0.20g at the site and on rock for the predicted maximum ground accelerations of the design earthquake and twice that value, 0.40g on the rock for the safe shut-down conditions."
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4 2.5.1 Geology Since publication of the 1969 SER, studies of the geologic-structure offshore of the ' site have been reported (Hoskins and Griffiths, 1971; Wagner, 1974)'.' These studies revealed significant geologic structure offshore of the Diablo Canyon site. To determine the 'detEiled structural relationships in the immediate offshore region, the applicant conducted extensive high.ssolution geophysical investigations along that reach of the structure. Profiles obtained by the applicant were made available to the USGS and those obtained early in the investigation were included in the independent interpretation of the offshore structure by Wagner (1974).
The applicant's interpretation, together with a summary of the results
- presented by Hoskins and Griffiths (1971) and Wagner (1974), are included in the FSAR for the Diablo Canyon site.
The Hoskins and Griffiths (1971) paper gives the results'of an ggggg,g interpretation of extensive deep penetration seismic reflection surveys
. along the California Coast. The surveys revealed a structural basin offshore of the southern Coast Ranges which they call' d the Santa
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e Maria basin.
It is described as being a shallow, synclinorium about 140 miles long and 25 to 30 miles wide. Structural grain within the basin trends northwest parallel to the trend of the basin. Major faults bound the basin on both the east and west. The eastern border fault as identified by Hoskins and Griffiths passes within about 5 miles of the Diablo Canyon site.
It is about'90 miles in total length.
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Wagner (1974). utilized deep penetration seismic reflection methods and high resolution seismic acoustic surveys. The ' configuration of the sea floor was obtained using precision bathymetic data' and, locall', by side-scan sonar. These provided~a considerable refine-y ment of the structure along the eastern boundary of the Santa Maria
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basin in'the region between Cape San Martin and Point Sal. The basin is indicated to have formed in Middle to Post-Miocene (26 m.y.) time.
It contains from 2,000 to 5,000 ft of Miocene sediments unconformably overlain by up to 3,500 ft of Pliocene (7 m.y.) section.
An' erosion surface is-indicated to have formed on these Tertiary beds during Pleistocene time. Post-Wisconsinan sediments, deposited during the past 20,000 years, overlie much of the Tertiary crosion surface.
Wagner (1974) concurs with the interpretation of Hoskins and Griffiths (1971) that a major fault zone forms the eastern boundary of the offshore Santa Maria basin.. He calls it the Hosgri fault.
In structural detail the Hosgri fault is a zone containing from 2
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to 5 subparallel splays. These faults locally offset Tertiary and Pre-Tertiary rocks with apparent vertical offsets ranging between 1,500 and 6,000 ft.
The fault is discontinuous and segmented in the late Tertiary and Quaternary section. The applicant interprets the East Boundary Zone (the Hosgri fault zone of Wagner, 1974) as being the boundary between synclinal downwarping of the offshore Santa Maria basin and regional uplift of the southern Coast Ranges. The style of faulting in the zone is extensional as shown by its locali-zation along the flank of a' regional upwarp and by its pattern of
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. structural highs at Point San Luis and Point Piedras Blancas.
Reverse drag downfolding is also.shown in the strata adjacent to the normal' faults, and is likewise characteristic of extensional deformation.
Normal faults with east-facing scarps have also been identified and are interpreted as being antithetic-faults of the overall extensional system. The applicant states that due to the lack of evidence for compressional deformation in the Pliocene and Pleistocene and the presence of the positive evidence for extensional deformation, the Sa'nta Maria basin is in a region that has probably been characterized by extensional strain during much of the time since initial deposition in the basin during the Miocene.
While the movement on the fault zone was predominantly vertical during Tertiary, Wagner (1974) cites evidence of lateral (strike-slip) movement in the upper section. Earthquake focal mechanisms for this M
zone determined by the applicant support a strike-slip component of movement. Thus vertical movement on the fault may currently be sub-ordinate to strike-slip.
Evidence of recency of movement on the Hosgri fault zone is found in offsets of the sea floor together with offsets of the Post-Wisconsinan sediments. Wagner (1974) found these offsets on three of his profile crossings of the zone. On other high resolution seismic profiles, offsets of the base of the Post-Wisconsinan sediments are observed but with no offset of the sea floor. Still other profiles show no offset of the Post-Wisconsinan sediments. This pattern of offset is l
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1 1argely supported by the applicant's investigations.
We, therefore, conclude that the Hosgri fault zone must be considered capable within the meaning of 10 CFR Part'100 Appendix - A,Section III (1).
The applicant places the east boundary of the Santa Maria basin in his seismic potential category of Level III which is defined as
" Potent [alforearthquakesresultingchieflyfrommovementatdepth with no surface aulting, but at least with some. possibility of sur-face faulting of as much as a few miles strike length and a few feet of slip." Although current movement on the Hosgri fault zone appears to be limited to local fault segments, we assume for the purpose of establishing the-safe shutdown earthquake (SSE), that the fault is continuous, 90 miles long, capable, and located.3-1/2 miles west of the site at its closest approach.
In its geological input to the Safety Evaluation Report, dated g
28 January,1975 (Appendix D of this report),' the USGS concluded that the East Boundary (EBZ) zone and the Santa Lucia Bank zone "should be considered inextricably involved with the strik~e-slip fault mechanics of plate boundary motions that are currently concentrated along the-San Andreas fault." The USGS further concluded that carthquakes along the EBZ should not be expected to be as large as those expected along the San Andreas, but that based on the limited information on the Santa Lucia Bank fault, "the occurrence of an earthquake as large as events characteristic of subparallel strike slip faults, which bound basins, such as the~ Santa Maria...." could not be precluded.
In the Seismology section of that report the USGS concluded that
"with the limit of the present information as to the interpretation of the relationship of the East Boundary fault to the Santa Lucia Bank fault, an earthquake similar to the. November 4,1927, event but occurring along the East Boundary Zone or the Santa Lucia Bank fault zone represents the maximum earthquake that is likely to occur near to the s'ite."
These conclusions consider the structural properties and extent of th'e Santa Lucia Bank fault to be the same as those of the Hosgri fault zone and, further, that the Santa Lucia Bank fault was the source of the November 4,1927, earthquake. We are pursuing a comparative evaluation of these two tectonic zones and will report the results in a further supplement.
2.5.2
_ Vibratory Ground Ibtion Our SER (1969) for the Diablo Canyon Unit 2 concluded that one of the following four possible earthquakes would result in maximum accelerations at the site:
ggg,g9 Earthquake A: Magnitude 8-1/2 along the San Andreas fault 48 miles from the site, resulting in a ground acceleration of 0.10g at the site.
Earthquake B: Magnitude 7-1/4 along the Nacimiento fault 20 miles from the site, resulting in a ground acceleration of 0.12g at the site.
Earthquake C: Magnitude 7-1/2 along the off-shore extension of the Santa Ynez fault 50 miles from the site, resulting in a ground acceleration of 0 05g at the site.
Earthquake D: Magnitude 6-3/4 af tershock near the site associated with Earthquake A Which results in a ground acceleration of 0.20g at the site.
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9 For design purposes, an envelope of the B and D response spectra was used.
The operating basis earthquake (OBE) encompassed Earthquake B with a horizontal acceleration of 0.15g and Earthquake D with a horizontal acceleration of 0.20g.
The use of two earthquake response spectra for the OBE was selected because the frequencies of ground motion for the two earthquakes would be different in consequence of unequal attenuation due to earthquake location, i.e., earthquake D would have relatively higher accelerations in the high frequency part of its spectrum. The same spectra and 0.40g were used for the SSE.
The earlier conclusions regarding the geologic structure of the region and its relationship to earthquake occurrence have been altered by the subsequent detailed offshore investigations discussed above.
We have made a specific evaluation of the potential of the Hosgri fault zone as an earthquake generator, using appropriate regional relationships between earthquake size and fault dimensions (Bonilla, 1970) and among magnitude, acceleration and epicenter distance (Schnabel and Seed,1973). We have considered the llosgri fault zone to have a maximum length of 90 miles as defined by Hoskins and Griffiths (1971), to have the potential for breaking over one half its total length in a singic earthquake and to have a mechanism that is inter-mediate between strike-slip' and dip-slip.
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Observations have been made of the relationship of fault rupture length to magnitude and fault displacement by Bonilla (1970).
Rupture length is seldom fully observed on the surface of the earth.
Of ten the slip surface on a fault plane is at depth and only a portion of it intersects the surface, or soil cover masks the ends of the rupture zone where displacements are small. Bonilla (1970) recognizes this by drawing'a line on his plot of rupture length versus magnitude to include all observations. That line corresponds well with data fror earthquakes which have occurred on the San Andreas fault (Algermissen, 1969). The crust of the earth along the California coast is thin compared to length of the Hosgri fault zone. Thus the shape of the' fault slip surface for the Hosgri fault zone would be similar to that for the strike-slip San Andreas and would have similar near field energy distribution characteristics. However, to account gggggyq for a potential dip-slip component on the fault, some additional conservatism in determining the magnitude was considered beyond that indicated by Bonilla (1970).
Bonilla's graph may be used to estimate maximum magnitude assuming that a fraction of the known total length of a fault may rupture in a single earthquake. Data indicating that no more than 1/2 of the total fault length is ruptured during any single earthquake has been presented by Tocher (1958), Bonilla (1970) and Albee and Smith (1966).
With the above considerations, a magnitude 6.6 earthquake could be derived for the maximum earthquake on the Hosgri fault zone.
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At a distance of 3.5 miles, the Diablo Canyon site lies within the near-field of seismic radiation from a potential magnitude 6.6 earthquake on the Hosgri fault zone.
A Tew pulses of high accelerations
- are, therefore, expected at the site in addition to lower accelerations continuing for the expected duration of strong shaking.
Graphs of peak acceleration versus distance and magnitude have been developed to account for the high acceleration pulses recently recorded very close to earthquake epicenters (Schnabel and Seed, 1973). These graphs, considering the mechanism of the Hosgri fault indicate a peak near field acceleration at the site of 0.5g.
Because the expected acceleration would be in the near field, a spectral envelope for checking design was determined by scaling two near field records of earthquakes having magnitudes and at distances that bracket the Diablo Canyon site-source conditions for the Hosgri fault. The
- WNNEN records were chosen from instruments located on foundation materials as similar as possible to those at the site.
These records were scaled to 0.5g maximum acceleration and their response spectra were compared to that used for the SSE seismic design. Spectra were used from the M=5.6 1966 Parkfield, California earthquake recorded at 3.2 miles from the fault. When scaled to 0.5g this provides a conservative estimate of the high frequency portion of the expected spectra froa the Hosgri fault.
Spectra recorded at 18 miles from the M=6.5 1971 San Fernando earthquake was also used. At this distance, high frequency spikes are well attenuated. Thus when scaled to 0.5g, this spectrum provides overly -conservative spectral values for intermediate and longer periods.
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Comparison of these spectra and the spectra used by the applicant for design of the Diablo Canyon units shows the design spectra to be exceeded only over limited frequencies." Because of the conservatism of the seismic response spectra used in the design, a 0.5g SSE (the value for a maximum earthquake on the Hosgri fault determined by the procedure described above) would require only minimal changes to the seismic design. Our evaluation of the maximum earthquake potential of the Hosgri fault zone must, of course, be considered tentative pending our further evaluation of the structural and seismic properties of the Santa Lucia Bank and Hosgri fault zones.
2.5.3 Slope Stability The stability of the cut slopes adjacent to the plant was evaluated by the staff and its advisor the Corps of Engineers. The report of the Corps of Engineers, which is enclosed as Appendix C to b6pme%#
this report, stated that the exploration, sampling, and testing was sufficient to define soil properties, the methodology used in the dynamic analysis is consistent with the latest state-of-the-art techniques, and the results are conservative.' They concluded that "the calculated maximum displacement of 10 inches, resulting from the selected double design earthquake should not cause damage to structures located near the toe of the cut.
However, provisions should be made to insure that the condition of the material on the slope is not altered, particularly by saturation due to poor surface drainage."
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2.4 182 -
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We have reviewed the stability of the cut slopes and the provisions for drainage to preclude saturation by groundwater, and have concluded that the slopes will remain stable during the occurrence of the SSE, and that Category I structures will not be damaged.
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,e REFERENCES Algermissen, S. T., (1969).
Studies in Seismicity and. Earthquake Damage Statistics; Three parts, Summary,and Recommendations, 23 pages;. Appendix A,142 'pages; and Appendix B, 68 p. ages, Prepared ~ for
- the Department of Housing and Urban Development, Office of Economic Analysis by the Staff and Consultants of the Department of Commerce, ESSA, Coast and Geodetic Survey.
- Albee, A'.
L., and Smith, J.
L., (1966). Earthquake Characteristics and Fault Activity in Southern California; Special Publication of The Los Angeles Section of the Association of Engineering Geologists, Arcadia, California, pp. 9-33.
Bonilla, M. G. (1970).
' Surface Faulting and Related Effects, in Earthquake Engineering, Robert L. Wiegel, Coord., Ed., Prentic-Hall, Inc., Englewood Cliffs, N. J.
Hoskins, E.
G.,
and Griffiths, J.
R., (1971).
' Hydrocarbon Potential of Northern and Central California Offshore;
~Auerican Assoc. Petroleum Geologists, Memoir 15, pp. 212-228.
Schnabel, P. B., and Seed, H. B., (1973). Accelerations in Rock for Earthquakes in the Western United States; Bul., Seis. Soc. Am., V.
No. 2, p. 501-516.
4 Tocher, D. (1958).
Earthquake Energy and Ground Breakage;. Seism.
Soc. Amer. Bull., Vol. 48, p. 147-153.
Wagner, H.
C., (1974). Marine Geology Batween Cape San Martin and Pt. Sal South-Central California Offshore; U. S. Geol. Survey open file report 74-252.
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