ML20212L901
| ML20212L901 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Diablo Canyon |
| Issue date: | 01/28/1975 |
| From: | INTERIOR, DEPT. OF, GEOLOGICAL SURVEY |
| To: | Gossick L NRC |
| Shared Package | |
| ML20150F500 | List:
|
| References | |
| FOIA-86-391 NUDOCS 8608250299 | |
| Download: ML20212L901 (10) | |
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United States Department of the Interior 7
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GEOLOGICAL SURVEY RESTON, VIRGINIA 22092 6
Ric8vt0 2 JAN 28 115-T Z
- u. aronic maar General L. V. Gossick 5g8lg8 JAN 2 8 *975 Nuclear Regulatory Comission m wm Washington, D.C.
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Dear General Gossick:
Transmitted herewith, in response to a request by your staff, is a review of the geologic and seismologic data relevant to the Diablo Canyon Site, Units 1 and 2 (AEC Docket Nos. 50-275 and 50-323).
This review was prepared by F. A. McKeown and James F. Devine of the U.S. Geological Survey.
kW We have no objection to your making this review part of the public record.
Sincerely yours, 4R h ovLt. b G
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Act.14 irector Enclosure C
B609250299 060001 PDH FOIA HOUCI(36-391 PDH Fole n-391 Let's Clean Up America f or Our 200th Birthday 8-83
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Pacific Gas and Electric Company Diablo Canyon Site, Units 1 and 2 San Luis Obispo County, California AEC Docket Nos. 50-275 and 50-323 T
This is a final review of the geological and pertinent seismological data in the. Final Safety Analysis Report (FSAR) and Amendments 11,19, and 20 for the Diablo Canyon nuclear power plant site. Units 1 and 2.
A preliminary review dated January 23, 1974, of the FSAR was transmitted to the Atomic Energy Commission by E. H. Baltz on March 28,1974.
The principal consideration in the preliminary review was that it did not provide information to evaluate adequately an offshore fault or structural zone that had been reported in the literature (Hoskins and Griffiths, 1971) since review of the Preliminary Safety Analysis Report pr (PSAR).
Since the preliminary review of the FSAR the applicant and its consultants have conducted extensive geophysical surveys and made geological analyses of them to determine the offshore geology, most of which is presented in Appendix 0 of Amendment 19. ' Prior to the applicant's surveys the U.S. Geological Survey on behalf of the U.S. Atomic Energy Connission had made a geophysical survey of a large part of the offshore structural zone. This information (Wagner,1974) was open filed to the public in September 1974 and the applicant has used it extensively in Amendment 19.
This final review therefore is directed mostly to evaluation of the data in Amendment 19, although all parts of the FSAR were reviewed.
No field examinstion of the site was made in conjunction sith review of the FSAR.
The FSAR and its amendments contain a reasonably accurate description and evaluation of a large amount of geophysical and, geological data.
The geologic maps (Plates III and IV, Amendment 19) offshore of the southcentral, Fol A E-89I A,as
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California coast agree in general with the offshore geologic map of Wagner (1974).
In detail however the maps differ at many places.
For example, the trends, location, and number of faults in Estero Bay shown on Plate IV differ from those shown in Plate I of Wagner. A synopsis of the geology on Plates I, II, III, and IV is that the offshore Santa Maria basin is bounded on the east and west by major fault zones.
Further, both fault zones are recognized as capable within criteria of the Atomic Energy Commission. The easternmost fault zone, called the East Boundary zone (EBZ) by the applicant and called the Hosgri fault zone (HFZ) by Wagner (1974), is of primary importance because it passes within four miles of the site and is about 90 miles long. As will be outlined in another part of the review, we do not concur with the applicant's conclusion that spnanguen the current structural environment of both the offshore and onshore' areas is dominated by vertical movements.
We do concur with the applicant that the faults exposed in excavation for the site and in the cliffs near the -
site apparently are not capable within AEC criteria. However, the age (80,000-120,000 years before present) of the youngest terrace materials was inferred,by long-distance correlation of terraces (p. 2.5-33). We accept the correlation as probable but an absolute age determination would be highly desirable. As these faults and foundation conditions have been amply documented and have not appeared to present problems that could not be managed by engineering practices, they are not discussed in this review.
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Regional Geology The applicant's description of the regional tectonic features given in Amendment 20, (p. 2.5-7 through 2.5-13f) is quite adequate.
In brief the 2
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plant site is located in the South Coast Ranges structural province which is characterized by northwest trending structural and geomorphic features.
The applicant lists five major structural features (fault zones) in the region around the site (p. 2.5-9, Amend. 20). These are the San Andreas, Rinconada-San Marcos-Jolon, Sur-Nacimiento, Santa Lucia Bank and San Simeon faults at distances of 45, 25,18, 28, and 18 miles from the site respectively (Table A, Amend.19). All of these faults are considered capable by the applicant (p. 2.5D-64, 65, Amend 19). The East Boundary fault zone at 2.5 to 4 miles from the site is not listed as a major structural feature although it bounds the offshore Santa Maria basin as the Santa Lucia Bank fault does and is connensurate in size with the Santa Lucia Bank fault. We consider the East Boundary fault zone a major WW structural feature.
In the vicinity of the site, that is the Estero Bay-San Luis Range area, three principal fault zones are discussed in addition to the East Boundary fault zone (p. 2.5-13c through 13f, Amend. 20).
These are the West Huasna. Edna, and San Miguelito faults at distances of 11, 4.5, and 2.5 miles from the site, respectively.
Nearly all faults trend northwesterly.
Highly defomed Mesozoic and Cenozoic rocks occur between the faults.
The available data do not indicate that any of these faults are capable according to AEC criteria. The trend of the Edna fault when projected to the nortFwest suggests that it could possibly intersect the EBZ in Estero Bay. The location and discontinuoes style of faults napped in Estero Bay however by both the applicant (Plate IV Amend 19) and Wagner (1974, Plate !) do not confirm intersection of the Edna fault with the EBZ. As the EBZ is larger and closer to the site, consideration of the Edna fault as a source of earthquakes is of less importance 3
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East Boundary Fault Zone As indicated previously in this review and by the applicant (2.50-9, Amend.19) the East Boundary fault zone has been the structural feature of most interest and importance. Nearly all of the extensive geophysical explorations conducted and analyzed during the past year or so since the FSAR was first issued have been directed especially to defining this zone and its geologic relationship to contiguous features such as the Santa Maria basin, structures in the San 1.uis Range, and the Transverse Range structures projected from the southeast. The importance of the EBZ and need to investigate it thoroughly was evident from the facts that it is a
less than four miles from the site, is more than 90 miles in length, and appears to have minor seismic activity associated with it.
The applicant yggs has made a comendable effort to define and explain the zone.
We concur with the applicant's description of the EBZ and his conclu-sion that it is a faulted zone of inflection between the offshore Santa Maria Basin and the uplif ted Coast Ranges (p. 2.50-37 through 2.50-42, and 2.50-98, Amend. 19).
It appears therefore that the zone once was more closely related to the vertical tectonics associated with basin development than to transcurrent tectonics associated with plate boundaries. As recognized by the applicant, the EBZ may also be a "---part of the San Andreas continental margin transform fault system-- " (p. 2.50-41, Amend 19).
Such northwest trending fault zones as the EBZ, both offshore and onshore, have been considered by others (for example, Hamilton and Myers,1966,
- p. 522 and figure 2, Atwater,1970, p. 3525) to be part of a system of faults with right lateral movement.
The applicant presents considerable data and arguments to support the concept"---that the current tectonic 4
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environment in the southern Coast Ranges and adjacent offshore region is dominated by vertical movements associated with general uplift of the ranges." (p. 2.50-63, Amend. 19).
It is clear from the offshore seismic reflection profiles in Appendix A as well as mapping onshore that vertical separations of as much as several thousand feet occur in Pliocene and older strata.
Evidence of lateral separation is less clear, probably because lateral separation can rarely be demonstrated unequivocally. The applicant concluded however that as much as several thousand feet of lateral displacement may have occurred on the EBZ throughout its history (p. 2.50-41, Amend. 19).
Evidence of lateral slip on the EBZ has been given by Wagner (1974, figure 13,p.7).
Similar evidence is apparent in figure SA (Appendix A) and sections B-B', and D-D' Plate VII, where marked changes in EMGEik thickness of acoustical units occur across faults and reverse sense of movement on the same fault is shown. Also, the San Simeon fault, which is considered the eastern boundary of the northern part of the Santa ttaria
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basin is reported to have about 1500 feet of lateral displacement.
Incomplete fault plane solutions (Smith,1974) are used by the applicant in an attempt to demonstrate the dominance of vertical movements. All three solutions given by Smith however have significant lateral components to the inferred fault mechanism. Additional seismological evidence that Coast Range faults currently have lateral novement on them is given by Greene and others (1973, Sheet 2). These authors show on Sheet 2 predominant right-lateral movement in fault plane solutions o' earthquakes in Vonterey Bay near projections of ncrthwest trending Coast Range faults.
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As (1) nearly all of the evidence of lateral movement is in the youngest rocks, some of which may be Post-Wisconsinan (Wagner, 1974, p. 13),
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and (2) the mechanism of current earthquakes has a significant component of lateral movement, vertical movements may now be a subordinate component on faults in the EBZ as well as other major faults in southcentral coastal Califon.ia.
Conclusions We conclude from the evidence in the FSAR and literature that large vertical displacements occurred in the EBZ, mostly during the late Miocene and Pliocene when the offshore Santa Maria basin was most actively developing.
Most current tectonic activity however is causing as much or more lateral as vertical displacement on northwest trending faults in the Coast Ranges and offshore region.
Both the East Boundary zone and Santa Lucia Bank fault zone may have a.first order genetic relation to the Santa Maria basin g@
and consequently are not regional in the sense that they do not transect structural provinces such as the Transverse Ranges as the San Andreas fault does.
They should be considered inextricably involved, however, with the strike-slip fault mechanics of plate boundary motions that are currently concentrated along the San Andreas fault.
Earthquakes along the EBi presumably would not be as large as expected on the San Andreas fault; however, from the information presently at hand we can find no evidence that would preclude the occurrence of an earthquake as large as events characteristic of subparallel strike slip faults, which bound basins, such as the Santa Maria, in the San Andreas system and which do not trarsect structural provinces.
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Seismology The portions of the Final Safety Analysis Report and Amendments 11, 19, 20 of the report entitled " Analysis of Of fshore Seismicity in the Vicinity of the Diablo Canyon fluclear Power Plant" and the Pacific Gas and Electric Company letter dated December 27, 1974,
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f concerning seismic response and its enclosures have been reviewed.
The seismological aspects of this site were previously investigated by the applicant and a review was prepared by the Seismological Division of the Coast and Geodetic Survey (since changed in organiza-i, tion in the flational Oceanic and Atmospheric Administration)' dated September 21, 1967.
As evidenced by the previous discussion of the Geology, a large e
amount of new data has been developed offshore from the plant site.
The interpretation of these data, as previcusly discussed, necessitate the placing of a moderate to large earthquake on either the East Boundary Zone or the Santa Lucia Bank faults.
The applicant, in Amendment 20, has addressed the significance of-this interpretation and has indicated a " potential for large earthquakes involving faulting over distances in the order of tens of miles:
Seismic activity at this level can occur along offshore faults in the Santa Lucia Bank region (the likely source of the Magnitude 7.3 earthquake of 1927)...." Elsewhere in the FSAR is stated "The East Boundary zone is considered to be seismically active...."
Our opinion, is based on these statements and the current necessity of considering these two structures as having similar seismic potential.
Due to the lack of instrumental data from sites within 10 km of the surface expression of a fault, it is difficult to describe the 7
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maximum acceleration, or velocity that would be recorded in this nearby zone.
In addition, the correlation of any of these parameters with damage is suspect in the near zones.
On the other hand, there are nunerous incidents of strue'.ures, extremely close to the fault undergoing movement and experiencing earthquakes, that experienced little or no damage. Also, it is apparent that the maximum peak acceleration does not continue to climb as one approaches closer to and reaches the fault break or as one postulates larger and larger earthquakes at a given point on the fault.
The efforts by the applicant to consider the effects of earthquakes on existing records of strong motion from sites near to the earthquake fault in terms of the frequency content of the response spectra 6EsMWE are worthwhile. However, a question of transferability still remains (the size of the event in one case and the distance in another).
Nevertheless, this analysis when used to match peaks of the spectra (nearby and more distant sources) to the response of critical com-ponents is in our opinion an important technique for assessing potential
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However, in conclusion, we believe 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 flovember 4,1927, event but occurring along the East Bour.dary Zone or the Santa Lucia Cank fault zone represents the maximum earthquake that is likely to occur near to the site. This event is in addition to the maximum earthquakes considered in the Construction Permit evaluation and subsequent hearings and reviews. As long 8
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i as this interpretation remains valid, it is our opinion that the design value of 0.5 g used as a zero period acceleration in the development of the appropriate response spectra is inadequate.
References Atwater, Tanya,1970, Implications of plate tectonics for the Cenozoic tectonic evolution of western North America: Geol. Soc. America Bull., v. 81,*,p. 3513-3536.
Greene, H. G. and others,1973, Faults and earthquakes in the Monterey Bay region, California:
U.S. Geol. Survey map MF-518.
Hamilton, W. and'Myers, W. B.,1966, Cenozoic tectonics of the Western United States:
Reviews of Geophysics, V. 4, no. 4, p. 509-549.
Hoskins, E. G., and Griffith's, J. R.,1971, Hydrocarbon potential of gggggp Northern and Central California offshore: Am. Assoc. Petroleum Geologists Memoir 15, p. 212-228.
Smith, S. W.,1974, Analysis of Offshore Seismicity in the vicinity of the Diablo Canyon' Nuclear Power Plant.
Report to Pacific' Gas and Electric Company.
Wagner, H. C.,1974, Marine geology between Cape San liartin and Pt. Sal South-Central California Offshore:
U.S. Geol. Survey open file report 74-252.
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