ML20212K943
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F Docket hos. 50-275 JAN 1 1 W4 and 50-323 APPLICAfeT: PACIFIC CAS AND ELECTRIC CCHFAhY (PG&E)
FACILITY:
DIABih CAbiTON U31TS 1 AND 2
SUMMARY
OF MEETIniG BELD TO DISCUSS RECENT OFFSHORE EXPLORATIONS OF USGS AND PC&E A meeting between representatives of PG&E, USGS, and the AEC was held at the US Geological Survey officas in Hemio Park, California, on January 8, 1974.
PC&E was alue represented by Douglas H. Hamilton of Earth Sciences Associates, one of their geological consultants.
J. Hardia5 of the Friende of the Earth was alas pra===e, but did not gggspp participate in the meeting. The complete list of attendees is given in Enclosure so. 1.
1he purpose of the meeting was to discuse faulting near Diablo Canyon that was discovered during recent offshore neologic mapping performed by both USCS and PG4E in the vielaity of the Diablo Canyon site. USCS conducted extensive work in this offshore ares during the fall of 1973, and in dovrebec reported the discovery of a possible fault in thin rer. ion (see mano from W. P. Camill to J. X. Hendrie dated November 21, 1973). PC&E performed additional mapplag work in this ares during December of 1973.
Mr. Holly Wagner of the USGS presented and described the offshore seisnic reflection survey in the vicinity'of the ulabio Canyon site. The survey de. sign consists of continuous reflection profiles along traverres that are approximately normal to the coast line and are spaced at one-mile intervals. The staff viewed both the seismic reflection recordina.s and a map abowing the locations and trends of three faults and tuo sea terraces that have been interpreted from the seismic reflection data.
For our discusalon the faulta were referred to as Faults A, E, and C.
F.ach was discussed as followas 1.
Fault At At its Hearest approach, this fault is located al.out 3 miles southwest of the Diablo Canyon site.
It strikes northwaat and has a total wapped length of less than one mile.
The fault is confined to the Mesozoic geologie section and does not offer.t the sea floor.
It Intersects one of the sea terraces, which has a 10 foot change in f
alevation, at a = mall angle, and it was at tbla noint of internoction that the origin.1 seismic profile (#139) crec, 'ag occurred. As a usoenow) uonl
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i 2-JAN 1 1 WI4 consequence of this latersection, fault A was originally believed to offset the sea floor. Subsequent review of the seismie profile and additional profiling show that what was believed to be fault offset of the ses floor is actually a sea terrace which has a height of 10 feet at this point and no offset of bedding.
2.
Fault B: his fault trende subparallel to fault A and is about four miles southwest of the plant site at its closest approach.
As with fault A, fault B is also contained within the Hososoic section. Terrace deposits cover the fault in one region and, while it is clear that it does not offset the sea floor, the fault may extend into the terrace deposits. We total mapped length of fault B is approximately six miles.
3.
Fault C: his fault also trends subparallel. to faults A and B, and is about five miles from the Diablo Canyon site at its nearest approach. It is contained within the Tertiary geologic section, and the youngest formations which are offset by it are Pliocene.
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Were is no evidence that the fault offeats the sea floor in its total mapped length of nine milse.
An offshore geologic feature described in a report by Hoskins and Griffith was also discussed at the meeting. Wis feature has been mapwd by Hoskins and Grif fith for a length of approximately 90 miles, at a distance of about 5-6 miles offehore from the Diablo Canyon site. Day described it as a fault zone, heading northwest, that separates a major Tertiary sedimentary basin on its west side from Hosozoic rocks on its east side.
We staff had previously requested additional information from PG&E on l
this fault (See questious from the completeness review dated August 13, 1973, and first. round questions dated January 4,1974; both of these requests were sent to PG&E as part of the overall safety review process).
We applicant is continuing his investigations of the seismic significance of this feature.
IMug Hamilton presented data from the PCR sponsered explorations of the same offshore area, and there was good general agr. ament between these results and the USGS data. Hamilton indicated that he is preparing a final report for PCM on the findings of the of fsho-se emptorations.
l He mentioned that this report would be available be the first part of February. Holly Wagner said that the USGS report should be finished about the same time.
i Hoskins, E. G., and J. R. Grif fith,1971, " Hydrocarbon Potential of Northern and Canerat. 0418.fornts Of fshore," in Cram, I. H. (editor),
Mure Petroleum Provinces of the United States -- %eir Geology and Fountial Amer. Assoc, Petrol. Geol. Hon.
15, Vol. 1, p. 212-218.
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. JAN 1 1374 We staf f has evaluated the offshore exploration data obtained to date by ll8GS and PG45. As a result of this evaluation, the staff feels that faults A and'B are local features which do not represent potential earthquake sources that would produce accelerations at the site which are greater than those produced by the safe shutdown earthquake set forth by PG6E in the FSAR.
Fault C may be related to the larger structural feature described by Hoskins and Griffith; however, its limited extent of nine miles makes it a minor source of potential earthquake activity, regardless of its relation to the Hoskins - Griffith feature. As with faults A and B, the staff feels that accelerations at the site produced by fault C would be well within the limits for which the plant is designed.
Origina.l S.lgned by.'
% cess J. Hirons Light Water Reastors Group 1-3 win Directorate of Licensing
Enclosure:
Attendance List cc w/ encl:
DISTRIBUTION:
RP Assistant Directors Docket (2)
AEC PDR RP Reading Local PDR LWR l-3 Reading RP Branch dtiefs S. Varga R. W. Klecker J. H. llendrie TR Assistant Directors
'IR Branch Chief s R. Cushman L. Chandler R0 (3)
V.11. Wilson R. B. McMullen J. C. Stepp R. Fraley, ACRS (16) oma..k: T7........
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