ML20213A358

Summarizes 861120 Meeting in Washington,Dc Re Facility long-term Seismic Program

ML20213A358
Person / Time
Site:	Diablo Canyon
Issue date:	11/28/1986
From:	Page B Advisory Committee on Reactor Safeguards, STANFORD UNIV., STANFORD, CA
To:	Seiss C ILLINOIS, UNIV. OF, URBANA, IL, Advisory Committee on Reactor Safeguards
References
ACRS-CT-1872, NUDOCS 8702030236
Download: ML20213A358 (2)

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' 6F/rfA STANFORD UNIVERSITY sT .C- - p >/g DEPARTMENT oF GEOLOGY 3rhaalof Enth $rimaces November 28, 1986 Dr. Chester P. Siess 3110 Civil Engineering Bldg. ,

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University of Illinois Urbana, IL 61801

Dear Chester:

V' The following remarks refet to the meeting of November 20, 1986, held in Washington D.C., regarding seismic studies in the area around the Diablo Canyon Nuclear Plant.

The Long Term Seismic Program of PG In E still seems well conceived and well planned, especially with the refinements of Phase III. One might wonder if the program is overly elaborate, diffuse, and lacking in focus, but I do not think so. Most of the 3 studies are certainly germane to the problem of seismic risk at the Diablo Canyon site, hnd the principal individuals carrying out the plan seem to be outstanding in ability and experience.

The main" geologic endeavor is, as it has been, the determination of the character, size, and behavior of the faults in the area, especially the Hosgri fault and any affiliated companion structures. The discovery by Crouch that the Hoagri fault may be a thrust was important, but we have not heard the last word on the subject. Geologists in the Lon; Term Seismic Program have confirmed the existence of Quaternary strike-slip faulting near San Simeon in a zone that we have long considered a probable continuation of the Bosgri system. To the no'rth, accrued strike-slip on the presumed extension of the zone amounts to at least 70 and possibly as much as 150 km of displacement, - an amount that could not die out altogether

, before reaching the latitude of the Diablo area. Enere is the locus of this displacement in the region of interest?

I Elsewhere in California there are well-known active strike-slip faults which are flanked on one or both sides by thrusts or high-angle reverse faults: Examples in

the vicinity of San Francisco - =-----' -

Bay include parts of the San l

Andreas, Hayward, and Calaveras N g g pg, j d,p 4 4

, fault zones. The reasons for this,-

spatial relationship are not obvious, but there is little doubt about the existence of thrust / strike-slip pairs. They are commonly reported i in petroleum geology literature.

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I Thus the PG 8e E team must examine their seismic reflection profiles with this possibility in mind. We have already discussed 8702030236 861128 PDR ACRS ~ -

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3 this with several members of the PG & E geology group. Of course, it may turn out that the above .model does not apply, but if it gains support it will reconcile seemingly conflicting evidence.

On the whole, the program appears to be capable of resolving possibilities like the foregoing. I expect it to yield more information in a few years than all the new ' information acquired in the preceding decade. '

With best regards and all good wishes,

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& lti. 0b Benjamin M. Page cc Richard Savio e

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