ML20237L576

Advises of Favorable Impression Re Competence of People, Thoroughness of Approach & Robust Resilent Methodology Which Allows for Introduction of New Data at Any Time,Per PG&E 870715 Workshop on long-term Seismic Program

ML20237L576
Person / Time
Site:	Diablo Canyon
Issue date:	08/06/1987
From:	Thompson G STANFORD UNIV., STANFORD, CA
To:	Seiss C ILLINOIS, UNIV. OF, URBANA, IL, Advisory Committee on Reactor Safeguards
References
ACRS-CT-1898, NUDOCS 8708280158
Download: ML20237L576 (1)

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STANFORD UNIVERSITY M '

SCHOOL. OF E ARTH SCIE'NCES h$ DYAf l MITCHELL BUILDING 101 Offue of the Dean

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STANFORD, CALIFORNIA 94305 2210 (415) 723 2544 i

August 6, 1987 7 j

" rA fil',iD., ; %i yd USNAC. j)

Dr. Chester P. Siess i 3110 Civil Engineerin6 Building rNJGJ2R9 i University of Illinois i I

Urbana, Illinois 61801

Dear Chester:

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I attended the P.G. & E. workshop cri their Long Term Seismic Program in

-San Francisco on July 15 I was not able to be there on July 16. The focus of the meeting was grounc motion, but. included were summaries of their pro-gress on the geology, seismology (including source mechanismo), a world-wide ocupilation of grounc motion as related to known fault rupture, and attenua-tion.

l They showed rather convincingly (again) that the Hosgri Zone is the main i l concern at Diablo Canyon, despite the numerous other faults that have become  :

better known from recent studies. They choose to model the Hosgri In two al-ternative ways (thrust or strike-slip) to avoid interminable debate about its c harac *.er . Their evidence suggests that the eastern fault of the Hosgri Zone is a vertical strike-slip fault and that the western part of the Zone is a thrust dippin6 about 35' toward the plant; these studies are still in pro-I gress.

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.j They seem to have the best data base on known faults and strong motion l that has ever been compiled, and they are proceeding to model ground motion l l numerically. I was favorably impressed by the competence of the people, the I

thoroughness of the approach, and the robust, resilient methodolo6y, which al-lows for introduc* ion of new data at any time.

Sincerely, l

a George A. Thompson or cc: E. Igne l

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l 8708280150 070006 PDR ACPS CT-1898 PDR DESIGNATED ORIGIIAL l Certified By -

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