ML20237L557

Summarizes Nrc/Pg&E 870715-16 Workshop in San Francisco,Ca Re Plant Ground Motion

ML20237L557
Person / Time
Site:	Diablo Canyon
Issue date:	07/27/1987
From:	Page B STANFORD UNIV., STANFORD, CA
To:	Seiss C ILLINOIS, UNIV. OF, URBANA, IL, Advisory Committee on Reactor Safeguards
References
ACRS-CT-1896, NUDOCS 8708280152
Download: ML20237L557 (1)

Text

p b A T d @ 9 fp YM/87 1

STANFORD i , UNIVERSITY DEPARTMENT OF GEOLOGY TELEPHONE: (415)723-2537 Schol of E4nh Sciences 1ELEX: 348402 SI6NFRD STNU l

.> l Stanford. Cahfornia 94305-2115 July 279 1987

{

Dr. Chester P. Siess Professor of Civil Engineering 3110 Civil Engineering Bldg. .

University of Illinois ,

Urbana , IL 61801 g2 3 ;jN.,RC, t

Dear Chet:

g ,.j. g/

I attended the NRC/PG & E workshop on Diablo Canyon ground motion held in San Francisco July 15-16, 1987, and was present for all the proceedings except the af ternoon of the 16th. I am sure that you have the agenda.  !

l The PG & E geophysicists and geologists, together with their I consultants (people like Kei Aki, Bruce Bolt, and Harry Seed) are a very competent group, in my opinion. They presented results of research which I believe is on the forefront in the areas that concern them. Their program is one of the most advanced and comprehensive of any study ever carried out for the seismic safety of a power plant in the U.S., it seems to me. It i looks as though they are successfully developing a rational, empirically-based I model of the ground motion that would be experienced by the Diablo Canyon plant in the event of a strong earthquake.

The Hosgri fault zone continues to be the controlling source of strong ground motion at the plant. The PG & E team recognizes two sub-parallel faults comprising the Hosgri zone near the plant. The main, landward fault is steep and characterized by strike-slip, whereas the oceanward fault is a thrust dipping northeast and joining the steep f ault at depth. However, 1 in order to cover all bases, the PG & E team is deriving ground motions that i would stem from (1) slip on a steep strike-slip fault passing within 4.1 km of the plant and (2) slip on a thrust fault dipping 350 beneath the plant, passing within 4.9 km of the latter. Hypocenters of the small earthquakes that occur in the region do not define a shallow, low-angle " detachment" f ault.

Rather, they are scattered to depths of 10 km or so. I The location and configuration of faults both offshore and onshore are better establ1shed than before. Possible seismic sources are reasonably well characterized. A valuable empirical ground motion data base has been com-piled, using only well instrumented earthquakes of known parameters and mechanisms. Attenuation curves have been refined a good deal. Ground motion at the site is being predicted by numerical modeling, and the provisional model has been compared with actual observations (at the site) of the Point Sel earthquakes. The model has also been tried at other localities where strong motion from well-understood sources has been adequately recorded, and the pre-dicted motion fits the actual records quite well.

All in all.1 think that PG & E has made very encouraging progress.

8708280152 870727 PDR ACRS With best regards, CT-18T6 PDR cc R. Rothman EESIGNATED OltIGINAL Certified By Benjamin M. Page

---