ML25167A169
| ML25167A169 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 06/04/1984 |
| From: | Page B Stanford Univ |
| To: | Okrent D, Savio R Advisory Committee on Reactor Safeguards |
| References | |
| Download: ML25167A169 (1) | |
Text
DEPARTMENT OF GEOLOGY irtioololEanhScienca Dr. David Okrent Dr. Richard Savio*
- STANFORD UNIVERSITY STANFORD, CALIFORNIA 9-4305 ACRS, NRC, Washington, DC
Dear Dave and Dick:
The following remarks pertain to the find5ngs o:f Dr *.Te.mes Crouch et al., as presented at the meeting held in Los ~les on May 24, 1984.
Main conclusions:
- l. I think the staff's dra:rt elements for the Diablo Canyon Lioense Condition e.re very good indeed. They appear to provide logical. procedures for dealing with the seismotectonic problems that are now arising and those 1.hat may e.rise in the :f'uture. There will surely be e nearly continuous inflow of data.
- 2. At the present moment, the latest findings (published by Crouch et a1.)
egarding the Hosgri and other of:f'shore faults do not necessarily increase 1:.he maxim-.2m ground motion that might be experienced by 1:.he Diablo Canyon plant, and do not necessarily increase the frequency of strong earthquakes.
As more information is acquired, 1:.he implioations could be either more favorable or less favorable to the perceived sa:f'ety o:f' the plant.
Further comments:
If 1:.he offshore Hosgri fault dips landward beneath the Diablo Ca:JYon plant, the vertical distance from the site to the fault could be either greater.~r less then the horizontal distance from the plant to the surface trace of the fault, depending on the curvature o:f' the fault profile, which ?las not been esteblished.
In any case, it is hishly unlikely that a strong ee.rthqual:9 would be generated et a depth less than 8-10 km, as a certain amoilllt of confining p:-essure is required. If the Hosgri fault were to pass under the plant at e vertical distance o:f' 3 km, say, it would be totally unree.l.istic to postulate a strong ea~thque.ke stei::::::1i:og from the fault directly beneath t~e p1ant.
The moderate to inconspicuous disturbance of the uppermost strata near the Hosgri fault, as seen in Dr. Crouch's reflection profiles, wocld argue for very infrequent (or very small) slip-events if the Hosgri fa~~ is largely a thrust fault. However, we must not be too optimistic, as we r.. ill do not know or sure,;hat the size and recurrence interval are :f'or sl.ip-events on the fault.
A d011'llwe.rd-flattening, thrust-like configuration would make it highly 372
unlikely that the Hosgri fault has accrued 80-150 km of strike-slip. The ault would be oharacterized by predondnent thrust-or obl.ique-slip, IID4
,he vibratory motion might differ somewhat from that which has been envisioned for the Diablo Canyon site. Whether the SSE and the ground motion would be more severe or less severe r~me1ns to be seen. It may turn out that, i:f' all other factors were equal, an SSE from a thrust fau11; would be more severe than an SSE from a strike-slip fault. However, if the Hosgri fault is really a thrust fault, the ":ner' Hosgri may be shor-ter than the "old" Hosgri fault. It may not be a part of the San Gregorio zone, e.:rter ell.. It may :not have a history of large slip-events. So, the various fac1;ors, when combined, may give a result compatible with the earlier postulations.
Sincerely, Benjamin u. Page Copies sent to each addressee.
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