ML20052J027

Lists Opinions Re Seismotectonic Questions Considered During 820412-13 Meeting & Field Trips Around Site

ML20052J027
Person / Time
Site:	Satsop, Washington Public Power Supply System
Issue date:	04/05/1982
From:	Page B STANFORD UNIV., STANFORD, CA
To:	Griesmeyer J Advisory Committee on Reactor Safeguards
References
ACRS-CT-1435, NUDOCS 8205240331
Download: ML20052J027 (2)

Text

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STANFORD UNIVERSITY

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STANFORD. CALIFORNIA 943o3 l

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Mr. J. Michael Griesmeyer N6CEfygg 4

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Dear Mike:

q he following are my opinions regarding seismotectonic questions which were considered during the meeting and field trips of April 12-13 in the region around the WPPSS site at Hanford, Washington:

1. We lineations on the gently sloping surface north of Rattlesnake Mountain are non-tectonic. Recent trenches across three of the lineaments sed-prove the absence of f aults in the exposures cf Pleistocene Touchet iments.

2. The Cold Creek - Horn Rapids lineament i s insigni ficant with regard to seismic implica tions. If it is tectonic, which is doubtful, it is rel atively trivisi. It has no expression in magnetic, gravi ty, or seismic profiles that would confirm the presence of a linear structure; moreover, intervals along its supposed trace. Pleistocene surf aces show no dis-at turbance. If it were indeed a f aul t.

its habit woul d be totally different from that of any other known structure in the region, as it would have to be a strike-slip feature in order to lack a geophysical si gna ture.

3. The Wenas scarps are landslide features, not tectonic fault scarps.

In one locality, a block which is bounded by two scarps meeting each other at right angles has simply subsided under the influence of gravi ty. A con-spicuous linear graben is a landslide " pull-away" feature. Most of the linear features trend about east-west and are obviously extensional. They are totally unrelated to tectonics, as the region is dominated by structures resulting f rom north-south compression.

4 I did not see the Moxee West "f aul ts", but judging from photos and reports by Woodward-Clyde geologists, I believe they are non-tectonic. Photos suggest that the lineaments were made by differential erosion along zones of closely spaced joints in basalt.

5.'The Moxee East fault, which I only saw at a distance, is probably a real f aul t. It is north-south trending and is a good deal f arther from the WPPSS site than the Rattlesnake-Wallule zone, so the latter would remain the controlling tectonic zone wi th regard to the SSE. Because of its trend, the Moxec East f ault does not aim toward the site, and in addition, it could not be related to the postulated CLEW zone.

6. Tlie'C1.EW zone, which is a wide nebulous band seen on maps and serial photos, is supposed to include the Wenas "f aul ts", Moxee fos tures, and Cold Creek - Horn Rapids - Wallula lineament. I think i t is non-existent as far as seismotectonics are concerned.

DESIGNATED ORIGINAL

[g 820S240331 820405 Certified P7- -

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PDR ACRS CT-1435 PDR I&

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7 The f aul ts on Gable Mountain, which I did not visit on this recent occasion, coula hardly threaten the WPPSS site. I examined trench exposures made by the USGS (I believe) about 1970 The main fault I saw is a rather small thrust f aul t which crosses Gable Mountain obliquely. It is related to anticlinsi folding and is doubtless very shallow as well as very short. I don't think it could produce an earthque'<c larger than M 3 at the very most, and there is some evidence that its last movement was somehow related to the great Pleistocene floods which swept over the Pasco Basin. The other transverse f aul t(s) which cross the Gable Mountain anticline must be rather similar, but I have not seen them in trenches.

8 I think real faults occur at Wallula Gap and at the base of Rattlesnake Mountain, and probably intermittently between these localities.

Although there are doubts as to the recency of the last movements, I believe this zone should be regarded as possibly seismogenic and capable of producing the SSE for the WPPSS si te.

With best regards,

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-Cs Benjamin M. Page I

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