ML20236M065

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Forwards Suppl to Rept on Seismicity of Diablo Canyon,Ca Area.Recent Geological & Seismological Info Re Region Around Unit 2 Reviewed & Evaluated
ML20236M065
Person / Time
Site: Diablo Canyon Pacific Gas & Electric icon.png
Issue date: 06/12/1970
From: David Jones
COMMERCE, DEPT. OF
To: Price H
US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20236J368 List: ... further results
References
FOIA-87-214 NUDOCS 8708100460
Download: ML20236M065 (7)
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/  % PHUL }llL. FAC.D*0

  • Y f r ;" 't U.S. DEPARTr.';En!T OF C0!UTTNG1C 0 Environmental Science Services Administration .

, \. ,' . " ' ,/ COAST AND GEODETIC SURVEY .(

Rockville, Md. 20852

.JUN : 21970 -

Ih' ply to i Attn of': C23 i

Mr. liarold L. Price' H Director of Regulation U. S. Atomic Energy Commission  ;

Washington, D. C. 20545 i

Dear Mr. Price:

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In.accordance with your request, we are forwarding the:

supplement to our report on the seismicity of the Diablo Canyon, California, area. The Coast and Geo- .

dotic Survey has reviewed and evaluated the recent geo-logical and seismological information concerning the ,

region around the Diablo Canyon Nuclear Str. tion, Unit 2, and we are submitting our conclusions as to its-significance.

Sincerely, - N c) S 300KE;is

[/,,,..,O.,c!s.a.- C1'l A

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Don A. ones il JUN151970

  • r Rear Admiral, USESSA ' 1y cm,., m :-mn o

-S Director, C&GS y,\ kr "r  ;

Enclosure > # .

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l 8708100460 870729 q PDR FOIA- i CONNOR87-214 PDR

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Supplement to the Se'Ismic Evaluation of the Diablo Canyon i

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Nuclear Power Plant Unit //2, AEC Docket 50-323 ) !

This nupplement is in response to the request of the l.!

Atomic Energy Commisulon to evaluate the significance of j l

some recent geological and seismological information con-corning the region around the Pacific .Gan and Electric ,

Company's Diablo Canyon Nuclear Station, Unit 2. Refer-ence has been made by an intervener to two features that have come to light since the completion of the geologic and ceismologic evaluation of the site. The first fea-ture consists of a number of moderate ear;hquakes that have occurred in the offshore region southwest of the  ;

Diablo Canyon site that appear to be defining a north-l east trending seismic zone. The second feature referred to is the Edna Fault Zone which is located north and east of the site. The Coast and Geodetic Surysy has reviewed the data on file, conferred with Geological Survey geolo-gists and marine geophysicists, and has c:nsidered the possible effect of these two features on the seismic evaluation.of the Diablo Canyon Nuclear S;ation, Unit 2.

Offshore Earthquakes Since June 12,.1969, the Coast and Geodetic Survey has routinely located 25 earthquakes in' this offshore re-gion. Their magnitudes range from 3.7 to 5 9 and the l

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l l 2 locations are computed from readings of 6 to 131 seismic ntat.lonn. Wh:11c the depthu of thouc events are difficult to determino accurately, it is believed that none arc i greater than 25-33 km and some are as shallow as 10 km. .

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Their distancos from the Diablo Canyon site range south- l westwardly and approximately 20 miles to 120 miles. The a.ttached table gives the location, depth, magnitude, and  !

l the number of stations reporting for each carthquake. ,

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In the past, two other earthquakes, including the 1927 macnitude 7 3 event, have occurred within the area described by the recent events. In addition, the histor-i ical record shows that 10 additional earthquakes with l

magnitudes less than 5, have occurred in a 120 mile align-mont near the shoreline and trend in a general NW-SE direction with the closest approach about 15 miles from

,the Diablo Canyon site. This alignment includes one of the 1969 events.

The conclusion of the Geological Surtey's report on this subject states that "The major structural patterns i

of offshore and onshore geology consist of NW-SE trending parallel belts of folds, faults, and basement rock highs."

This report further states that "There is no geologic evidence to support a northeastward structural trend in the offshore area of earthquake epicenters." -

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Although an examination of the alignment of the l recent offahoro noismic activity suggcats an apparent NE-SW lineation of the earthquake locations, there is no bacia for concluding that they delineate a NE-SW l

trending fault in view of the geologic structural in-l formation presented by the Geological Survey. On the l

contrary it is logical to conclude that they are asso-ciated with the established NW trending structural fea-I tures because the above mentioned 25 earthquakes may be aligned with them, thereby substantiating sources for the origins of these earthquakes. ,

Since there is no ceological structure trending in a NE direction from the source of the 1927 earthquake, there is no basis for concluding that a 1927 offshore 4

type earthquake could occur near the plant site.

Edna Fault Zone A review of the seismicity of the onthore area around the Diablo Canyon site by the Coast and Geodetic Survey indicates that this particular region of Cali-fornia is devoid of activity as reported in historical files or as instrumentally determined by close-in seismic stations. Therefore, there is no apparent correlation of seismic events with the Edna Fault Zone.

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- u' It is the conclusion of the Coast and Geo'dotic Survey that the offahore carthquake activity and Edna f I .

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Fault 7,onc do not have a significant bearing on the j carthquake potential for this sito because they present a hazard much less than that already considered in the a I

cvaluation of the site.  !

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U. S. Coast and Geodetic Survey

. Rockville, Maryland 2085.2 June 11, 1970 e

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PRELIMINARY DETERMINAT:10N OF EPICENTERS 1 l DAY ORIGIN TIME GE00HAPH10' DEPTH MAGNITUDE. No.

I UMT GMT COORDINATES KM. STA HR MN SEC LAT LONG l 1969 JUNE 12 11 18 53 2 34.2 N 121.0 W' 22 4.3 6 SEPT. )

6 13 44 46.1 35.2 N 121.1 W 13 4.0 22 I 1

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22 17 34 13 2 34.6 N 121.7 W 150 4.7 14 1

l l 22' 22 51 33 5 34.8 N 121.3 W 15G 5.9 131 )

l 23 00 03 34.4 34.9 N 121.3 W 10 5.0 28 23 02 05 47.2 34.9 N 121 3 W 10 3.9 16 23 03 43 14.9 34.8 N 121.5 W 10 4.0 15 l 23 04 33 22.8 36N 4 121.6 W' 16 4.2 10 1

23 06 41 21.0 34.6 N 121.6 W 15G 4.0 12 23 07 19 02.9 34.5 N 121.6 W 150 4.0 10 23 16 38 03.0 34.6 N 121.5 W 10 4.6 16 24 13 la 09.7 34.8 N 121.3 W 15G 4.6 15 24 19 13 07.4 34.8 N 121.4 W 150 37 14 28 0022337 34.3 N 121.9 W 26 4.5 22 l 30 15 36 19 1 34.2 N 120.8 W 10 4.2 10 31 09 12 13.6 34.6 N 121.5 W 10 5.0 17 1

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, NOV.

4 00 40 46.4 34.8 N 121.3 W N 4. 9. 23 l

l 5 17 54 13.6 34.8 N 121.2 W N ~5. 8 109 y 18 48 48.9 34.8 N 121.2 W 5.1 5 N 33 8 00 33 19.9 34.2 N 122.3 W N 4.7 18.

9* 01 27 40.8 34.4 N 121.6 W N 4.7 11 10 19 21 27.3 34.6 N 121.5 W N 4.6 20.

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3 22 10 37.1 34.6 N 121.5 W N 4.5 21 1970 JAN.

i 8 17 00 33.2 34.4 N 121.7 W N 4.4 18 i FEB. ,

23 07 52 11.9 34.5 N 121.8 W 100 4.3 19 1

0 - Depth held by Geophysicists N - Normal depth - 25 km l

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