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OtPARTM(Ni of LQN5(nVATION DIVISION OF MINES AND GEO!.OGY i
DIVIslON HEADQUARTERS go 1416 NINTH 5ftlif, RCCM 1141 g
3ACRAMINTO, CA 95314 (n...,i6-445 i 2s>
October 4, 1979 l
Mr. Robert Jackson l
Chief, Geosciences Branch
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U.S. Nuclear Regulatory Commission
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Washington, D.C.
20555 l
Subject:
Questions Regarding San Onofre Nuclear Project by the Division of Mines and Geology
Dear Mr. Jackson:
The staff of the Division of Mines and Geology has reviewed the Woodward-Clyde Consultant's report, " Report of the Evaluati'on of Maximum Earthquake and Site Ground Motion Parameters Associated with the Offshore Zone of Deformation, San Onofre Nuclear Generating Station, June 1979", in conjunction with the NRC meeting held at Menlo Park on September 13, 1979.
l We would appreciate having the following questions included withyourlist of questions which are to be presented to the applicant (it is to be noted that the 4
l Division may have other concerns, but the questions in this letter apply only to theWCCstudy):
I l
1.
Why didn't WCC use conventional methods in estimating the maximum earthquake l
magnitude such as employed in the Auburn Dam study? Any new method, no l
matter how promising, must be tested with the experience of established methods. We recomend that all methods of acceptable analysis be in tabular form and show magnitudes and accelerations.
2.
What are the limits of uncertainty in the determination of the slip rates i
for ranges of magnitude? The range of slip rates rather than single values i
should be plotted.
Plotting in this manner could move the maximum earthquake i
line toward substantially higher values.
j 3.
Why hasn't the Coronado Banks-Palos Verdes fault been considered in the and shows youthful and long, continuous fault features (Unpublished report, 1
earthquake analysis? The fault has in excess of 50 feet sea floor offset
" Final Technical Report, USGS, Office of Earthquake Studies, Contract No.
j 14-08-0001-17699, Xennedy,etal.") The slip rate on this fault may contra-i dict WCC's view that all faults west of the San Andreas fault have lower l
slip rates with increasing westerly distance.
4.
Has the 1812 Earthquake (M6.5) been considered as being associated with a local structural source in the analysis of the safe shutdown earthquake?
If such is the case, how does this conclusion affect the determination (CDMG Open File report 79-6 SAC)?
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..o.I' 's I
Robert Jackson, NRC' d l
'5.
Can the. San Miguel fault in Mexico be connected to the flose Canyon fault j
with some degree of certainty? The San Miguel fault was apparently the cause of the February 9,1956 earthquake of M6.8 in; the area.
If the-San Miguel fault is considered as',part of the Newport-Inglewood-Rose Canyon' fault system, can the suggested maximum M of 6.5 for this fault system offshore of the San Onofre site therefore be considered too small?
l 6.
Because the slip rate approach' involves only a small time. semple, cannot the trend.in figure 7 be derived from a nonrepresentative time window of..obser-vation? The WCC approach presumes.that the probability'of observing the l-largest magnitude on a particular fault during a given period is greater for higher rates of seismicity (slip rate).
Is the time period considered in a
the WWC study of' sufficient length to.give a meaningful conclusion?
7.
Has the focusing effect been considered in developing the design conclusions -
for San Onofre reactors 2 and 37 If it has not, we would recommend tha,t NRC and the applicant explore the possible design ' implications of.this phenomenon.
j If the focussing effect significantly modifies the design peak acceleration, 1
then does this also materially change the selection of.the appropriate design
.l spectra which would be adopted for construction.
l 8.
The "g-value versus distance" graph (figure 8, Woodward-Clyde report)-is compiled from data recorded at a range of about 20 km and'150 km from the epicenter; no data at closer distances were plotted to confirm the graph:
for the San Onofre site which is assumed to be located 8 to 10 km from the postulated epicenter.
Therefore, could higher ' accelerations than shown occur at closer distances in view of the lack of information as indicated q
on the graph?
sf y
Perry Y. Amimoto i
Advisory Services Officer APPROV
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ppffs/7. 0W' v '
t' ate Geologist
Enclosure:
Special Publication 54 t
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