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6 MEMORANDUM FOR:
J. Carl Stepp, Chief, Geosciences Branch, DSE FROM:
Richard B. McMullen, Geologist, Geology and i
Seismology Section, Geosciences Branch, DSE
SUBJECT:
NEW DATA ON THE SAN MIGUELITO FAULT ZONE NEAR DIABLO CANTON On March 23, 1978, and again on April 5,1978 Mr. Charles Jennings, senior geologist with the California' Division of Mines and Geology (CDMG) informed as of the results of a recent airphoto study by a CDMG geologist stationed at San Luis Obispo. He study included the area of a morthwesterly projection of the San Miguelito Fault sone.
I h e San Miguelito fault zone is shown on the 1973 map by Hall
" Geology of the Arroya Grande Quadrangle San Luis Obispo County, l
California." he fault some is shown to terminate about 21/2 miles east of the site where it is overlain by undeformed Quaternary deposits.
i he CDMG geologist believes that he has found geomorphic evidence ladicative of apparent poet Quaternary movement on the San Miguelito W
fault sene.. Se evidence consists of apparaat stream effsets and deformed alluvium deposits along a northwesterly projection of the fault sons. A morthwesterly projection of the fault some along l
trend womid cause it to pass about 11/4 miles east of the site.
Mr. Ja==4=t= plans to review the photos himself and ground truth 4
the area when aeones to the properties can be obtained. Jennings had earlier called my attentima to two p411mbed maps, Willis and l
Wood's 1922 Fault Map of california pelished by. SSA, and a 1947 map by Earry O. Wood. A fault is shoem on both aspe that in part I
coineidaa with the gan Miguelito fault some but also is shown to cross the entire peninsula and enter Estero Bay.
4 CDMG has reviewed a report by Dames and Moore entitled "0eshore Fault Studine Western Santa Barbara County " which was written in i
comaeetion with am 11Ned G site at Rattlesnake Cemyon approximately three miles meeth of Diablo Canyon. Me fault is called the Santa l'
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.o J. Carl Stepp MR 17 878 Maria River fault and projects to the Piano area, which would be s
approwi=.taly in line with a southeasterly projection of the San Miguelito fault sons. The fault is described in the report as being 4
active, with Quaternary and possibly Holocene displacement.
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All of this information suggests that the San Miguelito fault some any be longer and may have experienced more recent movement than i
is indicated in the FSAR.
Mr. Jennings said that he would contact as again in about two weaks after he has had a chance to review the airphotos, and a field reconnaissance has been anda.
On April 14, 1978, we contacted Jannings again and learned that i
access to the property had been acquired. We are asking arrangements to send a staff geologist to accompany the CDMG geologist into the area to determine the significance of this latest information.
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Richard B. McMullen, Geologist l
l Geology and Seismology Section Geoeciences Branch Division of Site Safety and Environmental Analysis i
co W..c --411 R. normann L. Reiter R. McMullen l
C. Jennings, CDIC l
DISTRIBUTION:
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w w1m MEMORANDUM FOR:
William P. (:causill, Assistant Director for Site Technology, DSE FROM:
J. Carl Stepp, Chief, Geosciences Branch, DSE
SUBJECT:
FAULTING N0ETE OF DIABID CANTON REPORTED BY JAMES DAVIS (CDMG)
Dr. Davis (CDMG) called me to report on the California Division of Mines and Geology investigation of the northern extension of the San Miguelito fault zone. He reported the following:
1.
Their work has shown the San Miguelito fault zone is not extended beyond the mapped position on the Hall map.
2.
CDMG personnel found two faults in the see cliff, 14,000 and 14,500 feet respectively north of the Diablo Canyon units. The faults trend north 20'W, are of unknown length, and the southernmost of them offsets the alluvium by an apparent 1 pater. The age of. the offset
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is unknown. The alluvium appears to be an older alluvium, but its age is not yet determined. The southernmost of these two faults appears on the basis of the limited field investigation to juxtapose Obispo Formation against Monterey Formation. The sense of movement as indicated by slickensides, appears to be predominantly dip-slip.
These faults are not aligned with any known major structure and are Y
not related to the San Miguelito fault.
Dr. Davis has drafted a news release which states the following two pointa:
1.
The CDMG has discovered fault offsets of smdetermined age 14,000 feet and 14,500 feet north of the Diablo Canyon Nuclear Plant units.
2.
CDMG has recommended to the NRC that we look into the matter.
Dr. Davis has not yet gotten approval of his Director to make the release.
He expects that approval will be obtained before the end of today so that the release may be given tomorrow morning. He committed to telefax a copy of the release to us as soon as it has re'ee g, g ggg approval.
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J. C. Stepp J. Carl Stepp, Chief Geosciences Branch Division of Site Safety and Environmental Analysis f
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H. Denton R. Boyd W. nammill D. Vassallo J. Tourte11otte D. Davis D. Goddard D. Haller J. Stols D. Allison R. Hofmarm D. McMullen J. Hauchett J. Devine J. Davis Local PDR PDR wm DISTRIBUTION:
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