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%,*****jl 3-MM 1 1978 MEMORANDUM FOR:
William P. Gammill, Assistant Director for Site Technology, DSE FRON:
J. Carl Stepp, Chief, Geosciences Branch, DSE
SUBJECT:
FAULTING NORTH OF DIABLO CANYON 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 sea 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 meter. The age of the offset 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 not related to the San Miguelito f ault.
M Dr. Davis has drafted a news release which states the following two points:
1.
The CDMG has discovered fault offsets of undetermined 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 coundtted to telefax a copy of the release to us as soon as it has received Director approval.
J. C r
, Chief
'osciences Branch ivision of Site Safety and Environmental Analysis
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l AiAV 1 578 MEHORANDUM TOR:
William P. Gammill, Assistant Director for Site Technology, DSE FROM:
J. Carl Stepp, Chief, Geosciences Branch, DSE
SUBJECT:
FAULTING NORTH OF DIABLO CANYON REPORTED BY JAMES DAVIS (CDMG)
Dr. Davis (CDMG) called me to report on the California Division of Mines cnd 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 sea clif f,14,000 and 14,500 feet respectively north of the Diablo Canyon units. The faults trend north 20*W, are of unkno'wn length, and the southernmost of them offsets the alluvium by an apparent 1 meter. The age of the offset 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 not related to the San Miguelito fault.
Dr. Davis has draf ted a news release which states the following two points:
l 1.
The CDMG has discovered fault offsets of undetermined 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 l
release may be given tomorrow morning. He committed to telefax a copy of the i
release to us as soon as it has received Director approval.
J. d 1
, hief G osciences Branch ivision of Site Safety and Environmental Analysis cc: See next page Y M 2,14..'1 B t
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MRT 8 575 MEMORANDUM POR:
John Stolz, Chief, Light Water Reactors Branch No. 1. DPM PROM:
J. Carl Stapp, Chief, Geoeciences Branch, DSE
SUBJECT:
DIABIA CANYOE NUCLEAR POWER PLANT PROBABILISTIC EARTHQUAKE HAZARD STUDY The Pacific Gas and Electric Company (PG&E) has performed a probabilistic evaluation of the earthquake hasard at the Diablo Canyon Nuclear Power Plant (DCMPP) site Blume,1977a,1977b,1977c
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Blume and Kiramidjian,1978. This memorandum addresses the study contained in these reports. It does not however address that portion of Blume, 1977a which discusses spectral response accelerations.
Several models are available for the calculation of earthquaka recurrance prbbabilities (Cornell,1968; Der-Eiureshian and Ang,1977).
Frq In their basic e1===nts these models are equivalent. i.e. they are based on the assumptions that the occurrence of earthquakes constitutes a Poisson process and that the distribution of earthquake in size is exponential or bounded expondatial. All require definition of source regions based on an interpretation of tectonic elements and seismicity in order to determine the distribution parameters of the model.
In addition they require the specification of attenuation relationships and. functions relating source M==osion to earthquake strength. The model used by Blume (1977a) for the DCNPP etudy is a refinement of the models in the published literature which have become widely accepted.
In addition to the PC&E study, the probabilistic earthquake hazard for the DCHPP has been evaluated by' Anderson and Trifunac (1976) and Ang and Newmark (1977). Each of,these investigations derives the distribution parametars based on different tectonic assumptions and data samples and uses a different attenuation relationship. I have not made a comparison of the impact of these different data assumptions and physical relationships on the results obtained in the three studies.
I have instead attempted to evaluate the reasonableness of the assumptions and physical parameters used in the PC&E study to represent the region of the DCNPP site.
The Blume, 1977a study incorporates a number of assumptions which Ng, are stated or implied:
(1) the seismicity of the Coast Ranges southwest of the San Andreas fault zone and the adjoining offshore region between 34.5' and 37'
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(2) the sample drawn from this region is adequate for determinating
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the distribution parameters of the model, (3) all the estimated earthquake activity in the sample region will occur on four faults (Santa Lucia Bank, Boogri Naci=*=nto and ninmanada-Osena) and none elsewhere, (4) the four faults all have the same activity rate, (5) earthquakes occur randomly in each soures, (6) the length of rupture is described by the relationship of Fatwardhan et. al. (1975).
l (7) attenuation of motion is described by the relationship given in Blume (1977d).
i h first four of these assumptions impact the degree to which the activity rates determined for the various contributing faulta actually reflect current tactonic rates. Assumptions $~and 6 govern the spatial distribution N
l of earthqaakas. h aestasption that the historic seismicity record (1930 to 1975) of the Coast Ranges and adjacent offshora area between Point Argeullo j
and Santa Crus represents the ongoing rate of tectonic activity in the region cannot be directly tested. Different sectors of the San Andreas fault some exhibit different rates of ongoing seismicity and it is not i
known how the seismicity may shift spatially with tima (Allen,1968). Thus a short seismicity sample drawn from a limited part of the San Andreas fault system may not reflect the true rate of tectonism. h applicant has addresses this in B1tane (1977b), in which the distribution parameters i,
(activityratesforfaults)weredeternigedfromtheirestimatedtotalslip during the past 10,000 years and 20 x 10 years. The applicant considers the 10,000 year interval to be the more appropriate internal for determining the rates of activity on faults in the site area. We consider this reasonable,
- .n since the cugreat tectonic pattern has likely not been active during the entire past 20 x 10 years. The probabilities of exceedance of grcund motions near those used for the reevaluation of the DCNFF units obtained by this independent method are lower than those obtained by B1me (1977a) by nearly a factor of two. This provides independent support of the adequacy of the seissioity sample used by Blume (1977a).
l h ass eption that the estimated earthquake activity will occur on only four through-going faults in the site vicinity may be conservative because it tends to result inaa higher activity rate for the Hosgri fault.
l All of the studies show that the probabilistic earthquake hasard at the DCNFF site is controlled at higher levels of acceleration by activity on the Boogri fault.
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1 Different attenuation relationships and fault r, lip-earthquake magnitude relationships have been shown to have a significant impact on probabilistic earthquake hasard evaluations (Der Kiuraghian and Ang,1977). Uncertainty in the fault rupture length earthquake magnitude relationship has apparently not been accounted for in the PG&E studies. Although uncertainty in the attenuation relationship has been accounted for, the Blues (1977a) attenuation relationships i
appear to produce values near the source that are low at all magnitudee when compared with the available data by possibly a factor of two.
The impact of this on the probabilistic earthquake hazard values obtaemed in Bluma (1977a and 1977b) has not been evaluated.
j References are attached.
Original Signed by l
J. C. Stepp DISTIRBUTION:
DOCKET FILE J. Carl Stepp, Chief NRR RDG Geosciences Branch l
GB RDG Division of Site Safety and i
DSE RDG Enviremnantal Analysis e
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As stated cc: w/ attachment H. Denton R. Boyd
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D. Goddard D. A111sen R. Hofmann D. HeMullen i
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References Anderson, J. G. and M. D. Trifunac,1976, Uniform ris). absolute
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acceleration spectra for the Diablo Canyon site' California, Report prepared for the ACRS.
Allen, C. A.,1968, Tectonic environments of' seismically active and inactive areas along the San Andreas7 fault cystem, in Proceedings of Conference and Geologic Proble?;s of the San' Andreas fault system, ed by William R. Dickinson and Authur Grantz, Stanford Univ. Pub.
Geological Sciences, Vol. XI, pp 70-82.
Ang, A. H-S and N. M. Newmark, 1977( A Probabilistic seismic safety assessment of the Diablo Canyon Nuclear Poser Plant, Report to the Nuclear Regulatory Commission, '/ashington, D. C.
Blume, John A. 1977a, Probabilities of peak accelerations and spectral response accelerations from assumed magnitudes up to and including 7.5 on all local faults, Appendix D-LL 11. -amendment 50, DCNPP FSAR.
Blume, John A.,1977b, Probabilities of accelerations based on the geologic record of fault dislocation, Appendir D-LL41, DCNPP FSAR.
Blume, John A.,1977c, Discussion of Attenuation' equations, Appendix
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D-LL43, DCNPP FSAR.
j UMNEMd Blume, John A. and Anne S. Kirealdjica,1978, D.sta sets and their
,preatment in obtaining attenuation' relationships Appendix A LL46, gNPP,FSAR.
Cornell, C. A., 1968, Engineering Seismic Risk Analysis, Bull. Seis.
Soc. Amer., Vol. 58, pp.1583-1606.
Der Kiureghian A., and A. H-S Ang, 1977, A fault-rupture model for seismic risk analysis, Bull. Seis. Soc. Amer. Vol. 67, No. 4, pp 1173-1194.
Patwardhan, A. S. D. Tocher, and E. D. Savage,1975, Relationship between earthquake magnitude and length of rupture surface based on aftershock zones, Abstract Earthquake. Notes, Vol. 46, No. 3, P. 20.
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