ML17083B846
| ML17083B846 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 01/08/1987 |
| From: | Schierling H Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML16342B258 | List: |
| References | |
| NUDOCS 8701140485 | |
| Download: ML17083B846 (28) | |
Text
January 8, 1987 Docket Nos.
50-275 and 50-323 LICENSEE:
FACILITY:
SUBJECT:
~DISTRIBUTION oc et-Fi-e~OGC NRC PDR E. Jordan Local PDR B. Grimes PD¹3 RDg.
ACRS(10)
S.
Varga R. McMullen H. Schierling L. Reiter Diablo Canyon Nuclear Power Plant G. Giese-Koch D. Jeng I. Alterman R. Ballard MEETING ON OCTOBER 21-24, 1986 ON LONG TERM SEISMIC PROGRAM E. Rossi NRC staff and its consultants met with PG&E to discuss the status of the Long Term Seismic Program (LTSP).
The meeting notice is attached as Enclosure 1.
The two subjects of 'the program discussed were (I) geology, seismology and geophysics on October 21-22, and (2) ground motion on October 23-24, 1986.
The lists of attendees for both parts of the meeting are attached as Enclosure 2.
Prior to the meeting, PG&E had provided to the participants a proposed
- agenda, outline and viewgraphs.
This information is attached as Enclosures 5a and 5b for the two sessions, respectively.
In the first part of the meeting (October 21-22)
PG&E updated the status of its efforts in the areas of geology, seismology, and geophysics by including the features that had been identified during the August 15-16 field trip, addressing their significance and describing plans for future investigations.
The focus of the meeting was the region encompassing the San Simeon and Hosgri Fault Zones, the Pismo-San L'uis Obispo Syncline, the onshore Santa Maria
- Basin, and the Transverse Ranges.
The detailed NRC staff summary is attached as Enclosure 3a.
Comments by R.
Brown of the U.S. Geological
- Survey, D. B.
Slemmons of the University of Nevada-Reno, and G. Thompson, consultant to the ACRS, regarding the PG&E efforts are attached as Enclosure 3b, 3c, and 3d, respectively.
In the second part of the meeting (October 23'-24)
PG&E discussed the status of its efforts with respect to ground motion.
Comments by the NRC staff and its consultants (K. Aki, R. Archuleta, C. Costantino, S.
Day) are attached as Enclosures 4a, 4b, 4c, 4d and 4e, respectively.
At the conclusion of the meeting the NRC staff requested PG&E to document the results of the meeting in a report.
Enclosures:
As stated Hans Schierling, Senior Project Manager Project Directorate ¹3 Division of PWR Licensing-A cc:
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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 January 8, 1987 Docket Nos.
50-275 and 50-323 LICENSEE:
FACILITY:
SUBJECT:
Pacific Gas and Electric Company Diablo Canyon Nuclear Power Plant MEETING ON OCTOBER 21-24, 1986 ON LONG TERM SEISMIC PROGRAM NRC staff and its consultants met with PGIIE to discuss the status of the Long Term Seismic Program (LTSP).
The meeting notice is attached as Enclosure 1.
The two subjects of the program discussed were (1) geology, seismology and geophysics on October 21-22, and (2) ground motion on October 23-24, 1986.
The lists of attendees for both parts of the meeting are attached as Enclosure 2.
Prior to the meeting, PG8IE had provided to the participants a proposed
- agenda, outline and viewgraphs.
This information is attached as Enclosures 5a and 5b for the two sessions, respectively.
In the first part of the meeting (October 21-22)
PGImE updated the status of its efforts in the areas of geology, seismology, and geophysics by including the features that had been identified during the August 15-16 field trip, addressing their significance and describing plans for future investigations.
The focus of the meeting was the region encompassing the San Simeon and Hosgri Fault Zones, the Pismo-San Luis Obispo Syncline, the onshore Santa Maria
- Basin, and the Transverse Ranges.
The detailed NRC staff summary is attached as Enclosure 3a.
Coments by R.
Brown of the U.S. Geological
- Survey, D. B.
Slemmons of the University of Nevada-Reno, and G. Thompson, consultant to the ACRS, regarding the PG8.E efforts are attached as Enclosure 3b, 3c, and 3d, respectively.
In the second part of the meeting (October 23-24)
PG8lE discussed the status of its efforts with respect to ground motion.
Comments by the NRC staff and its consultants (K. Aki, R. Archuleta, C. Costantino, S.
Day) are attached as Enclosures 4a, 4b, 4c, 4d and 4e, respectively.
At the conclusion of the meeting the NRC staff requested PGImE to document the results of the meeting in a report.
Enclosures:
As stated Hans Schierling, Se'r Project Manager Project Directorate P3 Division of PWR Licensing-A cc:
See next page
Mr. J.
D. Shiffer Pacific Gas and Electric Company Diablo Canyon CC:
Philip A. Crane, Jr.,
Esq.
Pacific Gas
& Electric Company Post Office Box 7442 San Francisco, California 94120 Mr. Malcolm H. Furbush Vice President - General Counsel Pacific Gas
& Electric Company Post Office Box 7442 San Francisco, California 94120 Janice E. Kerr, Esq.
California Public Utilities Commission 350 McAllister Street San Francisco, Cali fornia 94102 Mr. Frederick Eissler, President Scenic Shoreline Preservation.
Conference, Inc.
4623 More Mesa Drive Santa
- Barbara, Cali fornia 93105 Ms. Elizabeth Apfelberg 1415 Cozadero San Luis Obispo, California 93401 Ms. Sandra A. Silver 660 Granite Creek Road Santa
- Cruz, California 95065 Harry M. Willis, Esq.
Seymour
& Willis 601 California Street, Suite 2100 San Francisco, California 94108 Mr. Richard Hubbard MHB Technical Associates Suite K
1725 Hamilton Avenue San Jose, California 95125 Arthur C. Gehr, Esq.
Snell
& Wilmer 3100 Valley Center
- Phoenix, Arizona 85073 NRC Resident Inspector Diablo Canyon Nuclear Power Plant c/o U.S. Nuclear Regulatory Commission P. 0.
Box 369 Avila Beach, California 93424 Ms.
Raye Fleming 1920 Mattie Road Shell Beach, California 93440 Joel
- Reynolds, Esq.
John R. Phillips, Esq.
Center for Law in the Public Interest 10951 West Pico Boulevard Third Floo~
Los Angeles, California 90064 Mr. Dick Blankenburg Editor
& Co-Publisher South County Publishing Company P. 0.
Box 460 Arroyo Grande, California 93420 Bruce Norton, Esq.
c/o Philip A. Crane, Esq.
Pacific Gas and Electric Company Post Office Box 7442 San Francisco, California 94120 Mr.
W. C. Gangloff Westinghouse Electric Corporation P. 0.
Box 355 Pittsburgh, Pennsylvania 15230 David F. Fleischaker, Esq.
P. 0.
Box 1178 Oklahoma City, Oklahoma 73101 Managing Editor San Luis Obispo County Telegram Tribune 1321 Johnson Avenue P. 0.
Box 112 San Luis Obispo, California 93406
Pacific Gas
& Electric Company Diablo Canyon CC:
Dr.
R.
B. Ferguson Siera Club - Santa Lucia Chapter Rocky Canyon Star Route Creston, California 93432 Mr. Lel and M. Gusta fson, Manager Federal Rel ations Pacific Gas
& Electric Company 1726 M Street, N.W.
Suite 1100 Washington, DC 20036-4502 Regional Administrator, Region V
U.S. Nuclear Regulatory Commission 1450 Maria Lane Suite 210 Walnut Creek, California 94596 Michael J. Strumwasser, Esq.
Special Counsel to the Attorney General'tate of California 3580 Wilshire Boulevard, Suite 800 Los Angeles, California 90010 Mr. Tom Harris Sacramento Bee 21st and 0 Streets Sacramento, Cali fornia 95814 Ms. Jacquelyn Wheeler 2455 Leona Street San Luis Obispo, California 93400 Lewis Shollenberger, Esq.
US Nuclear Regulatory Commission Region V
1450 Maria Lane Suite 210 Walnut Creek, California 94596 Dian M. Grueneich, Esq.
Edwin F. Lowry, Esq.
Grueneich
& Lowry 345 Franklin Street San Francisco, Cali fornia 94102 Mr. Thomas Devine Government Accountability.
project Institute for Policy Studies 1901 gue Street, NW Washington, DC 20009 Chairman San Luis Obispo County Board of Supervisors Room 220 County Courthouse Annex San Luis Obispo, California 93401 Director Energy Facilities Siting Division Energy Resources Conservation and Development Commission 1516 9th Street Sacramento, Cal ifornia 95814 President California Public Utilities Commission California State Building 350 McAllister Street San Francisco, California 94102 Mr. Joseph
- 0. Ward, Chief Radiological Health Branch State Department of Health Services 714 P Street, Office Building P8 Sacramento, California 95814 Ms. Nancy Culver 192 Luneta Street San Luis Obispo, California 93401 Ms. Laurie McDermott, Coordinator Consumers Organized for Defense of Environmental Safety 731 Pacific Street, Suite 42 San Luis Obispo, California 93401
Pacific Gas and Electric Company Diablo Canyon CC:
Dr. S.
T. Algermissen U.S. Geological Survey P. 0.
Box 25046 Mail Stop 966 Denver Federal Center
- Denver, Colorado 80225 Dr'. Keiiti Aki Department of Geological Sciences University of Southern California Los Angeles, California 90089 Dr. C. J. Costantino 4 Rockingham Road Spring Valley, New York 10977 Dr. James Davis State Geologist California Divison of Mines and Geology Room 1351 1416 Ninth Street Sacramento, California 95814 Dr. Ralph J. Archuleta Department of Geological Sciences University of California Santa Barbara Santa
- Barbara, Cali fornia 93106 Dr. Steve'n M. Day S-Cubed P. 0.
Box 1620 La Jolla, California 92038 Mr. Don Bernreuter Lawrence Livermore Laboratory P. 0.
Box 808 Livermore, California 94550 Dr. George Gazetas JEC 4049 Renssalear Polytechnic Institute
- Troy, New York 12180-3590 Mr. Donald A. Brand Vice President, Engineering Pacific Gas and Electric Company 77 Beale Street, Room 2645 San Francisco, California 94106 Dr. David Perkins U. S. Geological Survey P. 0.
Box.,25046 Mail Stop 966 Denver Federal Center
- Denver, Colorado 80225 Dr. Robert D. Brown, Jr.
U.S. Geological Service Bui1 ding 8, 8977 345 Middlefield Road Menlo Park, California 94025 Dr. Morris Reich Structural Analysis Division Building 129 Brookhaven National Laboratory
- Upton, New York 11973 Mr. Loyd S. Cluff Pacific Gas and Electric Company 77 Beal.e Street, Room 266l San Francisco, California 94106 Dr.
Ken Campbell U.S. Geological Survey P.O.
Box 25046, Mail Stop 966 Denver Federal Center
Box 808 Livermore, California 94550
Pacific Gas and Electric Company Diablo Canyon CC:
Dr. David B. Slemmons 2995 Golden Valley Road
- Reno, Nevada 89506 Dr. Andrew S. Veletsos 5211 Paisley Avenue
- Houston, Texas 77096 Dr. Robert Youngblood Building 130 Brookhaven National Laboratory
- Upton, New York 11973
LIST OF ENCLOSURES 1.
NRC Meeting Notice, dated October 8, 1986 2.
Lists of Attendees a.
October 21 - 22 b.
October 23 - 24 3.
a.
NRC Staff Summary Details (October 21-22) b.
Letter from R.
Brown (USGS) to H. Schierling (NRC) dated October 29, 1986 c.
Letter from D. B. Slemmons, University of Nevada-Reno, to H. Schierling and G. Giese-Koch, NRC, dated November 30, 1986 d.
Letter from G.
Thompson to R. Savio (ACRS), dated October 25, 1986 4.
a.
NRC Staff Comments (October 23-24) b.
Letter from K. Aki, to J.
Savy, October 28, 1986 c.
Letter from R. Archuleta to J.
- Savy, November 17, 1986 d.
Letter from C. Costantino to N. Reich, December 4, 1986 e.
L'etter from S.
Day to J.
- Savy, November 6, 1986 5.
a.
b.
PGSE Agenda and Viewgraphs for October 21-22,
- 1986, note from C. Cluff (PG&E), dated October 14, 1986 PGSE Agenda and Viewgraphs for October 23-24,
- 1986, note from C. Cluff (PGSE),
dated October 14, 1986
~a
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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 October 8, 1986 I ~c~o5 Are L Docket No. 50-275 and 50-323 MEMORANDUM FOR:
FROM:
SUBJECT:
DATE III TIME:
LOCATION:
PURPOSE:
Steven A. Varga, Director Project Directorate II3 Division of PWR Licensing-A Hans Schierling, Senior Project Manager Project Directorate I5I3 Division of PWR Licensing-A FORTHCOMING MEETING WITH PACIFIC GAS AND ELECTRIC COMPANY October 21 through 24, 1986 8:00 a.m. to 5:00 p.m.
PGIIE Offices, 17th Floor Conference Room 77 Beale Street San Francisco, CA Review status of Long Term Seismic Program, including discussion of geological features, characterization of Hosgri Fault Zone and San Luis/Pismo Region; Ground Motion Input to Phase III St'udies and Ground Motion Instrumentation; Soil Structure Interaction Parametric Studies and Phase III Fragility Evaluation.
PARTICIPANTS:
NRC See next page PGSE D. Brand L. Cluff, et al.
Others J.
Crouch cc:
See next page Hans Schierling, Senior Project Manager Project Directorate P3 Division of PWR Licensing-A
~
~
Contact:
H. Schierling
, GGNQt4.~ ~y g CmhdP>~I j'gD g
'ateZ~~N 6 EKUQTM7BOCKEf BLK
ENCLOSURE 2a LIST OF ATTENDEES NRC/PG&E MEETING OCTOBER 21-22, 1986 C. Allen F. Brady D. Brand R.
Brown L. Cluff K. Coppersmith N. T. Hall E. Hart K. Hanson G. Giese-Koch K. Killen W. Lettis R. Madsen B. Matz M. McLaren R. McMullen W. Mooney S.
Nitchman L. Reiter J.
Rietmen B. Sarkar W. Savage J.
Savy H. Schierling D. Schwar tz R. Schweikert PG&E Consultant PG&E PG&E USGS -
NRC Consultant PG&E PG8E Consultant PG&E Consultant California Div. of Mines 8 Geology PG&E Consultant NRC UNR -
NRC Consultant PG&E Consultant PG&E UNR - NRC Consultant PG&E Consultant NRC USGS -
NRC Consultant UNR -
NRC Consultant NRC PG&E Consultant PG&E Consultant PG&E Consultant LLNL - NRC Consultant NRC USGS -
NRC Consultant UNR -
NRC Consultant
B. Slemmons P. Somerville B.
Swan R. Sydnor G. Thompson B. Tsai A. Trehu X. Zhang UNR - NRC Consultant PGSE Consultant PGI5E Consultant California Div. Nines 8 Geology ACRS Consultant PGSE USGS - NRC Consultant UNR - NRC Consultant
ENCLOSURE 2b LIST OF ATTENDEES NRC/PG&E MEETING OCTOBER 23-24, 1986 K. Aki A. J. Archuleta F.
W. Brady D. A. Brand N. Chokshi L. S. Cluff K. Coppersmith C. J. Costantino S.. Day J. A. Eagan J. Frazier G. Giese-Koch D. Helmberger F. I. Makdisi M. Mayer L. Mualchin L. Reiter R. Sadiqh B. Sarkar J.
Savy P. Sommerville G. Thompson B. Tsai W. S.
Tseng USC -
NRC Consultant USCB -
NRC Consultant PGSE PGSE NRC P.GKE Geomatrix -
PGSE Consultant CCNY -
NRC Consultant S-Cubed -
NRC Consultant Geomatrix - PGSE Consultant SAIC -
PGSE Consultant NRC PGSE Consultant Geomatrix PGSE Consultant PGaE California Div. Hines 8 Geology (CDMG)
NRC Geomatrix -
PGSE Consultant Bechtel/PGSE LLNL -
NRC Consultant Woodward 5 Clyde - PGSE Consultant ACRS Consultant PGSE Bechtel/PGSE
C
Enclosure 3a DIABLO CANYON NUCLEAR POWER PLANT NRC STAFF
SUMMARY
LONG TERM SEISMIC PROGRAM (LTSP)
- GEOLQQY, SEISMOLOGY, AND GEOPHYSICS MEETING - OCTOBER 21 and 22, 1986 TABLE OF CONTENTS A.
Meeting Summary 1.
Characterization of Hosgri Fault Zone a.
San Simeon RePort b.
Offshore Region form Point Estero to Purisina Point 2.
Characterization of San Luis/Pismo Region a.
University of Nevada Studies b.
Pacific Gas and Electric Studies 3.
Tectonic Framework a.
Pacific Gas and Electric Studies b.
University of Nevada Studies B.
Comments
The following is the detailed meeting summary by the NRC staff.
Comments provided to by PG8E at the completion of the meeting are stated in Section B.
1.
Characterization of Hos ri Fault Zone a.
San Simeon Re ion The onshore San Simeon Fault Zone is being investigated by PG8E to determine its relationship to the Hosgr Fault, and also because it is partly located onshore and therefore accessible to onshore investigative techniques, where the Hosgri is not.
Based on the studies thus far, which include geomorphic studies, mapping of ancient marine and fluvial terraces, shallow strati-graphic studies, and sea floor sampling, PG8E has tentatively concluded that the San Simeon Fault Zone is a right lateral strike slip fault with an estimated slip rate of about 5.8 mm per year.
Except for dating of soils offset by the fault, work by PG8E on the onshore San Simeon is essentially complete.
Offshore seismic reflection work is continuing to determine the relationship between the San Simeon Fault Zone and the Hosgri Fault Zone.
b.
Offshore Re ion from Point Estero to Purisima Point This area is being explored by PG8E to determine the relation-ship between the Hosgri Fault Zone and other structures in the region, particularly those east of the Hosgri; to determine the nature of the Hosgri Fault Zone at depth, i.e., to determine if it extends down through the crust at a high angle, or it rolls over and extends beneath the site area at a low angle; and to determine the amount, rate, and predominant sense of displace-ment on the Hosgri Fault Zone.
4 The offshore area is being investigated by means of (1) shallow penetrating high resolution seismic reflection data, which covers the subsurface to depths of 100 to 200 meters; (2) reprocessing seismic reflection data that gives high resolution between depths from 1 to 4 kilometers (interpretation of these data will be controlled by more than 100 existing deep borings both east and west of the Hosgri Fault Zone);
and (3) deep crustal seismic reflection and refraction studies that provide good resolution data from several kilometers to on the order of 20 kilometers.
4 The shallow seismic reflection data have shown the Hosgri Fault Zone to be similar to onshore strike-slip faults in the Coastal Ranges.
The characteristics are a pattern of anastomozing and en echelon faults, the presence of grabens, half grabens, and
,sag features along the fault zone trend caused by slight direc-tion changes in the various fault splays, and flower structure patterns in cross section.
These findings are consistent with those made by PG8E and the staff and its consultant during the operating license review stage in the middle and late 1970's.
The intermediate-depth seismic reflection profiles show the Hosgri Fault Zone to be comprised of two components, (1) a high angle fault that extends to the sea floor, and (2) a deeper low angle thrust component that does not extend to the sea 'floor but dies out into folds in the younger strata.
Reprocessing of these data is expected to show the relationship between these components and the nature of the Hosgri Fault in the upper 4 km.
The deep crustal studies were to begin during the week of Octo-ber 27, 1986, i.e., after the meeting.
However,'
similar type of line had been run from the Great Valley'to Morro Bay by the USGS.
In this line an anomalous low sei'smic velocity wedge of crust was detected at a depth of 14 km below the near coast region.
Oefining the relationship between the Hosgri Fault and this zone is significant to the Oiablo Canyon site in that it could constrain the amount of'ault surface available to cause a
large earthquake; an east dipping Hosgri Fault could form the
upper boundary of this zone raising the possibility of a large thrust earthquake; or if a high angle Hosgri Fault truncates the low velocity wedge, substantial strike slip displacement is indicated.
The offshore deep crustal lines will connect with the USGS line and onshore deep penetrating vibroseis lines which have nearly been completed.
It is anticipated that these data will answer the questions about the nature of the Hosgri Fault and associated faults at depth.
2.
Characterization of San Luis/Pismo Re ion a.
Universit of Nevada Reno Studies The University at Nevada and Reno (UNR) research team under B. Slemmons, NRC Consultant, in addition to independently assess-ing the results of geological field investigations by PG8E and consultants, has been conducting, for the NRC staff, independent geological studies in the San Luis/Pismo region and within the onshore Santa Haria Basin.
The dominant tectonic structure underlying the San Luis/Pismo area is the west-northwest, east-southeast trending Pismo Syncline.
The Pismo Syncline is truncated to the west by the Hosgri Fault Zone.
The syncline is bounded on the north flank by the Edna and Los Osos Faults, and on the south flank by the San Higuelito Fault and in part by the Wilmar Avenue Fault (called Pismo Beach Fold and Thrust Zone by UNR), which was first identified by UNR.
Results of the UNR investigations indicate that the San Luis Range area, within which the Diablo Canyon site is located, has been dominated during the last 5 million years by northeast-southwest compression.
That tectonic environment would be con-ducive to the development of thrust faults.
Evidence was found that indicates that the Los Osos and Los Osos Creek Faults to the north and the Wilmar Avenue Fault to the south are young and possibly capable.
Indications were found that the Edna and San Higuelito Faults were not capable pending the determination of
their relationship to nearby capable faults.
The faults and the magnitudes of their displacements are minor and, based on cur-rent knowledge, subordinate to those of the Hosgri.
Interest in these faults is mainly focussed on how they fit into the current tectonic framework of the region.
Additional field studies on these faults could determine their relationship to other faults in the vicinity.'hese studies are important, par-ticularly with respect to the Milmar Avenue Fault, because of 'its possible relationship to the San Miguelito Fault and closeness to the site.
Mapping of the marine terraces on the coast and the fluvial terraces along antecedent streams show no recent tectonic deformation of the Pismo Syncline except for possible minor uplift or tilting of the southwest flank.
b.
Pacific Gas and Electric Studies The region east of the Hosgri Fault Zone is considerably mor e tectonically deformed and seismically active than the offshore Santa Maria Basin west of the Hosgri Fault Zone.
The reasons for investigating structures east of the Hosgri Fault are to determine the capability, length, strike, dip, sense of dis-placements, age and other fault characteristics, and their significance to the seismic design basis of Diablo Canyon.
Deep and shallow penetrating high resolution vibroseis lines that cross and run parallel to the onshore Santa Maria Basin are nearly complete.
The results from Line SMB-5, which is a NE-SM profile, shows a monocline in the rocks at the location of the postulated Santa Maria River Fault.
A major concern of the NRC staff has been that the Santa Maria River Fault was a strike slip fault that connected with major faults to the southeast (Little Pine and Foxen Canyon Faults) and the San Miguelito Fault near the site.
The information from line SMB-5 indicates that this fault is not a strike slip fault or that it may not exist at all.
The monocline could,
- however, be underlain by a thrust fault, although the data so far do not show this.
Investigations by PG8E in the San Luis/Pismo area are just gett-ing underway by.
PGEE is investigating fluvial terraces and alluvial plains, marine terraces from Pismo Beach to Hontano del
- Oro, and the Sisquoc and Paso Robles plains in the onshore Santa Haria Basin to locate potential seismic structures and assess their significance to the Diablo Canyon site.
Studies of the marine terraces so far have shown that there has been no recent vertical offset along the San Higuelito Fault.
Studies are underway to test for recent horizontal displacement.
Broad amplitude warping of the terraces has been observed.
PG&E is also concentrating its investigations on the Wilmar Avenue Fault to determine its age of last displacement, offshore trend, continuity of strands and relationship to the San Miguelito Fault to the north.
These studies are important because both faults line up and the Wilmar Fault shows probable, recent tectonic movement.
Its relationship to the Hosgri Fault Zone also needs to be determined.
3.
Tectonic Framework a.
Pacific Gas and Electric Studies PG8E's approach to studying the tectonic" framework of the region seems to be evolving around a crustal model by A. Trehu of the USGS.
The Trehu model is based on a deep seismic refraction line extending northeast-southwest from the Great Valley to Morro Bay.
In this model, seismic wave velocity variations, horizontal and vertical, outline from east to west:
the San Andreas Fault, the Salinian Block, and the San Simeon Terrane.
They also indicate an east dipping, low velocity wedge at a depth of 14 km.
This low velocity wedge is interpreted to be a package of saturated sediments that were formed during subduction of the Pacific Plate beneath the North American Plate and trapped beneath the crustal block underlying the San Simeon Terrane and the western portion
of the Salinian Block.
The deep crustal studies described ear-
. lier will investigate the relationship between this low velocity zone arid the Hosgri Fault.
It is important to determine this because, if the Hosgri truncates it to the west, considerable strike slip faulting has apparently taken place.
The top of the east dipping low velocity zone may be a low angle thrust or de-tachment zone.
Additionally, if the Hosgri Fault cuts through the zone or is cut by it, constraints on the maximum earthquake size may be indicated by limits of the source zone.
For example, there may or may not be suf ficient fault surface available to generate a magnitude 7.0 to 7.5 earthquake.
The presence of the low velocity zone may have an effect on the accuracy of calculat" ing earthquake hypocenters.
Another method that is being used by PG8E to define the low velocity zone along with the refraction data is analyzing tele-seismic P-waves from 3 component seismograms situated along the California coast.
Results of analyses to date are compatible with the Trehu model.
Most earthquakes beneath the central coastal region occur between depths of 5 km to 14 km.
Distribution of seismicity relative to mapped faults was illustrated on several maps and profiles.
The San Andreas Fault is clearly indicated by the earthquake pattern.
Epicenters west of the San Andreas appear more diffuse, with clusters bounding the Nacimiento Fault, a
large cluster north of the San Simeon area and northeast of the San Simeon Fault, and relatively little seismicity in the Santa Maria Basin west of the Hosgri Fault Zone.
The vertical distri-bution of seismicity was shown along cross sections perpendi-cular and parallel to the San Simeon Fault and approximately perpendicular and parallel to the Hosgri Fault.
The base of the seismicity in both cross sections shows a shallow slope from west to east from 10 km to 15 km that suggests a detachment zone.
A third study described by Savage was a reevaluation of the 1927 Lompoc Earthquake.
By using data from the Netherlands, compar-isons are being made between seismograms of the 1927 Lompoc Earthquake and seismograms of the 1969 Santa Lucia Banks and the 1983 Coalinga Earthquakes, whose seismic moments and focal mech-anisms are known.
Preliminary results indicate a strike of 340 degrees and a dip of 66 degrees (similar to Coalinga) either northeast or southwest, or a vertical dip, and a hypocentral depth of 10 km.
The preliminary source model for the 1927 Lompoc Earthquake, developed from comparison with the Coalinga and other recent earthquakes, also indicates a moment magnitude of 6.6.
The purpose of this reevaluation are to determine the 1927 earth-quake's characteristics, to identify its source structure, and to get a more accurate fix on its magnitude.
w A plot of the p axes of earthquakes of magnitude 5 for the region was shown.
Along the San Andreas Fault, the p axes are oriented north-south.
West of the San Andreas the p axes are oriented more northeast-southwest, therefore compressional tectonics in that region is expected.
This p axis orientation is also consistent with right lateral strike slip displacement on the Hosgri Fault Zone.
One of the commitments in the LTSP by PG8E was to establish a
seismic monitoring network in the site region.
Several stations of the PG8E seismic network have been operating since July of this year.
The contract to install the remainder has been let and they are expected to be operational by about February, 1987.
b.
Universit of Nevada Studies A research team under B.
- Slemmons, NRC consultant at the Univer-sity of Nevada at Reno (UNR),
is conducting remote sensing analyses.
The types of imagery being used include multispectral
- scanner, low sun angle photography, high altitude aerial photo-
- graphy, and radar imagery.
The analysis will consist of lineament
- studies, comparison of lineaments to mapped geology and faults, construction of rose diagrams, and consideration of the implica-tions of the analyses.
A rough draft write-up of the findings is expected to be completed by April, 1987.
The results of this independent study have been confirmatory in nature so far, and no surprises are expected in the future.
UNR has been investigating the Little Pine Fault along the north-east boundary of the onshore Santa Maria Basin.
The purpose of this study was to determine whether these faults, which are on strike with the Edna and San Miguelito Faults near the site are principally strike slip or thrust faults, and to explore the histories of displacements on faults in that area.
Based on this study, it was concluded that the Little Pine Fault and associated faults are thrust faults and not strike slip as pre-viously postulated.
This finding is consistent with PG8E s
evidence to the northwest that the Santa Maria River Fault is not a strike slip fault, if it exists at all.
The UNR team is independently studying worldwide earthquake magnitude and fault rupture parameters.
The purpose is to compare the seismogenic structures in the site area with the worldwide data, particularly China and the USSR, to help assess the probabilities for future surface faulting and strong ground motion in the site region.
B.
Comments At the conclusion of the meeting the NRC staff, its consultants and the representatives from the California Division of Mines and Geology caucused to briefly review and evaluate the presentation and conclusions by PG8E.
As a result the following comments were provided verbally to PG8E at the completion of the meeting.
Written comments by R.
Brown (USGS) and G.
Thompson are provided on Enclosures 3b and 3c, respectively.
(j.)
PG8E's progress since the last meeting has been very good in that there is considerable data to work with.
The investigations are very thorough, well done and of high quality.
(2) It should be kept in mind by PG8E and all consultants during these extensive investigations that all efforts should be directed toward the Diablo Canyon seismic reevaluation.
During a study of regional proportions as the LTSP is, it is easy to lose site of the purpose of the program as stated in the Unit 1 license condition.
(3)
The staff need for actual data to review rather than interpretations was reiterated.
The type of staff comments on PG8E's work in the LTSP that would be most beneficial to the program can be provided only after detailed review of actual
- data, not based on presentations in a
- two-day meeting.
A means and a schedule needs to be worked out be-tween PG8E and NRC in regard to intermediate documentation and final reports that recognizes NRC needs for documentation and PG8E's need to proceed with the program without extensive effort being devoted to report writing.
(4)
The level of NRC participation in the November ACRS meeting depends on whether that meeting is held on the east coast or west coast.
It is PG8E's meeting to brief the ACRS on the progress of the LTSP as required by the license condition.
(5)
The tectonic environment of which the Hosgri Fault Zone is a part, is extremely complex and may not be analogous to any other place.
(6)
The variety of tectonic structures within the Hosgri Fault Zone, such as strike slip fault strands, thrust faults, reverse faults, grabens, folds, should have a strong bearing on the characterization of the Hosgri Fault.
The Hosgri Fault should be referred to as a fault zone rather than a fault.
(7)
The importance of determining the relationship between the vertical and thrust components of the Hosgri Fault Zone and the nature of the Hosgri Fault at depth cannot be overemphasized.
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(8)
The relationship between the Hosgri Fault Zone and San Simeon Fault Zone is extremely important in reassessing the seismic potential of the Hosgri Fault relative to the Diable Canyon Site.
(9) It is important to systematically examine coastlines for underlying
- faults, and geologically determine the rates of folding.
(10) Determining accurate ages of the marine terraces relative to the terrace elevations is critical to analyzing the significance of the faults exposed at Wilmar Avenue.
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