ML17095A511
| ML17095A511 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 07/17/1986 |
| From: | Schierling H Office of Nuclear Reactor Regulation |
| To: | Varga S Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8607230051 | |
| Download: ML17095A511 (72) | |
Text
July 17, 198 Docket Nos.
50-275 and 50-323 MEMORANDUM FOR:
Steven A. Varga, Director Project Directorate 83 Division of PWR Licensing-A FROM:
SUBJECT:
DATE 5 TIME:
LOCATION:
PURPOSE:
Hans Schierling, Senior Project Manager Project Directorate 83 Division of PWR Licensing-A FORTHCOMING MEETING WITH PACIFIC GAS AND ELECTRIC ON LTSP - GEOLOGY (FIELD TRIP)
Friday, Saturday August 15-16, 1986 8:00 a.m.
Diablo Canyon Energy Center US 101 San Luis Obispo, CA To visit significant geological features in the field that were identified by NRC Consultants and PGIIE.
PARTICIPANTS:
NRC G. Giese-Koch H. Schierling R.
Slemmons (Consultants)
PGSE L. Cluff, et al.,
PG&E Consultants
Contact:
H. Schier ling 301-492-8856 cc:
See next page Hans Schierling, Senior Project Manager Project Directorate 5'3 Division of PWR Licensing-A PDn JN HSchiePlfng 7/C+/86 D8 rga 7/
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Mr. J.
D. Shiffer Pacific Gas and Electric Company Diablo Canyon CC:
Philip A. Crane, Jr.,
Esq.
Pacific Gas 5 Electric Company Post Office Box 7442 San Francisco, California 94120 Mr. Malcolm H. Furbush Vice President - General Counsel Pacific Gas 8 Electric Company Post Office Box 7442 San Francisco, California 94120 Janice E. Kerr, Esq.
California Public Utilities Commission 350 McAllister Street San Francisco, California 94102 Mr. Frederick Eissler, President Scenic Shoreline Preservation Conference, Inc.
4623 More Mesa Drive Santa Barbara, California 93105 Ms. Elizabeth Apfelberg 1415 Cozadero San Luis Obispo, California 93401 Mr. Gordon A. Silver Ms. Sandra A. Silver 1760 Alisal Street San Luis Obispo, California 93401 Harry M. Willis, Esq.
Seymour 5 Willis 601 California Street, Suite 2100 San Francisco, Cali fornia 94108 Mr. Richard Hubbard MHB Technical Associates Suite K
1725 Hamilton Avenue San Jose, California 95125 NRC Resident Inspector/Diablo Canyon Nuclear Power Plant c/o U.S. Nuclear Regulatory Commi,ssion P. 0.
Box 369 Avila Beach, California 93424 Ms.
Raye Fleming 1920 Mattie Road Shell Beach, Califorhia 93440 Joel
- Reynolds, Esq.
John R. Phillips, Esq.
Center for Law in the Public Interest
'0951 West Pico Boulevard Third Floor Los Angeles, California 90064 Mr. Dick Blankenburg Editor 8 Co-Publisher South County Publishing Company P. 0.
Box 460 Arroyo Grande, California 93420 Bruce Norton, Esq.
Norton, Burke, Berry 8 French, P.C.
202 E. Osborn Road P. 0.
Box 10569 Phoenix, Arizona 85064 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 1321 Johnson Avenue P. 0.
Box 112 San Luis Obispo, California 93406
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Pacific Gas 8 Electric Company Diablo'anyon CC:
Arthur C. Gehr, Esq.
Snell 5 Wilmer 3100 Valley Center Phoenix, Arizona 85073 Mr. Leland M. Gustafson, Manager Federal Relations Pacific Gas 5 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 State of California 3580 Wilshire Boulevard, Suite 800 Los Angeles, California 90010 Mr. Tom Harris Sacramento Bee 21st and 0 Streets Sacramento, California 95814 Mr. H. Daniel Nix California Energy Commission 1516 9th Street, MS 18 Sacramento, California 95814 Lewis Shollenberger, Esq.
US Nuclear Regulatory Commission Region V
1450 Maria Lane Suite 210 Walnut Creek,.Cali fornia 94596 Mrs. Jacquelyn Wheeler 2455 Leona Street San Luis Obispo, California 93400 Mr. Thomas Devine Government Accountability
- Project, Institute for Policy Studies 1901 foe 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, California 95814 President California Public Utilities Commission California State Building
, 350 McAllester Street San Francisco, California 94102 Mr. Joseph
- 0. Ward, Chief Radiological Health Branch State Department of Health Services 714 P Street, Office Building ¹8 Sacramento, California 95814 Ms. Nancy Culver 192 Luneta Street San Luis Obispo, California 93401
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Dr. S. T. Algermissen U. S. Geological Survey P. 0.
Box 25046 Mail Stop 966 Denver Federal Center Denver Colorado 80225 Dr. Keiiti Aki Dept. of Geological Sciences Univeristy of Southern California Los Angeles, California 90089 Dr. Ralph J. Archuleta Dept. of Geological Sciences University of California Santa Barbara Santa Barbara, California 93106 Mr. Don Bernreuter Lawrence Livermore Laboratory P. 0.
Box 808 Livermore, California 94550 Mr. Donald A. Brand Vice President, Engineering Pacific Gas 5 Electric Company 77 Beale Street, Room 2645 San Francisco, California 94106 Dr. Robert D. Brown, Jr.
U.S. Geological Service Building 8, 8977 345 Middlefield Road Menlo Park, California 94025 Mr. Loyd S. Cluff Pacific Gas 5 Electric Company 77 Beale Street, Room 2661 San Francisco, California 94106 Dr. C. J. Costantino 4 Rockingham Road Spring Valley, New York 10977 Dr. James Davis State Geologist California Division of Mines and Geology Room 1351 1416 Ninth Street Sacramento, California 95814 Dr. Steven M. Day S-Cubed P. 0.
Box 1620 La Jolla, California 92038 Dr. George Gazetas JEC 4049 Renssalear Polytechnic Institute
- Troy, New York 12180-3590 Dr. David Perkins U. S. Geological Survey P. 0.
Box 25046 Mai.l Stop 966 Denver Federal Center Denver,'olorado 80225 Dr. Morris Reich Structural Analysis Division Building 129 Brookhaven National Laboratory
Box 808 Livermore, California 94550 Dr. David B. Slemmons 2995 Golden Valley Road
- Reno, Nevada 89506 Dr. Andrew S. Veletsos 5211 Paisley Avenue
- Houston, Texas 77096 Dr. Robert V. Whitman Room 1-342 Massachusetts Institute of Technology Cambridge, Massachusetts 02139
4
ioocket-File>
NRC PDR Local PDR NSIC PRC System PD83 Rdg.
H. Schierling C.
Vogan ORAS H. Denton H. Thompson C. Rossi S.
Varga G. Lear B. Youngblood Y. Noonan L. Rubenstein R. Ballard C. Berlinger J. Milhoan F.
Rosa V. Benaroya OGC-Bethesda J. Partlow B. Grimes E. Jordan ACRS (10)
OPA Receptionist PPAS/TOSB G. Giese-Koch R.
Slemmons MEETING NOTICE DISTRIBUTION
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UMITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 July 17, 1986 E~clos~re 'I Docket Nos.
50-275 and 50-323 MEMORANDUYi FOR:
FROM:
SUBJECT:
DATE 8 TIME:
LOCATION:
PURPOSE:
Steven A. Varga, Director Project Directorate ¹3 Division of PWR Licensing-A Hans Schierling, Senior Project Mianager Project Directorate ¹3 Division of PWR Licensing-A FORTHCOMING MEETING WITH PACIFIC GAS AND ELECTRIC ON LTSP - GEOLOGY (FIELD TRIP)
Friday, Saturday August 15-16, 1986 8:00 a.m.
~Diablo Canyon Energy Center US 101 San Luis Obispo, CA To visit significant geological features in the field that were identified by NRC Consultants and PGtlE.
PARTICIPANTS:
NRC G. Giese-Koch H. Schier ling R. Slemmons (Consultant)
PGKE L, Cluff, et al.,
PG&E Consultants
Contact:
H. Schierling 301-492-8856 cc:
See next page Hans Schierling, Seni Project Manager Project Directorate ¹3 Division of PWR Licensing-A
ENCLOSURE 2
LIST OF ATTENDEES NRC/PG&E FIELD TRIP/MEETING AUGUST 15-16, 1986 I. Alterman F,. Bickwer J. Blackeley F. Brady R.
Brown L. Cluff K. Coppersmith
- d. Crouch G. Giese-Koch N. T. Hall K. Hanson D. Hamilton K. Killen W. Lettis B. Matz L. Mezger S.
Nitchman W. Savage H. Schierling B. Slemmons J. Steritz K. Swanson R. Sydnor G. Thompson P.
Vaughn E. Vittori R. Willingham Z. Xiaoyi NRC ESA-PG&E Consultant PG&E PG&E USGS-NRC Consultant PG&E Geomatrix-PG&E Consultant
- Crouch, Bachmann
& Assoc.
Inc NRC ESA-PG&E Consultant Geomatrix-PG&E Consultant ESA-PG&E Consultant UNR-NRC Consultant Geomatrix-PG&E Consultant UNR-NRC Consultant Geomatrix-PG&E Consultant UNR-NRC Consultant PG&E NRC UNR-NRC Consultant UCSB UNR-NRC Consultant Calif. Div. Mines
& Geology (CDYiG)
Stanford U-ACRS Consultant ESA-PG&E Consultant UNR-NRC Consultant ESA-PG&E Consultant UNR-NRC Consultant
ENCLOSURE 3
1.
'NR Field Studies DIABLO CANYON NUCLEAR POWER PLANT NRC STAFF
SUMMARY
LONG TERM SEISMIC PROGRAM FIELD TRIP AUGUST 15-16, 1986 On August 15,
- 1986, B. Slemmons, NRC Consultant from the University of Nevada at Reno (UNR), and his team conducted a field trip pointing out various geological features identified by the UNR team during the recent field studies.
Several observations were made concerning well-known faults.
The work done by UNR, including field mapping, remote sensing of linear
- features, and analysis of terrace deformation, indicated to them the following:
- San Miguelito Fault:
'omes within 5 miles SE of the plant
'ome indications of quaternary (2 million years ago to the present) movement, possibly in the Pleistocene (2 million to 10,000 years ago),
may be related to this fault;
'o consistent sense of motion determined;
'apped fault is about 12 miles long; total length not known
- Edna and Los Osos Faults:
and 12 miles E and NE respectively at their closest approach to the plant
'o evidence of you'ng movement
- Lions Head Fault:
'5 miles SE of plant
'o evidence on shore for recent or young movement
- Pezzoni Fault:
'0 miles SE of plant
'ome evidence of possible Pleistocene movement
'nconsistent sense of offset, some normal, some reverse
'ge of faulted and unfaulted gravels not ascertained
I T,
- Honda Fault:
'0-45 miles SSE of plant
'leistocene movement suggested but not documented
'-M strike-slip sense of motion on fault 2.
PG&E Field Studies On August 16,
- 1986, PG&E and its consultants conducted the field trip near San Simeon.
The trip included examination of trenches across the San Simeon Fault.
The PGEE observations suggested to them the following:
- San Simeon Fault:
'0 miles NM of-the plant
'arge strike-slip component
'elatively young, but undated, movement 3.
NRC Comments At the conclusion of the meeting NRC staff and consultants made the following comments:
1.
None of the foregoing constitute conclusions.
No strong evidence for ages of the materials or the movement has yet been obtained for any of the faults with possible quaternary movement.
2.
The San Miguelito Fault, which may come closest to the plant of all known faults, has not been mapped in detail.
Its total length, which is important in determining its seismic significance, is currently regarded as possibly 10 to 15 miles.
Its sense of movement is not known.
3.
More information is needed to determine the significance of the observations of recent movement that may be related to the San Miguelito Fault.
Such information includes total length, northward extension, age of latest
- movement, sense and rate of movement, and relation to seismicity and regional tectonics.
4.
Staff comments to PG&E following the March 11-12 meeting made clear the need for documentation of progress and data.
5.
Although PG&E indicated, in a followup telephone call, that it is on schedule in its field data gathering, it is not clear how it will address the new observations by the NRC consultants, or what has been accomplished up to the present.
PG&E stated that it will be shown at the October meeting.
I 4
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ENCLOSURE 4
PGSE MEETING
SUMMARY
1.
Summary of Geologic Field Review of the San Luis Obispo/
Pismo Region, Held on August 15, 1986 2.
Summary of Offshore Geophysics Along the Hosgri Fault Trend, Held.on the Evening of August 15, 1986 3.
Summary of Geologic Field Review in the San Simeon Onshore
- Region, Held on August 16, 1986 4.
Detailed Task Plans Tasks 4 and 5 of the Geologic Program Element of the Long Term Seismic Program
<<;C
NRC/PGandE Summary of Geologic Field Review of The San Luis Obispo/Pismo Region Held on August 15, 1986 The following outline presents Pacific Gas and Electric Company's (PGandE) summary of the geologic features discussed by the University of Nevada at Reno (UNR) research team at each of the field trip stops.
The discussion leaders of the field trip were:
Dr. Burton Slemmons - Professor of Geology, UNR Steven P.'itchman - Graduate
- Student, UNR Eutizio T. Vittori - Visiting Scientist from ENEA, Italy Kati Killeen - Graduate
- Student, UNR Kirk Swanson - Graduate
- Student, UNR A, copy of the map provided by the field trip leaders is provided as Figure 1 and indicates the locations of the stops.
~Sto 1
Fossil Point - Marine terraces and San Miguelito Fault A well developed flight of marine terraces is present at this locality, some of which are fossiliferous The flight of terraces intersects the trend of the San Miguelito fault as mapped by C. Hall and does not appear to be offset or deformed by the faulting
~Sto 2
Squire Canyon Fluvial terraces and Pismo Syncline Longitudinal profiles of the modern San Luis Obispo Creek and elevated strath terraces across entire San Luis Range were reviewed Although not plotted on the diagram, the San Niguelito fault does not appear to deform the longitudinal profiles Similarly, the Pismo syncline did not appear to deform the profi 1 es A holocene buried thalweg, as indicated by water well data, generally exhibited a rgular long profile except that one point where the well location used for subsurface control showed a local deep point.
The well, however, may have encountered Pismol Formation rather than aluvium.
~Sto 3
Spirit Overlook - Fluvial terraces and Los Osos fault The same longitudinal profiles were reviewed as at Stop 2
Elevated terraces shown on the profiles stop at the eastern margin of San Luis Range at/or near the Los Osos'fault Evidence presented by Nitchman,
- however, suggested that the Los Osos fault is inactive at this locality
te
~Sto 4
Montana de Oro State Park - Marine terraces and possible extensi on of San Miguel ito fault A well developed flight of marine terraces was reviewed A small, localized, apparent break in an elevated older marine platform was reviewed that might be caused by minor faulting or landsliding or may be a paleo-surge channel
~Sto 5
Los Osos Creek Small fault in Paso Robles formation This stop was omitted so feature was not observed by the field trip participants.
A ravine-wall log was displayed by S.
Nitchman and was described as a fault break in "Paso Robles" interpreted as NE striking with apparent left lateral displacement.
~Sto 6
galls Vista Road Offset Paso Robles along Los Osos fault An obscured road cut exposure was observed, where dacite-bearing gravels appear faulted against Franciscan serpentine.
The field trip leaders noted that springs and topographic anomalies present along the southwestern margin of Los Osos Valley appear to define a lineation.
~Sto 7
Tiffany Ranch Road - Edna Fault Field trip participants were shown an interpretive geologic cross-section showing a Paso Robles alluvial fan deposit buttressed on the southwest against the Monterey Formation.
Nitchman suggested that field relationships indicate that the Edna fault does not cut the upper Paso Robles Formation at this locality.
~Sto 8
Orcutt Road and Lopez Terminal Reservoir - Edna fault Not visited
~Sto 9
Biddle Park Not visited
~Sto 10 Royal Oaks - Overview of concordant ridges Not visited
l
~Sto 11 Farm Boy Restaurant Area - Squire Formation Flat lying Squire Formation was observed offset by an apparent reverse fault with a small displacement
~Sto 12
(}uarry on NE side of Highway 101 opposite Stop 11 area-Squire Formation
~Sto 13 Steeply dipping to vertical Squire Formation was observed a
short distance (across the US 101 Freeway) from the horizontal beds observed at Stop ll Highland and Five Cities Drive - Deformed marine terrace deposits A small apparent thrust/reverse fault in elevated marine terrace deposits was reviewed
~Sto 14 Hilm'ar Avenue Beach Access - Marine Terrace Deposits Review was conducted of excellent exposures of Obispo Tuff and Rincon Shale(?)
intruded by diabasic dikes, and of the Squire Formation Contacts among these formations may be tectonic, depositional, or both A marine terrace platform carved across Squire Formation and cut by a small fault striking about N70W was reviewed The lowest emergent marine terrace warps down to the southeast and disappears beneath modern beach deposits near the Pismo Beach pier The Squire Formation may be strongly deformed into tight folds near the small fault; Nitchman suggested that the small fault may be interpreted as bedding plane slip "3"
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Summary of Offshore Geophysics Along the Hosgri Fault Trend Held on the Evening of August 15, 1986 Participants in the NRC/PGandE LTSP field trip met for three hours during the evening of Friday, August 15 for a discussion of recent and planned work involving interpretation of geophysical data along the Hosgri fault trend.
Mr. John Steritz, graduate student at UC Santa
- Barbara, presented the results of his nearly-completed masters thesis study of geologic structure in the region of the south end of the Hosgri fault.
The meeting was organized as follows:
Presentation by John Steritz.
Comments and discussion, led by Jim Crouched Presentations of the PGandE program for supplemental offshore high resolution and deep seismic data acquisition by N. T. Hall and C.
R. Willingham.
e Steritz presented work he has done as part of a a Masters thesis under Professor Bruce Luyendyk at UC Santa Barbara.
His work has covered a part of the offshore regi'on extending approximately between Point Sal on the north and Point Conception on the south, and has been concerned with developing an understanding of the structure at the south end of the Hosgri fault primarily based on the interpretation of shallow and intermediate depth seismic data available through the MMS.
Some deep seismic data and available offshore well data has also been utilized in Steritz'tudy.
The main points of Steritz'nterpretation were:
In the region south of Point Arguello the main Hosgri trace is offset by a northeast-trending cross fault, and the Hosgri fault's displaced southernmost segment dies out in complex thrust faulting and folding.
Between Point Sal and Point Arguello the Hosgri fault is nearly
- vertical, has a linear trace, and exhibits characteristics of a strike slip fault.
Some features seen on seismic records that exhibit moderate to shallow dip are artifacts of the reflection surveying process, referred to as "side swipe".
A tectonic model that accommodates significant rotation pf the Western Transverse
- Ranges, such as is envisioned by Luyendyk, seems to require a boundary structure such as the Hosgri fault, and it further requires that on the order of 140 km of right slip must have occurred along this structure since Miocene time.
- Steritz, however, only proposed about 20 km of right slip along the part of the Hosgri fault he studied.
Crouch's discussion centered around recapitulation of his published "compressional tectonics" interpretation.
His view is that geologic structure in the region of Steritz'tudy is characterized by listric thrusting, which he believes to be caused by a component of convergence along 'the plate boundary which is most pronounced in the region opposite the "big bend" of the San Andreas fault.
Crouch considers that the zone mapped by Steritz as the Hosgri fault is really a zone of gas-charged sediment that lies above the true Hosgri, interpreted as one of a series of blind thrusts that underlie the offshore Santa Maria Basin.
Both during the Friday evening discussion and during individual discussions along the course of the 2-day field trip Crouch emphasized his belief that surficial expressions of deformation observable by mapping and trenching work along fault traces could not be regarded as significant to assessing either the tectonic model or the seismic hazard for a region of compressional tectonics such as the Santa Maria Basin-southern Coast Ranges-Western Transverse Ranges.
Following the Steritz and Crouch discussions and comments, C.
R. Willingham presented, for discussion
- purposes, a proprietary interpretation of the region where Steritz had shown the Hosgri fault to die out in thrust faulting and folding.
The proprietary interpretation placed less emphasis on any individual fault extending into the region from the north, such as would correspond to Steritz'osgri fault, but otherwise agreed in general with Steritz'tructural interpretation.
The evening meeting was concluded with brief presentations by N. T. Hall and C.
R. Willingham describing planned additional high resolution and deep seismic data acquisition programs for the LTSP and by W. Lettis and N.T. Hall introducing the material to be covered on the field trip the following day.
I
Summary of Geologic Field Review in the San Simeon Onshore Region Held on August 16, 1986 Introduction The field trip on Saturday, August 16, 1986 was conducted by Dr. William Lettis of Geomatrix Consultants and Dr. Timothy Hall of Earth Sciences Associates.
The trip focused upon presenting the preliminary results of field investigation of the San Simeon fault zone near San Simeon, California, Two key parameters under investigation are the rate of slip and sense of slip on the various faults within this zone.
Piercing points currently being investigated include both marine terrace shoreline angles and fluvial deposits and channel margins.
Back round Information The San Simeon fault is a 100-kilometer-long zone of faulting within the system of central California coastal faults that includes the San Gregorio and Hosgri faults (Figure 2).
Although the Hosgri fault as mapped is located entirely off the coast of central California, the San Simeon fault is highly relevant in that a significant part of its total length is exposed onshore and is thus amenable to conventional paleoseismic investigations.
An understanding of the nature and paleoseismic behavior of the San Simeon fault is a necessary step in achieving an accurate characterization of the Hosgri fault.
From Ragged Point to San Simeon Point the San Simeon fault is
- onshore, defining the topographic base of the southern Santa Lucia Range and the structural base of the Piedras Blancas antiform.
Here the fault has the form of a narrow main zone, with westward splaying reverse fault strands cutting the basement and older Tertiary rock core of the antiform.
Some of these strands can be traced offshore where they displace the Neogene strata in the flanks of the antiform.
At least one such strand also displaces the basal deposits over the lowest marine terrace along the coast north of Piedr'as Blancas Point.
The genera'1 pattern of westward splaying of strands away from a main fault zone continues to the south in the offshore region between San Simeon Bay and Point Estero.
Field investigations are currently in progress by PGandE to assess fault activity characteristics and behavior of the San Simeon fault zone.
These investigations include detailed mapping of marine and fluvial deposits, trenching, drilling, and seismic refractipn profiling. Preliminary results of these investigations were, presented during the August 16 field trip ~
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Field Localities A brief description of each stop and an outline of the topics discussed are presented below.
Stop locations are shown on Figure 2
~Sto 1
This Highway 1 Vista Point is located on the Tripod marine terrace with views westward toward San Simeon Point.
The Vista Point affords an excellent view of the east-facing escarpment along the San Simeon fault zone; exposures of the modern wave-cut platform, shoreline angle and sea cliff; and an elevated flight of older marine
.terraces to the east.
A.
Primary objectives of the San Simeon Fault Zone Study were reviewed.
These objectives include:
1.
Locate potentially active fault traces in the region 2.
Evaluate late Pleistocene and Holocene slip rates 3.
Assess overall fault slip behavior and regional tectonic setting 8.
Discussion of marine terrace development and characteristics 1.
Modern wave cut platform (WCP) and shoreline angle Irregularities on the modern platform (stacks, fractures, ridges, etc.) in Franciscan melange were noted The shoreline angle represents a line in space, originally horizontal at a former mean high sea
- level, and makes a good piercing point from which to assess vertical and horizontal components of displacement.
2.
Tripod marine terrace (on which Vista Point is situated)
The WCP is exposed in present sea cliff and is veneered by marine gravel lag overlain by eolian sand Large sea stacks are present near the Tripod shoreline angle east of Highway 1
The tripod terrace is correlated with.124,000 year-old marine terrace at Cayucos (U-series and amino acid dated).
This correlation is based on lateral physical continuity of the terrace demonstrated by Weber (1977)
-7"
1 yl
~Sto 2
San Simeon State Beach The San Simeon Fault Zone is partially exposed in the modern sea cliff.
The Monterey Formation, "Careaga" Formation and quaternary marine and eolian sands are juxtaposed in the fault zone.
Portions of the sea cliff have been
- cleaned, gridded, and logged.
Principal features evident in the exposure include:
1.
A minimum of two major fault splays are present which bracket the exposure of "Careaga" Fm of Plio-Pleistocene age 2.
Significant vertical and lateral displacements are indicated by the juxtaposition of Monterey and "Careaga" Formations and late quaternary sand deposits 83,000 year-old (?) sandy marine deposits are present over both Monterey and "Careaga" Formation with an apparent 2-3m vertical separation These faults are not directly observable in the sea cliff, however, because of cover by colluvial and wind-blown sand 3.
Several small faults cut the "Careaga" Formation but are truncated by overlying marine terrace deposits 4.
The fault trace corresponds with a major east-facing escarpment to the north 5.
Thermoluminescense dating will be attempted on eolian sand overlying the faulted "Careaga"
~Sto 3
Tripod shoreline angle west of parking,lot for Hearst Castl e A.
Explanation of techniques for recognizing, correlating, and mapping marine terraces and shoreline angles Determine the elevation of the WCP by mapping the distribution of bedrock beneath terrace deposits Locate distinct steps in elevation of the WCP to identify the shoreline angle B.
Review of techniques for estimating ages and predicting elevations for marine terraces Use paleo-sea-level curves and an assumed constant uplift rate based on the known age of the Tripod terrace Preliminary uplift rates of 0.25 mm/yr and 0. 17 mm/yr were estimated for structural blocks SW and NE of the San Simeon Fault Zone, respectively "8-
I )
l"
C.
Discussions of importance of projecting the Tripod shoreline into fault zone to assess net slip and slip rate
~Sto s 4-6 Soil pits on Tripod, Oso and Airport Terraces west and east of the San Simeon Fault Zone A.
Dr.
Tom Rockwell (San Diego State University) reviewed the relative degree of soil profile development as a
method to correlate marine terraces Soil pits were located on distinct and separ ate terrace surfaces based on detailed field mapping Discussed detailed soil profile descriptions for soils exposed in soil pits were presented Preliminary results indicate significant contrasts in the degree of soil development on the Tripod, Oso and Airport terraces
~Sto 7
Sorrow Pit Trench Locality - Trenches 1 and 2
A.
San Simeon Fault exposed in backhoe trenches Preliminary observations indicate a minimum of two major fault splays with numerous subsidiary fractures Apparent vertical displacement of the Tripod(?)
- WCP, down to the southwest, was noted across each fault splay.
Tripod WCP cut across Franciscan bedrock The eastern splay displaces overlying late Pleistocene eolian sand; slickensides suggest predominant component of lateral slip Slickensides plunge 4-6 SE Trench data document the presence of a prominent strike slip fault with multiple displacements in late quaternary time B.
Discussion of the origin of the topographic ridge east of borrow pit as a large pressure ridge in a zone of strike slip displacement Discussion of immediate plans for future exploration of the San Simeon Fault Zone Seismic refraction line across fault system Program of solid-stem auger drilling subparallel to the refraction line Additional trenching at the crest of and on the eastern flank of the ridge east of the borrow pit Thermoluminescence dating of the silt and very fine sand fraction of eolian sand at the trench site
DETAILED TASK PLANS Tasks 4 and 5 of the Geologic Program Element Long Term Seismic Program As a part of the Long Term Seismic Program (LTSP),
a comprehensive, multidisciplinary plan of activities addresses the refinement of seismic source characteristics for potentially significant seismic sources in the San Luis Obispo-Pismo region.
The task plans for these activities have been summarized in the Phase II Report (dated January -, 1986) in the Geologic Program
- Element, Tasks 4 and 5.
Since the San Luis Obispo-Pismo region is a focus of the University of Nevada, Reno/Nuclear Regulatory Commission studies, it is appropriate to include the following detailed description of tasks with the summary of the August 15, 1986 field trip in the same region.
Maps showing the key field localities, as discussed
- below, are attached as Figures 3 and 4.
The planning for the work elements in the subtasks of Tasks 4 and 5
is complete for initial elements.
Results from Subtasks 4.1 and 5.1, the office reviews'hat are currently in progress will serve to better define the specific field activities to be conducted in the subsequent subtasks.
It is anticipated that the major portion of Tasks 4 and 5 will be completed by the end of 1986.
TASK 4 Studies of Edna and San Miguelito Faults and San Luis-Pismo Fold Trend Ob'ectives o
To review and characterize the Edna and San Miguelito faults, focusing on evidence concerning their capability, sense of slip, segmentation, and slip rate.
o To develop an understanding of the structural evolution of the San Luis-Pismo fold trend.
o To evaluate the local site area for evidence of late quaternary tectonic deformation.
Pro ram to Achieve Ob'ectives A coordinated office (remote sensing, subsurface, geology/geophysics),
field (reconnaissance and detailed exploration),
and offshore eo h sics program is being earned out.
The major elements of this program are outlined as follows."
'b
Subtask
- 4. 1 - Review and Anal sis of Available Geolo ic Data Available geologic mapping, oil wells, and geophysical data in the local area will be reviewed with emphasis on faults and the relationship among the Franciscan,
- Obispo, Monterey,
- Pismo, and Paso Robles.Formations and the unconformities that separate them.
The geologic history of the San Luis-Pismo fold trend will be reviewed.
Balanced cross-sections will be prepared to the extent possible, or other structural analysis appropriate to illuminating the style and rate of deformation will be performed.
These studies will provide a framework for conducting the geologic field studies (Subtask 4.2).
Specific work items for Subtask 4.1 are as follows:
Compile topographic base maps at 1:24,000 scale.
Assemble remote sensing/aerial photograph data set.
ERTS NASA high altitude conventional and false-color infrared Available intermediate scale conventional 1:36,00 and 1:24,000 scale, in flight lines flown along the structural grain of the region in 1986 Interpret remote sensing/aerial photo data, emphasizing fault, fault-line, and any deformed geomorphic features; compile structure/lineament/geomorphic anomally map; identify areas for initial field reconnaissance and exploration.
Compile available geologic map data.
Compile deep well data.
Compile seismic reflection data (Seisdata Line 4).
Compile gravity and magnetic data.
Develop a 3-dimensional structural analysis of the San Luis-Pismo fold trend using surface, deep well, and geophysical data; prepare structural contour and isochore maps and at least one balanced (retrodeformable) cross-section drawn across the fold structures.
The analysis will emphasize evaluation of the structural relationship between folding and faulting along the fold flanks.
Formulate field mapping, exploration, and geophysics program necessary to evaluate structural anomalies indicated by the above structural analysis.
Subtask 4.2 Geolo ic Field Studies Geologic field studies are planned to concentrate on the following features:
Los Osos fault trend Edna fault trend, including Indian Knob fault San Miguelito fault trend Southwest flank of Pismo fold, including boundary of fold with Nipomo structural high Structural section across fold, along line of balanced cross section 4
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Internal structure and contact relationships of the Obispo Formation at and near Diablo Canyon Geomorphic features, especially marine terraces, fluvial
- terraces, and stream channels, that can provide indications of the existence and extent of any late-quaternary-age tectonic deformation.
Upon completion of the photogeologic and geophysical-structural interpretation of the various strands within the Edna, Los Osos, and San Miguelito fault zones, key lineaments or sections of lineaments, will be followed on the ground and critical geomorphic and lithologic relationships recorded on the strip maps.
Shallow test pits, short trenches, and possibly bore holes will be excavated:
- 1) to expose stratigraphic horizons and geomorphic surfaces for identification, description and age dating,
- 2) to determine the depth and extent of buried datum features, and 3) to evaluate the origin of key lineaments and other fault-related topographic anomalies.
This initial phase of field mapping will help in the evaluation of various candidate sites for detailed subsurface investigations.
The principal work product result from this phase of regional mapping will be strip maps of the fault zones at a scale of 1:24,000 showing all major strands, lineaments, and other key displaced stratigraphic, structural and geomorphic features.
An integral part of the field mapping of the larger faults within and bounding the San Luis Range will be shallow seismic refraction surveys in those regions where the mapped faults project along strike through deposits of quaternary age.
The seismic surveys will be used to determine depth to the water table and bedrock surfaces and to locate faults by identifying such features as dislocated stratigraphic horizons, buried bedrock scarps, and offset buried channels.
In addition to the onshore work described
- above, a diver-geologist survey will be made offshore from the coastline between Avila Bay and Pismo, along th~trend of the San Miguelito fault. This survey will concentrate on location and sampling of sea floor outcrops.
Offshore rocks exposed above sea level will also be sampled.
The features to be investigated and candidate localities for detailed study, which will locally include both geophysical and subsurface trenching investigations, are listed as follows:
1.
Los Osos Fault Southeastern end of mapped trace south of Laguna Lake Central reach of fault zone where both Paso Robles Formation and Edna Member of the Pismo Formation are mapped as".cut by faulting Northwestern end of mapped fault trace east of Los Osos if geophysical surveys indicate that the fault is in the shallow subsurface in this area "12"
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Edna Fault Arroyo Grande Region southeast of Edna where Paso Robles Formation is in fault contact with Monterey and Pismo Formations Pismo Creek near Edna Water gap along San Luis Obispo Creek on northeast limb of Pismo synclinorium Summit of San Luis Range 3.
San Mi uelito Fault Avila Beach on the alluvial fill of San Luis Obispo Creek Harford or Wild Cherry canyons west of Avila Beach Highland area north of Point San Luis Marine terrace areas where fault trend projects to coastline 4.
Pismo Beach Fault Southwest Flank of Pismo Fold Sea floor along trend between Avila Bay and Pismo Beach (diver-geologist)
Pismo Beach fault exposure and geologic contact at mouth of gulch Area in vicinity of Highway 101 Freeway between Arroyo Grande and Los Berros Canyon Northeastern edge of Nipomo Mesa Southwest flank of Temattate Ridge southeast of Nipomo Valley 5.
Structural Section s
Across San Luis-Pismo Fold Alon Line s of Balanced Cross-Section s
Detailed field mapping will be performed across the range along the lines of the balanced cross-sections.
Along these strips details of the stratigraphy, structure and nature of key contacts will be recorded.
The data from the mapped strips will then be combined with well data, seismic reflection data, and potential field studies to help generate and refine the kinematically restorable sections.
6.
Internal Structure and Contact Relationshi s of the Obis o Formation at and Near Diablo Can on Detailed field mapping will be performed in the coastal area in the vicinity of Diablo Canyon.
These investigations will focus
. upon measuring the geometry of folding, and determining the nature of the contact, both in terms of alteration and structure, between the Obispo volcanics and adjacent Tertiary rocks.
The purpose of this microstructural analysis will be to determine if the deformation observed in the Obispo volcanics and the rocks with which they are in contact is related to the emplacement of the volcanic rocks or is a younger feature relate'd to the current tectonic regime.
7.
Marine Terraces A key element of Task 4 will be to analyze any late quaternary deformation of the prominent flight of marine terraces that is well preserved along the southwestern flank of the San Luis Range.
The study of these terraces will proceed according to the following steps:
Photointerpretation of the terraces using existing vertical and oblique aerial photography plus the new 1:24,000 color photographs flown for this investigation.
Compilation of pertinent existing data on the configuration and elevation of the surf-cut platform and the shoreline angle of the lowest marine terrace from the investigations already performed at DCPP (Units 1 and 2, Wastewater Holding Pond, etc.)
Field mapping of the marine terrace(s) using the photo-interpretation as an initial interpretation.
Standard U.S.G.S. 7.5'uadrangle sheets will be used as a base, but in some areas mapping may be done directly on the aerial oblique photographs of the sea cliffs.
Field mapping will focus primarily upon locating marine abrasion platforms and especially locating the shoreline angles as exposed in the sea cliffs and in canyon walls incised into the terraces'urveying techniques will be employed to accurately measure the elevations of these key reference features.
Seismic refraction surveys calibrated by drill holes will be performed where the shoreline angle is not exposed for a significant distance along the coast.
The geophysical and drilling program will be particularly important in the region north of the mouth of Islay Creek where the marine terrace is buried beneath younger sand dune deposits and south of Pismo
- Beach, where the terrace is downwarped below the beach level.
Age dating the marine terrace and its overlying deposits, from which rates of uplift of the southwestern flank of the San Luis Range and continued folding of the Pismo synclinorium can be estimated, will be accomplished as follows:
Amino acid racemization dates or U-series dates on marine shells found on or burrowed into the abrasion platform.
Test pits and logs of natural sea-cliff exposures to determine soil profile development on the overlyihg marine and non-marine terrace deposits.
This will.enable correlation with previously dated surfaces to the north in the San Simeon-Cayucos region and to the south in the Santa Maria Basin.
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Correlation with well-dated flights of marine terraces using techniques suggested by Bull (1986).
The major wor k products resulting from the investigation of the marine terraces of the San Luis Range will include a geologic map of the terraces similar to the one prepared by Weber (1981) for the San Simeon region, sections and profiles showing the current configuration of the abrasion platform and shoreline angle of the prominent terrace on which DCPP is situated, logs of bore holes and natural exposures showing the nature of the abrasion platform and its overlying deposits, and finally a summary and analysis of any post-terrace deformation by folding, faulting or uplift that has occurred along the coastal and valley margin of the San Luis Range.
8.
Fluvial Terraces and Channels In addition to using the marine terraces as tectonic strain
'gauges, there are several creeks whose channels are antecedent to the most recent uplift of the San Luis Range.
The channels and associated ter race deposits and surfaces may therefore provide additional datums by which to measure rates and styles of deformation of the San Luis Range - Pismo synclinorium.
The major streams to be investigated include San Luis Obispo Creek, Pismo Creek and Arroyo Grande Creek.
The investigation of the antecedent drainages is planned to proceed as follows:
Photointerpretation of each drainage system including a careful search of high elevations for uplifted erosion surfaces.
Field mapping and careful surveying of exposed fluvial erosional (strath) and depositional surfaces adjacent to known and suspected faults to assess style and amount of late quaternary deformation.
Geophysical surveying coupled with drilling to measure stratigraphic thicknesses of quaternary deposits, depth to bedrock, position and height of buried bedrock scarps, positions of buried thalwegs, etc.
Test pitting and logging of natural exposures in order to establish age of fluvial deposits and surfaces.
Correlation of these surfaces and deposits with marine terraces and other fluvial deposits/surfaces in the region in order to develop a well documented chronology of quaternary eustatic and tectonic events.
The major work products from this phase of Task 4 will be a
geologic map showing the major quaternary fluvial deposits and surfaces within and adjacent to known and suspected faults of the San Luis Range.
(This map will probably incorporate the marine terrace mapping as well.)
In addition there will be long profiles of surfaces and channels, both active and buried, that cross the "15"
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range; logs of test pits, boring and natural exposures that show the quaternary deposits; and a time-history of quaternary deformation of the San Luis Range.
Subtask 4.3 Offshore Geo h sical Studies The structural trend of the principal features of interest in Task 4 projects offshore across the southern part of Estero Bay.
Although some shallow high resolution and deep geophysical data are available for this area from past work, a new systematic high resolution survey to be made in the late summer of 1986 will be extended into the area.
Data from this and earlier surveys will be interpreted in order to map the Task 4 area structural features seaward.
Special emphasis will be given to evaluating any evidence indicative of late quaternary deformation, and to assessing possible structural relationships of these structures to the Hosgri fault.
TASK 5 Studies of Little Pine - Foxen Can on Fault Trend and Onshore Santa Maria Basin Ob'ectives o
To review and characterize the Little Pine-Foxen Canyon fault trend with particular emphasis on capability, total length, sense of slip, and downdip width of the faults that define this trend.
o To review and characterize the major structural features and trends of the Santa Maria Valley-Santa Ynez Valley region, in order to establish the structural relation of this region to the structure and neotectonics of the Western Transverse Ranges to the south.
Pro ram to Achieve Ob'ectives A coordinated office, field and offshore eo h sics program is being carried oot in order to achieve the objectives stated above for Task 5.
The major features of the program are outlined as follows:
Subtask 5.1 Review of Available Geolo ic Data The initial phase of Task 5 is to gather and evaluate all pertinent and available geologic mapping of the onshore Santa Maria basin and its northeastern and southern margins.
Oil Hell data including geophysical logs, structure contour and isochore
- maps, water well
- data, seismic reflection lines, and potential field data will be collected.
In addition, offshore data between the coastline and the Hosgri fault, such as high resolution and CDP seismic reflection lines, bathymetry, side scan sonar, dart core and isopach data will also be gathered.
Once assembled this very large data set will be used to develop a three dimensional structural analysis of the Santa Maria basin as it has evolved from the early Miocene to the present time.
During this analysis, attention will 4
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focus upon the nature of the northeastern margin of the basin.
In particular the trends of the Little Pine fault, the Foxen Canyon fault and the inferred Santa Maria River (and Basin) fault(s) will be carefully inspected both on aerial photographs; in subsurface, and in geophysical records in order to identify sites for detailed surface and shallow subsurface studies.
An important part of the subtask
- 5. 1 review is a structural synthesis of various stratigraphic units and key horizons within and along the margins of the Santa Maria basin including its westward offshore extension to the Hosgri fault. Anticipated work products include the following:
Structure contour map on the top of the Franciscan basement.
Structure contour map on the top of the Monterey Formation.
Isopach map of the Monterey Formation.
Structure contour map on the base of the Paso Robles Formation.
Structure contour map on the base of the Orcutt Sand.
One and perhaps more kinematically restorable balanced cross sections drawn across the Santa Maria basin from the Santa Barbara Channel to the Carrizo Plain.
Maps and long profiles on fluvial terraces, alluvial fans and other erosional/deposition features that are younger than the Orcutt Sand.
Maps and profiles of marine terraces showing correlations with fluvial systems inland.
Completion of the latter two products will incorporate data gathered during the subtask 5.2 field studies.
The review of available geologic data also includes review of existing aerial photographic coverage of the Santa Maria basin which will be focused in particular along its northeastern margin from the Little Pine fault east of Lake Cachuma to the Nipomo Mesa.
PGandE has flown new aerial photographs of this boundary at a scale of 1:36,000 that are oriented parallel to the NW-SE structural grain.
Both these new photographs and the older photocoverage will be reviewed.
Three strip maps are planned:
1.
A map that will abut the southeastern edge of the one prepared under Task 4 of the southwestern flank of the San Luis Range.
The Task 5 map will cover the Santa Maria River, Foxen Canyon and Little Pine fault trends.
2.
A map extending from Point Sal to Lake Cachuma that will cover the Pezzoni-Casmalia, Lions Head, Los Alamos and Baseline faults.
3.
A map from the coast west of Lompoc to Lake Cachuma that covers the Santa Ynez River fault (Sylvester and Darrow, 1979) or the Lompoc-Solvang fault as it has been called by Hall (1981).
-17"
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Before beginning the field investigation program for Task 5, a
detailed photogeologic interpretation will be made of the faults and associated structural features along each of the three strip maps.
This aspect of the investigations will focus upon identifying lineaments, deformed marine and fluvial terraces, closed depressions,
- scarps, aligned or deflected drainages and other features indicative of young tectonic activity.
The results of the photointerpretation will be compared with the mapping of Hall (1973,
- 1978, 1981),
Dibblee (1950,
- 1966, 1978,
- 1981a, 1981b),
Guptill et al (1980) and Hoodring and Bramlette (1950) and will be checked in the field by a geologic reconnaissance (with T.H.
Dibblee) especially along the northeastern margin of the basin.
He anticipat'e that the photointerpretation of the three structural trends outlined above for the Santa Maria basin will guide both the efforts to make detailed maps of each fault trend and the effort to identify sites where detailed surface mapping and subsurface investigations will have a high likelihood of yielding information critical for accomplishing the objectives of the LTSP.
Subtask 5.2 'eolo ic Field Studies Geologic field studies that can be anticipated at present will be concentrated on the following features:
Little Pine-Foxen Canyon-Santa Maria River fault trend Pezzoni-Casmalia-Orcutt-Los Alamos-Baseline fault trend Lions Head fault trend Purisima Hills fold trend Santa Ynez River (Lompoc-Solvang) fault trend Marine terraces along the seaward margin of the Task 5
Study area including the Nipomo and Burton Mesa areas Alluvial fan and apron areas in the central and eastern parts of the Task 5 study region These studies are grouped as A. Faults, B. Marine Terraces, and C.
Fluvial Terraces and Channels Alluvial Fans, and are described as follows:
A.
Faults Faults within and on the margins of the Santa Maria basin will be investigated in order to assess the following signi ficant considerations:
fault capabilities, sense of slip, total length and down dip width.
The various strands within the Little Pine - Foxen Canyon-Santa Maria River, Pezzoni-Casmalia - Or cutt - Los Alamos - Baseline, Lions Head, and Santa Ynez River/Lompoc - Solvang fault trends will be mapped by photointerpretation.
Key lineaments or sections of lineaments will then be followed on the ground and critical geomorphic and lithologic relationships will be recorded on the strip maps.
Shallow test pits, short trenches and possibly bore holes will be excavated/drilled:
- 1) to expose stratigraphic horizons and geomorphic surfaces for identification, description and age dating,
- 2) to determine the depth and extent of buried datum features, and 3) to evaluate a
l
the origin of key lineaments and other fault-related topographic anomalies.
This initial phase of the field mapping will help in the evaluation of various candidate sites for detailed subsurface investigations.
The principal work product that will result from this phase of regional mapping. will be strip maps of the four fault trends at a scale of 1:24,000 showing all major strands, lineaments and other key displaced stratigraphic, structural and geomorphic features.
An integral part of the field mapping of the major faults within and bounding the Santa Maria basin will be shallow seismic refraction surveys in those regions where the mapped faults project along strike through deposits of quaternary age.
The seismic surveys will be used to determine depth to the water table and bedrock surfaces and to locate faults by identifying such features as dislocated stratigraphic
- horizons, buried bedrock scarps and offset buried channels.
Results from the test pits, borings, seismic surveys, field mapping'nd photointerpretation will be integrated and used to identify one or perhaps two specific localities each on the Santa Maria River, Foxen Canyon and Little Pine faults for backhoe trenching.
The trenches will be positioned so as to pursue the following objectives:
1.
Confirm/evaluate the location and existence of major fault strands.
2.
Determine the capability of each fault by evaluating evidence for timing of last slip event and estimate, if
- possible, geologic slip rate and recurrence frequency.
3.
Demonstrate sense of slip on each fault as recorded in the pattern of deformation in the near surface section.
The major work products from the detailed studies of specific sites along the onshore Santa Maria basin faults will be shallow seismic refraction profiles, detailed trench logs and a
well-documented chronology of quaternary slip behavior for each fault.
B.
Marine Terraces A key element of Task 5 will be to analyze the tectonic deformation recorded by the prominent marine terraces that are well preserved in places along the coastal margin of the onshore Santa Maria basin.
The investigation of the terraces will consist of several separate tasks to be performed in the following sequence:
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'o Photointerpretation of the terraces using existing vertical aerial photography of various ages and scales.
The photointerpretation will focus upon both locating the prominent lowest emergent terrace and identifying any higher and older terraces mapped by Woodring and Bramlett (1950) and other unmapped marine terraces within the Santa Maria basin.
Compilation of all pertinent existing data on the configuration and elevation of the surf-cut platform and the shoreline angle of the marine terraces.
Field mapping of the marine terraces using the photointerpretation as an initial interpretation.
Standard O.S.G.S. 7.5'uadrangle sheets will be used as a base.
Field mapping will consist primarily of seismic refraction surveys augmented by drilling whose major focus will be to locate the marine abrasion platforms and shoreline angles exposed in the sea cliffs and in inland areas adjacent to mapped folds and faults.
Surveying techniques will be employed to determine accurately the elevations of these key r ef et ence features.
Age dating the marine terraces and'heir overlying deposits, from which rates of uplift, folding and faulting within the Santa Maria basin and along its margins can be estimated, might be accomplished as follows:
1.
Amino acid racemization dates on marine shells found on or burrowed into the abrasion platform.
- 2. Test pits and logs of natural sea-cliff exposures to determine soil profile development on the overlying marine and non-marine terrace deposits.
This will enable correlation with previously dated surfaces to the north in the San Simeon-Cayucos region and to the south in the Santa Barbara and Ventura area.
C.
Fluvial Terraces and Channels'lluvial Fans In addition to using the marine terraces as tectonic strain
- gauges, there are several terraces and deposits of fluvial
- origin, some of which are probably graded to marine terraces, that should provide additional datums by which to measure rates and styles of deformation of the onshore Santa Maria basin and its northeastern and southern margins.
Subtask 5.3 Geo h sical Studies This subtask will involve interpretation of both deep and shallow high resolution seismic reflection data for the offshore region between the Task 5 study area shoreline and the Hosgri fault.
Primary emphasis will be on recognition,
- mapping, and characterization as to structural style and structural relationship with the Hosgri fault, the boundary structural features of the
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basin (Santa Maria River, Santa Ynez River faults),
and the faults of the Pezzoni-Casmalia-Orcutt and Lions Head trends.
Evidence indicative of late quaternary activity along any of the faults'xtending offshore from the onshore Santa Maria Basin region will be sought through interpretation of available high resolution seismic data.
The evaluation of the structural evolution of the onshore Santa Maria basin will include a synthesis of surficial and deep crustal data both onshore and offshore.
The form, dimensions and rates of near surface deformation will be integrated with deep seismic data, well logs and kinematically restorable cross sections that reveal the deeper structural forms of the Santa Maria basin.
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STUDY FEATURES
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George A. Thompson 421 hdobe Place Palo hlto, CdiEomh 94306 F,(oS~r.
S August 22, 1986 To:
ACRS Subcommittee on Diablo Canyon via Richard Savio From; George A. Thompson, Consultant to ACRS
Subject:
Report on geological field trip to Diablo Canyon
- area, August 15 and 16, 1986 The first day of this field trip was led by Burt Slemmons and students from the University of Nevada.
Se
.examined work in progress on upli,fted marine terraces and river terraces:,
their ages, deformation by warping, and offsets by faults, Uplift rates of about 0,25 mm/yr for the last 100-200 thousand years are reasonably well estab-
- lished, Small faults that cut the base of terrace gravels are well demonstrated at several places These are gener-ally.high-angle reverse or thrust faults trending about N70otlI andhave displacements of a few cm to more than a meter.
Such faults are well exposed~
for example, at the NilmarAve, access to Pismo
- Beach, where the gravels are which about 100 thousand years old The Los Osos and Edna f ult may be connected, are also under active investigation.
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It is not clear whether or how much Quaternary offset these faults have, The second-day objectives were focused on the San Simeon fault, its relationship to the Hosgri. fault, its sense of, displacement~
timing and rate of movement, This trip was led by PG and E and its consultants.
The San Simeon fault appears to be a northward continuation on land~ of the
. Hosgri, Xt displaoes the eshoreline angle"
)base of oil sea-cliff) of marine terraces 125 and 214 thousand years old right<<laterally several hundred feet, The rate is about 1 mm/yr, Fault grooves in a deep trench indicate nearly horizontal movement.
Soil studies in pits establish the age and correlation of terraces across the fault.
The evidence and unresolved questions were debated at an evening meeting, where the views of Jim Crouch (thrust faulting on the Hosgri) and a graduate student from the Uni'-
versity of California at Santa Barbara clashed head-on, It seems likely that major questions about the Hosgri will be resolved by work now underway or offshore seismic work planned for the near future.
I was very favorably impressed by the investigations being carried on by PG and Z and its consultants.
They are focusing on the im ortant questions and doing first-class work Do Not Remove from 5
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