ML20235Z703
| ML20235Z703 | |
| Person / Time | |
|---|---|
| Site: | 05000000, San Onofre |
| Issue date: | 07/06/1972 |
| From: | INTERIOR, DEPT. OF, GEOLOGICAL SURVEY |
| To: | Muntzing L US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20235X376 | List:
|
| References | |
| FOIA-87-462 3721, NUDOCS 8710210271 | |
| Download: ML20235Z703 (13) | |
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.w 18tofY Regu United States Department of the Interior H
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'N GEOLOGICAL SURVEY WASHINGTON, D.C.
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Mr. L. Manning Muntzing d
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'I8l' Director of Regulation r;
U. S. Atcanic Energy Ccxamission u.l:g'T1 n
j 7920 Norfolk Avenue
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Dear Mr. Muntzing:
Enclosed in response to your request is a review of the geology of the San Onofre Nuclear Generating Station Units 2 and 3 sites, A.E.C. Dockets 50-361 and 5-362.
This review, prepared by F. A. McKeovn, supplements the preliminary review prepared by E. H. Baltz and transmitted to the Director of the Division of Reactor Standards A.E.C. on July 2, 1971.
These reviews have been discussed with members of your staff and we have no objections to your making them a part of the public record.
Sincerely yours,
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Director Acting Enclosure N
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4 S0trnlERN-CALIF 01:NIA K01 SON Co.: ANU HAN DIRCO EIECTRIC CO.
SAN ONOFRE NUdi.l:AH CKNKRATING STATION, llNITS 2.AND 3, j
SAN DIEGO COUNTY, CALIFORNI A 1 EvilW ' 0F RELEVAN;r CEOTAGY
.- 1 The onshore and offshore genlogic data for the proposed San Onofre
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nuc1har generator plants--units 2 and 3--presented in the PSAR (Preliminary l
Safety Evaluation Report), its amendments, and its appendices have been i
reviewed and evaluated.
The evaluation in particular' has been made with respect to the significance of the data for postulating the most appropriate fault model to consider as a source of the Safe Shutdown Earthquake.
Also, included. in the evaluation is-consideration of possible faults within or near the site area.
This review supplement,s the preliminary review transmitted to the J
Director of Division of ' Reactor Standards, AEC on July 2,,1971 by 1
V. E. McKelvey, Chief Geologist, U.S. Geological Survey, in the sense that many explicit details in the preliminary review are not repeaced here.
The present review does summarize the pertinent data f rom all amendments and treats in appropria te detail the large amount of offshore geophysical data acquired'since the preliminary, review.
In addition to the data in the PSAR, appropriate literature was'. '
reviewed and the knowledge and interpretations of geologists and geophysicists inost familiar with the geology of. the San Onofre area was solicited and used.
A field inspection of the site and of outcrops cut by the nearby Cristianitos fault zone was made in company with the applicant's geologists on February 8,1972.
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.e Ths principc1 ob'jectivos of this review are (1) to assess the applicability of' the fault. model used b'y ' the applicant for establishing the Safe Shutdown Earthquake, (2).to ascertain whether or not the 1
g applicant has established that no active faults of any size occur within the area; and (3) to ascertain whether or not the available data are adequata to establish the tectonic stability of the area.
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l With regard to,the-first problem,. the USGS stated.in the preliminary review of July 2,.1971 that "On the basis of present data there appears to be a linear zone of deformation in Tertiary and Quaternary rocks and sediments 'that extends southeastward from Santa Monica to at 'least the cl Mexican border."
Reference is also made to the review of the geology of' the site of San Onofre Nuclear Generating Station No.1 transmitted by the Director, U.S. Geological Survey to AEC Director of Regulations dated
-October 11, 1966, in which it was stated:
'The submarine'extensiun of' the l
Newport Inglewood zone, as mapped by Emery l(1960 fig. 68) also tre'nds northwestward and is about 7 miles southwest of the site."
I The additional j
geophysical data obtained by Western Geophysical Company for the applicant
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support this statement.
The zone of deformation is at least 240 km in length, and is appro,ximately 5 miles offshore in the vicinity of the plant site.
The available data relevant to the second problem do not show evidence of any faults 'that cut the Plio-Pleistocene rocks insediately underlying l
the planned roactor facilitics.
i With regard to the third problem, apparent warping of the terrace on 1.
which the site is located indicates that the site is in an area that is tectonically unstable, or has been unstable in the recent geologic past (i.e., ini the -last.70,000. to 130,000 years).
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The San Onofra recetor cito aran for unit'l and the prepssed unita,
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2 and 3 is adjacent to a beach and on thick-bedded, pourly cemented sandstone and minor thin beds of gravel and siltstone of the upper Miocene to possibly Pliocene San Mateo Formation. The beds dip 10 -15 to the northwest.
Drilling nqar the site shows the formation to be more than 900 feet thick; mapping' indicates the formation may be approximately 2,000 feet thick. The ' San Mateo Formation is unconformable overlain by marine terrace deposits and unconformable underlain by siltatone, sandstone, tuff, and diatomite of the Capistrano Formation of late Miocene age.
I Samples collec'ted by U$GS from correlative terrace deposits about 41/2 I
i miles northwest of the site were dated at 70,000-130,000 years B.P.
1 according to the applicant (Amendment 1, p. 2.9-3b).
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No faults are exppsed in the cliffs within one-half mile of r.he site.
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About three-fourths of a mile southeast.of the site, however, the l
Cristianitos fault zone is exposed in the cliff. Exposure of parts of this fault at the coast and at the Plano Trabuco excavations made by the applicant 16 miles north of the coastal exposure, shows that ' the overlying l
terrace deposita are not offset by the f ault at those locations.
As the fault zone is several hundred feet wide, however, and its full width is not exposed anywhere, some question remains about the age o,f the most recent
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movements on the fault., The limits of the extension of this fault zone offshore is somewhat controversial.
As the most probable maximum total length of the -fault is nbout 4G km and although the fault passes close to the site, it is, however, of lesser significance as a source of earthquakes when compared with tha 240 km-long of fehore zone of deformation.
Whether or not displacement of terrace deposits has occurred ~on the Cristianitos fault, evidence of warping of these deposits both locally l'
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and regionally is suggested by work of B. J. Szabo and J. G. Vedder (1975),
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They show deformation of the first terrace between IAguna Beach and San Clemente. - The applicant correctly assumes (Amendment' 1, p. 2.9-3b and Amendment 6, p. 2.9-5) that the terrace deposits overlying the i
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' Cristianitos fault at $he coast are associated with the same terrace as cited above. Warpi$g of the terrace must have occurred, however, l
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to account for approxiinately 55 feet difference in shore sngle elevation
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i of the terrace between the site and Dana Point, about 10 miles northwest of the site. Intermittent, if not continuous local tectonic instability, p
therefore, may be assumed during the last 100,000 30,000 years (using i
the applicant's information on age of the terrace deposits).
q The regional se'tting of 'the San Onofre site is important with respect.
l to the location of major active fault zones and to evaluating how an earthquake j
one of l
originating in /the' zones may effect the site. According to the applicant l
(Amendment 6, p. 2.9-7) the " plant site is approximate ly 60 miles ' from the San Andreas fault, 45 miles from the San Jacinto fault, 23 miles from the
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1 Whittier-Elsinore fault and 18 miles from the southeast terminus of'the Newport-I.nglewood zone." The proximity of the' Newport-Inglewood zone and j
its alignment with the South Coast Offshore (SCO) fault, which has been i
recognized to various degrees in most soismic profile data (Amendment 11',
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appendix 2E-9)-is the major structural problem to be considered.
Initial i
of fshore shallow penetration sparker data indicated discontinuous j
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faulting and folding in the SCO fault zone.
The latest inves tiga tions used i
I a deep penetration seismic reficction method.
These investigations i
L incorporated "... interpretation of 1,000 miles of deep reflection data, 4
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- 430 miles of magnetic-profiling data,'and 7 seismic refraction lines.
'i' In addition, the applicants and their consultants reviewed published gravity data, unpublished proprietary data obtained by others,. and.
approximately 275 miles of United' States Geological Survey (USGS) i l
sparker reflection profiling...." (Amendrent 11, appendix 2E, p. 2E-2).
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The applicant's principal conclusions as the result of this work are
' quoted as follows (Amendment II,. appendix 25, p. 2g-17):
"A.
Displacement on the fault, even at the deepest level of investigation, dies out t*o the northwest near Laguna Beach
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and to the southeast near Oceanside.
B.
In Miocene-age rocks of Horizon B, the fault shows much less displacement than in older rocks, and its trace.
appears as a series of short, discontinuous breaks.
C.- Die fault is not connected with other faults at its extremities.
D.
Investigation with side-scan sonar (refer to appendix 2A, and figure 8), high-resolution profil ng (refer to appendix i
, 2C), and Western's fathometer data as seen in figure 2E-4A l
show no evidence of tectonic displacement en this fault since the sea floor was eroded some 18,000 years ago during an e,atlier glacial ago (appendix 2A). - No evidence has been found in these investigations of surface rupture or offset of geomorphic features, or to suggest post-Miocene or 1
Quaternary activity on the fault.
E.
There is no macroseismicity associated with the fault '(refer to
, appendix 2A, figure 3)."
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(To continuelwith the quotation), " Based on the foregoing, it is i
considered that significant activity has not occurred in the South i
Coast Offshore fault in post-Miocene time.
This fault must not have generated a large earthquake since Upper Miocene time; i.e., millions
[p of years.'ago."
(Appendix 2E, p. 2E-17 and 2E-18).
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The U.S. Geological Survey does not accept these conclusions for the principal reasons' discussed below.
The discussions are keyed by capital lett,ers to the separate conclusions of the applicant.
A. and B.
Much of the inter'pretation upon which conclusions of 1
changes in displacement along striko of faults and with depth of fault j
planes is dependent upon the validity of the offshore structure contour i
i maps. An adequate explanation of the precision of determination of the B structural horizon is lacking.
For stratigraphic reasons, the least reliable part of the Horizon B map is south of the San Clemente~ core hole.
i Although the applicant-assumes Horizon B is in Miocene rocks, no~ Miocene 1
rocks are known onshore between Oceanside and San Diego, and their presence offshore cannot definitely be demonstrated.
Contours for that part of i
the Horizon B map may represent a marker stratigraphically lower than upper Miocene, possibly.2ven within the Eocene.
This concept might likely account for the apparent contrast in continuity between the offshore Rose I
Canyon fault and the South Coast Offshore fault on the applicant's Horizon B i
l' map.
The Rose Canyon fault as mapped in cider rocks would be expected to show greater continuity than at allegedly equivalent, but actually higher stratigraphic levels.
Another ! indication of the unreliability of the B i
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horizon is that the Cristianitos fault is shown by the sparker, profiles I
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and on the C horizon map but not on the B horizon map. Many of the j
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t higher resolution seismic pro' files-show more faulting and more' i
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, recent; faulting than acknowledged by the applicant's reports. -Furthermorsp
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even Western Geophysical Company states that no continuous reflecting.
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.p horizon is present'in the Miocene section across the' entire area
' (Amendment 11', appendix A-1, p. ' 29).
Also,.~ only. faulting defined -
by vertical offsets is considered, without assurance that no. lateral 1
displacements have. taken place on some, otherwise, unidentified faults.
Interpretations of.the existence of all significant' faults, the amount and direction of displacement on them and the age of any particular.
fault on the basis of the Horizon B map, therefore, are considered
.v neither complete nor -accurate.
I Horizon C is also unreliable.
According to Western Geophysical' I'
l Company "... Horizon C constitutes the base 'of sediments with formation l
intervs1 velocities less than 12,000 feet. per second...." (Amendment 11, appendix A-1, p. 26). As an example of the unreliability, USGS' analysis of velocity data in the " offshore high" indicates a maximum velocity there of about.6,500 feet per second.
C.
Connections between the Newport-Inglewood sone,. South Coast t
Offshore fault, and the, Rose Canyon fault cannot be precluded even if the Horison B and C maps were to be assumed
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junction of the Newport-Inglewood fault u.neiand.,,+he:Soudi Coast Of Cvhose. g,*.
- i fault is in an area of no data at the Horizon 'd Tevel and is> marked 'one*/'.-
f the Horizon B map either as'"no shallow resolution" or "possible shallow,
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l The assertion of,the applicants that the : Rose Canyon faultr' turns inland near Oceanside cannot be supported.
True, there are a number of.
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' h2rth-and northrast-striking faults alcng the esast between La Jollo
/ ' and ' Oceanside, but nearly. all of these are lapped by the Pleistocene -
I Lindavis'ta Formation; in. contrast, the onshore Rose Canyon fault is character'ized by vertical separations of the Lindavista Formation greater than 200 feet.
A connection between the offs.hore Rose Canyon fault and q
l-the South Coast Offshore fault is probable in the area shown as "possible intrusive." This is indicated on USGS profiles that show sea floor displacement on an' extension of the Rose Canyon fault to and beyond the alleged intrusives.
l D.
As stated immediately above.under C, ses floor displacement occurs on the extension of the Rose Canyon fault which very probably is 3
coextensive with the SCO fault.
Also, the SCO fault is mapped through the San Joaquin Hills offshore structural high by Western Geophysical l
Company, but the Newport-Inglewood zone is terminated by the high
,1 according to the Company (Amendment 11, appendix 2E, p. 2E 18).
This termination and the applicant's interpretation that no post-Miocene i
movement has occurred in the high is not consistent with the-geology of l
the landward extension of the high. 'The applicant's interpretation is largely based on what he believes is an apparent thin onlap of upper Miocene rocka on the high, which suggests the high has been stable since middle Miocene time.
Actually the folding of the onshore continuation (applicant's structural correlation) of the high-San Joaquin anticline--is known to be late Pliocene-late Pleistrcone in age.
No evidence is presented to
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demonstrate that the age of the rocks and the age of deformation in the I
offshore high is any d'ifferent than the onshore rocks.
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- Tha cilsgsd contrasts in tectonic style between the Los /.ngeles basin and the Peninsular Range Province (Amendment 11 -appendix E,p.- 2E-16) are' not clearly defensible.
The existence of different depositional basins
, does not preclude the extensive linear zone of deformation.
l Probably the -
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. most prominent structural features on figure' 9 are the northwest-trending i
I faults, subparallel to and aligned with the Newport-Inglewood zone.,
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i sone apparently has a very prominent offshore counterpart in the South Coast Offshore fault.
Comparison of section L-M with section C-D clearly. shows l
prominent similarities in structure between the basin and province.
The conclusion of the applicant that there is no evidence of ocean floor rupture and no olffset of geomorphic features is not compatible with the facts presented.'
Purther, the conclusion is not necessarily a pertinent l
criterion of the' potential tectonic activity of the offshore sone' of' l
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deformation.
According,to Western Geophysical Company interpretations "The South i
Coast offshore fault, approximately 40 miles in length, was active after the Offshore San Joaquin structure was formed."
(Amendment 11, appendix A-1 I
- p. 41). _ As ;the onshore extension of this structure is known to be late Pliocene-late; Pleistocene in age, even the deeper parts of the SCO fault observed on the aquapulse reflection profiles must be post-Pleistocene.
l The applicant has not demonstrated conclusively.whether or not Holocene r
later movement can be positively identified on this fault.
However, such s
ocean botton evidence is not necessarily germane to postulating that it is i
an active zone.
The evidence of movement on it is likely to be a function of the mode and depth of deformation.
It is reasonable to assume that the deformation has been similar to that which has occurred in the Newport-Ing1cwo fault zone.
As pointed out by the applicant's Board of. Review concerning the e
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Newport-Inglewotd 'sen"... (11 no mahar of tha fcult co: plex is known es-l cut strata younger than late Pleistocene and (2) no. surface-ground s
displacement.is known to have accompanied historic earthquakes associated l
with the zone...." (Amendment 6, appendix 2C, p. 13).
,l E.
The lack of macroseismicity is not necessarily an indication l
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that the' SCO fault system is wholly inactive.
It is well known that parts il of many major active fault zones, such as the San Andreas, may have little or no macroseismicity.
f The data presented by the applicant lead us to the conclusion that I
I the Newport-In'glewood zone of folds'and' faults, the South Coast Offshore d
. fault, and the Rose Canyon fault zone cannot be disassociated.
- Instead, i
an extensive, linear zone of deformation, at least 240 km long, extending l
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from the Santa Monica Mountains to at'least Baja, California, seems well established by the present evidence.
This was the tentative assessment offered also by E. H. Baltz,'in the preliminary review transmitted on July 2,1971, by the Chief. Geologist, to E. G. Case, Director,. Division 5
Reactor Standards.
This assessment is greatly enhanced by the new information, j
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I and is still pertinent.
It is quoted as follows:
I "A southeast-trending' offshore extension.of the Newport-i Inglewood "facit" or zone has been mapped in previously i
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published reports as passing of fshore of San Onofre and i
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extending to positions shown, variously, as near La Jolla and south of San Diego.
(For example see:
M. L. Hill, j
1971, fig. 1; King, 1968; Allen and others, 1965, pl. 1; f
and Emery,1960, fig. 68.). The offshore geophysical data recently obtained by the applicants and by; the USGS' appear -
to corroborate the published maps that indicate an extensive linear offshore zone of deformation although there are un-certainties owingl! to gaps in the data between Encinitas and La Jolla.
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.e Published References Allen, C. R., St. Amand,, P., Richter, C. F., and Nordquis t, J. M.,
1965. Relationship between scismicity and geologic structure in the Southern California region: Bull. Seismological Soc.
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America, v. 55, p. 753-797.
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Emery, K. O.,1960, The sea off southern California:
Wiley and Sons, t
Kill, M. L.,1971, A test of new global tactonics; comparison of northeast. Pacific and California structures; Bull. Am. Assoc.
1 Petroleum Geologists, v. 55, p. 3-9.
King, P. B., compiler,1968, Tectonic map of hrth America:
U.S. Geol.
Survey Map..
O Szabo, Barney J., and Vedder, J. G.,1971, Uranium-series dating of some l
Pleistocene marine deposits in southern. California:
Earth and i
l Planetary Sci. Letters, vol.10, no. 4, p. 283-290.
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