ML20236B997

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Forwards Revised Draft Review of Amends 31,32 & 34 of Plant FSAR
ML20236B997
Person / Time
Site: Diablo Canyon, 05000000
Issue date: 01/12/1976
From: Houser F
INTERIOR, DEPT. OF, GEOLOGICAL SURVEY
To: Gammill W
Office of Nuclear Reactor Regulation
Shared Package
ML20236A877 List: ... further results
References
FOIA-87-214 1474, NUDOCS 8707290308
Download: ML20236B997 (14)
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- 1-i United States Department of the Interior H @ j GEOLOGICAL SURVEY

  • - RESTON, VIRGINI A 22092

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1 January 12, 1976 ' .'j ,

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l Mr. William P. Gammill (

Chief, site Analysis Branch i Division of Technical Review Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Bill:

i Enclosed is a revised draft review of the Amendments 31, 32 and 34 of the FSAR for the Pacific Gas and Electric Company's Diablo l Canyon site, Units .t and 2, San Luis Obispo County, California, )

Docket Nos. 50-275 and 50-323. This review was prepared by i Frank A. McKeown, who reviewed the geology, and James F. Devine, l who reviewed the seismology. Mr. McKeown was assisted by Holly Wagner, David McCulloch, and Robert Yerkes; Mr. Devine was assisted j by Robert Page and Wayne Thatcher.

Sincerely yours, c .. l Fred N. Houser Deputy Chief Office of Environmental Geology Enclosure c_s, s

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. Draft Revjcw I F. A. !!cK< m (Geology) f J. F. Deva e (Scismology) ,

Diablo Canyon FSAR Amendments 31, 32 and 34 ,

January 12, 1976 ]

PACIFIC GAS AND ELECTRIC C0!!PA!.T l DlABLO C'. .;iN s1TE, UNITS 1 AND 2

' SAN LblS ODISPO COUNTY, CAL 1FORMIA

, AEC DOCKET NOS. 50-275 AND 50-323 3 l

. Geology and.Scismology .

I This is a revie'w of the geological and seismological information

, 1 contained in Amendments 31, 32, and 34 of the Final Safety Analysis j a i Repert (FSAR) fdr the Diablo Canyon nucicar power plant site. Amendment d 37, containing important discussion of the p- nd response pertinent to i

seismicity, was received in early November a .d too late to be considered j in this review. The amendments were prepared by the Pacific Gas and Electric Company (PG&E)'in response to a request in a letter dated February 12, 1975, from the huelcar Regulatory Commission (NRC) for certain additional information relevant to design basis earthquake l issues, which have been the principal problens requiring additional carth sciences information and analyses. To support assertions in the ,

FSAR through Amendments.11, 19 and 20, five requests for information (referred to as questions in the Amendments) were made.

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2.17. Provide additional discussion and arguments for determining the maximum carthquake that can be expceted on faults of various ranks within the San Andreas system. Relate the discussion to historic scismicity.

i 2.18. Provide additional documentation, including scismic reflection j profiles, on the intersection of the llosgri' fault ::one wit h the Transverse Range faults. Include geologic maps southward I of those provided in the FSAR showing the structural relation-ships of the Transverse faults and structures having a northwest trend.

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2 2.19. Provide additional documentation, including scismic profiles, on the northern reaches of the llosgri fault :ene. Include a L l

fuller development of your views on the structural relationship l

of the llosgri fault to the San Simeon fault.

l Provide a,dditional information on the location of the 1927 )

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cvent, together with its probabic mechanism. Discuss probabic . relationships of this event to the geologic

  • structure in the region. q 2.21. Provide your'cvaluation of the maximum credibic carthquake on the llosgri' fault zone. Assuming this event occurs along the segment of the llosgri fault zone nearest the site, evaluate its response spectrum at the site and compare it with the design r'sponse e spectrum.

The response in the TSAR to the questions has provided considerable i

l additional geologic and scismologic inf ormation and analyses.

Ilowever, unambiguous answers to the questions have not been achieved. J Ibny uncertainties in the data and interpretations still exist. I Among the most important of these are: 1) the location and mechanism of'the 1927 carthquake, 2) the exact relation of the llosgri fault zone to faults in the Transverse Range system and the San Simeon fault, 3) the continuity of some faults, 4) the relative *

one, amounts of dip-slip and strike-slip movement on the llosgri fault i 5) the sense of displacement on parts of the llosgri zone, 6) i identification and correlation of acoustical units, and 7) kinematic .

relations among different fault zones.

In addition to these uncertainties, some information shown on the profiles is not shown on the maps and'vice versa, and some p;ofile data are not included that are important to evaluate the extension or ch'aracter of some faults. Becausa geologic maps developed from seismic I

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reficction profiles are based upon much interpretation that may differ among several interpreters, it was necessary for the purposes of our review to make independent interpretations of the seismic profiles.

These independent interpretations are somewhat different than the a

interpretations presented in Amendments 31 and 32. The major l

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differences are briefly described in appropriate sections of this 1

review.

i Although sope changes in, and additions to, geologic and seismologic i

l details have been made in Amendments 31, 32, and 34 compared with I

prcvious data in the,FSAR, no major changes can be cade in our conclu-sions that were stated in the review of the FSAR, and Amendaents 11,19, and 20, which was transmitted to the NRC free the Director of the United States Geological Survey by letter cf January 28, 19'15.

The pertinent statement in oor previous conclusiot.s was as folicws:

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" Earthquakes along the EBZ presumably would not be as large as i

expected on the San Andreas fault, however, from the information presently at hand we can find no evidence that weuld preclude the occurrence of an carthquake as large as events characteristic of subparallel strike slip faults, which bound basins, such as the Santa

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Maria, in the San Andreas system and which do nnt transect structural pri.i. es." The size of an earthquakt on faults that bound basins was not specified in this conclusion. For reasons stated in subsequent i

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l 1$s defined in the FSAR, EBZ refers to the East Boundary fault zone, v[hichistheHosgrifaultzone.

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parts of this review, however, the magnitude of the design basis carthquake for tbc Diablo Canyon nuclear reactor site should be in the range of 7.0 to 7.5 and located on the llosgri fault :ene. This l

' i is based principally on the fact that the November 4, 1927, carthqual.c l had a magnitude'of 7.3 and that the best estimates of its location )

'i s' indicata that it, could have occurred on the Hosgri f ault.

Selected c6mments important to an evaluation of Anendtents 31,  !

32, and 34 are outlined below.

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Amendment 31 NRC Question 2.18 l

On figures 8 and 9 relative displacement on the Hosgri f ault between Point Euchon and Poiht Sal is shown to be doun on the east.

On figure 10 relative displacement on the southern extension of the Hosgri fault south of Point Sal is down on the west, which is compatible I

with the argument that the Hosgri fault is the east boundary of a pcrtion ;i

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of the Santa Maria Basin. Changer in direction of relative movement,  !

however, are very suggestive of lateral displacement, which may have  ;

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occurrred after development of the basin and bounding f aults.  !

On page 9, reference is made to fig. il as evidence that no scarp-forming scismic events have occurred on the southernmost part of the llosgri fault since prior to the Wisconsinan stage of the i

i PIcistocene.

It is true that no offset of the ocean floor is evident

, en fig. 11. Ilowever, close inspection of fig.11 shows offset of the post-Wisconsinan unconformity when sighting along it or placing a

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straightedge along the mapped trace. .Also, faulting of the post-Uisconsinan sediments cannot be precluded because a change in acoutical signature is evident across an upward projection cf the fault shown in figure 11. The change in the acoustica] signature of unit A2 across the fault is quite cicar and may be evidence of lateral

! movement on the' fault.

It is not clear from the pr ofiles in figures 13a and 13b that the disturbed zoned, in them that are inferred to represent the Uest iloscri fault'are the sa'me.

At 1 cast three additional faults can be inter-l preted in the profile of figure 13b. Also a disturbed zone appears l

to be between stations 133 and 136 in the' profile of line 13a.

}cicz, Bartlett, and Polaris survey' lines criss-cross this area and additional evidence from them to support or negate the suggested correlation of disturbed zo'ncs should be described.

l An independent. interpretati.on of the scistic profiles in the offshore .arca from about Point Sal to about five miles south of ,

Point Arguello indicates that the,Hosgri fault extends at 1 cast five

' miles south of Point Arguello and does not turn castward as suggested in Amendment 31. , l l

Although the Lompoc fault zone appears to have offset the sea ,

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floor, and may therefore be considered capabic of movement again, its length of only about eight miles as inf erred by the applicant appears to be incompatible with a magnitude 7.3 earthquake. An independent ihterpretati5n of the scismic profiles in the area of the Lompoc foult differs from that of the applicant in that it sfiows that the Lompoc i I o 1 t e

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6 fault zone is about twenty miles long; the longest single fault in the zone is about fifteen miles in length. Furthermore, the displacement l's interpreted to be dip slip or possibly oblique slip; rather than .

revctse slip as suggested by the applicant. i tiRC Question 2.19 As noted in, the, previous section the sense of displacement on  ;

the southern part of the Hosgri fault is up on the west side, figure 1 (N), and therefore is not compatible with its being primarily i

related.to basin development. However, an alternative interpretation suggests the displacement on the llosgri f'ault in figure 1 to be down on the west.

Figure 1 (N) has three buried faults not shown on Plate I. This leads to questions concerning the interpretation cf some of the data in the report. .

Another instance of faults shown in profile but not on a map is seen from comparison of fig. 4 (N) and Plate I. The correlation of faults bekween Lines 16 and 12 (figs. 3 (N) and 4 (N)) is questionabic.

. A profile along Line 14 would help. Also, an interpretation of Line 10 should be included.

Although the straight coast line between Car.bria and Point Estero suggests that the extension of the San Simeon fault is just offshore; data are lacking to prove this. None of the data presented in Amendment 31 preclude the San Simeon fault from intersecting the llo,sgri fault offshore between Cambria and Point Estero. The two fa'ults even as shown on Plate II (N) are less than 2.5 miles . apert.

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r 7 and could very well be tectonically coupled to each other by an en echelon ,

l or anastomosing peries of faults which is characteristic of faults in the l l

coast ranges. Such coupling of the Hosgri and San Simeon faults is supported l l

by interpretation of stratigraphic sections recently reported by Hall (1975). l

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i He infers that "-- ,the San Simeon and Hosgri faults are part of the same l 1

I l system,-- " and,that 80 km or more of right slip has occurred along the i

system during t;he last 5 to 13 million years. l l Figs. 7a (N) and 7b (N) are very puzzling. They show an inflection in' the seafloor over the Hosgri fault, and a drastic change in the thickness and acoustical signature of unit A2, assuming A2' is correlative with A2.

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In addition to vertical displacement, lateral displacement, which is not mentioned, could be interpreted from these profiles. F.owever, the basis i for separating A2' from A3 is not apparent. Similarly it is noc apparent

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why unit A', east of the fault, is terminated. It appears to continue'to the east edge of these profiles.

On figure lla (S) the A2 unit cast of the fault at station 119 is

! correlated with the Monterey formation (p. 6, NRC Question 2.19, amend. 31), l but the signature of the A2 unit west of this fault is coepletely different.  ;

I This inferred lithologic change, as elsewhere, sucgests lateral displacement.

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, NRC Question 2.20 j

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On page 10 it.is reasoned that both the Hosgri and West Hosgri l faults can be eliminated as sources of the 1927 earthquake because

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neither the sea floor nor the post-Wisconsinan unconformity are offset  !

I in the epicentral area of the carthquake. This reasoning is not satis-l ,

factory because typically surface rupturing of a fault is discontinuous, and of fset may not be detected if the displacement had a large lateral 4

Furthermore, as stated on page 4 of this review, the base component.

r 1 of post-Wisconsin'an sediments is offset, an.d a fault in the sediments I l

. cannot be precluded in figure 11. The evidence., therefore, to eliminate j the Hosgri fault as the source of the 1927 carthquake is inadequate.

As previously stated, the length of the Lompoc f ault shown by the applicant appears to be incompatible with the magnitude of the 1927 earth' quake.

Figure 1 shows that segments of the Hosgri fault zone, the Lompoc  !

1 fault, Purisima fault l and Lion's Head fault occur within the error j circle of dawthrop and error ellipse of Engdahl for the 1927 earthquake. ,

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However, all of the faults are outside of the area designated by Smith l l

1 as the " inferred distribution of af tershock sequence of the 1927 earthquake." The 1927 earthquake, therefore, cannot be unequivocally l located on any one of these faults. The Hosgri fault, however, is }

l closer to the center of the estimate of error than the other faults and, ,

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I therefore, must be considered as a possible fault on which to locate ,

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the earthquake, j

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. Amendment 32 NRC Question 2.17 l Although this section contains descriptions and explanations of

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the " kinematics of structural behavior in the south-central California region-- " contemporary seismic activity is not fully explained. Also, we do not agree with some statements given as fact. For example, on page 2 it is stated as fact that the 1927 M.7.3 earthquake occurred on the Lompoc fault. This is not fact but a highly controversial assumption. Item 2 on l

f l page 2 of this amendment indicates that the Lompoc and San Andreas are the l only faults in the southern Coast Ranges that " reflect substantial late Quaternary surface deformation." As defined on page 3 of this amendment, j " substantial" clearly includes the San Simeon fault, which as stated on 1

, page 7 of this review may be coupled with the Hosgri fault. The attempt to explain the large magnitude by using the logic that the Lompoc fault is in a transition zone between the Coast Ranges and Western Transverse Ranges applies to other faults in the zone including the southern part of the Hosgri fault.

Amendment 34 NRC Question 2.21 The masimum credible earthquake of 6 1/4 - 6 1/2 on the Hosgri fault zone used in this section to derive peak site ground acceleration is unacceptable because as stated previously the 1927 earthquake with a magnitude of 7.3 cannot be precluded from having occurred on the Hosgri fault. Although we believe that the 1927 earthquake should be used i

I to estimate the safe shutdown earthquake, fault length-magnitude relationships have also been considered. The uncertainties in these l

10 relationships and the assumptions involved to use them are well known. Nevertheless we may consider that the Hosgri fault is about 90 miles (144 km) long, or even greater if it is coextensive with the San Simeon fault.. The part of this total length that may rupture during an earthquake is highly conjectural, but we assume that one third of the fault. .

will rupture, which is about 48 km. This assumed length is supported somewhat if the range in S-P times for the aftershocks of the 1927 earthquake are considered. The range in times calculates to about 45 km as shown by Engdahl (1975). The fault length-magnitude curve for i

strike-slip faults (Bonilla and Buchanan, 1970, fig. 3) shows i

' magnitude 7 for a 45 km rupture. In our judgment it is prudent to consider

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this as a possible minimum magnitude exclusive of the consideration of the 1927 earthquake.

. Conclusions Although the FSAR includes a considerable amount of new informa-tion and analysis, the only change that can be made in the original conclusions transmitted to the NRC on January 28, 1975, is to be more specific in our estimate of the design basis earthquake. This is based i upon the following f acts and judgments.

1. The Hosgri fault zone is more than 90 miles long and may even tectonically coupled to the San Simeon fault as they are within 2.5 miles of each other and both form parts of the eastern boundary of the Santa Maria basin.

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2. Marked changes in thickness and signature of acoustical units across the llosgri fault zonc in several profiles indicates evidence of *

.i laterci slip. This s noted in our revicw of January 28, 1975, but such l . changes are even mo.re abundant in the profiles of' Amendment 31. Right i lateral movement is reported for the San Simeon fault. These data suggest that displacements on the Hosgri fault are related to the i

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highly active San Andreas plate-boundary system. l

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3. The length;of the Lompoc fault appears incompatibic with the magnitude of the 1927 earthquake.
4'. The llosgri fault is closer to the center of the estimates of l l

crror of both Engdahl and Gawthrop than any other f ault. It is there-fore a possibic source of the 1927 carthquake. l l 5. Equivocal evidence related to vertical displacement on the Hosgri fault in the epicentral area of the 1927 earthquake decs not climinate  !

it as a sourec. Surface rupture is generally discontinuous, and if lateral slip occurred, it probably would not be detected. Offset of the i

l base of post-Wisconsinan sediments and probable faulting of them is jj i3 cvidence of post-Pleistocene movement. ]

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For the above reasons and discussions given in the review, we conclude that the 1927 car'thquake could have occurred on the llosgri  !

fault and that a similar carthquake with a magnitude in the range of 7.0 - 7.5 could occur in the f uture anywhere along the !!oscri f ault.  !

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6. We repeat our opinion that, for, sites within 10 km of the 4 surface expression;.gf a fault, the description of maximum earthquake ground motion or design notion by means of a single acceleration value and a standard response- spectrum may not be an appropriate representation for design purposds. .

Consequently, we feel that it is appropriate that we describe the l

Safe Shutdown carphquake for this site in terms of near-fault horizontal ground motion. The technique for such a description is presented in the Geological Survey Circular 672 entitled "Gr'ound Motion Values for Use 1

in the Seismic Design of the Trann-Alaska pipeline System" (Ref. 4). .

It is our intention that the ground motion values as shown in Table 2 "Near-fault horizontal ground motion" of Ref. (4) for magnitude 7.0 l

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and 7.5 be used as a description of the earthquake postulated to have the potential for occurring on the Hosgri fault at a point nearest to the Diablo Canyon site.

The conditions placed on these values as described in Ref. (4) p. 3-13 also apply in this case, e.g. "They -characterize f ree-field ground notion, . . ."

The design values of motion should be derived by modifying the ground motion values to'implicitely allow for non-linear energy absorbing mechan'sms in the vibratory response of the structure and their application to appropriate response spectra as specified in Ref. (4) p.p. 2 and 3 and l

. appendix B.

l It is intended, also, that this potential earthquake be -considered in addition to all earthquakes considered previously by the applicant

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. during the construction permit review process.

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. References Cited Bonilla, M. G., and J. M. Buchanan (1970), Interim report on worldwide historic surface faulting: U. S. Geol. Survey, open file report no.

1611. .

Engdahl, E. R. (1975), Teleseismic location .of the 1927 Lompoc carthquake:

TERA Techr.ical Report, Berkeley, Calif.

Hall, C. A. (197'.5), San Simeon-Hosgri fault system, coastal California:

Economic and$ environmental implications: Science, 190, p. 1291-12:,.

Page, R.* A., D.,M. Boore, W. B. Joyner and H. W. Coulter (1972), Ground motion values for use in the seismic design of the Trans-Alaska Pipeline System: U. S. Geol. Survey Circular 672.

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