ML20235X681
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1 DAVID B. SLEMMONS
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CONsVLTING GEOLOGisi 2995 GOtoEN VALLEY ROAo. RENO. NEVADA 89506. (702) 972-8877 November 25, 1979 Dr. Robert Jackson, Chief Geosciences Branch Div. Site Safety and Envir. Analysis U. S. Nuclear Regulatory Commi'ssion Washington, D.C. 20666
Dear Bob:
I I have completed a review of the report " Report of the Evaluation of the Maximum Earthquake and Site Ground Motion Parameters Associated with the Offshore Zone of Deformation, San Onofre Nuclear Generating Station",
prepared by Woodward-Clyde Consultants, June 1979.
j 1 believe that this is an innovative new approach that deserves careful study, refinement, and testing.
I have reviewed the source literature upon c
which the report is based and, although there are a number of errors, and new data are rapidly becoming available on the fault zones used for the basic figures (Figures 6 and 7), the data do suggest for strike-slip faults i
a general decrease in maximum earthquake magnitude with decrease in fault slip rate.
Since the method is new, I agree with your staff, that this should not be the sole basis for the San Onofre site evaluation.
I am appending to this letter my preliminary list of questions and comments on the report.
There I
is a major increase in new data for both the general topic of the seismotectonic setting of the earthquake and the basic fault slip rate and earthquake magnitude data that should be included in Southern California Edison's final.
reporting, or their response to questions.
There were many new, and in part conflicting, reports presented at the recent l
l Geological Society of America meeting in San Diego.
These reports include i
l many contributions to the seismicity and active fault relationships, both on-shore i
and offshore. The following materials are pertinent to the Woodward-Clyde Consultants study:
l Crowell, J.C., and Sylvester, A.G. (editors), November 1979 Tectonics of the juncture between the San Andreas fault system and the Salton Trough, southeastern California:
Dept. Geol. Sci., Univ. California, Santa Barbara, 193 p.
Abbott, P.
L., November 1979, Geological excursions in the' southern California i
area:
Dept. Geol. Sci., San Diego State University, 217 p.
i Abbott, P.L, and Elliott, W.J., November 1979, Earthquakes and other perils, San Diego region:
San Diego Association of Geologists, 227 p.
i Among the papers presented at the meetings, several include new offshore data on mahr structures and the Quaternary history of sedimentation and deformation of the region west of California and Baja California.
I believe that the Southern California Edison response to questions should consider these new sources of data.
8710200079 a71014
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-462 PDR
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Robert Jackson, ' November 25. 1979 Page 2 of 2 i
l The new data of the Woodward-Clyde Consultants report included a thorough
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search of the conventional literature of major l strike-slip faults and their-1" recurrence intervals.
Several additional sources of information could be included in order to provide a more accurate and up-to-date record for some of the major faults. These include-1 Gerald Lensen, R.P. Suggate and H. Wellman for New Zealand and Iranian faults.
l Their data includes a number of detailed strip maps.of. zones of historic i
surface faulting and radiometric dating M marine and river terraces that l
have been faulted during the late. Quaternary.
Harold Wellman has
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undertaken many remote sensing and other studies of Iran; much of his work has not been published. Their data should be reviewed for the Alpine, Hope, Clarence, Awatere, East Wairarapa and West Wairarapa and -
possibly the Wellington (partly reverse-slip). faults. Many of these i
faults have new detailed strip maps of late Quaternary faulting. Some newer data may be available to scale the magnitudes of pre-instrumental earthquakes (e.g. Clark and others,1965, Fig).121; or more.recent studies l
by the staff of the Geophysics Division, DSIR.
I enclose copies of some of the relevant papers.
T. Matsuda, K. Nakamura and A. Sugimura of the University of Tokyo and the Earthquake Research' Institute;.and N. Ikebe of the Osaka City University.
They have conducted a number of detailed studies that may supplement or j
modify the data provided for Tanna fault, or make it possible to add 4
other strike-slip faults of Japan (Atera, Median Tectonic Line, or others).
j The relations shown by Ficjures 6 and 7 of the Woodward-Clyde Consultants report may not hold for dip-slip faults. The Pleasant Valley earthquake of 7.7
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magnitude as listed by Gutenberg and Richter (1954) has a low normal-slip rate.
This may also be true for reverse-slip faults also. The WCC report does not provide a model to justify their not including dip-slip faults.
1 If you, Tom Cordone or Phyllis Sobel have additional questions or comments,
-j please write or teleophone, j
Sincerely yours,
- A'.0 w.A David B. Slemons-Consulting Geologist I
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D. B. Slemons
' November 24, 1979-1 Seismotectonic Model:
The seismotectonic model for.this.part of southern California is based on an apparent. decrease in activity to the' west of the San Andreas fault zone.
The figures shown in this report suggest this relation, but_ the data shown
.3 for the 200 mile radius about the site as given in the FSAR, the surface q
faulting and earthquake activity to the southeast on the same structural.
1 trend as the OZD do not necessarily support this model. The. discussion of 1
the seismotectonic setting should include an analysis of the relation of the OZD to faults and earthquake activity to the south in Baja California and into the offshore borderland to the west of Baja California..The discussion should include the apparent increase in level of activity toward the San; Miguel and Agua Blanca fault zones, to the southeast along the. strike of the j
OZD. The analysis should include discussions of the possible structural continuity, either at the surface or'at-depth, with the Vallecitos, Tres j
Hermanos, San Miguel, Agua Blanca, and faults or structures between the i
Rose Canyon fault near San Diego, and the offshore features north of the i
seaward projection of the Agua Blanca fault zone. The discussion should 4
include, where appropriate, the ' general relationships of conjugate faulting,
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earthquake mechanism, recurrence relations or. other relevant data. In addition to the above features, the following should be discussed:
1 1.
Does the post-1975 ear?.hquake activity within a 200 mile radios' of San j
Onofre show any new patterns of activity for the greater than 3, greater than 1
4, and greater than 5 earthquake magnitude ranges, that is indicated by the -
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San Onofre 2 & 3 FSAR Figures 2.5-15,16,17 and 18?
l 2.
What is the rationale for dividing the OFZ into 3 sections? Does this 1
suggest that there is a tectonic segmentation, either into these three segments, 1
or into other segments? If segmentation is proposed, what criteria support the points o.f segmentation?
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3.
Describe the OZD in. relation to major geomorphic, structural and topographic l
zones of Baja California and its adjoining offshore areas.
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l D. B. Slemnons floyeniber' 24, 1979 l
G_eopgj:-HistoricSlipRateCorrelations:
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'tation of slip rate to maximum earthquake magnitude relations of Figures 6 and 7 suggest that maximum earthquake magnitude to be expected for stike-slip faults may have upper bound limits of some type. Several of the values used require more detailed descriptions of rationale, definitions, and possible basic differences from relations from dip-slip faults. The values selected do not show the error bands or variation in determinations, or detailed descriptions of the methods of selecting'or rejecting basic data. The design earthquake limits of Figure 7 do not include possible families of boundaries for such limiting ~ values as maximum probable, maximum credible, maximum possible, or other defined types of boundary values.
Some of the alternative types of boundary values include the definition of maximum earthquakes based on full fault length, half fault length, third-fault length or other methods of establishing limiting values for fault zones. These relationships suggest the need for more complete discussions of the following questions:
1.
What will be the effect on the San Onofre design basis, if the boundary of l
i Figure 7 is changed by either refinements in current data points by newer studies, or by possible generation of new earthquakes of higher magnitude on l
faults of low slip rate?
l 2.
Four faults, the San Andreas, San Jacinto, Hayward, and Calaveras faults are plotted by x marks for maximum design earthquake. Other values than those shown have been established by the U. S. Nuclear Regulatory Commission, or are given in U. S. Geological Surveyyor in other publications. What methodology should be used for selection or rejection of data points of this type and what l
results are obtained if other well studied faults also are included in this type of compilation?
3.
What effect on the boundary limits is obtained if the limiting maximum design earthquakes are based on maximum probable, maximum possible, maximum -
credible or on other defined types of maximum design earthquakes?
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4.
What are the relations to maximum or limiting values? Is the procedure of -
l using fault half-length, or fault third-length, or other types of calculated limits'.used?
5.
The data supporting the slip rate vs. magnitude points plotted should have more thorough descriptions of the details of data selection and rejection, and the range in possible error, including the M determinations. Describe any steps taken g
in this process that lead to results that provide conservatism in the results of l
the analysis.
6.
The sparse nature of the data for faults with slip rates of less than about 3 mm/yr average slip' rate may, in part, be due to a poor data base for faults with slow strain rates.
Statistically, what effect does this factor have in l
the validity of the data base and on the results of the analysis?
7.
The geologic time scale that was used should be tabulated for reference and the assumed age, where general terms are used in the primary literature, e.g.
Holocene, lower Pliestocene, etc., show the methods used in assigning an absolute age and show the error bands in the result that develop from the assumptions.
D. B. Slemmons November 24, 1979 8.
The slip rate data for the Newport-Inglewood section of the 0ZO is strongly dependent upon the stratigraphic correlations between drill holes on either side of the fault zones. The rationale for the correlations is provided in the text of the report.
Show logs for the holes that are correlated and for the adjoining holes that show greater mismatch or lack of correlation for each age bracket used to support the general slip rate.
Show the error bands or spread for each determination.
What are the error bands in absolute age for the sediments that have been correlated? What procedures or assumptions have been used and what is the effect on the conservatism in the result of the analsysis?
I 9.
Has M been used consistently throughout the analysis?
g 10.
Review of the data suggests possible corrections or additions to the data base used for the Woodward-Clyde Consultants report of June 1979. The following list includes those that have been noted during my review of the report:
a.
Ben-Menahem (1976) cites Girdler (1958) for a 10 mm/yr slip rate; s
this figure couldn't be found in this reference.
The 6.5 and 7.5 j
mm/yr rates appear to be sound.
The pre-instrumental earthquakes have suggestions of magnitudes of 6 to 7 (M ); see p. 46.
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b.
The data of Dewey and the Woodward-Clyde Consultants study of the late 1960's suggests a mainly strike-slip mechanism. More discussion of the j
style of faulting as a matter of debate is needed. The Woodward-Clyde Consultants study suggests 320 ft/10,000 yrs or 9.9 mm/yr, a similar value to the values of 7, 10, and 8-10 obtained by other workers.
The microseismic data suggests the 1812 earthquake had a magnitude of 8i 0.25. The data for this point appears to be as good as that as many cf the other points used for the figures 6 and 7.
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c.
The data for 5 to 6 mm/yr slip rate and the 8.0*0.25/ appear to be fairly good values for plotting the data on figures 6 and 7.
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should be a discussion of why this data point should be rejected.
The magnitude is listed by Slemmons (1977) and is estimated in several i
New Zealand publications, including Clark and others (1965), who show I
much larger isoseismal areas than the 1929 earthquake of Me = 7.6.
The guidebook by Lensen (1973) shows two rates for the fauTt slip, 4
with a preferred estimate of 9.4 mm/yr for the Waichine terraces.
i The linearity of the fault shows a nearly vertical fault plane.
(seeappendedreprint). The many well studied terraces of this area should permit a rather accurate appraisal of the error bands.
i d.
The paper of Schwartz et all (1979) appears to support a slip rate of 1.5 to 6 mm/yr, rather than the 6-10mm/yr rate cited for the Montagua fault zone.
e.
The data for the Tanna fault in Japan shows for Matsuda's(1976) figure 1, a 1 km displacement for 0.5 my.
This suggests a rate of about 2 mm/yr, rather than the 3.2 mm/yr rate of WCC's Table G-1.
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- 0. 8. S1 canons November 24,.1979 f.
Kopet-Dagh should show Me = 7.3 according to Gutenberg and Richter (1954).
The best value for slip rate appears to be the 3.6 mm/yr-for the irrigation systems.
This appears to be.a boundary zone event, g.
Calaveras fault should show Herd (1978) as 12 to 15 mm/yr rate. The source data for this should be checked. The N. R. C. values for maximum design earthquake should be 7.0 to 7.5.
h.
The San Jacinto should use new data from Sharp, if possible. May be possible to open file the data,
- i. The San Andreas fault (Cholame to Cajon Pass sector) should recheck the data of Seth (1979) who now gives a M = 8.25+ for this zone, 3
37 mm/yr slip rate is a reasonable value j.
The northern San Andreas doas not have any satisfactory values.for the average slip rate, although the figure 20 mm/yr year is widely cited.
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