ML20136J238

Forwards Response to RAI Re Geologic & Seismic Issues

ML20136J238
Person / Time
Site:	San Onofre
Issue date:	03/14/1997
From:	Rainsberry J SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9703200063
Download: ML20136J238 (19)

Text

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ENk SOUIHIRN CAlliORMA WF EDISON """**

Manager. Plant Licensing An t insov ilitExarlbx41. a' cunpany March 14, 1997 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:

Subject:

Docket Nos. 50-361 and 50-362 Request for Geological and Seismic Information San Onofre Nuclear Generating Station Units 2 and 3 As a result of a 10 CFR 2.206 petition to shut down San Onofre Units 2 and 3, the NRC requested information regarding geologic and seismic issues. Provided as an enclosure is Edison's " Response to NRC Request for Information Regarding Geologic and Seismic Issues." At the NRC's request, a copy of this letter, along with the enclosure, is being provided to Mr. Stephen Dwyer, the petitioner.

If you require further information regarding this matter, please feel free to call me at (714) 368-7420.

Sincerely, Enclosure 9703200063 970314 PDR ADOCK 05000361 p PDR a cc: J. E. Dyer, Acting Regional Administrator, NRC Region IV ,

K. E. Perkins, Jr., Director, Walnut Creek Field Office, NRC Region IV j j J. A. Sloan, NRC Senior Resident Inspector, San Onofre Units 2 & 3 il M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3

, ph f S. Dwyer l 200007 San Onofre Nuclear Generating Station P.O.Ika 128 San Clemente, CA 92674-0128 k 714 368-7420

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l RESPONSE TO NRC REQUEST FOR INFORMATION GE0 LOGIC AND SEISMIC ISSUES SAN ONOFRE NUCLEAR GENERATING STATION i

Woodward-Clyde Consultants and Geomatrix Consultants, Inc. prepared the following responses to NRC's request for geological and seismic information for i San Onofre Nuclear Generating Station. The responses pertain to the I probabilistic seismic hazard assessment performed in 1994,for San Onofre 1 (SONGS PSHA). The SONGS PSHA report is the " Seismic Hazard at San Onofre U Nuclear Generating Station, Final Report," dated August 25, 1995 and prepared i by Geomatrix Consultants, Inc., Risk Engineering, Inc., and Woodward-Clyde Consultants.

Question 1:

"Five empirical ground motion attenuation functions were used by the l estimation of the probabilistic seismic hazard at San Onofre Nuclear Generating Station (SONGS) for the Individual Plant Examination for External Events (IPEEE) program. Did the development of these functions include data from recent southern California earthquakes such as the Northridge and Landers events? If not, how do the estimates of ground motton using these functions compare with the data recorded from these two events?

Response to Question 1:

As stated in Appendix D of the SONGS PSHA report, the five attenuation relationships used in the SONGS IPEEE study were checked with their respective author (s) to be sure they were current as of 1994. In general these attenuation relationships reflected all the recent southern California earthquakes including the Landers event in various ways, but not the Northridge event. In addition, the Landers event was included in the detailed evaluation of the five attenuation relationships presented in Appendix D of the SONGS PSHA report. The Northridge event was not included in that evaluation because it was considered an inappropriate event for the SONGS PSHA purposes as discussed below.

By far the most important seismic source for the SONGS site, which is a soils site, was the Newport-Inglewood-South Coast Offshore Zone of Deformation (SC0ZD)-Rose Canyon Fault zone, which is a right-lateral strike slip fault with a maximum magnitude of about 7 and a closest distance to the site of about 8 km. Therefore, the evaluation of the attenuation relationships for the purposes of the SONGS PSHA focused on the use of recordings on soils sites from strike-slip events (27 stations)

and oblique events (14 stations) having magnitudes ranging from 6.1 to 7.3 at distances no further than about 18 km (see Table D-8 of Appendix D of the SONGS PSHA report). One station from the Landers event, the Joshua Tree station, qualified in this category, and, therefore, was included in this selected database for the evaluation. The evaluation including the study of residuals indicated the reasonableness of the five l attenuation relationships when compared to the selected database (see, for l example, Figures D-6a through 0-69 of Appendix D of the SONGS PSHA 1 report). On the basis of this extensive evaluation of the five ,

attenuation relationships under the conditions pertinent to the SONGS PSHA, these attenuation relationships were considered to be consistent i with the Landers event as well as with other recent pertinent data as of l 1994.

The Northridge event was a thrust or reverse event, not a strike-slip event, and, therefore, was considered not pertinent for the evaluation of l attenuation relationships for the purposes of the SONGS PSHA. Even in 1994, it was well established that thrust or reverse events result in l ground motions that are different from those due to strike-slip events, and mixing them in assessing attenuation relationships mainly for strike-slip events likely would be misleading.

Nevertheless, because Question 1 mentions the Northridge event, Figure 1-1 compares the peak ground acceleration versus distance from three of the attenuation relationships using the soils site data from the Northridge event. The median as well as plus-and-minus one standard deviation relationships for thrust or reverse events are shown on Figure 1-1. As can be seen from Figure 1-1, the three attenuation relationships appear to be reasonably compatible with the Northridge event data with most data plotting between the median and +10 attenuation curves, even though they are considered to be not pertinent to the SONGS site.

The two attenuation relationships not included in the comparison should provide similar results as those shown on Figure 1-1 as can be seen from the comparison of the effects of all five attenuation relationships presented on Figures 6-11 and 6-12 of the SONGS PSHA report.

Question 2:

" Provide the results from any geological or geophysical investigations performed in the SONGS region that contain information about the tectonic regime, the potential for thrust earthquakes, the existence or non-existence of buried or blind thrust faults, or the potential for surface displacement on the order of that which resulted from the Landers earthquake."

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Response to Question 2:

( The development of a source model and the characterization of seismic sources completed as part of the probabilistic seismic hazard assessment l at the San Onofre Nuclear Generating Station for the Individual Plant l

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Examination of External Events program (SONGS PSHA report) incorporated recent research and data on the tectonic setting of the site region. The l assessment explicitly considered the seismic potential of recognized blind fault sources as well as the pote"ial for unknown blind thrust faults near the SONGS site based on consideration of the tectonic setting and style and rate of Quaternary deformation in the region. The potential for surface displacements along strike-slip faults on the order of that which occurred from the 1994 Landers earthquake was considered in assessing the potential for large-magnitude earthquakes resulting from multiple segment und multiple-fault ruptures in the characterization of seismic sources in the site region. Each of these issues are addressed in more detail in the following sections.

l Tectonic Setting l

The SONGS site lies within a relatively stable structural block bounded by major northwest-trending strike-slip Nults. Relative motion be. ween the Pacific and North America plates in tb site region is characterized by transpressise dextral shear and is accommodated largely by dextral strike slip centered along the San Andreas fault system and faults in the l

borderlands of southern and Baja California, and to a lemr degree, by a l component of basin and Range extension parallel to the plate boundary, l extension in the Guif of California, and contractional structures in the Transverse Ranges and Los Angeles basin region (Zcback and others,1981; Weldon and Humphreys,1986; Argus and Gordon,1988; Stein and Yeats, 1989). Recent analyses of geodetic data (Feigl and others, 1993; Larson, 1993) indicates that a significant component of dextral shear occurs on offshore faults along the southern California borderland. These data in addition to fault-specific slip rate data compiled from offshore observations and paleoseismic studies of onshore extensions of faults,

! were used to provide constraints on the range of likely slip rate values l for faults along the southern California borderland.

The tectonic setting of the site is significantly different from the

complex tectonic regime of the Los Angeles basin that is marked by north-i south convergence associated with the geometry of the " big bend" in the San Andreas fault. This differert.e is reflected in the markedly different

rate of earthquake occurrences between the two re ons and a more diffuse spatial pattern of seismicity than the linear patt. ns associated with I strike-slip faults to the south ( see Plate 1, SONGS PSHA report).

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. 1 Blind Fault Sources 1

Recognized and potential blind thrust fault sources in the Los Angeles l basin were included in the source model used in the SONGS PSHA (see Response to Question 5).

The presence or absence of blind thrust faults in a region is indicated by the presence or absence of significant uplift and folding of late Quaternary deposits and geomorphic surfaces (e.g., Stein and Teats, 1989).

Information regarding the nature and rate of Quaternary deformation along the coastal region in the vicinity of SONGS is provided by marine terrace investigation. Mapping of marine terraces along the western flank of the San Joaquin Hills to the north of the site indicates a uniform uplift rate l of 0.25 m/kyr for the past 80 to -120 ka (Barrie and others,1992). l Lajoie and others (1992) estimate a similar long-term average uplift rate of 0.19 m/kyr for the coastal region between San Onofre Bluff and Torrey Pines north of Soledad Mountain in San Diego. They note that there has been no significant crustal tilt perpendicular to the coastline during much of Quaternary time. Also, there is no indication from the marine terrace studies of significant tilt parallel to the coastline during much of Quaternary time (Lajoie and others, 1992). The Pleistocene uplift rates in this region (0.19 to 0.25 m/kyr) are comparable to uplift rates l for other fault-bounded structural blocks within regions dominated by '

right-lateral crustal displacemenu in coastal California, which are 0.1to0.3m/kyr(Muhsandothers. ;]92).

The marine terrace data and other mapping indicates that geologically 1 young folds, such as those associated with known blind thrusts have not '

been mapped or identified in the vicinity of the SONGS site. On the basis of the apparent lack of late Quaternary anticlinal fold development, it was concluded that there are no seismogenic blind thrust faults in the nearby site region (excluding the recognized blind fault sources characterized in the Los Angeles basin) that are capable of generating significant earthquakes. In the hazard analysis, we allow for the possibility of unknown sources, including smaller-scale (maximum M,,

5.5 - 6.5) blind thrust faults, within the areal source zenes.

The seismogenic potential of the San Mateo Thrust fault, a 30-km-long fold and thrust belt that underlies the continental slope seaward of the Newport-Inglewood-South Coast Zone of Deformation (SC0ZD) fault zone (Crouch and Bechman, 1989; Fischer and Mills, 1991), (Fig. A-6, SONGS PSHA report), also was evaluated in the hazard analysis. Crouch and Bachman (1989) and Crouch and Suppe (1993) interpret thrust faults within this belt as rooted into an older regional detachment that has become reactivated locally. They consider development of this fold-thrust belt 9

to be the result of northeast-southwest shortening that is normal to, and decoupled from, the northwest-trending strike-slip deformation along the Newport-Inglewood-SC0ZD (Crouch and Bachman, 1989; Crouch and Suppe, 1993). Mills and Fischer (1991) note that this " blind" thrust ramp may j

extend as far south as Encinitas. They state that the thrust ramp may represent a major basement discontinuity offshore of San Onofre near the left-stepping break that separates the Dana Point and Oceanside segments of the Newport-Inglewood fault zone. They describe a series of fault-propagation folds and thrusts extending upward from the thrust ramp into l the overlying Neogene sequence. Vertical slip rates on these thrusts are estimatedtobe0.08to0.5mm/yrforthePlioceneand0.01mm/yrfor Quaternary time (Mills and Fischer, 1991).

Fischer and Mills (1991) separate structures in this zone into an inner thrust-fault-fold complex, which is probably a part of the flower ,

structure of the Newport-Inglewood-SC0ZD, and an outer thrust-fold complex l

! (Fig. A-7, SONGS PSHA report). Fischer and Mills (1991) note that the )

outer thrust complex appears to be cut by the main thrust fault of the  ;

inner complex. They infer that the thrust faults along the inner margin j are active, as is evidenced by their surficial topographic expression and the displacement of Quaternary reflectors.

l A key factor in the assessment of the seismogenic potential of these i thrust faults is the geometry and downdip extent of these structures. As shown on Figure A-7 (SONGS PSHA report), thrust faults within the inner j thrust-fold complex that appear to coalesce with the main trace of the Newport-Inglewood-SC0ZD within the upper 4 to 5 km of the crust, have the

l. appearance of positive flower structures along strike-slip fault systems and likely are the result of local strain partitioning (Lettis and Hanson, 1991) along the SC0ZD. The outer thrust faults, which appear to represent '

rer,ctivation of an older detachment fault, likely are truncated by the mair, uner thrust fault within the upper 3 km of the crust and, therefore, would not extend to seismogenic depth. Based on these observations, none of the thrust faults within the San Mateo thrust zone were judged to be independent seismic sources that will contribute to the seismic hazard of j SONGS.

Potential for large Displacement Events

The M, 7.3 1992 Landers earthquake produced approximately 80 km of surface l rupture within a preexisting, integrated system of faults separated by

complex intersection points (Unruh and others,1994). The magnitude of the horizontal offset varied along the fault trace, but was typically 2 to 3 m (Kanomori and others, 1992), with maximum strike-slip offset around l 6 m (Sieh and others, 1993). Rupture length, area, and displacement were

! consistent with other M,, 7.3 earthquakes (Wells and Coppersmith,1994).

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l Th'e potential for similar large displacement events that would contribute significantly to the seismic hazard at SONGS was addressed in the SONGS PSHA in the identification and assessments of the maximum magnitude for i individual fault sources.

l The maximum earthquakes associated with the faults identified as seismic 1 sources in the SONGS PSHA model were evaluated by assessing the maximum dimensions of rupture for an individual earthquake on each of the faults l and then employing empirical relationships between earthquake rupture i dimensions and earthquake magnitude developed by Wells and Coppersmith (1994). The rupture dimensions considered in the SONGS model were maximum l

rupture length, maximum rupture area (length times downdip width), and displacement per event. The thickness of seismogenic crust is well-constrained for onshore regions of southern California due to the density and quality of seismic networks. These data allow for reasonable  ;

estimates of the downdip width of most structures. The assessment of '

rupture length is less well constrained. To capture the uncertainty in the estimated rupture length, a range of values based on single- and multiple-segment and multiple-fault rupture scenarios were incorporated into the assessments. Knowledge of regional fault kinematics and paleoseismic evidence regarding fault behavior was used to assess the potential multiple-fault and multiple-fault segment ruptures.

Paleoseismic evidence of large displacement events (e.g., displacement per event data from trenching or scarp heights) that is available for some of the onshore faults was considered in the maximum magnitude assessments for these faults. In the absence of specific displacement per event data, empirical relationships relating magnitude to subsurface length and l magnitude to rupture area were used to assess each seismic source. Where  !

paleoseismic evidence for slip per event is available, these data were included in the analysis, with relatively equal weight given to the three approaches. The final result of the analysis was a probabilistic distribution of maximum magnitude for each source (see Appendix B, SONGS PSHA report) that reflects the uncertainties in rupture parameters and  ;

judgments about these parameters.  ;

Rupture length scenarios for all the significant strike-slip faults included in the SONGS source model included multiple-ngment ruptures comparable to or longer than the rupture that occurred during the 1992 Landers earthquake (see Table A-1, SONGS PSHA report). The maximum magnitude assessments for the SC0ZD, the controlling source for the SONGS site, included multiple-segment and multiple fault-rupture scenarios that

~dlloW for ruptures of 75 km and 115 km. The resulting maximum magnitude l probability distribution for the SC0ZD includes maximum events of M,,7.25

! to 7.5, comparable to or greater thar. the Landers earthquake.

l Question 3:

" Provide any assessment of the ground motton at the SONGS site from a ,

magnitude 7 earthquake on the South Coast Offshore Zone of Deformation at a distance of 8 kilometers. Did any such assessments consider the ground mottons recorded from earthquakes that have occurred since the licensing of SONGS, Units 2 and 3, such as those at Coalinga, Petrolto, Loma Prieta, Landers and Northridge?" 1 Response to Question 3:

As presented in the response to Question 1, the five attenuation ,

relationships used in the SONGS IPEEE study were extensively evaluated l

using the selected database consistent with a magnitude 7 strike-slip or oblique earthquake at a distance of 8 km within the limitation of the available recorded data. The results of this evaluation were reported in Appendix D of the SONGS PSHA report. The selected database used in the evaluation of the attenuation relationships included oblique events, such as the Loma Prieta event, as well as other appropriate strike-slip events because the available recorded data pertinent to the SONGS PSHA were very limited. The inclusion of oblique events in the database should be ,

conservative because ground motions from oblique events in general tend to l be higher than those from strike-slip events.

l A part of this extensive evaluation of the attenuation relationships at a i magnitude of 7, for example, was shown on Figure D-10b of Appendix 0 of the SONGS PSHA report in terms of normalized horizontal pseudo-spectral l response accelerations. In addition, Figures D-14a through D-14e of Appendix D of the SONGS PSHA report showed the results of standard error i evaluationatmagnitudes6-1/2and7. As presented in Appendix D of the l SONGS PSHA report, the results of this extensive evaluation of the attenuation relationships indicated that the five attenuation relationships provide the ground motion data at the SONGS site consistent with the selected database pertinent for the site: magnitude about 7 at a distance of about 8 km from strike-slip (as well as from oblique) events.

As discussed above and in the response to Question 1, the attenuation relationships used in the study, which form the basis for the ground motion assessment at the site, are quite consistent with the Landers, Ncrthridge, and Loma Prieta events. The Coalinga (magnitude 6.4) and Petrolia (magnitude 7) events like the Northridge event are reverse and thrust events, respectively, making them not pertinent to the strike-slip focus for the SONGS site, i

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l Since Question 3 mentions the Coalinga and Petrolia events, Figures 3-1 l and 3-2 compare the peak ground acceleration versus distance from three of l the attenuation relationships using the soils site data from the Coalinga and Petrolia events, respectively. The median as well as the plus-and-minus one standard deviation relationships for thrust or reverse events are shown on these figures. As can be seen from these figures, the three attenuation relationships appear to be reasonably compatible with the data from the Coalinga and Petrolia events with the data falling between ilo of the attenuation relationships, even though they are considered to be not pertinent to the SONGS site.

I Question 4:

"The SONGS Final Safety Analysis Report states in Section 2.5.1.1.3.4.2 that there are foults east of the South Coast Offshore Zone of Deformatton that are the types of foults that result from deformatton associated with folding and appear to be intraformational faults generated by the folding of the sediments. What type of faults are the intraformational faults?

Are they fold axis faults, bedding plane faults or some other type? What is the sense of motton on these foults (i.e., normal, reverse)?"

Response to Question 4:

The intraformationa) faults discussed in this section are those faults which are the result of flexure folding within the younger, competent material overlying the Monterey Formation. Thistypeoffold/ fault feature is common in mildly deformed terrain involving competent strata.

As noted by Fischer and Mills (1991), this type of deformation is a typical response of thick, younger Neogene sediments to right-lateral shear. According to Moore (1980), broad folding of the underlying Monterey Formation caused development of a series of anticlines and synclines in the overlying Plio-Pleistocene sediments. The faulting and buckling that occurred within these anticlinal /synclinal folds, confined to the unit overlying the Monterey Formation, resulted from squeezing of the beds of very incompetent and impermeable material which developed high pore pressure. Ehlig (1980) notes that the faults associated with the folds do not extend deep into the section, upward to the sea floor, or to the Pleistocene erosional unconformity. The length of these features is on the order of a few hundred meters.

According to Moore (1980), the intraformational faults are minor, confined l to the axes of the folds and do not display any well-developed sense of j displ acement. However, the high-resolution profiles suggest possible

extension across the crest of the fold and possible normal displacement on l l l

the flanks of the fold. There was no measurable sense of reverse / thrust

! displacement or a thickening of the section by incompetent or flow folding.

Question 5:

" Provide any assessment in your possession regarding the potential for blind thrust faults in the SONGS site region. Provide any assessment regarding the size of earthquakes on the faults, if they exist, and any -

estimates of the vibratory ground motion at the SONGS site from these -

events.

• Response to Question 5:

The source model used in the recent probabilistic seismic hazard assessment for SONGS (SONGS PSHA report) explicitly incorporated blind thrust fault sources in the site region. The recognition and  :

characterization of the seismic potential of active blind thrust faults in  !

the Los Angeles basin continues to be an ongoing and evolving topic of 1 research. The geometry, activity, and slip rates for these structures are l not well constrained (WGCEP,1995),and alternative models available in ,

1994 (e.g., Davis and others, 1989; Shaw, 1993) were incorporated into the l source model used in the SONGS PSHA. Given the distance of the recognized blind sources and the uncertainties in the geometries of these potential fault sources, the potertial blind thrust sources were generalized into two blind fault source zones, Los Angeles basin source zones A and B. The parameters used to model these blind fault sources are summarized in Table A-1, and the contribution to spectral acceleration at 10 Hz and 1 Hz are shown on Figures 6-4 and 6-9, respectively, of the SONGS PSHA report.

The Elysian Park thrust system as originally defined by Davis and others (1989) extends from Orange County in the southeast through downtown Los Angeles and westward beneath the Santa Monica Mountains along the Malibu coast to Point Mugu. Dolan and others (1995) conclude based on geomorphic analysis that this zone of contractional deformation actually comprises two distinct thrust fault systems, an east-west-trending thrust ramp beneath the Santa Monica Mountains that they refer to as the Santa Monica Mountains thrust fault, and a west-northwest-trending system (the Elysian Park ramp) that occupies the northeastern part of the Los Angeles basin.

They further subdivide the Elysian Park ramp into two segments, the Los Angeles segment extends from the Elysian Park Hills northwest of Los l Angeles through downtown and East Los Angeles, and the Puente Hills segment (referred to as the Whittier segment by Shaw and Suppe, 1996) that

, extends southeastward beneath the Puente Hills.

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The SONGS PSHA model, which was developed prior to publication of Dolan i and others (1995), also treats the Santa Monica thrust fault and the l Elysian Park thrust fault system as independent seismic sources. The l Santa Monica thrust lies at a distance of over 100 km from the SONGS site, and.thus was not included as a fault source. The Los Angeles basin source zone A included in the SONGS PSHA model incorporated a blind thrust fault l geometry comparable to that of the Los Angeles segment of the Elysian Park thrust as shown by Dolan and others (1995) and Shaw and Suppe (1996). The maximum magnitude probability distribution for the Los Angeles basin l source zone A (see Appendix B, SONGS PSHA report) incorporates maximum magnitude estimates up to M, 7.1. This magnitude distribution captures the magnitude estimates for single segment (M, 6.6) and multiple segment (M,6.9) ruptures as proposed by Dolan and others (1995) and Shaw and

Suppe (1996).

The Whittier (Puente Hills) segment of the Elysian Park thrust underlies the Whittier fault, a documented active strike-slip fault. Dolan and others (1995) postulate that the Whittier fault may represent partitioned strike-slip above the blind thrust fault zone, but the structural interaction of these fault systems is not well constrained by available l data. The cross section presented by Shaw and Suppe (1996) does not l extend far enough east to show the intersection of the Whittier fault with the Elysian Park ramp. Davis and others (1989) in their modeling of the Elysian Park thrust require the Whittier fault to be inactive. The SONGS

, PSHA model did not explicitly include the Whittier segment of the Elysian Park thrust, but did account for the possibility of. blind thrust events of up to M, 6.5 in this part of the Los Angeles basin in the characterization of the Central Los Angeles basin regional source zone (Figure A-2a, SONGS PSHA report). The Elysian Park thrust, including the Whittier segment as l modeled by Shaw and Suppe (1996), at its closest approach lies about l 70 km from the SONGS site. Given the proximity of other major active strike-slip faults to the SONGS site and their relative contribution to ,

hazard at the site (see Figure 6-6, SONGS PSHA report), the Elysian Park I thrust will not contribute significantly to the total seismic hazard at the site.

Los Angeles basin source zone B incorporated the possibility of a significant blind fault source in the western Los Angeles basin. When the ,

SONGS seismic source model was developed, a number of alternative l l

geometries and dips for blind faults in this region of the basin had been i proposed. The SONGS model incorporated two alternative geometries, a

northeast-dipping and a southwest-dipping ramp, to address these uncertainties. The low probability (0.2) of activity assigned to this l 3

source zone was based on the judgment of the likelihood that significant deformation in this region results from activity on buried thrust faults.

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Models that require an east-dipping ramp under the western part of the Los Angeles basin imply uplif t in the west basin that is not expressed geologically (D. Ponti, U. S. Geological Survey, personal communication, March 1994). On the basis of the geomorphic position of marine deposits in the Torrance and Long Beach plains, vertical tectonism during the past 600 ka in this area has been negligible (Ponti and Lajoie,1992). The Pleistocene uplift, evidenced by elevated marine terraces in the vicinity of the Newport-Inglewood fault (Lajoie and others, 1992) and the Palos Verdes anticlinal uplift, is consistent with models of strike-slip or oblique-slip along the Newport-Inglewood and Palos Verdes faults (WGCEP, 1995). Local uplif t of the Palos Verdes anticlinorium likely is caused by the dip-slip component of fault motion, which may occur as oblique slip in a restraining bed (Ward and Valensie,1994) along the principal strike-slip Palos Verdes fault system (Nardin and Henyey, 1978; McNeilan and others, 1996; Stephenson and others, 1995). The rate of uplift

( 0.710.2 m/kyr) expected beneath the anticlinorium based on the ramp geometry modeled by Shaw and Suppe (1996) is greater than the 0.3 to 0.4 m/kyrupliftratesreportedforthePalosVerdespeninsulabasedondated marine terraces (Bryant,1987; Ponti and Lajoie,1992; Muhs and others, 1992, and McNeilan and others, 1996). Shaw and Suppe (1996) suggest this discrepancy may be due to incomplete or incorrect fault geometries, errors intheircalculatedslipratefortheComptonthrust,and/orthe assumption of rigid-block translation above the ramp which does not account for isostatic compensation or relaxation of the crust.

The northeast-dipping blind fault incorporated in the Los Angeles basin source zone B, incorporates the geometry of the Compton thrust ramp as modeled by Shaw and Suppe (1996). Both models allew for an approximately 25 degrees northeast-dipping ramp that at their closest distance are 40 to 45 km from the SONGS site. The maximum magnitude probability distribution for the Los Angeles basin source zone B (see Appendix B, SONGS PSHA report) ranges from M,6.3 to 7.4. Maximum magnitude estimates of M, 7.3 (Dolan and others,1995) and Shaw and Suppe (1996) fall within this range.

In summary, the characterization of blind thrust fault sources for the l SONGS PSHA explicitly incorporated all published information regarding blind thrusts at the time of the analysis. As noted above, the additional information that has been published since the SONGS PSHA is subsumed within the range of source characteristics included in the analysis. All

of these analyses show a negligible contribution to site hazard due to the proximity of several nearby strike-slip faults. Therefore, it is concluded that continued study of Los Angeles basin blind thrust faults will not lead to significant changes to the SONGS site hazard.

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RE'FERENCES Argus, D. F., and Gordon, R. G., 1988, Sierra Nevada-North America motion from VLBI and paleomagnetic data--implications for the kinematics of the Basin and

' Range, Colorado Plateau, and California Coast Ranges: EOS Transactions, American Geophysical Union, v. 69, p. 1418.

Barrie, D., Totnall, T., and Gath, E.,1992, Neotectonic uplif t and ages of Pleistocene marine terraces, San Joaquin Hills, Orange County, California, in Heath, E. G., and Lewis, W. L., (eds.), The Regressive Pleistocene Shoreline Coastal Southern California: South Coast Geological Society, Inc., 1992 Annual field Trip Guide Book No. 20, p.115-122.

Bryant, M. E.,1987, Emergent marine terraces and Quaternary tectonics, Palos Verdes Peninsula, California, in Fischer, P. J., (ed.), Geology of the Palos Verdes Peninsula and San Pedro Bay: Pacific Section Society of Economic Paleontologists and Mineralogists, Guidebook, v. 55, p. 63-78.

Crouch, J. K., and Bachman, S. B.,1989, Exploration potential of offshore Newport-Inglewood fault zone (abs.): American Association of Petroleum Geologist Bulletin, v. 73, p. 536.

Crouch, J. K., and Suppe, J., 1993, Late Cenozoic tectonic evolution of the Los Angeles basin and inner California borderland: a model for core complex-like crustal extension: Geological Society of America Bulletin, v.105, p.1415-1434.

Davis, T. L., Namson, J., and Yerkes, R. F., 1989, A cross section of the Los Angeles area: seismically active fold and thrust belt, the 1987 Whittier Narrows earthquake, and earthquake hazard: Journal of Geophysical Research, v.

94, p. 9644-9664.

Dolan, J. F. , Sieh, K. , Rockwell, T. K. , Yeats, R. S. , Shaw, J. , Suppe, J. ,

Huf tile, G. J., and Gath, E. M.,1995, Prospects for lar,ger or more frequent earthquakes in the Los Angeles Metropolitan region: Science, v. 267, p. 199-205.

Ehlig, P., 1980. FSAR Appendix 2.51, Edited Transcript of Dr. P. Ehlig discussion of geologic setting, SONGS area, September 23, 1980.

Feigl, K. L., Agnew, D. C., Bock, Y., Dong, D., Donnellan, A., Hager, B. H.,

l Herring, T. A. , Jackson, D. D. , Jordan, T. H. , King, R. W. , Larsen, S. , Larson, l K. M., Murray, M. H., Shen, Z., and Webb, F. H., 1993, Space geodetic measurement of crustal deformation in central and southern California, 1984 - 1992: Journal of Geophysical Research, v. 98, no. B12, p. 21,677-21,712.

l

. l Fischer, P. J., and Mills, G. I., 1991, The offshore Newport-Inglewood-Rose I Canyon fault zone, California: Structure, segmentation and tectonics, in

! Abbott, P. L., and Elliott, W. J., (ed.), Environmental Perils, The San Diego Region: San Diego Association of Geologists, San Diego, California, p.17-36.

l l Kanamori, H., Thio, H. K., Dreyer, D., Hauksson, E., and Heaton, T., 1992, i l Initial investigation of the Landers, California, earthquake of 28 June 1992 l using TERRAscope: Geophysical Research Letters, v. 19, no. 22, p. 2267-2270.

l l l Lajoie, K. R. , Ponti, D. J. , Powell, C. L. , II, Mathieson, S. A. , and Sarna-l Wojcicki, A. M. ,1992, Emergent marine strandlines and associated sediments, l coastal California; a record of Quaternary sea-level fluctuations, vertical

! tectonic movements, climatic changes, and coastal processes, in Heath, E. G.,

and Lewis, W. L., (eds.), The Regressive Pleistocene Shoreline Coastal Southern l California: South Coast Geological Society, Inc.,1992 Annual field Trip Guide 1 Book No. 20, p.81-104.

l l Larson, r.. M.,1993, Application of the global positioning system to crustal

! deformation measurements, 3, result from the southern California borderlands: l l Journal of Geophysical Research, v. 98, no. B12, p. 21,727-21,740.

I Lettis, W. R., and Hanson, K. L., 1991, Crustal strain partitioning:

implications for seismic-hazard assessment in western California: l Geology, v. 19, no. 559-562.

McNeilan, t. W., Rockwell, T. K., and Resnick, G. S., in press 1996, Sense and rate of Holocene slip, Palo Verdes fault, southern California: Journal of Geophysical Research, Mills, G., and Fischer, P. J., 1991, Thrusting associated with the offshore Newport-Inglexood-Rose Canyon zone, California (abs.): Geological Society of America Abstracts with Programs, v. 23, no. 5, p. A198.

Moore, D. 1980. FSAR Appendix 2.51, Edited Transcript of Dr. D. Moore discussion of offshore recent seismic reflection profiles, Southern California Edison Co., September 23, 1980.

Muhs, D. R. , Rockwell, T. K. , and Kennedy, G. L. ,1992, Late Quaternary uplif t i rates of marine terraces on the Pacific Coast of North America, southern Oregon

! to Baja California Sur: QuaternaryInternational,v.15/16,p.121-133.

Nardin, T. R., and Henyey, T. L.,1978, Pliocene-Pleistocene diastophism of Santa Monica and San Pedro shelves, California continental borderland: American j Association of Petroleum Geologists, v. 62, p. 247-272.

i

l -

l .

l .

l Ponti, D. J., and Lajoie, K. R.,1992, Chronostratigraphic implications for l tectonic deformation of Palos Verdes and Signal Hills, Los Angeles Basin, California, in Heath, E. G., and Lewis, W. L., (eds.), The Regressive Pleistocene Shoreline Coastal Southern California: South Coast Geological l Society, Inc.,1992 Annual field Trip Guide Book No. 20, p.157-160.

" Seismic Hazard at San Onofre Nuclear Generating Station, Final Report,"

Geomatrix Consultants, Inc., Risk Engineering, Inc., and Woodward-Clyde Consultants, dated August 25, 1995.

l Shaw, J. H.,1993, Active blind-thrust faulting and strike-slip fault-bend folding in California: unpublished Ph.D. dissertation, Princeton University, Princeton, New Jersey, 216 p.

Shaw, J. H., and Suppe, J.,1996, Earthquake hazards of active blind-thrust faults under the central Los Angeles basin, California: Journal of Geophysical Research, v. 101, no. B4, p. 8623-8642.

l l Sieh, K., Jones, L., Hauksson, E., Hudnut, K., Eberhart-Phillips, D., Heaton, l T. , Hough, S. , Hutton, K. , Kanamori, H. , Lilje, A. , Lindvall , S. , McGill, S. F. ,

i Mori, J., Rubin, C., Spotila, J. A., Stock, J., Thio, H.-X, Treiman, J.,

Wernicke, B., and Zachariasen, J., 1993, Near-field investigations of the Landers earthquake sequence, April to July 1992: Science, v. 260, p. 171-176.

Stein, R. S., and Yeats, R. S., 1989, Hidden earthquakes: Scientific American,

v. 260, no. 6, p. 48-57.

Stephenson, W. J. , Rockwell, T. K. , Odum, J. K. , Shedlock, K. M. , and Okaya, D.

A.,1995, Seismic reflection and geomorphic characterization of the onshore Palos Verdes fault zone, Los Angeles, California: Bulletin of the Seismological Society of America, v. 85, no. 3, p. 943-950.

Unruh, J. R., Lettis, W. R., and Sowers, J. M., 1994, Kinematic interpretation of the 1992 Landers Earthquake: Bulletin of the Seismological Society of America, v. 84, no. 3, p. 537 -546.

l Ward, S. N., and Valensie, G.,1994, The Palos Verdes terraces, California:

Bathtub rings from a buried reverse fault: Journal of Geophysical Research, v.

j 99, p. 4485-4494.

Weldon, R., and Humphreys, E.,1986, A kinematic model of southern California:

Tectonics, v. 5, p. 33-48.

4 e

1 i .

Wells, D. L., and Coppersmith, K. J.,1994, New empirical relationships among magnitude, rupture length, rupture area, and surface displacement: Bulletin of l the Seismological Society of America, v. 84, p. 974-1002, i

! Working Group on California Earthquake Probabilities (WGCEP), 1995, Seismic l hazards in southern California; probable earthquakes, 1994 to 2024: Bulletin of

! the Seismological Society of America, v. 85, no. 2, p. 379-439.

Zoback, M. L., Anderson, R. E., and Thompson, G. A., 1981, Cenozoic evolution of

the state of stress and style of tectonism in western United States

l Philosophical Transactions of the Royal Society of London, Ser. A., v. 300, p.

407-434.

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