ML20126D519

Summary of Div of Reactor Licensing 720517 Meeting in Menlo Park,Ca Re Seismicity

ML20126D519
Person / Time
Site:	San Onofre
Issue date:	05/17/1972
From:	Advisory Committee on Reactor Safeguards
To:	Advisory Committee on Reactor Safeguards
References
ACRS-SM-0174, ACRS-SM-174, NUDOCS 8005020158
Download: ML20126D519 (15)

Text

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,O' l 8 005020 IN i

SUMMARY

I DL MEETING ON SAN ONOFRE 2 & 3_

Menlo Park. California May'17. 1972 4

Discussions on the geology-seismicity of t!.e San Onofre site were held at the.USGS offices in Menlo Park, California, on May 17, 1972. The draft USGS report was reviewed. Participants in the meeting included representatives of USGS, NOAA, Regulatory Staff, 4

and Drs. Page, Wilson and Mr. Steinbrugge, ACRS consultants. High-lights of the meeting are as follows:

1

1. Regulatory has set a June 1, 1972 deadline for reach-ing a conclusion which can be communicated to the g

applicant.

i A 2. The USGS has raised new questions regarding the in-j

' activity of the Cristianitos Fault.

t 3. The offshore zone of deformation is felt to be more or less continuous from the Newport-Inglewood Zone to the Rose Canyon Fault.

4. The one-chance-in-a-million earthquake is assumed by NOAA to be a Mag. 7 3/4 - S on this zone of defor-mation. .

5. This Safe Shutdown Earthquake (SSE) will be assumed to result in 2/3g - 3/4g at the site; the larger value will be recommended if the plant foundation ,

f conditions aren't good.

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' . J I, DL MEETING ON SAN ONOFRE 2 6 _.3_

MENLO PARK. CALIFORNIA May 17. 1972 g

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" At tend ee s ACRS NOAA Reaulatory 1]1G_S.

f J. Devine J. Wilson t , H. Coulter B. Page i

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H. Denton F. Houser K. Steinbrugge W. Gammill F. McKeown (part time)

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A. Cardone R. Yerkes J. Hard l F. Castle

' J. Ziony H. Wagner J. Vetter J

Intr Muetion - Denton and Cardone-- 1.

y The /.EC's coal is to reach a decision on this project by June j The purpose of the meeting is to review the draft GS report. j 1 (Copy attached) - McKeown_

Summary of Draft CS Report the recent k The of f shore zone of deformation is more or less continuous,The Cristianitos l data does not disprove this. Some warping of the terrace fault is not exposed in its entire width. Horizons B&C are 3

deposits is present, suggesting tectonic instability.There is a lack of data bet 1

somewhat unreliable. (SCO). Similarly, at the fault cannot be 1 (N-I) zone and the South Coast Of fshore fault j south precluded.

end of the SCO, a connection with the Rose CanyonAlso, i j Therefore, the whole zone should be considered potentially act ve, Apparently zone is an en-echelon type zone.However, there is no Dr. Wilson asked if the fault g

y there is no evidence of this in the of fshore work.

sea floor evidence of a San Andreas type either.

6 1

Cristianitos Faule h McKeown The There is no obvious displacement of the terrace deposits noted that the fault i lack of information is on the. southeast side.

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. 2 the strike of the Cristianitos is about N60 E instead of Also, the N10 the W I strike of the main fault. (This is new information - JEH) is 70 SW. The j dip of the main trace, about 12 milgs from Zionythe coast, felt this data may dip of the seacoast strand is 60-70 NW.the seacoast ' exposure may just be a stran 4 indicate that

., Cristianitos.

At 15 miles north on the fault, about 870' of stratigraph'ic (vertical) j movement is evident.

P. Morton (State of California) reports (in an unissued report) that 2 miles south of the trench at Plana Trabuco, This is on f

displacement of the terrace-bedrock interface can be seen.(This also is new informatio i a different trace of the Cristianitos.

Ziony noted that he, Baltz, and Morton inspected this area about 1 years ago and saw, along the fault, evidence of what may be sag ponds and landsliding. Ziony also reported a ground water cascade near the Cristianitos at San Onofre Creek. Page noted that this is not neces-I sarily evidence of recency of movement.

Page suggested that the elevations of the terrace materials on both I the seacoast could give a check on sides of the landslide area at 8 any vertical movement of these terrace materials. McKeown' felt that the precision of such measurements might not be adequate to so prove.

j Apparently there is no evidence of surf ace f aulting anywhere along 1

the Cristianitos.

I 1

All seemed to agree that more trenching is needed at Morton's location of possible terrace displacement.

. Southern Coast Offshore Fault .

Wagner reviewed his interpretation of the offshore data including sources which were not available to the applicant. This showed, for example, surface faulting in the area where the applicant indicates the Rose Canyon turns back toward the shore.

i Wagner also noted that the applicant's " acoustic basement" is based on 6000 fps material in the " offshore high" rather This than casts the "more than a question 10,000 fps" material stated by the applicant. The offshore high also on the interpretation of the " offshore high."

appears to be of f set from the onshore extension of it (the San Joaquin Hills) by right slip. .

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f Wagner commented that the offshore pattern of faults is similar to that in the Newport-Inglewood zone ; that is, a pattern of en-echelon e faults. Page characterized the SCO fault as a throughgoing zone of deformations though there may not be a thrcughgoing place of displace-

. ment except at great depth. Wilson tended to agree with Page. Page l also noted that there are large differences between San Andreas and Newport-Inglewood such as rates of displacement and f requency of move-

{ ment.

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• Wilson asked about evidence of displacement. Castle reported about a I mile of right lateral motion with some vertical slip in Quaternary The CS representatives felt there was possible evidence of recent I time.

j moveme nt in the Newport-Inglewood anea and that the burden of proof would be on those thinking otherwise. Movement along this zone seems to j be principally lateral.

Regarding the Magnitude of quake to be expected on this zone, Coulter pointed out that a " super-dooper AEC-Interior panel" put a Magnitude 8 l quake on the Newport-Inglewood zone (talking of the Bolsa report).

h Other Discussions N Evidence from af tershocks indicates that the Newport-Inglewood moved over ,

l 26 km during the 1933 Long Beach. Wilson added that the Magnitude (energy) l of a quake, in some models, is proportional to the stress drop and to I the cube of the fault length. In the western United States, it appears that the longest break length is +70km, per Wilson. Page commented that

' either the frequency or amount of slip / event is much smaller on N-I than on the San Andreas. Wilson added comments from their studies on the relationship between fault break length and Magnitude. Page didn' t see how the fault length concept could be used. Devine commented that they

. can' t use Brune's theory to come up with the once-in-a-million years

' earthquake that they've been asked for by the ACRS. Coulter later com-4 mented about the 10-6 that "Dr. Okrent keeps hitting us with" in the i sense that it's hard to see the difference in probability of major 1 earthquakes on the San Andreas as compared to the Newport-Inglewo'od.

l Page added that there appears to be very little evidence of high

- accelerations (~ 1g) once one gets just a few kilometers from the l rupture zone. San Fernando was cited as an example of this observa-tion.

I

' There was a considerable philosophical discussion on the subjects of fault lengths and Magnitude, changes in ground frequency w/ distance, amplitude vs. frequency for different evento, Magnitude vs. recurrence interval, etc.

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l Wilson felt that the business would, in the next 10 years, get away I from the Magnitude-vs.-recurrence interval way of doing things and toward the stress level approach, which works with the total energy stored in the rock. At this point, Denton added that Newmark's op. inion j

is that 0.5g is too little and that 0.75g is too much. Devine com-t nented that the spectra are important in this conclusion. Wilson noted that the spectra, which come out of Brune's theory are close to those l

used by the engineers.

1 Seismicity I Devine stated that the seismic picture has not changed significantly -

- with the new geologic work. NOAA is leaning toward 2/3 - 3/4g. The higher value would be used if' foundation conditions aren't good. This NOAA quake is Magnitude 7 3/4 - 8, Int. XI; the same as it was a year i

ago. However, Devine stated that NOAA may not be doing its job if a standard response spectrum is to be applied to this value. Wilson re-l peated that Brune's spectra look very much like those used by Newmark.

f Steinbrugge noted that the g value is only part of the game in that dif-I ferent amplification f actors and design methods can be applied to this.

The overall result may or may not be conservative as a conscquence.

He felt that a new approach, such as time-history, may be warranted.

• Wilson suggested that NOAA compute spectra for the smallest quake which

' might be accepted and for the largest, and that these spectra be coa-pared to see how tne g vs. frequency stack up for the two events. A magnitude 8 with a 25 km fault length is not possible in So. Cali-fornia because the stress level is not high enough, according to Wilson.

Page agreed that more than one quake should be considered on the zone of deformation for essentially the same reason given by Wilson.

According to Devine, duration of shaking may be mentioned in the NOAA report whereas this has not been included in previous ones.

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Attachment:

Draft CS Report 9

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GXi DIic.GU COUi'fY, Cl.LII'04!I.T l 1&NIEU Of ICILVI.hT GEOLO3Y i l

The onchore and offshore coolo.;1c data for the proposed Sc.n Onofre (Preliminary ,

a j nucicar cencrator planto--unita 2 and 3--precented in the PSAR . l Cafety Evaluation deport), its amendmento, and its appendices have been l with ,

I The evaluation in particular has been made I revicued and evaluated.

the most appropriato ,

i re:,pect to the significance of the data for postulatin3

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' fault model to consider as a cource of the Cafe Shutdown I:arthquehe may ef e '

t'he cite. Islco, included in the evaluation is consideration of possible faults vithin or near the site area. .

This review cupplements the prelimincry review transmitted to Director i 12, 1971 by the Chief Geolc31t s, of Divicion o? Reactor Standards, AEC on July

\

U. S. Geological Survey V. E. McKelvey, in the sense that many explicit detai tl The present review does j

in the preliminary review are not repeated here.

summarize the pertinent data from all amend:nento and treats in appropriate detail the large amount of offshore geophysical data acquired since the

' preliminary review.

In addition to the d'ata in the PSAR, appropriato literature uno reviewed t

1 and the knou. ledge und interpretations of geolo3 cta and geophysictets mos

! faniliar vith the coology of the San Onofre area van Lu11 cited and used.

A field incpcetion of the cite and of outcrops cut by the nearby Cri:tienit.oc fault zone vaa r,cde in company with the apalle it's 3cologists i 1

on bbru3t'y O,1972.

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• The principal objccriv(n of this revicw orc (1) to oncesa the applicability of the fcult I.iodel uccd by the applicant for establishin.3 the :h.Cc Chutdoun Karthquake, (2) to ascertain whether or not the uppliemit lu :. entabliched that no act1ve feults of any sisc occur uithin the crca; '

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$ data to establich the tectonic stability of the area.

I With regard to the first problem, the USGS stated in the preliminary review of July 12, 1971 that "On the basis of present data there appears

) to be a linear zone of deformation in Tertiary and Cnaternary rocks and i

4 sediments that extends southeastverd fra:n Santa Monica to at least the Mexicon border." Reference is al::o made to the review of the geology of the site of Gon Onofre Nuclear Generating Station il transmitted by the Director, U. S. Geological Survey to IEC Director of Regulations dated October 11, 1966, in which it was stated: "The submarine extension of Ij N.m l the Ucwport Inglewood zone, as mapped by Energy (1960 fig. 68) also trends northwestward and is about 7 miles southwest of the site." The additional I geophysical data obtained by Ucstern Geophysica' Company tends to 5

corroborate this statementidespite the applicant!s claims to the. contrary. -:

1 The zone of deformation ic at least 240 lun in length, and is approximately 1

5 miles offshore in the vicinity of' the plant site.

3 The avuilable data relevant to the second probleu does not show evidence VG . (.h d . ., , c , b- Nie. ' ..

of any fcults that cut thc% rocks, underlying the planned reactor facilitics.

With regard to the third probica apparent varping of the terrece on which the site iu located .inc'icates that the sito ucs or is in an area that has been or D

is tectonically unstable, g l N8t y

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The G:,n OaoJre rr. cec / .;ite are:-  !'

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b dded, poorly cemented thita a una 3 in adjactnt to e bcuch und on thic- e #

l f the Plio-Pleistocenc i .~.und.ctone and ninor thin beda of aravel and ciltatonel>orilling near the

'the bcdc dip 10-19 0 to tLe northucat.

l han i'ateo Formation. .

f. cite shouc the formation to bc riore than 900 feet thic~.-:; napping indicutes I

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The Sun Untco fornation the "ornation may be approzits.ately 2,000 feet thick.

in unconforucbly overlain by narine terrace deposit., and unconfon:.cbly underin i by ciltctone, candstone, tuff, and dictomite of the Capictrano Formation of l

i late Miocene uce, Ocmples collected by USGS from correlctive terrace depocits i

70,000-130,000 years

' about 41/2 milec northucst of the site were dated at DP necording to the applicant (Anendment 1, p. 2. 9-3b).

j The Cristianitos fault, a Generally northerly trending fault, obout 4

three-fourths of a mile southeast of the cite, is the major structural i Exposure of parts of this fault at the coast and at the feature nearest the site.

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t Plano Trabuco cxcavationc nade by the applicant chcr.tc that the overlyin; As the fault zone is ceveral terrace deposits are not offset by the fault.

hundred feet vide, however, and its full width ic not c:: posed anywhere, comt question rc alns about the n;;e of the most recent movementn on the fault.

Whether or not diapinceuent of terrace deposits hun occurred on the 1

Cristianitos fault, evidence of varpin:; of these deposits both locally end (1971). Thef .

' re ,ionally in co;J,cated by vork of 3. J. Szabo and J. G. Vc6 der I i

show deformation 01 the first terrace between Lnr,;una Beach and Can Cle:r.cnte.

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The applicant correctly accu.acs (1.nenGr.ent 1, p. 2 9-3b nue amnda:nt 6, Lh:..t the terrace depocita cycrlying the Crictianitoc Invit et the corct tre Uarrin.; of the terrace .c.vut

," :cociated with the arr.e terraec as cited abovc.

have occurrcd, houever, to acc mat for appcyti: i.tcly 'j5 Ject difforcace in chor 4

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. r.n;3.< : clevution >? the terrace L<_t. rec:. i InLcmittent, if not continuous loen1 tectmic uu r:- norLhvect of the site.

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inntrbility, therc ;' orc., .my be oscu.:.c0 during the last 10J,000 _ 30,0JJ .rects. t ,

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re ncet ll i The recional acttins of the Gn:. Gnofre site ic i:mortant vitti

. how an r.uth- f to the locction of 2cJor active fault zones cnd to eva'iuctin3 '

I Accordin; to the applicant riunke in one of the zonco may effect the site.

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(/w. cud.aent 6, p. 2.)-7) the "plcat site is approximately 60 mile s from the

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i Son Andreac fcult, h5 nilca from. the San Jacinto fault, 23 miles from the l 1 j Uhitticr-Elsinore fcult and 10 miles fron the coutheast terminus of theI 3

Newport-En31cuood zone." The proximity of the Newport-Inglewood zone and its alignment uith the South Coast (SCO) OCfshore fault, which has been j

i reco;nited to variouc decrecs in most scismic profile data (Ismendment 11, i Initial oppendix 2R-9) in the major structural problem to be considered.

I offchore shallo'.i penetration sparker data indicated diccontinuous faulting end 1 The htest investicationc used a deep penntrction j folding in the GC0 fault zone.

Thece investigationc incorporated the interpretation seicaic reflection incthod.

of 1,000 milca of deep reflection data, h50 milec of nuJnetic-profilin; date, and in adriition, the appliennte find their cor.cultenta i

'( cein.t1 e refraction lines, i

revicued publiched cravity data, unpubliched proprictcry data obtained by

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othcrs, and approxinctely 275 n.iles of United States Geolo;ical Survey (UG35 Tbt.

? cparker reflection profiling (haendent 11, appendix 2E, p. t..2E-2).

• I npp?icant's principal conclucionc ec the result of thic work arc,ac follorc 1

(&inndment II, appendix 2E, p. 23-17):

I A. Dicplacement. on the n: ult, even at the deepest level of invemti3ntio::, dico out to ti e nortln.est near Lastne. Deach and to the uoutheast near Occancide.

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1 In blocenc-c;;e rocl'x of :Irizon h, the .Javlt shows much i  :

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less dicpluccucut than in older roche, cud its trace appears as a series of short, discontinuous breuhn.

t C. 'fhe fcult is not connected with other faults at its j cxtreniticc.

9 D. Investigation with side-scan sonar (refer to appendix 2A,

' and fic;ure 8), high-resolution profiling (refer to appendix i ?

i I 2C), and Ucstern's fatho. toter data as seen in figure 2E 4 A show no evidence of tectonic displacement on this fault since I f

the cea floor vac croded scme 18,000 years ago during an earlier j  !

i glacial oce (appendix 2A). No evidence has been found in these  !

invectications of curface rupture or offset of ccctnorphic features, l'

4 or to suG5est post-liiocene or Quaternary activity on the fault.

E. , There is no macroseismicity associated with the fault (refer to.

8 appendix 2A, figure 3). t I b . , L . .. . il : Is ,, J.J . C ')

,Uased on the foredoing, it is considered that significant activity has not i

.l This fault occurred in the South Coant Offshore Fault in post-Miocene time. .

l i.e.,

j munt not have concrated a large certhquake since Upper Rioccnc tine; millionn of years ago." (Appendix 23, p. 2E-17 and 2E-18). .

I The U. S. Geological Survey does not accept these conclusions for .

1

the principal reasons are outlined below.

Much of the interpretation upon which the conclusions are based in l An degndent, upon the validity of the offshore structure contour maps.

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:planation of the precision of deter, tinction of the D. structural I .

! hociv.u.1 is luching. Leact relinble is that part of the Hori ,on D map couth '

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i 0:l the Unn Clem.cnte core holc, but for stratigraphic reasons.

if uN 1 leant, noswaea Itorir.on D is in niocene rocha,'no 1.*iocenc rocks are known onahoro hetueen Oceanside nna Den Dic:3o, and their precence offshore ennnot  ?

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! Contcurs for unt pcrt of the IIorizon L 17. : l t.

... ;tely be dcwn:.trcted. ibic .ceen m; c.jreccut a anrier straticraphically lo'..*er thnn Up, cr ..iocene, po.n Thir, co:.ccA nicht cecount for the apparent continuity s,it.in the Eocc.o. .

l Occ Canyon fcult, in contract with the '

on thc. !!orizou 3 'v.'.p of the offshore 1:

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' cryo. cd diccontinuous ncture of the South Cocct Offshore fcu f'

!inother indication of the unreliability of \-

c.quivnlent stretisenphic level. rofiles and on l

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the D horinen ic that the Cristicnitoc fcult is shown by the apar er p 14any of the hi:;her resolution i

on the C horizon map but not en the B hori2.on map. 1 knowledged j scionic profilcc show nore faulting and more recent faulting than ac i

Furthemore, ',lestern Geophysical Company ctates by the applicants repo"ts. i acroca that no continuous reflecting horizon is present in the Idiocene cect on Also, only faulting defined l the entire area (Amenchent 11, appendix A-1, p.29).

displacements by vertical offcets is considered, without assurance that no lateral

'. Interpretations of have taken place on some, o'ghterwice, unidentified . . : . faults. Horizon 'S'

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' the existence of A faultc an!t the o;csN of fdults on the basis of the i,

sr.cp, therefore, are not concidered complete nor accurate, According to Ucstern Geophysical Company llorizon C is also unreliable.

". . .llorizon C conctitutcc the bacc(Acen/Lnentkl, of r.ediments appendi:: /L-1, with forma l

velocitics lecc than 12,000 fcct per cecond,..." i

p. 26).

An an exm::ple of the unreliability, USGS analynia of velocity f data in the " offshore high" indicates a rxximun velocity there of about o,2 per cecond.

Connection.: between the lieuport-Ir21evood conc, South Coast Offsho i

f:u 16, and the l'oce Canyon fault cannot be precluded even if the Hor The possible junction or the Ecvport-H and C napa vere to be nuctuat.d corrcet.

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no 0;.La et the liorizon C level and ic ..:anca on ti.c liorizon b :mp c na ".o challou recolutici or "rocsible ciudlo.7 fault."

The conertion of the applic: nts that the ?.ose Canyon fault turnt i l

True, there arc o. number of i.

I inland near Oceancide cannot be cupported.

j the coast botvcen La Jolla cnd

' north- cnd northcuct-ctrikin; fcultc alon3 4

i Occenoide, but thecc are lapped by Fleictocene Lindavicta For:r.ation; in conL act, the onshore Boce Canyon fcult is characterized by verticci A

i scperations of the Lindavicta Formation greater than 200 fect.

connection betueen the offshore Rose Canyon and the South Coast Offchore This is indicated fcult is probable in the area shown es "possible intrusive,"

t on an extension of the Rose

,on USGS profiles that show sea floor displace.T.en Canyon fcult to and beyond the alleged intrusives.

i Termination of the Neuport-Ir.;1cuood zone by the San Joaquin Hills offchore structural high, as inferred by the applicant (M.mendment 11, tl appendix 2E, p. 2E-18) is not consistent with the geolo2y of the landward cxtension of the high. The applicant's interpretation in lcrcely based on v

high, what. he believec ic en apparent thin onlap of upper Miocene rocho on the Actually which su3ccata the high has been stable sinco middic idiocene t h,c.

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i the folding of the onchore continuation (applicent's ctructural correlation of the high-Gan Joaquin anticline--is kno;tn to be late Pliocene-late

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i No evidence is precented to demonctretc thet the n;c

( Pleictocene in use, f t of the rocks and the age of deformation in the offshore high is any dif ercu then the cachorn (.bendncnt32, -!tl, p.--hFyr #The -South-Coact ~ Of Psho nppro- rinLely h0 miles in-len3 th_.

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• The,, contrasts in tectonic style between cae Los Angeles basin an '

• 11, appendix E, p. 2E-16)

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the Peninsular Range Prevince (Amendment .

i Probably the most prominent structural are not ' clearly defensible.,.

feature 5 on figure 9 are the northwest-trending faults, subparallel to

' This zone apparently l and aligned with the Newport-Inglewood zone.

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has a very prominent offshore counterpart in the South Coast offshore i

fault.

Comparison of 'section L-M with section C-D clearly'shows j

s prominent similarities in structure between the basin and province.

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According to Western Geophysical Company interpretations "The t

South Coast Offsbere fault, approximately 40' miles in length, was active (Amendment 11, 1 af ter the Offshore San Joaquin structure was formed."

appendix A-1, p. 41). As the onshore extension of this structure is known to be late Pliocene-late Pleistocene in age, even the deeper

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parts of the SCO fault observed on the aquapulse reflection profiles

/ The applicant has not demonstrated con-1 c:ust be post-Pleistocene.

a clusively whether or not Holocene or later movement can be positively I

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F

. Mu c, such ocean bottom evidence is not f

1 identified on this faulg'het A 1 necessarily . germane to postulating that it is an active zone. The I I on it is likely to be a function of the mode evidence of movement '

t the I and depth of deformation. It is reasonable to assume that i

f l deformation has been similar to that which LM6 has occurred in the .

i the Board of Review Cc.va

. Newport.Inglewon (fault zone., As pointed out t.- ,

, m. ,. er A -4.gm% "..;)LT17Ycri -A_ yn.ttbE~r of the fault co= plex is known to cut strata youn[

~

than late Pleistocene . and (2) no surface-ground displacement is

• i 4

' known to have accompanied historic earthquakes associated with the f

zone." (Amendment 6, appendix 2C, p. 13).

1 The lack of macroscismicity is not necessarily an indication JJLy 94e It is well known thht many I> that the SCO fault system is3inac.tive. . mq x y.A&.U;,

. S4 % aw pan.s-j major active fault zones,$w-e* amp-h@ the San Andreasj a.. ,

y -wit.$litticorno,scismicity.,

x4-j The data presented by the app 1'icant lead to the conclusion that i

the Newport-Inglewood zone of folds and faults', the South coact .

Offshore fault, and the Rose Canyon fault zone cannot be disassociated.

Instead, an extensive, linear zone of deformation, at least 240 km 1

i long, extending from the Santa Monica Mountains to at 1 cast Baja, This was i

California, seems well established by the present evidence. .

alw the tentative assessment offered by E. H. Baltz in the preliminary

. -irk transmitted on July 2, 1971, by [' :.- MoHe4ved Chief Geologist,

~

draft, i This assessment to E. G. Case, Director, Divisfon Reactor Standards.

l Io 4 %'Lt y k l..z a.C I l is confirmed by the new information, and [shems--applicab4encil,',}

[6cpec-ially..with re gard- t.o. i nadequac'ymof fcu4t--deter:ainat-i-cr ir r ne.ar.

.h .sen.fb>ow. -R -t:r- qtrocedir-f ol-lowg o [

-_ g yr

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: ' ; .2 ~ c q

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O

' "h southeast-trending offshore extension of the Newport-Inglewood "f ault" or zone has been mapped in previously 1 published reports as passing offshore of San Onofre and '

extending to positions shown, variously, as near La Jolla M. L. Hill, 1971, and south of San Diego. (For example see:

fig. 1; King, 1968; Allen and others, 1965, pl. 1; and Emery, 1960, fig. 68.) The offshore geophysical data l 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 i uncertaintics owing to gaps in the data between Encinitas

, F -~ -.~ g and La Jo l la . "

d. m.t A6n-4-k.a 'R. 1 j Et i.,c'iSformation the E3 e.ufee 4+ z.. -one has gone on intermittently or Lw\' M Avv Lww4.- %t

)

)

continuously sinec at 1 cast middle Miocen)e and Ger+-ts] no eviden As

' presented to show that the stress system is inactive or altered.

j a number of earthquakes have occurred near the north end of this j

zone in historic time (the largest is the 1933 Long Beach M 6.3 j s&owo earthquake) and the south endifaBevidence of movement in Quaternary time, the whole zone must be. considered potentic.11y active and a

) ' as. .

capabic of an carthquake whose magnitudc[ma]be commensurate with ci- % K $.,, c.e 4 the length of the zone; c%d. wb mv.-d 4 1

t 6 5 ,.J A k &t g& WM LgW .w+t~ph .

. . ,~ik u .. w ..:( e sb u. h d " P d  %

mu . . .:.t m.u, ,c 4e ,orceaa paA.g A t M e .-

' > a .t. u i,eJ. o A . . > e ts a.. u , cn4mm  %%~cu c .w.y g.L w.,,.;.w..a ~ _ u , - ._

i

) k -;/l:-ce j ct t.v-6 rt( .% 7-L. C Mr.

!: Sh u. - c.ce q s s.. L,. u cU.oc A h _v _ o.__wh.y .%. w U

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