ML20118D337
| ML20118D337 | |
| Person / Time | |
|---|---|
| Site: | 05000214 |
| Issue date: | 06/04/1964 |
| From: | COMMERCE, DEPT. OF |
| To: | |
| Shared Package | |
| ML093631134 | List:
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| References | |
| NUDOCS 9210120123 | |
| Download: ML20118D337 (15) | |
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REPORT ON THE SEISMICITY 3F THE t
MALIBU, CALIFORNIA A~.EA l
l At the request of the Divisinn of Licensing and Regula-tion of the Atomic Energy Commission, the 5eismology Division of the Coast and Geodetic Survey has prepared a report on the seismicity of the Malibu, California area.
In the report the Survey has reviewed and evaluated the seis11 city information
(
presented by the Department of Water and F:wer of the City of l
l Los Angeles, et al., in their application for a construction pecmit arid a license, particularly Appendiz II, "on the Seis-micity of Malibu."
In addition, the Survey has independently determined the seismicity factors and has estimated the maxi-mum ground motions to be associated wi*h them.
The site is located in Corral Canyon Ebout 30 miles l
northwest of the center of the City of Los Angeles.
The ac-tive faults in the area are the San Andreas at distance 40 miles and the minor-Santa Ynez-and Inglewo:d faults at 20 to l
30 miles.
The Malibu fault which is cited in paragraph 2.4 I
of the Geology report as being inactive runs quite close to the site.
9210120123 920520 PDR ORG NRCHIST PDR Q _ }.r
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In the reference report, the Survey believes the applicant
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has submitted a comprehensive and. accurate-_ description of.the-1 Malibu geology, fault systems in :he immediate vicinity, seis '
1 l-mic history, and ground motions.. 'Although for each one of d
b these elements the reference material, field observations and 1
l the analyses of'the data are not extensive, the interpretations j-follow standard practices and-in general, the docunentation is i
b adequate for the evaluation of the seismicity and ground motions
[
of.Malibu.
A survey of the seismic history of-the region, = extending -
f f
back to 1769 shows intensities at the site have been as high as.
VII (Modified Mercal11) on two occasions.
Intensity VI was I
experienced 4 times and V - VI on 5 different occasions.
One
[
of the grade VII intensities can be identified as the' result of' e shock on the San Andreas fault and two of the Intensity VI shocks can be associated with the Inglewood and'one:with the 2
San Jacinto fault.
The fault systems connected'with the re-l maining shocks of this group can not-be identified.
?
Among the earthquakes producing Intensity V at the site I
was one which' occurred at'34 01'N, llb 588W on April 16, 1948.
l This epicenter was off shore but may have been associated with 4-4 the Malibu fault.
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- l Studies of the seismicity along the San Andreas fquit for the past 57 fears show that a magnitude 6 to 6.9 "arthquake l
occurs every 7 years on the average and only one magnitude 7 - 7 9 earthquake occurs during this period.
This fits the pattern determined by Gutenberg in Seismicity of the Earth which predicts a magnitude 8 earthquake about once every. hun-i dred years.
Although seismic activity in general shows a marked correlation tn fault' structures, its distribution along these faults must be considered random with time.
Hi! ory may I
show concentrations of activity in seeming Oomplexes or at hinge points of intersecting fault systems but the entire fault I
is a zone of weakness so that it is logical to suppose that the strongest activity of the past could well be duplicated at a point on the fault nearest the site.
In line with this reasoning, tho effects of a Magnitude 8 5
earthquake on the San Andreas fault at a point 40 miles from-Malibu must be consid7 red.
This.would produce an Intensity VIII at the site with atten>'at accelerations of.25 Based on the fact that seve or eight shock if Magnitude 6.5 occurred within macrosei mic'distanct the site during the past 5 years it is more probable to expect a shock of this order on an extension of the Inglewcod or Santa Ynec fault at a. dis-tance of 18 - 20 miles.
However, such a' disturbance would incur
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4 a maximum intensity at Corral Canyon between VI and.VII and an acceleration of only.07g maximum which would not merit critical consideration in the design of the facility.
The Malibu site must be regarded as sus eptible to tou--
nami damage.
For the most part, tsunamis are generated by submarine earthquakes or earthquakes located close to coastal areas although only a small percentage of f;is type of earth-quake generate measurable water waves.
The most common ex-planation of the cause of these waves is that they result from the vertical displacement of submarine blo ss of the eartn's crust.
Since it has been observed on land that grelt' earth-quakes have caused uplifts of 30 - 50 feet and affected crustal blocks hundreds of miles long and up-to a hundred miles wide, it follows that such a crustal movement under the-ocean could impart the necessary energy to the water te generate water waves of destructive proportions.
Slides sions the coasts are also possible sources of tsunamis.
In the-case of great l
earthquakes originating on the sides of deep oceanic trourbs, i.
huge masses of unconsolidated material may slide into the l
depths, displacing a great-amount of water.
It has been sug-I gested also that there is a possible coup]'.ng mechanism be-tween tsunamis and great seismic surface wsves with periods f
over a minute.
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It is not surprising that the tsunami peril was not men-l tioned in connection with the California coast since -with the exception of a wave reported generated by a local earthquake on December 21, 1812, near Santa Barbara-there is no record of-a destructive tsunami being generated along it.
The 1812 wave reportedly reached land elevations of.50 feet at Gaviota, 30 -
35 feet at Santa Barbara, and 15 or more feet at Ventura which are on the section of coast containing.the:Malibu cito..
4 Inasmuch as historical records for locally generated tsu-f 4
f namis are so sparse, the dimensions of tsunamis that have-been f
established through relatively frequent occurrences 1n' Japan
~
j should be considered.
Iida has done considerable work in es-t tab 11 thing statistical relationships on the available Japanese data using both earthquake magnitude and fc:a1 depth.
His i
formulas show a small tsunami will be generated for a ' shallow earthquake _ of magnitude 6}-7 and _ disastrous tsunamis for i
shallow earthquakes with magnitudes-of 7 3/3 or -greater.
Based on Iida's formulas, a tsunami classified as destruc.
tive will have a height of-about 10 meters or greater.
The l-earthquake of March 3,1933, off the sanrika; coast of Japan, t-a had a magnitude of 8.3 and was of shallow focal depth; tha i
l-wave. rose-to heights of 23 meters onLthe coast.
The recent i
1, Alaskan earthquake had a magnitude of 8.4;-maximum waves of l
30 - 35 feet were reported at Kodiak and'may have been ex-ceeded elsewhere.
Local waves were-reported of 15 - 20 meters I
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for the Chile tsunami of May 1960 (Earthquake magnitude of 8 -
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Sh).
Thase support Ilda's formula as being reasonable (even
- hough far from being rigorous evidence) and suggest that his conclusions for the Japanese area may apply approximately in 3
j other areas.
In confirmation of these facts, statistics are tabulated for a few major tsunamis generated in different geographical I
areat.
The middle column represents the dic:ance between the l
l places named on the left and the epicenter.
The right column is maximum wave height ordinarily meacured tetween trough and crest.
Those heights followed by an asterisk-(*) are believed i
l to be run up above some datum. {Possiblymeansealevel).
Prince William Sound - March 28, 1964 - 61 ::, 147 5 W, Mag. 8. 4 Cordova 55 miles (Hau:)
30* feet i
Kodiak 190 35 i
Seward 80 30*
Sitka 445 23*
l Crescent City 1,460 13 San Francisco 1,700 7
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O Chilean earthquake - May 22, 1960 - 38 S, 73. 5 W, Mag. 8}
17{4 feet Talcahaano, Chile 90 miles (Naut) 5 Valparaiso 312 4
Antofagasta 875 Crescent City 5,529 10 9 Hilo, Hawaii 5,740 354 Kamaisi, Japan 9,150 12.9
4 Aleutian earthquake - March 9, 1957 - 51 N, 175 W, Mac. 8.3 Adak, Alaska 81 milas (Haut) 26(?)* feet Unalacea 355 4.5 Kahalui, Hawaii 2,005 11.2 Valparaico, Chile 7,384 6.7 Kamchatka earthquake - Movember 4, 1952 - 52) N, 159 E, Mag. 8 Attu, Alaska 495 miles (Naut) 8.0 feet Adak 893
- 6. 9 Hilo, Hawaii 2,893 f.9 San FrIncisco 3,265 S.1 Aleutian earthquake - April 1, 1946, 53) N,163 W, Mag. 7.4 Scotch Cap, Alaska 85 miles (Naut) 80* feet 35*} (?)-
Hilo, Hawaii 2,05o
-8 San Luir Obispo 2,090 Honshu, Japan earthquake - March 2, 1933, 39 N, 144} E, Mag. 8.5 Syoya, Japan 175 miles (Naut) 30* feet Tanoha:a 125 27*
Koyatori 115 40*
Ryori Sirahama 125 624
- Hirota Atumari 130 75++
Even though little is known about tsunami e.neration, there is evidence that c potential for a tsunami exists along the California coast, particularly along the San Andreas fault off the California coast and that the occurrence in 1812 of a locally generated wave along the section of the coast near the site indicatec a definite hanard to the installations there.
As indicated by the tabular data above, an ear;hquake anywhere on the periphery of the Pacific can cause a wave that will trave thousands of miles to strike with nearly undimin-inhed force.
While California has not been particularly
8 Julnerable to thic tip o:
..a v e fro, distant courceu, frca he
'lilliam Cound earth ;uake in Alacr:3 on March 3, l;Q
- ~rince
- . ached arr'.ituden of 14 feet at Creccent City and 10 feet at Santa Catalina.
Thece illustrate the cucceptability of even the most ur.likely chorelines to thece phenomena.
- '?NCLUSIO!!E (1)
Since the porcibility existr for accelerationc to
. li at the cite for the period range from 3 to.6 cec, it 10 recommended that the critical elemente to decigned to withotand
.x noricontal acceleration and componento which have no hacard rotential or are not critical to the continued operation at the reactor be designed to witbutand.0g horicontal acceleration.
i (2)
Tnere is a Jerinite potential for a tcunami to affect r.e Malibu cite due to ita proximity to the cource of the only locally generated cea wave of record on the California Coact.
It ic there' ore recommended that any propoced reactor be co acnctructed that tounami wave heightc of 25 to 30 feet above mean cea level and a run-up of 40 to 50 feet will not impair it: operation and the cafety of the neighboring communitiec.
U.
S.
Coact and Geodetic Survey
'iachington, D.
C.
20230 iune 4, 1964 t
t 4
GEOLOGIC CONDITICNS AT FROFOSED SITE FOR A NUOLEAR PCVER STATION AT CCRRAL CANYCN, MALIB'J AREA, LOS ANGELES COUNTY, CALIFORNIA l
Statement prepared by Rienard H. Jar.ns, Geologist,
1 for Atonic Energy Commission hearing at Brookhaven, Lcng Island, on July 9,1964 Tne general site area is unserlain by stratified marine The sc: tion exposed on sedimentary rocks of Miocene age.
both sides of Corra t Canyon immediately ncrth of U. S. High-way Alternate 101 has been correlated by m:s't geologi sts unit that is with the Monigrgy formation, a stratigrapr.i:
Parther very widespread in coastal southern Califcrnia.
north, approximately a quarter of a m;1e from the highway, these rocks are in contact with an older Miocene section, representing the Topanga formation, along.ne steeply-dipping Malibu Coast fault, The surface trace of tnis old break has a trend rousnly para;1e1 with the present :castline.
The Mor.terey strata are essentially hnOSif,nal in their present distribution, with prevailing;y ncrthward dips at angles of 20 to 60 degrees.
As traversed northward from the nighway, the sequence comprises the following gross 11thologi,c units:
1.
Shaly-w3athering siltstone and claystone with numerous layers, lenses, and b; cks of f riable feldspathic sandstone.
2.
Friable feldspathic sandstone anc graywacke,
with interbedded siltstone and :laystone.
3.
Claystone and siltstor.e with loci;;y abundant tellets, lenses, and tr.in ;ayers of tuff consists princi; ally of unaltered vol-that
- anic glass.
Snaly-weatherir.g siltstcr.e and f riaole reid-
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spatnic sandstone, witn nume rous lenses, blocks, and dikes of sar.dstone.
5 Siliceous shale and sandstone, with '.ocally abundant beds and lenses of silicified limestone and snale.
Among all these rock types, the silicified limestcnes and shales are by far the hardest and most re sist ant to weather-ing and erosion.
The sar.ostones, many of whi:n form beds and lenses 3 feet or more thick, also are resistant despite their friability.
The shaly rocks are sof t :o very hard, but all of them yield fairly readily to normal processes of e rosion because of their ready separation a;ong bedding sur-f aces and numerous cross-f ractures.
The claystones' appear to have bean pervasively l snattered where they are observable in surface and near-surface exposures; this intimate separa-i tion along countless curved surfaces, however, is.actually an l
expression of normal slacking in the zone cf weathering, and l
Inese very fine-grained, clay-bearing rocks are massive and l
compact where f resh and unweathered, i.e.,
below depths of 10 to 25 feet.
i.
l Prominent among the surficial naterials in tr.e site area are marine and 'nonmarine terrace deposits of Quaternary age,
j They underlie the surfaces of broad topogra;nic. benches on both-sides of Corral Canyon, where they appear at altitudes ranging from 100 to 250 feet.
These naturally ecmpacted f
i accumulations of silt, sand, gravel, and rubble. range in thickness from a few inches to about 25 feet, with an average s
l thickness not greater than 10 feet.
They are only slightly consolidated and hence are;readily gullied ty stream erosion, yet they are remarkably stable and retain ;their gross posi-y tions on the steepest of slopes.
Large slide masses, involving both bedrock and over;ying terrace deposits, are present alor.c the nighway botn east ar.d west of Corra; Canyon.
Nene of them, however, extends to-
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points in or along the canyon itself.
A mu:n sma;;er com.
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, cur.d s;ide c. ass, embracing ar. oval-snaped area app r0ximately j
2;3 ty 30 feet, occupies tne easterly wa;; of the canyon arcut 5;S feet north of ti.e nigr.way.
Tne maximur. thickness cf this nass alnost certair.;y is less than 30 feet, and its a erage tnic'c.ess is en the cr$er of 12 feet.
Tne sliding
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' u invc;ved surficial dep;.si:s an: 30mc weathere: tedrocx, 1
ar.c nas occurred over a vertical range only s;ightly less i
tr.an tne height of ne car.y:n aal'. at inis ;ocality.
7:ncue-and aprcn-like accumu.at;ons Of s'. ump,
- reep, 1
I A:.3 slope-wasn materials are pr?sent on botn sides of tne re.r. yon within tne site area.
7.iey occupy broad swales in the j
canyon whils, and consist cf '.oose, uncompacted debris that not been migrating slow;y co n steep s'. opes.
These deposits s
are main;y roc,: f ragments cf varicus sizes enactically dis-4 t ribute tnrougnout a much fi ne r-g rained, dark colcrec silty
- clayey matrix.
They are surf.cial-features witn maximum i
inice. esses ger.erally 12 feet cr 'ess, and Oney do not contain largo detached masses of bedrock derived ficm poir.ts beneatn i
' t. ) 7:r.e cf weathering.
The ficor of Corra; Canyon 1: un;erlain by 5 to.5 feet s
vf c rean-laio alluvium, c.iefly,ccrly-t: we'1-bedded l
si.*.y sand, pebbly san, and gravel.
These deposits rest
' pen 1 rather irregular tedro:< surf ace.
MOst of tnem are na:.:ral;y compacted.
S*.ructural features in tne tecro:% section are of two f t.ndar. ental;y dif f erent types:
(;) tr. se tr.at represent crigina. deposition of the 7.cnterey sedimer.ts and disturtance 4
of these sediments on tr e an;ient sea flo:r during Miocene t;me, and (2) : nose ine' re p re s er.: much later disturoance of th? Section after the s ir.&T.tu L3d DOen c;r.verted into ro:xs.
Ersults of tne earlier L.s; rbantes.iere, in effect, " r.e al e d "
t, tr.e sutaequent lithir' esti:,n cf tr.e se : ion, a matter of co.si*eratie significance in te:-.s cf pre sent s t a t i. '. '. y o f ne re:Y.s.
De t a i ' e r. s *.ud i e s ir nin,, p :. r t s of c oa s t a; sou t: ::-
fa'-
iftrniu r.a,e re.ca.vc tnat,he M. i c : e t.e sea J.ocr in inis region.ust t.a ve been tne general site of repeated sliding ar.d slumping witnin the ;.rogressi.ely accu. u'.ating sof t sed.
inents.
These disturbances, many of them ;e rr.aps triggered Fy ancient earthquakes, gave rise to tones cf slippage and convolutions in the sedimentary section.
At numerous local-ities lenses, blocks, and even large
. asses of " foreign" materic1, derived from higner points en the sea floor, were introduced by slicing.
At other localities masses of sedi-ment were injected as dike-like bcdies int: other sediments.
The Miocene reeks in the Corral Canycn area reveal many features of contemporaneous defonnation, in:1uding sandstone dixes, large discrete blocks of sandstone within shale, and zones of highly irregular small-scale fold;r.g and wrinkling.
Tr.cse features occur within otherwise undeformed parts of the section, and in general tne boundaries of the dikes and blocks of sandstene do not correlate witn fault or shear sur-faces in tne enclosing rocks.
Younger deformation of the section ir. the site area,
'.e.,
deformation postdating the conversier, of the sediments ir.to rocKa, is re'.ated almost wnolly to fLuits.
The Malibu Coast fault, mentioned earlier, is the nor.nernmost break in a broad zene of faulting that trende east--est in this part of southern California.
Tnis zone of faulting, known as the Santa Monica or Malibu fault zone, lies mainly offshore at the ger.eral longituoe of the st"e.
1; is at least a mile wide in this area, and ccmprises sub;arallel major breaks with intervening broad slices of relative;; unbroken ground.
No major fault has been found within tr.e site area, but there is direct evidence of a sna.1 east-r.;rtheast-trending fault in the r.ortheastern part of the area.
A second small fault, trer. ding east-southeast, may also ;e present in the southwestern yart of the area, but eviden:c of this break is mucr..ess c.ehr.
Neither of these fault would exter.c rou gr. t n e gr.und to te occupied by ren:::rs and ger.e rators
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on the east side of Corral Canycn.
No fa4 : appears to te present within the reactor-generator area proper; no evidence of post-lithification displacements can te observec in-the i
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exploratory bench and trenches extending inrough tnis critical area on the east side of the canyon, nor :an any exposed fault j
be reasonably projected into the area frem points elsewhere 1
within the site.
I j
The faults within and immediately north of the site area do not transect and offset any of the terrace deposits, which a
j antedate the last glacial epoch and hence are at least 10,000 years old.
Renonstruction of the geomorphic history of this
}
region suggests that these deposits probatly are at least an l
order of magnitude older tnan this, which squares up very well f
with a recently determined radiocarbon age of 500,000 years for similar deposits at comparable levels in the Talos-Verdes i
Hills area to the southeast.
Thus the fau' ts= here under dis-1 3
cussion evidently have not noved for at least 10,000 years, a
j and more procably for at least 500,000 years.
This is in.ac-cord with available seismic evidence, wnica indicates that j
currently active parts of tne genecal Santa Monica or Malibu j
fault zone 21e offshore frem this area and onsnore only in j
areas that lie at considerable distances to the east and west.
4 i
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Seismologists do not regard the Santa Monica or Malibu j
fault tone as one of major seismic ' activity, and their' records of earthquakes indicate very clearly the tasis for this view.
1 Only one earthquake epicenter has been located in the general
- [
vicinity of-the site for the proposed nuc' ear power plant, and
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this location lies well offshore.
In terns of all available 1
earthquake' records for the southern Califcrnia region, the
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Santa Monica or Malibu fault cone-is almost quiescent'asLcom-
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pared with other active fault :cnes.
This, together with the' evidence for great antiquity cf tne latest movement -in on-shore parts of the cone in' the vicinity cf tne site area, in-j
- cates that the possibilit/ cf f ault movement witnin tne s'.te 2 4 r.ng the plannea ;! f e of tr.e power s taticn is ext re
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It is conceivable tnat a major tsur.ami, or seismic sea wave, might er.croacn upon the coastline in the Corral Canyon site area at some time in the future.
One sucn event occur-red in 1312, out available recorce of its magnitude and effects are both fragmentary and in substantial conflict.
It is clear, however, that the principal damage was confined to those portions of the coast where estuaries and other in.
centations are preser.t.
The straightr.ess of the coastline in J
the Corral Canyon area would tend to minimize the effects of a maj o r t a ur.ami, and ne a '. e va t i on o f t he ;. owe r p'. an t snould insure its safety even in the ever.t of a maximum credible sea wave.
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j It le my opinion tnat, in terms of all known geologic 4
conditions, the Corral Canyon site is a satisfactory cr.e for j
the intended use, provided that the reactors and other struc-tures are er.gineered fer appropriate earthquake resistance i
and ', hat ner.e of the critical structuras would te placed across a recognizabic f ault.
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Richard H. Jehas Er.gir.c e ring eo'ogist e