ML19250B671
| ML19250B671 | |
| Person / Time | |
|---|---|
| Site: | Skagit |
| Issue date: | 09/21/1979 |
| From: | Menard H INTERIOR, DEPT. OF, GEOLOGICAL SURVEY |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19250B664 | List: |
| References | |
| NUDOCS 7911010292 | |
| Download: ML19250B671 (13) | |
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United States Department cf the Interior h '} '
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GEOLOGICAL SURVEY
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b ['T yw , . RESTON, VA. 22092 e:.'.;. -
,5 " In Reply Refer To: -
~ ^
. Mail Stop 905
. Mr. Haro d Denton Director of the Office of Nuclear Regulations. _ .
U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Dear Mr. Denton:
Transmitted herewith, in response to the reques t by your staf f, is a supple =ent to our reviev (February 23, 1978) of the geologic and seiscologie data relevant to the Skagit Nuclear Power Proj ect, Units 1 and 2 (NRC Docket Nos. 50-522 and 50-523). . This supplecent was prepared prior to the cenpletion of a review of
. certain proprietary seismic profiles which have-not yet been received by the U.S. Geological Survey. Any i= pact of the review of these profiles will be transmitted at a later date.
This supplement was prepared by Willia = H. Hays and Stanley R.
,. Brock =an. Assistance was provided by Richard J. 3lakely, Robert H.
Morris and J.ucs F. Devine. . Sincerely yours, ~
/
b H. Willia = Menard Director Enclosure p p ,, , .. 1280 157 y.- . i l i k * /_g .\ One Hundred Years of Earth Science in the Public Service I **r,. ~.\ ,* .t - i t O loctCO e
- .. . _ _ . . . _ 2 _l _ _ . _ . .. . . _ _ _ _ _ _ _ _ _ _ _ _
7 911010 OfV
l QQ7 0 Q O i D Status Review .- [.. d w N) e .S. I s.i Septo:bc 13, 1979
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Puget Sound Power-& Light C::pany .djn[? . Skagit Nuclear Power Project, Units 1 and 2 fif ' Project No. 514 Skagit County, Washington
*(: -- NRC Docket Nos. SIN 50-522 and 50-523 7' .
Since submitting its last Status Review on the p cposed Skagit
;, Nuclear Power _ Project on February 2_3, 19 7 8, _ the_ U.S. Geological Survey ,
(USGS) has received and reviewed a major sub=ittal f ro= the Puget Sound Power & L1gh't Company (PSPL) entitled " Report of Geologic Investigations in 1978-1979" and dated May 27, 1979. This submittal and a f ew new "r- . questions that have arisen from ongoing stud.ics in the site region ar,e _, .
~~
discussed in this review. c., Geolog7 The extensive investigations represented by the submittal of
, May 27, 1979, were sticulated by new ideas regarding the geology of the . site 'vici'nfty that developed in the coarse of. .the long-ter=.progra=. of _
the USGS f or mapping the geology of northwestern Washington. The new
- ideas concern a tectonic cixture of meta-igneous acd cetasedi=etary ,
rocks that is widely exposed south of the plant site in the Table -
, ,- Fbuntain-Raystack Mountain-Bald Mountain region. .(These rocks are hereaf teY 'te'rmed!"CH/Ju rocks", a ter=. coined-from sy=bols for these..,;. . .
~' ' ' rocks on' the maps of the applicant and of .J. T Whetten.) In the . , , ,,
Preliminary Safety Analysis Report (PSAR) of early 1978, the applicant
- identified these rocks as part of the Church Mountain thrust plate, -
- - . . dragged or pushed into this region from the east by the overriding
' Shuksan' thrust, and as being generally correlative to the Chilliwack
' " ~
Croep of largely Paleozoic age rwhich co=pos.es that thrust. plate in the, .
, . Cascade Range f arther east (Misch, 1966, 197.7,.1979). In id.cn,tifyin.g, ,,
'the CH/Ju rocks with the Church Mountain plate and the Chilliwack Group,.
the applicant was probably influenced by the fieldwork of G. M. Miller
-(1779, in press); who has sought to extend Misch's capping westward into
-the Cascade foothills. At NRC-USGS nectings with the applicant _ in May,
, 1978, and at. the Atomic Saf ety and Licensing Board (ASLS) hearing in June of' that year, J. T. Whetten of the USGS, who has been: =apping in ~
the San Juan Islands (Whetten and others, 1978) and was extending his work eastward into the mainland, proposed some =arkedly dif f erent , x relationships. He correlated the CH/Ju rocks south of the plant site with the' Mesozoic Decatur Terrane (including the Fi_dalgo Ophiolite cf , Brevn [1977] an d Brown and others (1979}) that he had =apped as a thrust sheet in the eastern part of the islands--a correlation that is f 1 - 1280 ;58
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supported by petrologic and radiometric data. Whetten presented. - > , _ . . .I , .
'- ,7 ' ctidence thnt the:c roche cre not pert cf the Church Mountain thrurt
./3fk) , .
. . pl. ate,. structurally underlying the Shuksan. thrdst, but, rather, pcrt of. ,
2' f st; j a higher plate that has been thrust ever the Shuksan plate. These nev
' [,'- ideas, later crpanded in publications (Whetten 'and Za rtman, 1979; t f'-j,",!
Whetten and others, 1979; Whetten and others, in press) have produced }-yp uncertainty and division in the thicking of the geologic con: unity j,9 regarding the basic structural frs=ework of parts of the Cascade . ,;, _ , foothills. Such uncertainty is of significance to review of the site proposal.in that it could limit-1dentification and understanding of, younger', post-thrust deformation of the rocks of the region. _ In hope of' resolving quickly _the; question of the basic structural; __ relationship of the Shuksan thrust plate to' the CH/Ju rocks and also" J--
.nore specific concerns regarding possible high-angle faults of post _ .
thrust age, the NRC and USGS requested, on June 9,1978, that the.
,, applicant make additional studies, including (1) core boring, to determfac the orientation of the fault contact between the Shuksan. and .
a Ch/Ju rocks near Little Haystack Mountain; (2) acro =agnetic surveys, to help define tha~ location and the attitude- of the sc=e contact regicnally and to investigate.an anomaly southeast of Butler Rill that had been '. - revealed- on. an earlier, less detailed survey; and . (3) further, studies, . including examination of Quaternary deposits, relative to the possible-presence and significance of f an1 ting in -the vicinity of- and parallel to
. . Gilligan and Day Creeks. .
~
The applicant responded vigorously to the NRC-USGS requests and
- extended. the scope of its studies slightly beyond;the requests in. order . .
-"to address more fully concerns regarding the hypothesized "B-and - -
Jault." The applicant was unable to carry _out .co=pletely...the.. reques ted .. . drilling near-Little Haystack Mountain, but drilled 11 core ho.les __there: -- and elsewhere; carried out an extensive detailed ae'r.ocagnetic survey and 2- ' - analysis thereof; markedly increased the density of data on its regionale . geologic map . including data near Gilligan and Day . Creeks; carried outl..__ on-ground gravity and magnetic surveys across the lower parts of the two creeks; reexamined photographic and radar imagery; and studied Nanaimo-- Chuckanut stratigraphy in the northern San Juan Islands. , , In May and June 1979, the applicant distributed its report, " Report of Geologic Investigations in 1978-1979" (hereaf ter ter=ed "RGI"), on the studies outlined above. The principal topics addressed by the applicant in 'this report and o'ther aspects of regional and local geology -
- " __ tthat hsva sucmed important in._recent considerations of the proposedm r; . _ ,
plant site are discussed briefly below: *
- 1. 1The' basic tectonic fra=cwork of the region--In its 1979 RGI, the applicant concludes that the controversial CH/Ju rocks south of the.
_ plant. site and other exposures of similar rocks in the region. are
, indeed parts of the Church Mountain thrust plate and structurally louer than the Shuksan thrust plate--a -conclusion consistent with m c f
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- that in the earlier PStJ1 and in conflict s.it.h k'hetten's =edel of fp'w' -
the region. The applicant does =odify itsj earlier position so=cchat (p. 3.1-5) in :::: tin:; thnt the CH'/Ju rc eks probnbly 5.]k.; Z. include sone Mescaoic rockc similar to rocks in the castern San k, f Juan Islands, and the mI includes (p. 3.1-4, 3.1-5) a brief s(M. pff . description of a third structural =odel, that cf Joseph Vance,
~& . which incorporates so=e f eatures of the other two. ', 1 .
It see=s clear, regrettably, thc_I_.the issue _ raised by khetten
- regarding the place of the CH/Ju rocks in the basic tectonic _
.-. framework of the foothill region around the proposed plant site has not been resolved by the considerable new data acquired in thc.past
~ - 18 months and that..no..ccascasus on this_ proble= can_be_ expected _ _
. /. - until some future ti=e when cuch = ore of the regica has been capped - _;, . geologically in detail and = ore geophysical data have beca p acquired. The present situation of uncertainty in the geologic-e '" '"
--com= unity is exemp-lified by recent. studies. in the vicinity, of. , m., ,
. -C Little Haystack and Talc Mountains, where the aeromagnetic and
- core-hole data recently supplied by the applicant can apparent 1p be
- ~
acccc=odated both by the applicant's capping and interpretation of the thrust and by L'hetten, Dethier, and Carrol's (1979) very "4 -' ""-diff erent mapping and interpretation.. The. =os t logical and -- . . .
. responsible present course 1:2 the,_ evaluation.of the Skagit site seems -to be acceptance of the existence of so=e major uncertainty .
'aciottg' geologists regarding the geologic f racevork- of. the .sitenw3
~
'~ -
. region and recogition of this uncertainty in conservative - .-
.. evaluation'of the bearing of specific geologic features on_, site _,,,, _.
-' safety.
~
'. " . 2r --T-High-afgIe: north-trending f aults near- the plant site-The,, applicant; _.
. e , u- has*' fairly i conclusively de=ons trated,- by detailed .observatiozigiGif-~- . ,
_, mappin,g supported by geophysical surveys, .thatNno significant, _ , . . , 1,
... north ' trending faults follow the valley floors of Gilligan.and. ~ '7- Iower Day Creeks. The applicant has found little or no evidence _. .
E ~ for-faults within the Shuksarr metamorphic rocks. on the slopes. above .3, . g .
...<.. +~" thee creeks; but it is prudents to hear,in mind.'tha.t .s.uch _f.aulting j .,a a n]-"r might be difficult to detect.R .-Y ' O .>- - - . ... .m ,....g .
'In two localities in-the vicinity of the plant site, on the
* ' - a routh side of the Skagit valley, the- s.trong possibility. or , . ; ;. -
-- -likelihood of high-angle f aulting younger- than- any r.cgional. ,.. uw thrusting is a present concern east of Gilligan Creek, along the .
contac't' between the Shuksan 'and CH/Ju rocks, and in the valley of Loretta Creek, at and near the Chuckanut-Shuksan contact. , The applicant's mapping (RGI, -fig. 3.2-2 and Appendix H, sheet.
.1-);of the' f ault between the Shuksan; and- the. CH/Ju rocks in . sect,iona.
12, 13, an,d 24 or T. 34 N. , R'. 5 E. accords closely with b'hetten's mapping (1979), and all agree that the dip of the fault is steep there.' In section 1 of th,e same township, bedrock exposure is . _ i 3
';d 7-yq 1286 ;60 i
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h~ cot =only poor, and the contac.t can be icss , accurately located. Availabic outcrops and probable outcrops. suggest that it, continues, j'.. J ,- with : northerly trend, threugh abcut the ckmter of the section. .d$' i . , In the northern quarter of the section, the} f ew outcrops =ay pernd t qtif j an inference that the caatact turns abruptly cast, so as to join U the thrust contact betve:n the sa:e rock units in the northeast M.h quarter of section 6, T. 34 N. , 'R. 6 E. Even if the Shuknan-CH/Ju contact follows such a courne, it sce=3'likely t!.ct ti.e sc=illnear
~ . ,J. -
high-angle f ault that for=s the contact for =iles south of section '24 1 continues on across the section to the north. Rather than a steeply folded seg=cnt of a thrust, the fault cast'of..Gilligat
' ~
, -T , _ . . G. Creek (hereaf ter termed the "Gilligan Fault") is probably a younger
),I. #-"' . . .* . . . *'".* uts acrose the thrust. - - -
The extent of the Gilligin TaulFto theEo? h'an'd Fod'Eh Is -
' ~ ~ " ~ '
tit'
.? unknown and perhaps al=ost indeter=inable. If it extends ncrthward
~,i beneath and beyond the Skagit valley, it enters a large mountainous
= ass of rather poorly exposed Shuksan =cta= orphic rocks; to the 5- " '"so6th, beyond upper Gilligan Creek, It is within the tectonically.
1 ^-' - nixed CH/Ju rocks. In both the Shuksan and CH/Ju terranes, the identification and '=spping of f aults can be very dif ficult. South ,
- of upper Gilligan Creek, the fault is conceivably related to a
. discontinucus linc. ament, apparent on_ side-looking radar (RGI, p.
i ~ 3.228 ' t 6 ~3.2-11) , that ex't ends ' south to a point near the' vest end ... , ~ ~' ~
~ ~ of- Lake Cavanaugh, but there is little or-.no evidence that this. . . . , ,
,- lincament is related to the Gilligan Fault or to any geologic
' TtrEcture'. The of fsets in glacial lake > deposits about where this.
~
~~~,,,
lincament crosses the Lake Cavanaugh Road (Bechtel, Inc. , 1978) are
'.,- probably contectonic. , .., , , ,
~ " E!second locality where there is concern regarding high-angle
,s
t -
~ faulfittg, the valley of'Loretta Creek (RGI,. Appendix H, . sheet.;.1;; .
~,-
, ~ W erten and others, 1979), was-called to the attention of.USGS , . . .,.
,f. ,
' ' reviewers by J. T. Wetten and-P. -R.: Carrol. Ii2 the course of',,. . ,,
. ! _. .. . . tapping geologically the lower, part of the valley, Wetten and , ,
-n ,
Carrol encountered an exceptionally good exposure of the Chuckanut-
-Shuksan contact in a s=all waterfall, 'at an elevation of about. -
r r mI,25 0"f'cet. ' Here the contact consists of a near-vertical.. shear. -... zone, at ~1 east about 6 fect wide, that appears to strike north ...; . . northwest. The zone very probably represents a significant high-a'ngle f ault of post-Chuckanut (post-Eocene?) in age. In the .
" 'ib'scnce' of strongly supportive data, the acceptance of.any other s.
' ~ l'n'tcrpretation here would be highly i= prudent. The length of . this_,,.
fault (hereaf ter termed the "Loretta Fault") .and the a=ount and , , , exact sense of displacement on it are unknown. If it is present north of the Skagit valley, the difficulties _in =apping it there would bc s1=ilar to those described in the- case of the Gilligan ~._ Fa ult. ^ To the south, the f ault =ay follow the Chuckanut contact or-
=ay take another course. -.
t l '
;, j hh@yg,. . 1280. 61 u.i .
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. ,... -...... A , . .. - .: - . . . . .. . .-
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'e
- 3. ne "Loveseth" Fault--The "Loveseth" Fau: t, capped as a fault by
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T. P. Loveseth (1975) and H. D..Gower (IE78) 'is interpreted by the applicent (RGI, Sect f,, 3.4.2) and by C. (M. Miller (RGI, f't. 31-M g .A ; 3, sheet .2, and in prean),. a consultant to Bechtel,.Inc., as.the .
.C' basal sedinent.ary contact of the Chuckanut For=ation, disturbed ".- A -
only 17 local shearing asso, dated with Tertiary folding. The applicant does not mention t'he. existence of any clear exposures of
)I).:."; ~
e -[.,(1. 'g the contact, and apparently its dip cannot be accurately ceasured anywhere. The geologic constraints on its location, though fairly .Y- .. tight in the northeast quarter of section 10 and perhaps in section 1.t' - - 3, T. 33 N. , R. S E'.', are co==only loose f arther southv-- On .the b'a sis of evidence of strong shearing and of probable discordance of beds. to the Chuckanet ru/.4 centeet, it seecrs ost likely that the
? ;, _, ' contact capped in sections 3,10, and 11 is a f ault. ne. ~
applicant's- interpr'etation cannot, perhaps , be rule'd out -here r bu6 .
-.e l
. . . .it.-is surely not unique. Farther-south, the =os: likely. course.ofc such. a f ault lies probably along the. sou,thwest side of the large volcanic body in section 14 and through the Chuckanut beyond, but other courses cay' be possible. - 'The applicant's~ espping, which
. established the presence of Chuckanut cast of the large volcanic
~
.. body. in section 14, as wel1 as. vest of -it, suggests that-the - -
"Loveseth" Fault'is not a =ajor structure. The discordant dips in the .Chuckanut in the northwestiquarter of .section 13. suggest.that. .
the contact there may be si=11arly f aulted. , . . . . -- -- m- a . . - ~ . .. z . :.r..-. ~.; . .p . .._, m ;
... - .<:.w-
- 4. m The '.'B and B Fault"-The possibility of a "3 and 3 Fault" was. . ,
discussed at the ASLB hearing. in March 1978, largely as a result of. USGS concerns regarding a letter received f rom Peter Ward, a -
..._. .stratigrapher who had been carrying on research in the. northern. San . .
- m. Juan Island.r. Ward suggestedethat the- Nanaimo and Chuckanut - 1- -
. . . __ sedimentary rocks had been depcsited_in separate sedimentary basins . .
- = ';nnd ;that their prese'nt juxtaposition across the strait - betweenc- - -?
Barnes and Clark Islands and Lu=..1 Island might be best explained '
.l .,. .-
-by:large-scale strike-slip faulting. - The USGS' had not fullym . - >-
-- .i
.. .. ...., ..' , .. evalua ted War d's s ugges tion a.t the ti=e of the hearing and could *
.- only speculate regarding the' pr'oposed f ault. In infor=al ,.
,, consideration of possibly per=issible courses for the proposed',-
f ault' south of Lumni and especially of such courses that were1..-~ "-
.[- '
. - - closest to the proposed plantw ite, it was thought that sueh a 2 "
f ault might possibly becd eastward and pass through the Table--
- Mountain vicinity south of Cultus Mountain. It was this highly speculative, " worst-case" f ault trace, between the vicinity of Samish Bay on the north and the vi'cinity of Lake Cavanaugh on the south, that W. H. Hays sketched-on.a. =ap at the March 197S hearing and that was there somehow christened the "B and B Fault." .
Since that ASLB hearing, st6d'les by the applicant and others have led to doubt regarding the possibility of large post-Chuckanut f aulting west of Lu=mi Island,.: but scem to have established the - presence of faulting near Table Mountain. In the northern San Juan 5: I f -l,-
. .. ;.'. . 5, s . ' __
.. ~.
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., , .; ~.
Islands, a major fault tetween Lu==1 loland and Orcas Island <was . ,
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first suggested by Misch (1966), and censiderable evidence pointer f g' . to faultius there t'at has affected rcch as ycung :: the ";per-M4 --Cretaceous Nanaimo Group. The possibility of faulting younger.than N il
- the Chuckanut Formaion en Luc =1 Island is, hawcVer, core dif ficult
..,Q to evaluate. Stratigrr.phic studies by the cpplicant (?.GI, section ' .9, ' . 3.4.1) suggest correlation of the Chuckanut for=ation on Lu =1 .
- y. *. .
. . Island with strata on part of Sucia Island and on se=c other. . .- - .U_ islands west of Lu=si and thus support so=e of the earlier similar n , conclusions of Vance (1915,.19771. _ This_ c.orrelati.pn sec=s to lack
~~. ;' the-:npport of conclusive evidence for the various deposits being
- ,3. - of'the same age but, if valid, it would sce= to preclude inference ~
Q -
~~o f'ic ge-scale faulting west of Lu==1. Island sincc Chuckanut _.
. . . .. _ (Eocene and older) ti=e. -
g . :. - . . .. .. maAnother development since the March 1978 hearing has been: . . e. . -- T-r"*. - increasing realization that the Chuckanut is probably younger than J.
.i ,1 .- almost all, if not all, of the marine Nanai=o For=ation on Barnes w.- ~
' '- and Clark Islands and elsewhere west of Lu==1 and that the _- -
2: .,.- Chuckanut probably need not have been deposited in a basin . .
?- - --
" distinctly separate f rom the Nanai=o basin,- as Ward suggested. J . :
.. w --
;Thus, while large-scale post-Chuckanut. f aulting west. of. Lu==1.. . .
' ^IsIrnd cannot at present be ruled out, strong evidence for such .
, '" f aQlting appears to be lacking. If there is no such f auIting. -' A '-~
ry . .
. . .c ..a..,. theresis ,~;of course,. no -necess,ity of acco==oda ting gi=ilar =ov_enent.. .. .
, e to-th'e south, along sace such structure as' the "3 and B Fault." -
- I- 1 LIn the T.ible Mountain', vicinity f ar to the south, which Eays' . ..
spec 61ated to be on one possible" southerly course of -the '.majore - -w - J- -- --
-Jault(suggested by Ward, continued . geologic .=apping has. Indicate.df. ;.. *- - 1. N ife' presence of a northwest-trending . fault or'. fault. = cue:(Whetten c. .. . ' I. , and others, 1979), an interpretation that is no.t necessarily' ,
fr'- ' - 1 - ' 5- inconsistent with the applicant's -field studies' (RGI, p.;:3.'4 14) ~. . - - . Whetten (oral co==. , 1979) believes that this f ault or f ault zoce ---- I s - has near-vertical dip and has considerably d.isrupted the CH/Ju and; .
. Shuksan plate rocks in the Table MountafE-upper Nookachamps Creek.7 '. .
J. '
., , vie ~inity. { The age of this structure '(hereaf ter ter=ed .the. "TableJ '.].J .
--- ~ Mtfustnih-Eault") and its extent to the northwest and .setrtheast are . . -
unknown. . _S. The age of hich-angle f aulting in the site vicintv--It _see=s_ clear _ _ that a conservative geologic analysis of the site vicinity =ust m .- rvtake=futo account the probable presence of f airly numercus high- - . angle Tertiary f aults, one or two of which =ay pass within a few
- --- miles of the plant site. These faults include the Gilligan,. _.
'Loretta, "Loveseth," and Table Mountain Faults ~ discussed above; u ,-
~
probably-some of the f aults mapped by Whetten, Dethier, and Carrol t-C-'(l'979) and the applicant west o'f uiddle and upper Day Creek; and perhaps the Shuksan-CH/Ju contact- at "No Na:e Creek." All of these Y gm .g g LW ; 6
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'l ' ' , f aults should probably be presu=cd to bc younger than latest CliUckanut deposition (Middle Eocene), .thcugh so e cay be -older., Sc== pr:bably f or:cd during the enly Tertiary (Socenc?) dcfor=ation.
- -b.[d "
7 that folded the Chuckanut, but the near-verticci dips of at 1 cast many of the f ault surf aces and the linearity of the surface traces 'f(,45 ~. of the Gilligan Tault and prohnbly other f aults suggest thst scme i'T. . .,..- of these structures for:.ed af t.er that, deforca:1on. . ... ..
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In discussing the possible age of this f aulting, it =ay be instructive to consider the nearest faults that have, tcatatively
~
S.i , at least> been ebasidered cae' abler nc D evi'1's Mo unt'a in- Fau h , . N. .. t . ~. .W - which passes 21 km southwest of the plant site, is considered 5 , capable by the USGS, 1 rgely en the basfe of a lack of evidence' h-JF that it could not be capable and of probable displace =cnts as - ~
' ~ ~
depicted in carine~ profiles located ~ vest ~o f Whidb'ey' Island.~ n e
~
[.Y.'- i.% Straight, Creek Fault, 48 k= cast of the site, has probably =cved a
' littl'c since =id-Tertiary ti=e and is " tentatively classified as . %[:
Pc',i capable" (McCleary and,others , 197 3, p . 11) in a study carried-cut c.-{j~ ._ .. 7 g yd consultant to the 'n'ashington Eublic .Fower Supply Syste=.
'31-
- While it see=s legiticate, in a conservative site analysis, to .
consider both of these f aults capable, it should be rc=c: bared, that. _ N/ - ~ ' i.f.:;) both are very long,'very large regional structures, which hava
- doubtless coved many times; that displace =ent along the. Straight I,'7
- 1 t.f -L
' ' ^ * "Creck' Fault was very-largely, if not al2:ost entirely, accompli @ed; s, 1 O by Miocene time; and that there is no_ evidence that_ =ove=ent alon'g , .
M.7 .' the Devil's Mountain Fault was not also largely corpleted by that.
?! - -' ' - ~
"" time.' he capability of two = aster faults. of the region does_ not ~ 3 ,. . .
.F logically establish capability for the cany s= aller f aults. .I t. .
],
seems-likely that most, if not all',. cf .the. high-angle f aults ,of the,. .
~; site vicinity have not . coved in Quaternary time. _ There is ,no . . .
ff.g f' [ sh o6g'cvidence of such cove =ent on any of them. On .the . o.ther .L ., ,, .g .m ~ r ,. - - y hand, Tdisplace=ents, especially' =1nor displacements,..that cight..,, . [$2,' ' ", "" ' ' ' concelvably- have occurred on these. f aults .between 500,000[ years.; agod .
- - and the end of the last glaciation. (about_13,000 years ago) .could, - ' . , - -
.1 1 _.
".-..V .' ..
.ha,ve~ been covered._or,. obscured by that glaciation;. and the app 11 cant-J. C ,, . _.. _ . , . .
%.y-j has presented no ' strong evidence against such conceivable
~ _ ' , - movement. In summary, it appears that the high-angle f aults of the g,. , , .c
$@d ..
. ...~ ' site vit:inity are very probabl.y-but uncertainly-ducapable...M *'g,-t g....- .
.-:3 . W 1: n .~..
.. v . W 6. ' .: v.: :
j,*.6 6. he' 19A6' eartheuake near the northeast ceast of central Vancouver- . - .
' , Island--Several papers dealing directly or indirectly with the.,1946- ,.
'(, , '
' ' 'caithquake have been published since submittal of the la.st USGSs
'. ' ^
Status Review in Februar*y-1978. Rogers and liasegaua (L973) . _, m,
. recompute the epicenter of the earthquake and place _it on Vancouver. .
1sland near its north 'ast coast, rather than under the . Strait of. , Georgia. They favor a fault-plane solution calling for.a noYthwest-striking f ault surface, possibly in close proximity to. ,_. 1the similarly striking Beaufort Range Fa :t, but they do not rule . .
"'otit .a,' northeast-striking surf ace. ,. Riddihough (1978) relates the- ,
1946 event to a northeast-trending f ault in the subducting plate . gy
. ,m . .
=
- . .. .g.. s... ....,.~,. ... . ~ .: . . ,
. . ...r' . ' . ' . .. -;y . ..
^
s.** T ,* . . . .
,. s a. - ' '..
.f.~..,... ,
,g
. ~ . . . - - . . _ . . . , . . -
. s:
. . bcncath the crust of Varcouver IcInnd. Slawson and Savage's (1913) . . .
. resurvey of an old triangulatior, network .rcicaled distott ens' i
~
consfatent with covement on the Secufort Range Fault, but
' ' .. .. l QM,
- association of the carthpake vith} surf ace geology appears to ,
.,sn j remain couattul.. . . . . . _ .. , m %, y z
.m .n
.;.. - . .:;. '; - . . .... . . . .. . 9 i '9 9 a 3
~;' .f.'x' ' R. :-j%y..'.L.'h,.A5 .- >W- '. QU)[ - @ . -
.Y'.b.,.\ ...A.ero.na netic Data
. c, u ... . . . . . .. . .., . . .. , . .
. . o .,..<
V.,. . .. ;;;.lT.:z. n..,. y - . , . , .. . -' - A *,-g. ~ u,.gw ?' 1- ,. Q .
"Ihe USGS has reviewed the analysis of acrecagnetic data by Qi.d '
' Exploration Data-Consultants;-In T-(Edcon) and foual it to be generally-_
.$ d - Q,"' ' satis f act'ory. Alternative interpretat' ions are possible'in sc=e caues, ^'-. however, and the data do not una=biruously establish the correctness of V.. . the applicant's capping and tectonic codel. The f ollowing are scvural F ~.Z - " general ~ conclusions ~ arisibg f rom our review of these data and the7.dcon_
. -. . . ; =
-l report: '.'.:'%.
N r .e .. . y . .
-N
.. .,c.-.
~
~~~ '
- x. L ..-
. ., . .a . , p y , d , ; '. . . ,. , . .- . . . . . g , . . c. -
, 2 .
..E . . . (a) . ~ Aeroc. Yetic anomalies help to define the shape and location :,
.'; of high y =agnetic rock ' types, which are probably
~
' ' 2.-
In particular, acrocagnetic data
.' ; m
~~,
serpentinites in,this area. . were used to deduce the nature of the contact betvect Shuksan , meta =crphic rocks and the CH/Ju rocks. However, the dips of
~,.
..m the surf aces of the serpentinite bodies =ay be unrelated to the attitudes of the thrust because (1) the serpentinite r.ay,.
fT not be originally associated .vith thrusting; -(2) serpenti. nit,c ,; } ' l
.m.. ,is a highly obile rock when subjected to stress; and (3)
{,3 serpentinites possess highly lvariabic bagnetic properties. .
...- .....w.....,.<
.. .. ....r . ... . .. ..
.: .\
' " ' (b). Concern regarding an a3rupt change in trend of the . -
,II _ , neromagnetic contours southeast of. Butler _ Hill,, on s=al.}, , scal _e USGS'aero=agnetic maps (see RGI fig. 3 3-2), was expressed in , " i .- .. 3 [.? .' the NRC-USGS reguest' to the [ applicant of Juna 19 7 3. . .Th e, . . .l . ._
~
'~
S.'. '. [..' ',' . .
. ,c.f' -
e.; .'. .'. additional more detailed aeromagnetic survey data provided by._
.t
. ':.'.'- e .
-- ...the applicant. indicate that there is no =agnetic basis. for a ..
-> f ault with an east-West trend along Skagit Valley south of _ _ , . .
....,., . ~
. , .~-. . ,.- , , ., . , , . . ,.- ,
Butler Hill __,, . _ , , _ ..>.:_..~.~..._..g.... s , .y.., , . , . . - :..
- '*,a :>: m: :.-.----' "-
. -. :- . ., c.- . .
- ..r-
'l c{b;..;.- ? .omalies ~the thrust. .. Wcontact in the vicinity.of. Talc f- ,
../ ,U.
t . ? l' aloig;. . .- I .p. . :.'. Mountain are caused by rock bodies (probably serpenticite) :. . . . '
.. :: which appear to have northeast-dipping northeast faces.
Bowever, these bodies extend to only about 2,000 feet below ground surf ace and could, thercfore, be confined within a th'in thrust sheet. 8
'(d) The absence of f ault-related aero=agnetic ano=alics near the
.. mouth of Gilligan Creek, south of Butler Hill, and elsewhere does not necessarily preclude the existence of f aults. in these . .
areas. . _, .
. ... l ..
1280 :65 S i -
.~. . ../.2 .
m- g;
..c.. . .
3 . g , b c{ - m- . .
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. . x.
. - y. ..
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. .. y. n. .,.. . , .s. .- + . ,.a~
- u. .. . .. . . . . . . . ,.. . . . ....n........,. ...
Y" *
~ .. . j q. . ..;'s E , " (e) Acromagnetic =aps show that ano=clics characteristic of CH/Ju.. .~ reci.. usually ternicar.e at the. thrust , contact between Shuksan .
%.,,.d- . and CH/Ju rocka. nfa a"=.etr that if CE/Ju reeks underlic g.y.g Shukaan, as the applicant has suggested, they lic at depths in
. -. W excess of 10,000 feet. As CH/Ju f requently crops out in c=all 3.M -
- M " areas surrounded by Shukaan and away f rc= the thrust (e.g. ,[ a t -
.$5,j /.Ad ~ ~'. Butler Hill), this lack of ano=afies 'over Shuksan terrace ". ~ ~ g 5, .a -[' forces a rather co= plicated geologic =edel.' ' " (, ' " - [f' - ;IO& _- . . _. __. _ : _ ;f '_.' ^l ' -e . i~'.2. E { 1; .L-- .
-'~C^-*' :~
Y
. Scis=o glll.:(* . .
b . . ,b.-. . .
. A de tai _ led d_i_sc.us_s_ ion .in th.e.. C.e.o.l_ogy-and aero=ao n_e. tic. _. data _s ection a--
M,.l y t., a of-this_revicw is. presented concerniog.the existance and age _of numerous J. :. . _ high-angle faults in thn site vicinity. The conclusion offered there is N that these f aults are "very probably, but uncertainly, incapable."] ' '- q.;. .
. - . 1.-: .;: ': .. : ~; ; o3 :-~ -
*p
?,} ';.c. On the other hand, there have been nu=ercus s=all carthquakes in . a.13.f . the . area -containing the site. Their:cagnitudes range f re= 1.2- to 3.3, ._ 'i .F and several have been felt locally. An align =cnt of epicenters has been-g- .noted in the Skagit .31ver Val. ley but there are. doubts about._the. absolute.
@.- - accuracy of' their. locations. The stated accuracy of events located.by.- -
.i f -
, the-University. of. Washington-operated reis=1c. network is 1.r. to 2. 'eaa T . n.
~g (Crossen,. 1974). . However, the seis=ograph stations in the Skagit . Valley:
-vicinity-are-' f ewer and more videly spaced than those further to the ~ ~ '---
{.[ vl , , south and because the locale is near the northern li=1t of the network .. . .
- -- coveragerthe accuracy is not likely- to- be that precise. -The-re=aining ---
5.L . . .
,, . epicenters appears to be essentially. random in the site . vicinity. ;3one .. .._ _
of; the small earthquakes ' cave been associated with identified f aults.q-3 ~ '.?' . :Itrisrpassible. that these. carthquakes. are associated witht structuresh'y ,Jf/ . W.T - that are eufficiently small' that no surf ace-expression has beenQ-g.'.;;
- 7-3 ~r
,;;W , rqcognized by- the geologigc investigations., ;-.:.-i.5--
- n. . .
- n. 9 .,g.-^:,s. ce n . -
-G ..r ~
' . ' :; ,:s.j;::; -- *....- ' ,
. '" , , & y.: _ . '.
Co'nsequently, it is our judg=ent- that for purposes of nuclear---l---. . . -_:
% reactor design ~it 'should be assu=ed. that' carthquakes as large as'N ' -C'~ ~-7
.7:D '
.- s magnitude 4.0 cduld originate en any"of / he- t identified f aults .ora'a _5.* *./U.S.- - ~
%]. ,*
~ .: .ac. un= app.ed. fault. in. the =cgina cf=thc. plant:. site.: Howeve=,; itis'.ouR~cy.~~4'. ,
judg=ent that even if an earthquake _ of. this sire were to occur on.one of".'" these structures, its consequences at.tha plant site would be less than that .riready postulated to result fr=m- the two =uch larger carthquakes --
- discussed ~1n our previous' reviews '(Jan. 30, 1978 and Ieb. 23, 1978). --
__ Since our last review, other articles relating to the tectonics of - the Pacific Northwest, in general, and the Vancouver Island vicinity, in, - particular; -have been published. They reinf orce the oncept that the > - 1946 earthquake was related to the present-day subdt regi=e of the region -rather than regional north-south compression t.%ers and s. Hasegawa, 1978). Rogers (1979) suggests that the occurrence of
. . .m.earthquahes .having a northeast. align =ent across Vancouver. Island are.. ..
related to differential movements, of '.he Explorer and Juan de Fuca
'..e s
M...,
- s.I. ...c . '1. 28. 0. YW L.
. E.-Ic - .
'~~~~
* .- = - -
- ' . . . . , -. .. s.,. .. %. - :. -~ . ..- .-.. .. ...'...
.,: U: .. '~... ,.....YA' 1
~. 5 % - ' = % - 'I-
.- .. : .. - .:.l r; ;.\ . ':_ .i.:./.
- b -.e- .. f . ? ': ' 9; *.&;5~~r...f
k, . . % .. v- platen. Two interpretations of the teernnie s, ttings are preaented; his d.M - . t. m .. , preferred setting nuggesta that the subducted Nootka f ault cac (na:cd . . by Hyndean, et al, 1976) would represent, in effect, a tectonic "f%l boundary, north of which earthquakes would occur because o ' intcase local north-south co=pression resulting f rom the Explorcr-A=crica plate 99 Q-
- .Tip
^
interaccion. . To the s'outh of the Nootka f ault zone, subduction of the' Juan de Yuca plate bcncath the A=e'rica plate would proceed in a nor=al ., g B- but ascic=1c fashion." In view of these considerations, we belicyc that the constraints' on the . locus .cf .an_ event ai=ilar_ to. the .1946 carthquaka
~
2.@.',.) - 4:7. vould make its significance less than the two postulated controlling
-*- earthquakee (USGS Jan. 30, 1979, nd ?ch. 23, 1978).
.9. 7
.- ,3 .. ,. - .
--- - - In su==ary, there is..a recogaition thac--there has-.beca-a large
- amount of new geological and-geophysical-data provided by the applicant .
, ,1,, and others since the preparation- of our -last review. However, there
; ?, remains a major uncertainty as to the co=pleteness, significance, and
[;;. , proper interpretation of both the new and previously discussed data.
a . Consequently, it is still our jug =ent that f or purposes of nucicar reactor design the- folleving two earthquakes should be censidered as
". controlling:
, , 4 ,- , ,
' (
- 1. an earthquake similar to the one that occurred Decc=ber 15,
'1872 but having its epicenter suff%iently close to the site- -
j.-
. that n'o attenuation eff ects be cor '.dered, and. * ' ._t , , , ., , T , . ~. .p..- a shallow magnitude 7.0 to 71/4 carthquake on the Devils' . .
- 2. .
'.. Mountain Fault 21 km. from the site. , ,., ,
. s.
The USGS reactor site review team agrees vith. the applicant's . , . ,
.,' propose,d use of 'a bedrock acceleration value .of .Q.35 g as .the Saf e -'
Shutdown Earthquake f ;r use with the Safety Guide 1.60 design spectrum ,,.
. J. . for nucicar power plant design. . _. ,- '
Q _ . . . . . . . . . . . .
....~...!
...,.'.. . u.
.ve
.. .~.
. .g 1280 ;67 DF o- -
j
; l-
. ~
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. . .k s 4
. .L4 . 10 '
.,1 ,
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..s
'l}
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,...m . - .- . . ..< .
.{ . .
*- ~.
Q. :', .: - e- .
.a - ~ . + - - - . .
r..
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,t ,...
i9.u
. .m . r.
f y D
,q- t
? di.'E T 'DJ D
' 'W t
.e mP ,3 .
References j c!O, J e . -
- i. . . .
..h.:;;'.;.g l - .
.. <...\,,,..
. r...h . :
- ...... ~. .R .. : :
..at . . .z.ul '. M'd , :.
T-;.G.' ... ... Eechtel Incorporated,,19 78, Subsurf ace investig ation of dis turbed.. glacial depcsits on Lake Cavanaugh Road: Report to Puget Sound 7 ,. :-; .
< =W . :. .-U.. . ...Powe r T.i .l g.at Co. .. ; n ,.--; .. .. . .
~ - .-
.u .
, . .-~ .
' : - *. ,..c :: - - -
. l . , . ...$ .' '; E. .' - B rown , E. H . , 19 7 7, Th e Fid a lgo Oph io li c e , i.n. 3 rewn , E. S . , a nc Elli s , R . . C. (eda.), Geologf cal excursions in the Pacific Northvcst: ~ ,j I, 7C. ,
. . . , . - . _ . . - . . . _ . . . . _ . . Western Washington . . - Univ. . . . , ., -. p.. 309 . _ . _320. - @.I ... .. .
Brown, E. B., Bradshaw, J. T., and Mustoc, G. E., 1979, Plagiogranite
' F.a 'I .-
i W, _ . , and keratophyre in ophiolite on Fida~ go , Island, Washington: Ccol.
-- .-?. Soc. of A=crica Bull., Part I, v. 90, p. 493-507.,
. . . .J '
.. ... .'.3...-....... .
. y . . ,.. ,. .. .
Crosson,"R. .S. ,1"474, Compilatien of ecrthquake hypocenters in vas tern
! J [. . _ Washington 19N-1972:
. j, . Division ~of Gi. ology and Earth Ecscurces l - . . .;. ,
. Inf. o- -rma ti.on .C.i,rcula r. 53,
.. 25 p .". . . ..... . ' {.7 - 9 :..
- 1. . . . .... --:.
~.
u.,-.. c.m... . - 1%.:- Crosson, .R. S. ,1975, Co=pilation of earthquake hopocenters~ in ves tern Q. . .'. ' " .
.Vashington-1973: Division of , Geology and Earth Resources - .?. . ~. .
Inf or=ation Circular 55,14 p. . M .: . _ ;: . . . ,% - - - Crosson, R. S. and Millard, R. C. , 1975, Cc=pilation of earthquake' M- . hypocenters in wes tern Washington-19 74: Division of Geology und
.~.,S
.. Earth Resources Information Circular 56,14 p. ,
, r. . . . ,. .
. . . . . . . , . . . . . .. . . .: . aa n . . a .+ ..
. . . . ~ . ..:. . ... .
.9".- -
~
Crosson', R. S. and Noson, L. J. ,19 782," Cerpilation of ea'rthquake
.'p' f,,
'.?
. hypocenters in vestern Washingten-1975:' Division of Geole'gy and-h*::^ # : .T... Earth Resources Information Circular 64',12 p. ..~: '-
....._'. . ., .: ,r .
,. . . . . . . r. .. -: .. . . . \.. -: ;
....~.
Crosson,R. ... S. and y'" - _.. . , . Q.. - J -- Noson, L. J. , 1978b, Ccepilation of earthquake - IR . hypocenters in western Vashington';I976: Divisica of Geo1~c;y and ,, ,
- .:..:.r~. -.
-,- c Earth Resources ...-.;.
Infor=ation Circular ~ 65, ' .. '
- s. .
. . . . .- ~......:.. -. .. . .
..v -
.,..i-;,.2' Byndman, . R. D. , Rogers , G. C. , Bone , M. N. , Lis ter, C. R. 3.,-Vade, ..~
U. S., Ba rre t t , D. L. , Davis , E. ' E. , levis ,
T., Lynch, S., and Seemann, D.,
1978, Geophysical =casurecents in the regien of'the Explorce ridge off western Canada: Cana~dian Journal of Earth , Sciences, v. 15, pp. 1508-1525. - - Miller, G. M.,'! 1969, Western extent of Mid-Cretaceous thrusting in Whatcom and Skagit Counties, Washington: Ccol. Soc. of America Abstracts with Progra:s, part'3, p. 42'. ~~ Mille r, G. M . , in pres s , Wes t ern c.x t ent of the Shuksan and Church Mountain Plates in Wha tcom, Skagit, and Snohomish Counties, Washin-ten: '?rthecc: P i a.:2.
..r>. ,
i.V..b . .
. 1280 168-
.. 11
. . . r,. .. .'
.r,,, . > +
~ s ,
.~- E sl 7 a '... -
,. ,.s ~a-
'%.. ..~
..;;; y .,g.
_. ..*..y. .'j. ...y: ; *, . . D.. w-
.2 .
-2 .1 ,
7 ,; x . .. .
. . . . . . . . . ~ - - - - . . - . .
2...' Misch, Peter,1966, Tectonic evolution of the Northern Cascades of
- 9. ~d, W::-hin*-::n it:te, in Tectenic histe y sadi incre.1 daposite of the V- Western Cordillera in Sritish Colu=bia and neighboring parts of the United States: Canadian Itat. cf liining and Metal.,1964 Aan.
'".;GlQ;1 -
Wes tern Meg. , Vancouver, B.C. , p. ,101- 148 ; ', f...'-- ,
- y '- .".&,0 *p .~ ,-l . .
. , .. ' : m.
,,-' 3: . ? . .'.: : .
j- Misch, Peter,1977, Eedrock geology ~ef the North Cascadec, .,i_n, Geological excursions in. the Pacific North.* cat -. Cool Soc of. A= erica.19 77 _
-- Ann.-Meg, Seattle, Washington; publ, by Dept. of Ccol., Western _
Washington State Univ. ., .,. . Misch, Peter,-1979, Geologio-cap-of-the Marble =ount Quadrangle ,
~ Washington: Washington Dept. of Nat. Res. , Div. of Geol. and Earth Resources, Geol. Map CM-23. --
s .. . J
.g , _-
. q;
_. .g ., ; .
'g -
Riddihough, R. P.,1978, The Juan de Fuca Plate: A=crican Geophys. ' ' , ~
, Unica, EROS, v.59, no. 9, ,-. p..836-84 2.' ..- -
". . ' J, ._. '
. .. . : =. -
,' ~
Rogers ,'G. C. ,1979,' Earthquake fault plane solutions near Vancouver
~
- Island: Canadian Journal of Earth Sciences, v.16, pp. 523-531.. -,. -
. Rogers, C . . C. ,' and Ha.c e c ,awa , H . S . , 1978, A second look at the british .
' N ' Columbia carthq d a of June 23,-1946: -, Se'icmol. Soc. of, America Bull'.~
, v. 68, no. 3, p. 653-6 75. .
- c. .-
Slawson, W. F. , and Savage , J. C. , 1978, Geodetic defor=ation asso'ciated
~'
with the '194,6 Var couver Island , Canada, earthquake -(abs t.): -. - American Gecphyr ion, EROS. -v. _5 9, no . 12, .p .1210. . > . - , ..
"n Vance', J..A., 1975, a.s . .s ,.mol.ogy of San Juan County, .i.n. Geology and __
. . . water rescurces of ie S.:n Juan Islands: Vsshington Dept. of-Eco1ogy, Water Supp y 'ull. 46.! 'a...,-
?'E
~
- .. 1Vance , J.- A'. , 19 77, T.. . satg caphy and structure of OrcasvIsland,. San..
- n. Juan Islands , .,1n, Cco Aogic excursicts . in the Pacific Northwest,,.i . - -
Q',i.j'- ' Geol. Soc. of America Ann. Meg., Secttle Washington; publ. by Dept. of Geol., Western Washington State Civ.c ps 170-203.', 6{ . . . .
- Whet ten , . J-. . T. , Jones , D . L. , . Cowan ,. D . . S . . . a nd- Za rt man,. R. E., 19 7S , . .
s Ages of Mesozoic terranes in the San Juan Island's, ,,'ashington, A
-- Mesozoic Paleogeography of the Western United Sta'tes, lacific Coast Paleogeography Syeposium 2: Pacific Sec., Soc. of Econ. Paleon.
and Mineral., p. 117-132. . . Whetten, J M. , Zartcan, R. E. , Blakeley, R. J. , and Jones , D. L. , i'a ' , press, Allochthonous Jurassic ophiolite in northwe st Washington: Ceol. Soc. of America Bull. s 280 69 1 c' 12 . , n, j . i
~~
, , 3-/3 ' --
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., . . .x ; -- . n > ::, ; . .. .
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