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SUMMARY
OF ENGINEERING GEOLOGY OF TB PROPOSED NUCLEAR .
! . - - .R
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. POWER FIANT ON BODEGA HEAD, SONOMA COUNTY, :
i CALIFORNIA by Julius Schlocker and M. G. Bonilla
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CONTENTS Page Introduction----------------------------------------------------- 1
. Tsunam1. hazard--------------------------------------------------- 2a 1
i 1 Geo lo gic s e t t in g--- ---------------- --------------------------- - - 3 1
t .
t l . Granitic rock of Bode ga Hea d------------------------------------ 3 '
It Joints and faults----------------------------------------- 4 We a t he r in g -- - -- - - - - -- -- - -- - - -- - --- - - --- - -- ------- -- - - - - - - 7 Ple is tocene and Recent depos its --------------------------------- '
7 Fo s s il s an d a ge -- ------ - - - --- --- -- ----------------- --- -- 8 l' Tilting of sediments and its significance to the site---- 9 o .
/ i!
S ha f t Fa ul t -- ---- -- - -- -- -- - -- - -- ----- --- - -- - -- -- - -- -- -- - - ---- -- - 11 Origin of Shaft fault------------------------------------ 12
! Magnitude of movement of Shaf t fault in sediments------- 14 I
- Age of movement of Shaft fault in sediments----------- 18 Surface ruptures west of San Andreas fault zone---------------- 22 i
i:
S significance to Bode ga Head site------------------------ 27 l l
1 Shaf t fault and San Andreas fault zone ----------------------- 32 P 1
l i :
Significance of Shaft fault and future faulting in granitic il i
rock of reactor foundation shaft and vicinity---------- 34 l
references---------------------------------------------------- Ao
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LIST OF TABLES Table 1. Branch surface ruptures, San Andreas fault zone, formed during
,
- I earthquake of April 18,,1906, and described in the 1908 report ;
of the State Earthquake Investigation Commission.
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i Sur.nnary of engineering geology of the proposed nuclear power plant ',
i on Bodega Head, Sonoma County, California, ,
By J. Schlocker and M. G. Bonillab , U. S. Geological Survey f i
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INTRODUCTION
,l j
! The purpose of this report is to answer pertinent questions
- I, . i asked by the U. S. Atomic Energy Conmission staff in connection
.j with an application by the Pacific Gas and Electric Company for a ,
license to build and operate the plant. Additional background and
/
detailed geologic data is given in U. S. Geological Survey Reports !
E
, .[
TEI-837 (Schlocker, Bonilla, and Clebsch,1963, part I; Eaton,1963,
- l l
part II) and TEI-844 (Schlocker and Bonilla,1963).
The main aspect of engineering geology that will be discussed i
here is the one relating to sudden permanent displacement by rupturing
)
of the foundation zone of the reactor during an earthquake. The .[ l I,,'
j i,
aseismic design aspect, however, has not been neglected by the AEC I
briefly i
staff and is discussed /below. From the brief historical record and
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- O This report was prepared by Schlocker at a time when Bonilla was t
, in Alaska; it bas not been reviewed by Bonilla. '
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from theoretical considerations (Benioff,1964, p.1,% it is believed 1
that 2 to 4 episodes of severe shaking from a strong earthquake may 1 1
occur at the site in the next 200 years. The plant should therefore i
be designed to withstand damage from these seismic vibrations. We - ,
i
- t 8 >
understand, however, that the accelerations, amplitudes, and frequencies [:
b
- of seismic waves likely to be encountered at the site have been esti-e mated by experts in engineering seismology, consulted by the AEC, and '
I that the design criteria include consideration of resonant frequency {
and strength and flexibility of critical parts.
b .
Ali the outset it should be made clear that the granitic rock I foundation on the floor of the present reactor foundation shaf t is i
J generally capable of gorting heavy loads. Ultimate, unconfined ~l compressivestrength/resultsrangefrom1,037to16,800poundsper i
square inch. In our opinion most of the rock on the present floor ,
[} of the shaft has strength properties in the upper half of that range. J 9
i Nevertheless it is recommended that the foundation preparation include .'
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" dental work" to remove sof t and plastic zones along faults in granitic S s 1 -
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, TSUHAMI HAZARD i
Tsunami effects on the shores of the site have not been investi-gated. The only data obtained was tentative informat on supplied by .
J the Chief of _ the U. S. Coast Guard station located a Doran Beach, .
' )
o l about 1 mile east of Campbell Cove. He reported y telephor.e that the h
i I
~l largest' tsunami effect at Bo ga Harbor, in connection with the Alaska re tively rapid drop of sea level.of 3 feet followed by a / ,
I earthquake of March 27, 1964, caused afrelat 4Aby ra'pid rise of 2 feet.
i l
He suggested that more reliable informatio could be obtained from the i
s P. G. & E.tida gauge located in Campbell ove. The plant working level y i
! [*
of 25 feet above sea level is probably a ove the reach of most tsunamis
] e l
. - that would enter Campbell Cove. The submatine ridge between Tomales {
Point and Bodega Head would probably end to prevent buildup of large I
tr.unami rise in Bodega Harbor. Ney reheless design of cooling-water intake pipe should consider the po sibility of strong stresses from .;
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rapid surges of tsunamis and also the possibility of temporary sea.
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levels 5 to 10 feet below lowest reported low tide. a 1 - j 2 '
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GE014)GIC SETIING
. The site is adjacent to Campbell Cove on Bodets Head, a granitic
- . rock body that lies along the west border of the San Andreas fault y
4 sone. The shaft for the reactor foundation is approximately 1,000 , ,
)
l feet west of the zone. The granitic rocks are partly covered by -l 4 '
i
.I Pleistocene unconsolidated sediments consisting of interbedded near-I .
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shore marine, beach, dune, marsh, stream, and slope debris deposits that have a maximum thickness of 180 feet.
-- The site is on a buried valley system that was eroded in granitic j
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rock by a surfac'e seveam and its tributaries, when sea level was i
. TEI-84 '
i relatively lower (pl. /). The valley was subsequently filled with marine and continental deposits. The main buried valley crosses Bodega Head in a more or less east-west direction. At its deepest
^
point, on the east shore of the Head at Campbell Cove, it is more . ;.
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, , TEI-84 .h.
l l than 80 feet below sea level (pl. 2). "
, a i ,
i GRANITIC ROCK OF BODECA HEAD The granitic rock of Bodega Head is mostly a foliated coarse- ,
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grained biotite-hornblende quartz diorite. Pegmatite and apli.t..- dikes
. up to 7 feet in thickness, and dark granitic rock inclusions are common. l l
A leucodiorite dike with a maximum width of a foot cuts the granitic 4
I'J , ./ _ rock of the shaft.
Joints and faults
- m. '
- i Joints and faults are cocinon, although
- they vary greatly in I , .
abundance from place to place. Closely jointed rock is cut by 4 or -l
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- mora sets of joints and also by irregularly branching joints. Most rock ,
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- I is broken by joints and faults into blocks 3 to 5 inches wide, though 'I l
, the range in sizes is from less than an inch 5EDNN?C in fault zones i-F.
to 4 to 6 feet between some joints and faults. Paults and joints seen l f
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between elevations -66 and -73 feet on the perimeter of the reactor
~
foundation shaft are shown on plate 3, TEI-BM. ,
, . Traverses along the western and southern shore of the Head reveal .
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shear sones 3 to 10 feet in width in the granitic rock about every 150 t
I to 300 feet of t9 averse, as well as a great abundance of narrower sones
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4 of shearing o'r faulting. The wide zones consist of complex 1y inter- k
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chweically altered rock) and breccia (coarsely broken rock), and mylonite (pulverized, but firm rock). Breccia and mylonite in most i
shear zones is also altered chemically.
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'.j All faults seen along the shore traverses are persistent in 3 -
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.j g ' length for at least 50 to 100 feet in the well-exposed rocky shore f l L T .f.
t 'j and adjoining seacliff, and those that are more or less parallel to ;
4 the shore, were followed for 200 to 800 feet. Faults in granitic .
rock away from the shore and above the seacliff are not as conspicuous !
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as those on shore because of the. cover of vegetation,
- weathered rock i . . .
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[ debris, and other Pleistocene and Recent deposits. Stereoscopic study (,
1 of sit photogrpphp gives indications of lineations in such area that are probably faults. Some of these can be traced on the photographs for hundreds of feet.
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- The fault zones in the granitic rock along the shore and in the
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l ,. ' shaft are conspicuous zones within which the rock has been more. severely .
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., -altered physically as well as chemically than the rock between these :
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, .- . .c sones. The magnitude of movement on the faults is difficult to measure ,
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( in some places because of the massive nature of the granitic rock. .
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Nevertheless,'thedikesandthedarkinclusionswithinthegranitic )
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rock serve as markers, and where these are broken by faults, the broken segments are separated from an inch or two to more than 20 feet.
of ghearing is also, evident from microscopic examination of thin ,
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' - e I6 sections of granitic rock collected at widely separated localities on '[
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the western and southern shore of the Head and at the reactor shaft.
' )
. Abundant shears on a microscopic scale cut the quarts and feldspar I
crystals. Shore traverses and examination of aerial photographs
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show that trends of the largest faulte are, in order of abundance,
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mostly northwesterly, northeasterly, and east
- west. Hundreds of i
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i measurements on faults exposed in granitic rock during the excavation
' '! of the shaft showed the dominant fault bearing is within the range of e
N. 70* W. to S. 80* W. and the predominant dip direction of faults of
'this bearing range is 50' to 75's.
f
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!- The abundance of faults, plastic gouge zones, and microscopic F M l' **
a y ; *, shears in the granitic rock of Bodega Head is considerably greater
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.- . .: than that for the vast masses of granitic rock in the. Sierra Nevada, i,
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.; Weathering The granitic rock generally has a 5 to 30 foot thick mantic of
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. weathered rock and soil. The soil is a mixture of sand, clay, silt, and l
gravel.
"~ -
PLEISTOCENE AND RECENT DEPOSITS
. .These deposits lie on granitic rock in the general vicinity of the s
site and are possibly thqdnost extensive accumulation of such deposits on Bodega Head. They are thickest, more than 180 feet, over the main buried i
valley south of the shaft and wedge out on the flanks of the partly-buried
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granitic rock hills north and south of the site at elevations of about 35 r ,
feet above sea level.
i l.
One of the prominent sedimentary matetials in the shafe area is gray,
! massive (unbedded), gravelly, sandy clay, that generally lies directly on i
t l the granitic rock and reaches a thickness of more than 30 feet (plate 4).
I i -
l , In many places the granitic gravel in the clay increases downward forming a I
- gradational contact with the underlying granitic rock. In the south part l
. of the shaft the gray, massive clay is interbedded with 0.1 to 1 foot thick ,
e.. .
't beds of sand and clay, probably of marine' origin. All of these sediments e.:
.c., . ,
4
. . . . . . .. s, are covered by a thick beach or nearshora marine sand deposit that lies ,j
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inasmallvalleycutintheunderlyingol/dersediments. The sand thickens to more than 40 feet southwards towards the main buried valley.
North of the shaft interbedded wendy clays, clayey sands, and sands all containing varying smuunts of gran'itic gravel are exposed to elevations
-? .
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j of about 85. feet above sea level.
i a . '
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Fossils and age 1
i ..
The topmost 5 to 10 feet of sediments, mostly soil and wind-blown i
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sand, are believed to have accumulated in the last 10,000 years or so and se are designated as Recent. Fossil wood is abundant in the sediments below those designated as Recent. Wood collected at elevations 77, 55, and 49 feet above sea level, all within 240 feet of the center of the shaft, 1
i yielded radiocarbon ages greater than 42,000 years. A study of the l
fossil flora in the sediments 5, to 25 feet above sea level by Jack Wolfe, Paleobotanist, U.S.,* Geological Survey indicates:
- 1) The flora is similar to the P1'aistocene flora of the northeast shore of a l Tomales Bay and that both were deposited about the same time and in a l
pine forest environment. Invertebrate fossils in the beds at Tomales ,
. I
.y
- 4
., j Bay indicate an age younger than the ' folded early Pleistocene beds of 1
the Merced Formation of the San Francisco Peninsula area, i *
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[ 2) Beds near the northeast rim of the shaf t at an elevation of approximately
,' t 7 feet were probably deposited in a fresh water marsh.
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Imuderback (1951, p. 86) estimates that the folding of the Pleistocene j
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- part of the Merced Formation took place from about 240,000 to 400,000 years - !
- . . , , ,j
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4 ago. Thus.the sediments between these containing the wood at an elevation of 77 feet and those containing the fossil flora at elevation 5 feet are i
older than 42,000 years and probably younger than 400,000 years.
f i
l Tilting of sediments and its significance to the site l
' ~
A general southeastward dip of the beds to as much as 8' is believed
.\
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Locally dips vary from to be caused by southeastward tilting of the Head.
I .
i sero to 15 degrees. Most are southeastward, though some are westward or t'
northward. 14cally variations are believed to represent initial dip of the sediments acquired when they were deposited. Evidence of tilting of
.beca believed to be of Recent age was not obtained because bedding is
- 3 y poorly developed in them. Thus evidence at hand indicates that the tilting
. occurred some time after the deposition of sediments that are more than
- ,.'42,000 and less than 400,000 years old. ,
- *. p,, ., ,
j
~
Observations of the effects of the severe earthquakes in Chile in r 1960, and in Alaska in 1899 and on March 27, 1964 indicate sudden tilting .
9 r, . ;- - r . ..
., m..~ ' ;a. 4 , , .. % . , - A ..a. ..
5v .-' 'i _- ; g.g,.
' [ 4 . ,t 'et. .
']E.
. + . . . . . . ~ ..
=
- A- X '- - : <. . c l.. . .
a.+1 e,.
c
. .y ; ,. ,. ... ,, .. , c. .;. , r . ,
@1 ~w. , n -;,.;..e..
on a regional scale. In other places, however, it is believed that tilting.
, has.been gradual. Tilting is not considered a serious geologic hazard to ,
j .
the plant because:
'} q *
.j , generally j -- -
, ~ , !1) Tilting /affects a wide arca;. 2) tilting may be gradual and its ,
y .
effects in 200 years may be imperceptible or nearly so; 3) the
^
l
[ A.r y ,.
probability of sudden tilting during the next 200 years ishry 4
1 low. 1$m significant regional tilting was detected in connection n
i
- with the severe California earthquake of 1906.
- i. . .
.j SHAFT FAULT l
,l - . ,' e ~ ~
a _ i . - . . , . t .. r
. ...* .,j The Shaft fault, a major structure among abundant faults seen in the
^
I t
[ granitic rock of the reactor shaft area, is the only one seen there that i
.i 1 is accompanied by faults in the overlying Pleistocene sediments. The i
, j direct connection between the Shaft fault in granitic rock and in Pleisto-i cene sediments is well established' on the south wall and on temporary '
u
- floors of the Shaft. Its general trend is' N. 40' E. from the south edge j .
l' of the Shaft (For location, see ple. 2, 3, 4, TEI-844). Its dip in
. t, i ,
granitic rock is 65* to 85* W (dip is measured downward from a horizontal :
r.-
. n 3 plane); in sediments it 'is variable (pl. 4, TEI-844). An en echelon branch I 11 r .
t I 4 . , ..a. ,. 2 . u ma -
.e.#,m em e- **< --
- e.
' ': 43 '. .. o,6. , ,
. .. . sy,x , + s tt < N 3. < , .4 g l ? ' , s.. - *' . .? , ,. , ..
.,].$ $*.l' Q h EQ , k L
- y sg...g$h %gw $ h'1 & w- Q *&r,.g,;?y , , QsN'rQ'rhQU j f .
- Y.,;mn,~{.y:$;:@ f g,. W=, s. aqu.
- .p,y'tdf wh7M.p:. y q,,
5QAlt . u. & 'Qs; ;s.
> ~
uw]:#' *'
..:. m -- .
. . . - . .. 7. . -.
g
, ___ -4 -
q .
4 -
f
- *' , [
j -
i
,l .
t ir. e adiments was followed from a point 2 feet from the Shaft, at approximate 2
elevation ~5 feet to a point 170 feet SW of the Shaf t at approximate. ele ,
vation 21 feet. Though it did not terminate at. this point it us not seen
- i j
'J in trench 3 (pl. 2, TEI-844) at elevation 51 to 52 feetg 250 feet SW of the Shaft.
The Shaft fault could not be seen in some places in the gray, massive, gravelly sandy clay in exposures of this sediment on the south wall (pl.
l i
- 4. TEI-844), on temporary floors of the shaft in a belt about 10 feet l
wide on the south border of the gra[itic rock, and above tihe Shaft fault
' ROC Y ;
in granitic on the northeast wall. ' At the last locality the fault splayed out in a complex of small, intersecting faults 5 feet below the top of the granitic rock. The complex may represent the chaotic jumble of granitic blocks created by an ancient landslide. The Shaft fault was not seen in -
the embankments northeast of the shaft. . -
i Origin of Shaft Fault l-
, The origin of the Shaft fault in the sediments is fundamentally 'l s ,
~
impoAnt in any evaluation of its significance to site acceptability and 3-4 .
plant design. Tectonic faulting is considered to be the most probable origin.
L <
r 12
,m
.,.w.f ..+e- e-" "
I q 9 .
m j 'h 4 = '# ED
, th ," .a 4' '
4$
A* . ** '4 *-
it-bi N 2 *;9 $ & )$5Q .lGx C, - .
r & 4 g . _ .a i. -
' $'iJ$?S/$5khQYlWik?]
_ . [I "Q$$U*'ECb ~
CO U Y U$iY?N l
- p .,-:y....ca:.rd.' ^ W ' %*' ' z = * ^.L = u : = .:= " '*~ ~ = "" "'#**~*~~***"""
.y . .. . , ,
a *
, , . . . . . ~ .
,. , ,. . . - - - ~ - - - - - < -< ~ -
4,, ; .
- 3
. . 4 Other :aechanisms considered, but rejected are landsliding and subsidence from compaction of sediments. Lurching caused by earthquake vii> rations was also considered, but this origin is fundamentally parti of the last i
4 '
- two origins listed.
u jj ' '
y Faults othe' r'than the Shaft fault were found in sediments and may be caused by landsliding. 'One, located about 35 feet south of the south rim of the shaft, trends H. 70' W. and several interrelated faults are located about 100 feet northeast of the northeast rim on the south cut of the ramp leading S
- i .
l to the shaft, trend about N. 55* W.
I
!\ .
Tectonic faulting is used here for rupturing fundamentally related to i,
crustal stresses, such as those that produced the 1906 earthquake. The Shaft fault in granitic rock is obviously tectonic. The broken segments 1 of the leucodiorite dike exposed on the final floor of the shaft suggest
- , that the cumulative horizontal component of movement on the Shaft fault was t
probably at least 24 feet in a right lateral sense, that is, the dike southeast J
of the fault is found 24 feet southwest of its location on the other side of the fault (see attached additional data for Pl. 3, TEI-844). Two small faults .
shown on plate 3'about 2 to 6 feet west of the main part of the Shaft fault O
13
.-my. , . en * '
- lt S 'Jh. , 5' . uNEf[ ~ . s ~.
.. C- . :e .. : .. . 2 e w*>. r- ;.;.ug .w ff- .Mu.,N,
,. + e.g.ram As . . .
yQ'JJg 'a , [4' _ d$
5,'.,N: 4 . ; '[ 2,Jj . [:
w - [ q. .j57 h- "' _-Y[ : ',.:
.f
- ly;%+w. n.w[ m m - ..> r . r w ~ +mm m,. .a : .N T.a.-, i~ .. .
.- - . .r * .
c-- ?-- -?r'*~~~ ~ - ' " "~~ 7
eg- . .
l n '
,.Lya _ _ - .w,w.ag . :
a,3, ,_ 43gy.4
- ,& y . . ~ . . . . . ~ . . _ , . . . . .,y. . _ , , . , , , ,, , ., , , ,,
y n * .m ,,' ,
j.' tt* ,,. ,
.c ,
. ,),
offect the dike, also in a right lateral sense, more than 3 feet.
- ! .)
,i- The unbroken extension of the Shaft fault into the overlying Pleisto-
' .; .. ~ >
cene mediments and the close coincidence in trend of the Shaft fault in .)
,J i .
-5 gre itic' rock with the' Shaft fault in the sediments within the shaft as 9-
, we. as along the en echelon extension for at least 170 feet southwest of .i
.~ l
- q. ,
the shaft indicate that the displacements measured in the sediments along- -,
1 4! l-this fault are also the result of tectonic activity. .J HAGNITUDE OF SHAFT FAULT IN SEDINENTS
.s j.
- The greatest well-established v'ertical separation of beds across the
.l
.I 4 e
Shaft fault in the sediments, measured directly on the wall, was 14 inches.
j !
An offset of 19 inches was measured between elevations -32 and -29 feet, but
- i l
this' amount is inneertain because the correlation of beds across the fault 4
, was not clearly established. That the movement of the Shaft fault in the q
i j sediments also had a horizontal component is suggested by: 1) differences
-1
. u in thickness of beds and inability to match beds across the Shaf t fault as
] )
[
seen on temporary floors of the shaft, on the south wall of the shaft, and 1 [$ i:'
l '.] s
. l, ' in teenches 1 and 2 and the 20-foot embankment between them; 2) changes in
~ - -
t . . a ,
, i I 'I I dip of the fault,'particularly the right-angled bends of the es.sternmost TEI-84
.i andhighestbranchshownonplate4,/nearverticalcontrolline39at ,.
14 N r
,.. 1 ? _i; f5 ; f . . . '. .S$[,. } ; ; ( f. *.
.}L; ,
-o , . 9 .,. . ,. , y , , . _ , .
-- s. . .- ., _ , !
j y , ,.. ;*: .
+-
- j .
, ,4 l
' i. .. j E.
2- ,
' elevation -14. Wholly dip-slip (vertical) movement would probably not 4
1 permit the sharp edges of these angular blocks to remain intact as they y
iI '
are now, but would break across them to form.a' smooth surface with no .
i
.q .
s .! keyed-in interlocking projections and hollows along the dip direction t
, of the fault sur b a -
1 x- .
The difference in thickness of beds across the fault affords a clue to the magnitude of the horizontal component, if we use data on the lateral
change of thickness of the beds. Such changes of thickness of beds across I /
-}
3-l f
the Shaft fault as from 8 inches co' 5 inches, and from 2 inches to a range q 1 !
1I
- l j of zero to 1/2 inch suggest a minimum lateral component of fault movement of i ,
4 to 6 inches, though the actual movement may have been much more. The principle used here is to choose a reasonabis minimum amount of lateral 3 I
l distance along's bed that would show the same change in thickness as shown
- ,.l s t across the fault. The unevenness in thickness of the unfaulted beds in the -
m ..,.. . . ,
, r 4 ,
walls of the shaft makes this method of judging the horizontal component of fault movement obviously unprecise. .
i ,
i.
.',. An apparent vertical offset of beds.can be producid by a wholly
. l ehorizontal fault movement of beds, if the beds lie at an angle to the l 1i horizontal. Though the sediments across the Shaft fault generally dip ,
- l 15
' r ~-- - . -,. . : _ . _ . . . _ _ . _ , _
j
' I .. . -
3 ;
' 1 . . .
. L -a L -e. ~ 1 : w.,; 8,.: s& .n ; . m,m._+ 4 aa44.n.a t.4%b.~W ~~ ,ys.~ _
_ ;,y <. . .
6 - * . 1, , ,. ... - , .~.,e..,.._;..,_...... '
c' .
.c. . .
.;w . 3, -
.t' t
.u.
, southeastward, we cannot' use this method of calculating the horizontal component e
f' k ,
of movement because it involves the assumption that the vertical component of 1.
"a =
movement is sero. The actual movement in the Shaft fault may have been. oblique in that it involved both horizontal and vertical components of unknown magnitudes.
'Nevertheless, if the following assumptions are made: la horisontal component of j movement is 6 inches; 2) component of dip of beds along shaft fault is 15 degrees; e,l
- 3) movement is right lateral; 4) vertical separation of beds is 14' inches, then the vertical component of displacement on the Shaft fault in the sediments is
. . . ? . .
calculated to be 12.4 inches, and tho' total oblique-slip displacement is calcu- {
- c.
e ., 3 . . .
. s .,;w ,;. . m :
...w<-
i
. cia.g;. .,. '
.l -
laced to be 13.8 inches. ' The' following chart shows the calculated amount of '
oblique-slip displacements and the corresponding amounts of vertical component of
'. displacement using various values for assumptions 1) and 2), but keeping the other
~3 I assumptions the same as given above:
d Horizontal component ' Component of dip of Vertical component Total oblique- i of displacement (inches) beds along fault' of displacement slip displace- I
- (degrees)
(inches) ment (inches) I e
l, -
s i ,
6 15 12.4 13.8 :
, '12 ~ ' ; fl .'r "15 ,,
10.7 16.1
' '"E- ""
12 , 10 11.9 ,
16.9 *l
_ ' 1!
12 '5' 13 17.7
.,;:. ~x;a w i.y .
6
, f5 13.5 14.7 6 1 13.9 15.1 ,
12 -1 13.8 18.3 ,
45.4 10 6 45.8
- s. ,,
. ,, /. 6 ,
, y, .: ..ur . ' . . .,.Acyr - 3.*gg. . % f.1 ., '.. . ., h pQQ ' , . . . *' * . . ,, ( . w . r.w., .
f fft
..f.+.. . . . . . , . . , 3 w mlt..e.m.usews$?, , ,ff' .m, _'m.
pf*f fi -fkj$',({;Y'he$ Y f,a f;, [! ' h .
hQ , b 'f*; *'f' db
.u.um,JfQ}+? . m, w. **, Qhn*,1*,, ~ a s'
. i.*% .
.m u)*1 _
w :v.~
- f
. . g . m x a, ,,,, . _.,.
n e w w n - a s .a. <. m m
,a. .
c+ ,.-..-
It should be emphasized that these total displacements are obtained by 4
assuming a component of horizontal movement of only 6 or 12 inches, which demands a vertical component of displacement of about one foot. If, for l..
l 4 example, the vertical component of displacement is assumed to be only 6 i 1 .,
j- inches and assumption 2) is 10 degrees then the calculated horizontal component J
' of displacement is 45.4 inches and the totsi oblique-slip displacement is
- ,\
45.8 inches (see bottom row of chart). Thus a decrease in the vertical component of only about 6 inches gives a substantial increase in the calcu-i laced total movement. This emphasises the importance of having a reliable i
3,
.)
figure for the vertical component before a meaningful calculation can be made l .f l ' of the total displacement. ' The calculations were made for l' dip to show that l +
the change in calculated vertical component and total displacement is relatively small between 15* and l',and because the dip in the direction of the shaft I
1 o
j ,
fault is believed to be between l' and 5* SW.
i I ..;
N In evaluating the fixed geometrical relations of dip of beds, vertical 7.. '
and horizontal components of d' displacement, the measured vertical offset of
, ll 4
1 l component of
, beds' of 34 inches, and the geologic evidence for a horizonta
- t 1 movement, webelieve it is not unreasonable to surmise a total displacement l
- }
of between one and three feet in the sediments. .
17
< . .:. . . ./ . a
.> l,
' * * * ~ <
j , ,
J5kOF s, yk _k ._ _ am*h w9 N ahSM m m .r UI"N , m ;. ,/ W Y,k,s.Y., G ,;.h
, . . . . ,,gy,2 U.S R %n:s;g g ,7,.3 3 4a'
- u.w . +- - naMt > '
A s ~,-
7 , ,.,.
,. ..w.. ., . , . . _ - . . ..._ _ . . .y , -. , ,
-.m.+r:-so r- w
. ~ . . .
,/ . . i . . , * +. ,
, . l j.j a
- 4 r
,.>l -
r Age of movement of Shsft fault in sediments The absence of the shaft fault in trench 3 (pl. 2), located about i
250 feet southwest of the shaft can be attributed to 1) dying out of faulting u ,
'[
4
- upward and/or laterally, or 2) deposition of younger sediments af ter faulting.
d j, Tectonic faults are characteristically- discontinuous en echelon, or
. s i
, branching. Many examples of this can be found in the literature on the i
l
, surface ruptures associated with the 1906 earthquake (see descriptions in '
- i Lawson and others 1908, p. 70-72 for the Woodville area 27 miles southeast
- of the reactor site, and on p. 63-65 and map 3 in the atla's for the Fort
' Ross area 18 miles north of the reactor site, also see Table 1 of present .
report. ) Surface ruptures, several hundreds of feet in length, are des-
~
cribed for the 1906 ea'rthquake which show a few feet of horizontal offset in their central portion but no offset at their ends. Lawson(1908, p. 53)
- j describes the en echelon and branching nature of the 1906 ruptures as i - ,
follows.
"I'he width of the zone of surface rupturing varied usually from a few feet up to 50 feet or more. Not uncommonly there were auxiliary cracks
' either branching from the main fault-trace obliquely for a few hundred feet or yards, or lying subparallel to it and not, sofar as disturbance of the soil indicated, directly connected with it.' Where these auxiliary cracks were
< . 18 -
enf. .
b *M # ,.
./' I f* ,n',',' ).,.i1
,. . a. w,w..m a n n ,: 1.Q,[n', .s[*.(~ m! ~ [ 5. ,'; p, .n. .i.ig
~ - ,+ ".-
r c.w.e JC../Y , n.' , 9.5w y.m.e.w[a..?%' 'g .<<
' ' WJ, i
, y;ya - ' w- u.i % y . . + - .
.n .-. n ;. ,
,_,u_.,._,_ p.a.,,, . . . .
..7.,..... , . , .
. .I ..o
}.- .
ya .
q' ( .
features of the fault-trace, the zone of surface disturbance which included them frequently had a width of several hundred feet. The displacements appear i
7 4
- t thius not always to have been confined to a single line of rupture, but to have
..! / .
],
], ,been distributed over a zone of varying wicch." ,;
4 . .
The discontinuous, en echelon nature of the 1906 ruptures can be ;
/
p' applied to the shaft area to explain the absence of the Shaft fault: 1) in
- , .h* I
., ' trench 3, at elevation 51 to 52 feet, 250 feet SW of the shaft; and 2) in .
the embankments, at approximate elevations 2 to 25 feet, 50 to 100 feet NE of c ' ),'. k the shaft, by upward and lateral dying out, rather than by behis covered over.
J ; '
_ . .. . _ ,s '.
]o . If so, then the last movement along the Shaft fault cannot be dated, from this
,' evidence, more precisely than any time following the deposition of the youngest beds in which it is found, that is,! at any time between > 42,000 - 400,000
/
l years ago to, say, a few years before the st aft was excavated. )
The absence of the Shaft fault in sediments on the south wel.1 between
./ . -
- .. . . ~ , , . . .
( ,
- !~ elevations -23 and -26 feet, and at some places on the floor of the shaft, and above the 'cgranitic rock on the northeast wall is attributed to the ,
av .
'i massive,~strudcuraless,'and plastic nature of the gravelly, sandy clay at .d 9 ,
J ,
l) these places. The clay may have been sheared but the visible evidence 19
- g *
- c-E wi e . -
., . . . .. .w.,.- . .
?- . . . . , ; . .a .** t. . , y , 2 t., , . - . . ., . .f oYv U f l** ' YJ {&_f s.' %Q:h.' yg!0f?.'"'?di .'A ts J !
^
% :. T . f l ;,** * 'Q ' ,.
' Q[.: . ; x ,, e
. ,;n ? " " *. !
. y.yp s
- ,, Qe
.,pr..m..w,a.
y~-.~:~, m y w . w. y y m.- ,, fag y,_y.,. ;g,p.e..,,;r.;og,,.g h p y, .gs.m..,. gqqw; p '*; ,.~f.ty, gg,0,.g :,, .
- . ~ . y .,.,+ ,-, n .n. : ,.., , . _.Qgl
,,. w n :n. n :..~ . ,.,s.c _ :w '){ :ww -
. ._ =q . ._ ..w e -
. sgga,,, . :_t rg- t
...~..~.--....--...sf..._.,a.#...7....;.+,-..,.,
e .a- .
y . . .- .. 7. . , p -
- '* ,A- ' ' .
., f. ,
' A,
[6'
- . ', ,, .A. ./
ji ,
7 , a ,
. q..
";. s. . , Si ,; r '
.i; j!. .
s - .
' [p '
,, . ql f($\;.
- , a for shearing may have been concealed by subsequerIt "rehaaling" by' re- /
'y
- t
. : .. i distribution of clay, or by the lack of marker beds in this struct f. cele.ss <
y i v 1 r
4 I~
,,pq,'f 6
?
'f r. ' ? ,j '.
material, or the ' stress may hav.s been taken up by plastic deformation. < e. .
3 1
ratner than by shearing. 5 ,
.);
1
- i .
. i ,
s,; ,
. m .- ,
5 a- ,1 y.
j '
.j - It' che absence of the Shaft fault in trench 3 is attributed to depo- .,
siti.s of sediments.af ter the last faul+[ mover.ent rather than to dying out, J i
- . .I f
a *i , .
6 then biting of the sei.tmen a took place > 42,000 years ago, the age of the -
f t , s t
- Y. g unf tted audiments according to radiocarbon measurement of fossil wood.
. I ./-
, y, The Ateiptocene beds at the site are probably younger ths ,t a crustal d M- ,
j ,
~
'1 turbance thct is estimated by Iouderback(1951, p. 86) to have taken place
- d' I
from about 240,000 to 400,000 years ago. Thus under this 's.sse * ; ion, the I
t
' Shaf t fault in the P'etstocene beds may have originated between .:,000 and P-g
' i
, u l >1 400,000 years a q , .
s r
! The evidence afforded by tren oxide color-banding for age of the P $
Shaft fault in the sediments is not vav.' helpful because the banding is l 3 believed to be truncated by the fault. Thus it is older than the faulting.
. 1-o e "j . ' - .-
The reasons for this belief are: . . .
.9 a
- 1) The width 'of n. arrow bands is preservid to the fault itself; [
4 20 -
- /
.. m .. , , ,
+
-.- . - . - - - - - . . -4 m .s e... . .a .
p iMy y +: g n :: M n M m g@h p cu nc.;,a. .( .:.r wsb. ob z : ., , .v.
m ,,h%,ww&pu. nstywW;n &.; y,w;h, &. :t.Gm%
. n., .:m w..e >xn n#yww : w<4M.Mc.
ymyr. m;r .+-m.
a, m..c ?
4 -
3 ~* a c-3 .
~ - + -yg
1 i ) :. 6 '
i ( ,,;+ .
a' h~.x ,. . .... , , n , m g ,g j
, ....g.,,_ , an. s _.,,_.,, ..u.,__ , , . , _ ~, .....3... ., , , ,, , .., , . ,_ , q
)
- s. e , . . . - ..... , . . . . . . , . . . . . . . . _ . . , ,
+ , i i
- , \
pJ ,.. ' ,c
~ .
.. )
%q M ..
-[ [: , } - 2) Bands do not spread laterally along the fault as would be 4 ~g ;t.
i . >
expc.ctMd if the fault were a barrier to the migration of iron-
/.
J i ,
j
, p i t-9
.~ y rich solutions; a
)
j > ,
e, ,,
d S- M. ;3) CoI c hands do not cross the fault as would be expected at a 9 eI l
a J6
- J
.. c 3 L 1 i
- 1 ifih. laces along the fault where the fault is not a barrier to j
.i ,
1 golutions; 8- ,
N~
Q Color bands do not appear to represent oxidation in place of thin 1
\ I 4
< . bearing ,
s beds, rich in iron /nineral grains. If they did,the iron staining
.i .' , .
)
%, )y .' could have taken place before or after faulting. .1 1-
'(- ,
}
t , e Iron-staining in the fault-filling itself is paler, somewhat green in 5
i
/s l
\I s , hue, and more diffuse than iron-staining and color banding adjacent to the is j
s i 1
- , r i i fault. The explanation appears to be that color-banded sediments were cut e s
\ I 4,by the fault and whatever chemical processes were active removed some iron i' from the pre-faulting color bands and/or reduced part of it to the ferrous
) ~
b]
oxidation state. The rate of this process cannot be judged because we know s
- nothing about the chemistry of the ground water that caused it.
J i J . .
1
- .. . Thus the geologic evidence bearing on the age of the latest movement l 4.
. 3- of the Shsft fault is not especially useful in predicting geologic events s that may occur in the next 50 to 200 years. That it cells us is that .
, , jf N ', ,
21 -
. a ,- .- -
v *
, W = .*,,T.' 'q fh . j'* , -( /[v ' y , 5" .~k
- , N '* , =g ak + .
[
d ; 8 e s} 'd 4 f', i. v#
.q.. . ~ . ., , ,9, m .
y- . x, c..- m .
r,w-.u. ,
nn.M. b ;;t.;. p _ 4. W
,,,.,,m.,
Q - n, o . ,.
,, . 7
,.. ,;c,. vi
...,y, 3 y.. ,..c,-. .
.g % ,7 :n o. .h..4
,, . :.g.tq p, . ,
. u.,e .. -
..,%,w_,,,.% %%_w_ . . s
,~_e..... . . .. ...,.. ,.. .. ., .
.,_a_,.4,,,,,,._m.___
j ,- .~ .
't either the last movement on the Shaft fault took place 1) more than 42,000 but less than 400,000 years ago; or 2) between > 42,000 years l ago and, say, a few years before the shaf t was excavated.
[. The Shaft fault in the sediments may represent only one episode
- of faulting, .the last one on f.he Shaft fanit, though no conclusive field r
evidence for this belief was found. On the other hand, no coaclusive evidence for repeated movements was found. If, as is cny best guess, only one episode of faulting created the faults seen in the sediment, we may
. .. s
+
l conclude that there has been only o'ne episode of faulting in more than
. 42,000 years, or possibly in as long as 240,000 to 400,000 years. Note that this conclusion is valid if the faulting took place only a few years ago. .
Sorface ruptures west of San Andreas fault zone Geologic evidence for faulting west of the San Andreas fault zone was investigated to determine its genetic relation to the zone for use in evaluating the probability of future surface rupturing at the proposed site m ,
,on Bodega Head. Some of the most meaningful evidence was that related to i
, Surface rupturing created during the 1906 earthquake the 1906 earthquake /and said to be of tectonf.c origin is described at many
+ t .
22 +
g is .e g.s .g.e-. ,, umme mmesm _
...,e., ..w., 9,.. . ,p,.,,,g .Q,
.. s . . . . /
f ., ?- [f *., ,\ D
- $ * , s. V ' . - , ; M* s [ '2*. , . ' , ,
- i, I* bgg , a.y- , .**if. Ley q,
( ., , kdy gj ' ' . , , VE QgN { * , _ _ _
]Tary."'{_ p,j.; '_,[,*. .. ,, ,} "?.
.; Qg. h
' *~
t's
^
- - . , ui _ _ y. L ; _
- - = - . L,w-ga ,, .
- r. .
9 1 g .,
f _' :,1, .".'
. * : i;[ .
n
, , a -
'l ,
. II
-places west of the San' Andreas fault zone. 'It is unforcundte , in light of its obvious importance to the evaluation of the site, that Bodega Head 1
, was n::t examined by a geologist for the 1906 State Earthquake lavestigation ,
l q j Commission. Though it neglected Bodega Head, the record of ever :s of the t , , ,
,j . .
c.% , .r,s,
't I C 1-l 1906 earthquake is the only useful one we have, consequently we must rely
.:,i ,
L
~
heavily on it for clues to future earthquake phenomena. Some of the places described on Point Reyes Peninsula and in the Santa Cruz Mountains southwest of Los Gato s, at the site of the Morrell ranch, were examined by us .
- 2
. , and the rupt'u res at some localities appear
- to us to be of 1
.. ; . . ..,~.
g zu
. . 3',, . ,
'~$ "uddoubted tectonic origin . Of great significance is that some of them are
~
farther away from the San Andreas fault zone than is the reactor shaft on Bodega Head.
The State Earthqpake Investigation Commission report (Lawson,1908)
, contains numerous descriptions of rupturing outside of the San Andreas
, ., .. am.m. . _. . ,, _.
4 3 .
, fault zone. Ruptures were abundant at some of the localities. For example, ,
1
, Gilbert (Lawson,1908, p. 75) says: " Bedrock cracks occurred at many points .'
> - , .i
. ,w; y, ,- -,a -.
4;
~
, - 4 within the Rift, usually appearing as branches from the faults. They were ,
.c u_.; g, . . , s.
J' , .
3, y.g .
y _.
I a seen also at a numb'er of points west of the Rift, their distribution reaching L
t g
to the ocean in the vicinity of Point Reyes,10' miles from the fault-trace. ,
y -
. 23 -
y.., .. .
}d '.~g% N C 21p /2,04SN,u
,4 . .
QUf . .... 3. . n g y ... . a . .. ,yi Jk.y. Q @
f itifqg,/Q,bg-
[; d O t. j'f q4.wyy.. /^;y dgjgg.'p e[( ti':ygAsy,y,w 3 J
- Q.gsgy)MMm@M.( ' yM, g;$$^2qW
- gh;y..w.sA,7 .
- g. .
- A;b c,,e. .O .
w
, , j m.g m y ._ ~- ~ -
- - - w ,Ju '
,v ,
- . . , , .~ . .-... - . . . . _ ~~ . .
?- .
i .,' .i, ,
y :
a- , ; '
t At the most remote points they were quite small, often barely discernible, and no system of arrangement uas discovered. They are peculiar).y prominent
'I I
j along the summit of the' ridge constituting the southwestern rim of the main i
i 1 i j Bolinas-Tomales ' trough :This summit was visited on four lines of road, and . i^
- q. .. .
1 d at each locality conspicuous cracks were found. On the road from Inverness to 1 e i .
Point Reyes Post Office, about a mile in a direct line from Tomaleo Bay (that is, a mile from the San Andreas fault zone) a crack'was traced for more than 800 feet. Its general trend is east and west, but its course is not
/ .
}l straight .and it has s' branch diverg'ng i at 45*. Along this crack there is a lll
. :- Y -
,'r.., .
x, ,::. .
., , , s. ,o, horizontal throw of from 2 to 6 inches- ". (Underlining and parenthetical note is ours). {
Table 1 is a summary of all descriptions in the 1908 report of branch faults outside the main San Andreas fault zone as well as some notable ones !
- . )
- . l within the zone. It shows that branch faults are common in the zone and r
in some stretches near the zone. It also shows that most branch faults were I -
shows ;
d,,
not adequately' described or located, and/a scarcity of adequately described .,
~ .
.] . .. ' .- ;l
'.q' .
e.xamples of branch faults outside of the, San Andreas fault zone. ;'
e n
I h
i I .
N
'} y . . . _ . . - . . . - - - . - . - -- - ~ ~ - ~
- -/ ~ ~ " ~ ~ " 1 1 yi s . >m ? *, s ,>. ' t' w.ds ' . - . .'. ** *I.,*- . -[t, -
- ij,h'.N, 4" ., . 4 s
't 'h ' ,,' $ 's '; d' . ,
. . '.'; l .
,,I
'* , [-
- t<
k & ' W @'L?fy"?$k' iN, b' '. ..M* ?!? ,5 ${ f 9 kj- " E *A +'N #
' ' N',[ #.h ,' fl1. ] '
i '1 '
" H * * *^#' M M -;
- - P*'*"*
. . , , . ' , -o w ,,
. .. s ~ - . ,em' . :. , a.sa:.ama,s.l.ie - - -
4 ... . . . , . - . - .. . . . . .e . .
, , . . _ . _ . - . . . s....., _m .. . . . . . .. , ~.
- e. . .
_a , , , .
, ge , .
i.9 - ,,e. . p.- . .
cl . .. ,
+ .p.
I .
? 'Ubert's (Lawson,1908,p.76) opinion on the extent of bedrock fracturing in connection with widespread modification of flow . prings on
.j
) . Point Reyes Peninsula is expressed thusly: 'The spring phenomena and the ,
, visible cracks' may be grouped together as indications of bedrock fracturing, .%,.. , ,
t r . . n . ,
,. m ;,.,., .
., and their distribution indicates the regions 'in which the rocky foundation a .
'j ,
o of the land was more or less shattered. That region includes the Rift and o
e extends from it to the ocean. The phenomena diminish somewhat with distance from the Rift, but the fracturing appears to have .been important and general
'~
through a belt 4 or 5 milec broad." /In connection with s"pring flow mo.difi-
- . _ J.: . . .# . -
,. . . Tl l.' " ... . , ' ?. . ; . ' '
,V -i W .' ,
Lawson 1908, p. 76)
, oat, ions east of the San Andreas ' fault' sone he writes . ., .
&.h^ -- -1 "I heard of no changes in springs east of the fault-tracal, although a number of inquiries' were made."
In addition to ruptures created by the 1906 faulting, undrained topograph'ic depres'sion features were seen at many places along a stretch ,
i-
. :. o
- a. -
., n
. , ' .:,a , . _ - 2 ]
i of the San Andreas fault zone extending about 200 miles south of Bodega j :
Head, and as far as a mile west of the zone, that appear to be created by
,c,,,
- l. 4
...n. y .& .,~ -.,
.- 1 n . ., '
[ -
f 'tectotd.c movement 'such as' faulting or folding possibly in the last 20,000 .
- . :. . . v. 'y
. i ,. . , . ;.g ;.:. .
1
- years. Ed Lake on Point Reyes' Peninsula (pl.1, TEI-844) is such a 4 ,
- )
1 feature. It is about 3,000 feet west of the San Andreas fault zone. .
.r. .
25 .
t -< = _u . . _ .__ _. ,,
. y .c' ..
wh
.+; x. s,2-rw s_<, e J. w r . ;. .;.h = g ; w.g . wv -..J. 2m. .u.x-mm.,us Y,
4
. . ~ . . - , . .
? , .. ,
r i
.i 1 It lies in an elongate steep-walled depression probably fomed by sub-sidence, estimated to be more than 40 feet, en a block bounded by faults.
I Similar opinions on such fencures have been described by other
.]
.1 J geologis ts. Higgins (1961, p. 57) discusses the area between Point Arena
,.i .
.t -
1
! , and Fort Ross,18 to 59: miles NW of Bodega Head, as follows: "---numerous I
j
> small ponds and depressions on the rolling summit of the ridge west of the i
1906 fault trace could only have been caused by small dislocations along faults that are either part of, or closely related to, the San Andreas.
i Yet most of these depressions are at- least half a mile southwest of the 1906 i<
, . .e
- 2 , ,.
. ,, z ; < .y,e
.I fadic trace.,, s , s. : . c., . :
x, . . . -
..t 4- . .
r i
, e i
.l s a '
s f o.r.&.,, y. .e,2..,,....,
s
.~ .
q ,
~! -
- m. ..+ , , . , .
. 't :
,.; 4 ,- .~ . s. c ,,
.4
,e - .. u . . . . ,% ~ ,, m
,, ^ , ,
y ..
.} > . ,
. .x. ,
26 h
e, se d
..y-- . - - . -.. en-....., ; .
s 1 ! .., . t#* .."
~
4, 2. , * . 4 - 3,. * ,.e
,' , ' h y',,p*,1 .' )
- ',.,7. *
.{
',~ ~ ' . r. .Ne,... [ . . *. .Q. .A [.hftQ er s.','.-,[, ( 4,(y ') M m o m,'.q' .',*'.$.. . > '. ," . s.g .3*gd .4p
. ., w. .,,;
w.y M,:'e,T'. .*[ CC,'% }' 9*.%.'.',s.,,A,. js,.*M, # .j' ',A, g . "'g)*,,,-jt);* . . q ,. , .
yi,y',4,*g "f, ka M.e.%. 'P..' %,.s
, 3+
ph, - -Q.~ 'g p.h ,3?
, . .. s. . :. .
t
- l. I .
7T 'i.r.,,,S,*'),.f.c.
AvJ,,' . :,4 .t yr,.
.A 6,,L'.G.;yy .... 3.E ' .; t.f 5...w,
. ,m ,,,.,5If
- ,/ _g,,%?y'...
lf,_y ..,.i . A .E , g . ,.
.,.r.....M.1 - w
- f ..y W . . . .. . . ,. m. .
..re, '-.,. y
.. .,_,,~.
_ -d
...-... n.--
- s' usud.,v.u.w.re"~^
- y y ,,
/
. . . 'l
- e' ,. ,,3 - ..
Significance to Bodega Head site
, How do these observations relate to the question of the probability e
I j and magnitude 'of surface rupturing at the site during the lifetime of j y . - . ,
- c. m .
6 4
.4 plant? Surface rupturing by tectonic faulting has occurred in 1906 on terrane geologically similar to that of the site and at localities
.i 1
.]; that range from those that are closer, to those that are farther away ,
from the San Andreas than is the site (Table 1). Table 1 shows that 3
ruptures were not' reportied for many stretches of the sone: In general 7
t i Win th abundance and magnitude'of the cracking and displacements increased j ,
i . ,
q towards the San Andreas fault zone. They were seen as far as 10 miles k
a west of the San Andreas in the Point Reyes area, but the onas farthest t
a i out were " barely discernible 7'] at a mile away, one had 2 to 6 inches of v.
I g horizontal displacement; and some at Inverness, about 2,000 feet from
., . e .. ,
r the zone, had horizontal displacements of 2 feet. With respect to
.Y
- magnitude of displacement Lawson (1908, p.148-149) writes
- "The
,.. 6
, , ,.s -
recognition of the distribution of the movement on auxiliary cracks,
- {
, ,,, . , . , , , . n w f. .. -
!l aome of which may not have appeared at the surface, and the deformation I
, i
. i
.. 27 +
L e
- I d.,
I, , p . .
%r.
r J.w. .d .' . L . . . .
E.. .. . - . - - =
.. d
...t.
e' *; *iI M.a'.- ..
.i .' f.py.{ l'pi -. ~ .,'
t @p.M f. s'p. y @J
- I,,,o,.- .Kg D,, gg e < f l y 'E ;,_,
9,. p~s*{ ;M k';'y;' y. .mg_vh_. ..,,bw.:g
. , g.,j s.,.agg:an..: :a.my..y 7, , , e w
. c.. w v w,...~1-.
~
n .
- . _ ,o
.,, ;p,7p,5Q ;..';.. f
.,_..3.c_.,o,
,,.- g
,.. .. < Q
l (g ~ y
.,,u. ',e6 e . .y3_ CA r ;. gq; g o-- ~ - q = 3.. m %. m s: ._
._ _.m. -,,.ma%m _ j
..; ,,.7.-. . . -. - . . . . . . .
.n . . . . . . . . .. . . .. 3
.- e '
4 s
1 i
1 si of the grotmd alonst the zone of ruptura. juatifies the conclusion that, t
a J
M
,] except under peculiar conditions--such, for example, as in the marsh at q .
1
- the head of Tomales Bay--the maxima figures obtained for the displace-i-
ment by the measurement of offsets at the surf' ace must be a mininann y expression for the true extent of the smoment in the firm rock below."
1
, l 4
j The trend of the branch faults showed greatjvariability, though t
i
, j table 1 shows that most were generally, but not ersrywhere, aligned l.
northwesterly. ,
. s .
4
... . l The 1906 ruptures, both within and -outside of the sone, generally l_ w- u .
1 followed scarps or sags which were believed to mark old lines of repeated faulting. That tihis tendency was not universal, however, is i
shown by Lawson (1908, p. 53-54) in the following statements
]) t - "This differential vertical movement was made manifest by the t - , c< _ . < , . a .. . m . ,
' appearance of low, abrupt fault-scarpe, ranging from less than a foot i
up to 3 feet. Many of these occurred along the slope of somewhat a
degraded fault-scarps due to former movements, and served to revivify .
^.
l .- .: ..: . ,
- them. In other cases the new scarps have been developed on slopes where ,
i j .
,l 28
=
., 1 l
.l; g
J %
e; .. Seq bgi h,,s.k id m wQet,yy.m,,.,n.--,r;,.
. ' -, .rgg%.&au.ww.h i : %nj&g:g;%.+l' .,. , y. >Qg ; ; v.
t ;r .~.,..p,.. vp v_ w : m ,..n : u.
% y m 9w .ua 7;-,,, w.<,u, , ,
.y x
%.,q.., ,., .
f.,,
., e as y ..,.m .i . ,. . . :c., :
. n.a .- . . , ,
qg 4
y ,
- _ a ,.;,
. . y Q s ,
.] no trace of a previous scarp can be detected. The low scarp which j i
.1.,
1
- .j l
, fonned on April 18 is by no means a continuous feature, but appears at i 1
. I a great many places not widely spaced along the fault-tra'ce, extending 1 s: ... ,+ , ,.' , I q,
i
- often for hundreds of yards at a stretch, with intervals where no .
- .I a
q . abrupt scarp can be detected. In the latter places is it probable that i
l i . the differential vertical movement has been distributed over a zone of
.I some width, underlain by formations in which the deeper seated
.ji -
, fracture would be taken' up by plastic deformation." .
9 . +
., At Black Mountain near. Palo Alto cracks were exceedingly abundant s'
.i ' l, $
for as far as # miles from the San Andreas fault sone in a wedge-shaped i 1
i 1
area between the sone and a 10-mile long, northwest-trending fault that )
T' intersects it on the east. On the other hand, no ruptures are reported l
j at many other places where large faults ' intersect the San Andreas at a )
j 1 ... . . ,
l 1 similar angle. Thus, the geologic control for the location of many j
! . i
! . - 1 l
6 ruptures is unknown. )
I
'l n . _ i Only the most general application of these observations can be
- y:. . . i.e. q[ a - '
3 made to the site, because of our general ignorance of the geologic '
.l al
.i control for some of the 1906 ruptures, and especially because of our 29 +
y +- ,
e .p nt. g :W. u.
.f : :.%y.u
. ,s.d z g w s n .. . . g.;u.zix
.- ~ -
mg.w w y:S s ~ , . : : ,
v,
~ c s , an. ~ .
,, w. > u, . _ .
. .y ,_.y y
.wL ..
3 l
. = . .L -
yy. , 'l
. . . . - - ~ . . . . . - . . . ,
-~. u... .,,..... . , . . . . .. . . . :.. . . . .:
. s.
y:) . , ,
1
.! ; ~.. o, .
. . . . ,j L3 .
- l 1
l general ignorance of the magnitude and direction of prepasstion of the I
~
e energy which created the ruptures.
i I
. Tentative interpretations are:
j- . .. , . . . .~.m , . . . . . , . . . , . . . .,_ .
, ,. yu (1) A possibility exists, however remote,'that a strong
+
. earthquake associated with faulting on the San Andreas c .
fault sone like the 1906 one, in magnitude and epicenter ,
location, may be accompanied by surface ruptures.somewhere 4
- I i
., ,e
, _ .or. Bodega Head. ..,.' ]
I !
' - * .l
- p
- .y'.
. , . . ~ , . . ,
l
- %(2) Because the site is about as close to the San Andreas
- s .
fault sone as some 1906 ruptures for which substantial i
horizontal displacement was reported, if a surface rupture )
i j
i did occur on the site, in connection with a 1906-type
)
., earthquake, it may have a horizontal displacement as j ,
6.. -. w ' :. ..y .. ..
. ,. , x .
l (greatas feet. As is discussed later, the probability f
i
) - of such a displacement is thought to be low, though the t _
.m , . . ,
I l Jf, . ,ossu,isty sho.id not 3. Lied o.t.
a .
. w ,.s . w. . . ;.; . .
f, .
- e 1 -
4 .
. . t z .- . _. ,
..W'
^
' * ,, .a4 , ,. ? 'F : r. g i. . ..
p
/[, .N $(; , . r[!. , .d N s ,
h', N j
- hl. / .t44@ , # '
,' w eT 4* 4, '_F
- r ,I , ' *Q,(('l y P.5 -' **;( , . , p 'J,Q y "_ e, _,[ h
- h.'.' J
- g .at M p en[w qygg_s,e:sp.p,9,.>%gn.w'J2j# m sl,g. w s . g ,. .:7..w :..'...,2.2:7. :..,,y s,.,.g ;,,GRy[* ,.'J ,
L'..fk
y ._;._ - - -. - - >
- - ^ u :- ,
y..,/ . . . . . . - .
,...,m.. . . . . . . . . , . . . . . . . . .,
.g
.;/
a- . .
r . ,- ,
't d m. ~ .
~
a p.
(3) Surface ruptures are more likely to follow existing
, northwest-trending fault zones, rather then those of other .
'a
, .{ '
}; trends, like the northeast-trending Shaf t fault. The 1
n w-- .
- tg.
1 pattern of involvement of existing faults may be
-i ,
I '
slightly different if the epicente.r of some future
. strong earthquake on the San Andreas is significantly different from that of the 1906 earthquake, which is thought to be some 30 to '40 miles southeast of the 1 '
.y l '
s' .. .. .
.j ' '- *
.. site.-!I'lokal[epicentermayalsogiverisetogreater j . , .
movement on ruptures than in 1906.
(4) Because many 1906 ruptures touched scarps and other surface expressions of established faults, the scarp
. or trough features on Bodega Head, especially the
- ' low northwest-trending troughs and bedrock scarps j in the hilltop south of the site, should be considered J -
4
. .n . ,
potential locations for ruptures, until it is proven ,
o .. ,, .g. ,
- that they are not fault controlled.
31 * '
)b j +5 4 A g,','.g ,N $ l' '
^n + '
,b *'a ,J.,',',)
. g,rapu, Pg;.--. ' $eg --
,, p. *f.',
..e n;. ' e
% 1, t.
, j ., ,' ', 'l'., 4n _ Arn *'.*C
- , ., .s ,r r. m,. o.,'*,,'.3,,4 .# , a
. .m m. ,. : . . . ;
73
wp ~
6q.
,._,~.,.._<....m....,.,.,,._..__.- . . _ . .. . , ,,,. .. .. .._ , , , .. - s. /.
3 .,
.x, y
.o. -7 <* .,. ,
.} .4. a. ;,,. . s.. ,
. ,g .
- 7, q
Shaft fault and San Andreas fault sono u
,p y ,
The San Andreas fault zone is a more or less vertical complex of
- l 4 ,
N' '
faults whose major movements have. been right lateral. The stress field 3
j . . . . . , . .
- %. 3. . m. ._ c ,. ., .3 g. ., . . , . ., ,
. . ~ , . . . .. . . . ,
[
_ that keeps the some active is located in,a belt many miles, perhaps l . s -
hundreds of miles, wide along the sone and at a depth of many miles.
From the orientation of the sone, N 37' W in the Bodega Bay area, th's e.
direction of the principal stress is generally thought to be horizontal 1 d
, and oriented nearly north-south, or possibly a little west of north.
j
.n - ,, .
- l. t ".The shaft fault is oriented N 4(R, at a high angle to the San Andreas,' {
] . - . . . .
and dips steeply westward. The Shaft fault probably also has right-lateral movement.
The nearly north-south principal stress direction postulated for
- the San Andreas movement is inconsistent, by most shearing theories,
.J .
- , - ~ . - . ,; ; n. ,
3 ' with the orientation and sense of movement of the shaft fault. Never-t
- . theless the Shaft fault does exist, is within the stress field of the 4 ,
.s. . .
~w... .
2
- f I
-San Andreas fault mona, and the :
field evidence for its right-lateral e .- . :. . . e .
.g ,
.. ...< -e. p g;g ,.ga; ,% .. ; .- .j t
'I movement appears reliable. Furthermore, its activity at least once I 32
_ . 1 i,.. .i t e > . 4 i
,g
.- id5$h..b.e.o.m: h Qy,e,w.j-Qy,.;. kO ,Rb l$sf', N ,,q,. Jh{; . l.
r
. c; m,. w a mm ,#.m ;,m m.mu,.
m,:.lgs[. ;K.Lp e
~h l f.: , _ .0 '.*tj'g. ..x.s l,. ;,k A
- r. ' +
.m .! . s . 4.
f_ ;.., a. _ _ g c ,,,,,s. m n o. ,,
- 7. s3/ se.........-.....m, c v, .
. . . .. , , . . s. . .. . . . . , ._ . _ , ,_ g
- g. , s , .,
.g7., ,: . p.fy. . .. . . , ,
'i * .i q.
F
- l*
. during the last 240,000 to 400,000 years establishes its contemporaniety
[lj and close genetic relation with the active San Andreas which is only a
~ .. . p., ,, . .. ~ _ . a . . . ,. gn , .,
short distance away and has been active for millions of years. Further
]
]
4 i
support for the genetic connection between the two faults is the 4
i J abundance of northeast-trending faults seen in the shaft and along the shore, and northeast lineaments seen on air photographs, on Bodega Head and along the San Andreas agne on Point Reyes Peninsula. ,This support s
.- .r *. !'
l is weakened, however, by lack of data on the direction and time of -
l
.n. . ..s.s.c m , ,e . , . . ,
, *- *.. .]. . g . ,. '
i movement along these faults. P=--^ as the actual orientation of
- I stresses in the crust in the Bodega Bay region is unknown it is possible that in the vicinity of the shaft the local principal compressive stress axis is more northeast-southwest compared to the regional axis, which is
'theoreticallynearlinorth-south. He right-lateral movement on the ;
I
-. I j Shaft fault can also be explained and correlated genetically with the l l
i . . .
. -l 1 . stress field.on the San Andreas if the active part of the San Andreas l li J, < , v . j ., , ,.-
,j 4~
2 fault sone makes a band to the northeast within the sone itself east of
. s U
the shaft. Hills (1963, p.174) gives an exangle of this fram a locality
. in Australia.
, 33
.4-o .
. , s;, .m. ,
3
. . . , . I5 YN
- <p.v ' ' %, '?.'r 1 aw,,wys,;r
- ;at.5r, d.# ?wf;,.. .,4ph[f w.e.[0. 2. [ W;,x 2
EkiY y . '. 1 [ i o,' d+' .f', - * ,I.,' ,, ff.' k
. cp >>.?. qc,h: .;,...,
Af, *[L
- ,k,i, f
.t.;12 & :.s,.. ;s,.,y, ; p ,.;: y M ; p , y ,Q
. ... {
~!
=A 2 c.. ..;....
..._ ,. m .. ... - 7. _ .. . m_._
~
&Jaa,,.x,2.:.. L --
.q .
1 2- .-
,* a. * % '".D lN',*f . ' ' l'l. '
t < .s
- i . i
'! Significance of Shaft fault and future faulting in granitic )
j rock of reactor foundation shaft and vicinity l
.., I Foults are abundant in the granitic rock of the shaf t, however,
~
j 1
1
! i one of the largest is the Shaft fault. The size and complexity of the 1 i
. .I i .
2
- l . Shaft fault in the granitic rock indicates that it has been the locus
,} , . -. . . , m._ , , . .. . . .
,. ; , . - a.,w r . . .. , , .,
.i 1 a ,
of strain relief at many times in the past. Offest of dikes indicates i
.,A !
i 1 .
- that its movements have been primarily horizontal like that of the
- 1..
San Andreas. The ruptures in the Pleistocene sediments evidently formed i
. ,I i.
" ]
. during the latest movement along the Shaft fault. They, too, show l
i ! '
i e .
i evidence of some horizontal component of movement.
, i ..
s % *p O s ;,; ' ,
I The strong development of the Shaft fault indicates that local l l 4
I strain release in the vicinity of the shaft favored northeast-trending faults though a more or less east-west direction is prominent for l
l ; smaller fault's (see figs. 1, 2, TEI-844). The ruptures in the Pleistocene sediments on the Shaft fault, especially in light of our uncertainty b c.? . , , , a . .v .; 5 ' . . w. . .
~. , ,
, 'f o the time of occurrence of the ruptures during the last 240,000 to l I
I 400,000 years, point out the possibility of future significant tectonic 1 . - . < .,.
- 3. ,.
.4 .
j '- fault movement vest of the San Andreas fault zone on Bodega Head. ;
.w . s. m.. y; .. -
l 3 r- :. .
,,p.. jy ,
l y a .
. o
..} ,
- r. J.., .
e ,
t 34 l
\
'+
.. ~
m .w ~ . - -
. . . . . . . . ~ .. . _ . . .
f.y-. .e sN'e/,f_QG%'.' !fh $ -m s:.;h,y.d l
x_ keu 'w.m.
NFA{Ql n. u'. A :w..m fi q'f';!hf* -f$, . , Jia[b \. *>
- A l g . . . .a .x .
,ls} h.... a.lC~..es
. } ,
u..s za.a.a n.e. . 9 . ~ ..
L .q .. . . . . . . . , . . . . . . + , . . . .-.. o .. .. -........ .,. ,.. , . .,
l
. ... e..
~}
3 l*n-l i
t l
.i '
\
Although the cumulative horizontal component of movement during 3
- .i. -
t ,/ the lifetime of fhe Shaft fault, which may be millions of years, is 4 i !
1 1 ~!
j ; possibly a minimum of 2k feet, it'has probably had only one large )
movement, probably of 1 to 3 feet of horisontal displacement in )
~
> I i the last 240,000 to 400,000 years.
It is tempting, then to say that the probability for a movement
- j of a similar magnitude on the Shaft fault during a 200-year occupancy
.O
'l p y
.! l of the site is between 200 chances in 240,000 and 700 1p 400,000, F f1
' G 8n
_ whichgivesbetween1chan'ceinlEe00chancesand1chanceinp?UW C00
.i e t I
- 1 chances. Such a probability calculation, however, i a almost meaning- )
i i less in light of our general ignorance of the local details of the i
i rate, magnitude, and pattern of strain accumulation in the crust below
- the shaft that ultimately leads to fault movement and earthquakes.
i .
.i ,
l Indeed our knowledge of the regional strain buildup anywhere along j l ! the San Andreat fault' sone itself is very inadequate and is t .
'$ a i g g
/
j
, 4 i l 35 t
. . . , _ __ _. _ _ _ __.. ~ __ _._ 4
- s. , , . . ~._ . .
.~ . .. ,r . _ ~ .
.,y,' i pf5.((q'N* hkN7l QE* "*
r*
- s . . ms.a' a' k,' N anee[n b . e(rm. s,, . f,'N4a w" h '= "d,**,f.[,w ~ s e'th(.*g.,h.eah' i .E' u.. Or,'*
' y - (,d ' ; ..f .T [
e [ j% w .
& Mgk
,;.7rC ". _ ~. ... . .z -
' 1 'i" > ' -i - 2 4 ._ '. m u' r, .
..u *
,,,e 1
I .
. reflected in our inability to predict the time, magnitude, or j epicenter of earthquakes along the zone. The inference that only one episode of significant displacement occurred on the 1 shaft' fault in'.240,000 to 400,000 years does not permit us to 1
- , .-....w:,.,..,.n. .
- . :. ;t.t g. ..w. .
A,I '
i ,
dismiss lightly the possibility that a large movement may occur
? during tho'first year of reactor operation, nor does it support
.l
< or deny the possibility that no movement or no large earthquakes
. n -
will take place during the next 2/Miyears.
t t ,
- Our opinion is'that thbush' the possibility 6f a movement
, m,g. .h s ,
j ..WOj d ." $ l.,1,,.y ,
.on the shaft fault'from a few inches to a few feet should be
.].
- .x -a -t . . _ .
anticipated during the lifetime of the reactor, the probability i
of such an event is low. This oP i nion is based, admittedly not very soundly, on: 1) The trend of the Shaft fault is nearly ,
- perpendicular to the San Andreas and its j
., q , w n .4,,....,,,,.,.,.,..-
i t ,t . .,-- - ,
,_,,,,y,. ,
i .
'right-lateral movement ..is contrary to what f
1 - - would be expected if it were a shear, conjugate q
- u , .p.Q:.
.to the San Andreas',,,
~ ~ - ^
9 !
fg ~ . . 2; v 4 ;.~ ;;eg,-.:
- .0 /
- 2) Though conclusive evidence was not found to
- a support it, we believe it is pos'sible that only i ,,' 36
. - . ~ . . . . . . , - . . ,_j si . . . . . . - . . . . . . . . _ . . . . . . . , , .
3
,iItk.;.n.
, . . y , ..,( g z,pf. ; .g 1 mI? p oW+ 9t.i. e [a @ r M'~ih.MU h 3 h y'sk[mg.[i.,.c,(ll. o w .c k,h:m.;, c_'em .; g,; s d jg h e w.:p;.yp s..ja.g.g,,,.g;m,,f;s
a.. a z _. - .w _ .
m y p -.;,,...,, ,.-.
- t., __a,, ,,__ , ,._ . _ __
. . z ,.
- n. .. ... . ._..._..... ,. ...... , , , , . , , _, , ,
r s . . , . .t _
4 one movement took place on the Shaft fault over i
a period of time when several, or perhaps thousands of, 1906 magnitude episodes of fault-displacements
. i
- - t .
. and' earthquakes occurred on the San Andreas fault -
a .- , . . , .c -
,m. ,, .
f z o'n e , some of them presumable close to Bodega Head.
[ .
]} .
- 3) Most of the ruptures of large displacement that 1
i
. occurred west of the San Andreas fault zone in 1906 l
f trended northwestward whereas the Shaft fault trends ,
a J
northeastward. . /
p- . . ~
- e. 9, I (;..; em, , f.- . ' ' . ,, 3, ;g.;., .h ., ..g . . ,
'. o "4
- 4) 3 . . Lack of rupturing.of Pleistocene sediments on all 1 ,
t l
faults except the Shaft fault suggests that northwest-I trending faults in the vicinity of the shaft are l
.j, . 4
'. ; i l
generally of low Recent activity.
i i The' probability for displacements of about 1 to 3 feet in j ' =- . <.,7 C. . . , . . w . , ., .x g , ._ , , , , ;,;M.4,, , ,,. , .
. , . . a -
s ,e , t, , % , .g , p ,
. connection with strong earthquakes originating nearby on the 1
w - .
- l (San.Andreas, on Bodega Head along strong, well-developed
< \
u s . . . . .
g ,,
j ....u. ,
.7 , , ,;
,.-.x . , . , . _ , 4 .. . . . . .
. northwest-trending faults is believed to be low, but slightly j
,. c u. ;- p . ; w .y ,:,... :. . . ;.m. y , q ,; , ,. . , ,
~- . . ,.
.d . . - .. ... ,. .
I fgreater than the probability of such displacements along'the q
, . . 1 s .'
j 4 ."
. ., - 37
b', .
_ ; ~ :. - : n .* n .w..:
~ .. ..-,....: .. - . . .,
.g.g:,m . . , ..-
.. ,, * % .m,.. .. M. :. ,, .
y.4w3 ..1.:
1 q'N.ymin@rg
EE
.agy, . . gg,.ygg;.g.gp,.n,,k.,
t h .(k h.h .h .[/.
., g. ;g 4m{g':U.c
. ( , L . ,,; $ ( ? g t ;' - .g f p gg:f y
g m_._.. . . . ___ _
_, . , , , .,m._ .,
. .g . . . . , .
. hr ,
' }y *. *
.c . , _ .
e i ,
.' Shaft fault. Strong faults of northwest trend are not present-1
,1 in the shaft, but are present elsewhere on Bodega Head. Their
>1 ,
potential geologic hazard .-to engineering struc'tures should be
'l j li considered, o ..
, s
. - . rg , ;.., . . . . . .
$ If we assume that a large earthquake, say of 8.5 Richter
, 3erte, y magnitude, has its. epicenter in the San Andreas fault Ain Bodega
) .
l Harbor the following chart gives our estimate of the probability 1 ;
, i 9 of the stated fault movements'in the granitic rock of the reactor l
1, a ii foundation shafts i ,
) n /,;).r. . . .
4
,' Horizontal' displ, ace, ment
~
.. . .o . ,
Probability i ,
! on a fault in granitic ,
l rock of shaft
, j 41 to 2 inches, perhaps Moderate to high i j 't l
4 on several faults l
I l
approximately 1 foot Low l 1
i feet Low, laver than above, s i , , . . . '. .. , . .
but still a possibility i
3
. L'5 feet Remote 1 ./-
s m ,
'h ,,,
j 's 3
- . 7,, r * ,1
) *-
Ce- -
J a ;' c _ , ,
e # ,
}
I h -
t 5s !
j .-
j ! -
1
- i. __ m .
.-_,.__m...._...._._._..._..y .
? *
?P
& 4 . . 4 $ ', s
, * ~
,p .,,....~ , .. .:.
..,.,f d Q M g irgi g g u .sa g.s v e ce.a k u u w w w. w e - -
a .
r q ,, . ... -
4
- i
. s .
- - - 1
,, / -
We estimate the probability of a 2-foot tectonic displacement at a - ;
1 r
- t )
3 distance of one mile from the San Andreas fault zone opposite the epicenter of .1
?
f '
l a 8.5 Richter magnitude' earthquake, to be very low. Under sbnilar circum- 1 i -
, i
. . j
-. --stances we also estimate the probability to be very low for a 1 foot
. 3.;,.y-j I
tectomie displacement at a distance of 2 miles from the sone.
'i I f
o i i
i
/
t
. r
.q -
'p-I
- j. ..%
6
, a. . . . '
-ec . ..
8
. qrr , ..
lf f.**'..g.*f.. , , . , u . g4 . .$ ed [ j,, , < , s ; ., ,4 i i -
J
, i i
1 l
\
1 l
s n
a i
f a 4 .s J-k o i .. ., . . , . s -
- I e !
- +
. 0 1
O f =4 **g .'-_
, , 4..t.s. <
, 8
, 8 n
- 4 t '.
9$
a ' ; . .. . ,
- .; .-~;. <
vz .. .i; ,
j .
., 1 1
39 - I 4
s; . 4 7 n . ;, . ". .-. . . . . . . - - .: ,
. A
.. .~. . . . . . -
J P av1. '
s e W, fr4 wA% W.' h# w; 0 .$t i'.f .M AqQ t; 1res?g@y'q. t
. ,.(. ea
- .*u, ,t.o.
suAm u No,% -? m---~ MC # - - -a' --
t
- . ..'. . V;Nfr!
y- F.o:- + % ~ i.?
- M : 5.5 t r.# / @t: <t.e. <W'1,/
'y'.-l.gr.y-fGiff.
%
- i. ,rr .i, e - r >*r i d'.-
- i Q , ' '*" W 4
. _ . - - + - - - .u ,_ _ _ , , , , _ . , _ _ . _ _ _ , , , , _
f i'
Ry,FERENCES l . Benioff, Hugh,1964, Earthquake source mechanisms: Science, v. 143,
? !
t
- 1
- n. 3613-1,406.
i , .Higgins, C. G.,1961. San Andress fault north of San Francisco, California ;
1
- Geol. Soc. America Bull., v. 72, n. 1, p. 51-68.
I Hills, E. S., 1963, Elements of structural geology: John Wiley & Sons 1
Inc., New Yor, 483 p.
I lawson, A. C., and others,1908, The California earthquaks of April 18, t . ~1906 Report of the S tate Earthquake Investigations Commission:
1 1 j ll !
Carnegie Inst. Washington Pub. 87, v. 1, Pt. 1, 254 p.; pt' 2,
. [
- p. 255-451; atlas 25 maps and seismograms.
Louderback, G. D.,1951, Geologic history of San Francisco Bay: Calif.
Div. Mines and Geology Bull.154, p. 75-94.
i 1
Schlocker, J., M. G. Bonilla, and A. Clebsch, Jr.,1963, Geologic and l
seismic investigations of a proposed nuclear power plant site on Bodega Head, Sonoma County, California, Part I - Geologic investi-1 I-
, t j . gations: Part II - Eaton, J. P., Seismic hasards evaluations: U.S. I l-
. s .
Geol. Survey r3 port TEI-837, 51 p.
'i tr - . ._ . -. .....,.. .,. , . _ _ , . _ . _ . . _ _ _ _ . . __ . , _. _,
. -n , .
4
- ' *F b.h_ . M _ , .g j7 -
. A. M .: __ *
.. . . , , 3
,, g.,., sm . y: .. .
.- ,c
~ __:
,,_ww ,_ w . -
1 -
g -
- 6
- . i, 1
. ,, ,>- p'.. 4 -
-?
..,f-
- 4. #
= a w. = 3 - t
- 7. i .
4
, It Schlocker, J., and E G. Bonilla,1963, Engineering geology of the ,
proposed nuclear power plant site on Bode 8a Head, Sonoma County, 1
~l. ; ,
a ,
'.,.j .- '; 'l Califersia U. 8. Geol. Survey report TEI_-844, 37 p. '
c.. i l
.l j
-: * >>e. .r, ,
}- { u s, e e
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i l
i .
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+
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-
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i e
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4
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- f I t > ' . ?
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- es. S' .
' p .. ms. . No . *r m e e . m . . ~.. e, m.o w . ,. m e. .mm. ~ m. .J
' .e s
, 7 . . <>a' +,,%.;.4 .
.- 4
- s. . , .
^= 1* .,T,,y
= * '
- fG[.; , .l%. *f./. ..*.. , , %..K], M *IA,'a f"Mb a 'h ?jM. , d. .t.J,~ A ;D. .. 3.'i h, , ys'. yg( t. ) . '
.Nj g ,. 1 ,,, e ' ...,.,.s.,,. . .,. .p._
W,.---- . L*>ti yy *. ta'.' .3 %. ,* .-
,- 3. . ,
- .c, , , f . ,l , .; ,.7 ; s, '_ ;. ,4, y L;g;h ,, . 7,.w 'i~ 3'
','g .t','
- '{.e r ,
- ___._~m_=(.,. . & .,4, Q .7_; . + _,
- ;s'pr. , ,-
. - .c - -
n--
m,.y .4 .- , .
, . . . ~ . . _ . . . . < . . . . . ._. . . . . . _ _ , . ... . ........... . , .
. . . . - ;m ,
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1
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a
- 15. Bibliography i 4
(d) la Review:
1 Griscou, Andrev, and Kane, M.F., Aeromagnetic and gravity data is
~
i- )
the Bridgewater quadrangle, chapter in, . Geology of the !
't Bridgewater quadrangle by Louis Pavlides, U.S. Geol. Survey l
.i publication. !
j Kane, M.F., and Snyder, 0.L. Structural shape of gabbro body Lebemos, i , Cconecticut Submitted for publication im U.S. Geol. Survey,
.I
', c,v "short papers in the Geological and Rydrologieel Sciences 1963.
h
,; Kane, M.F., and Carlson, J.E., A gravity staty of lithology and structure in Clark County, Nevadas Submitted for publication as a U.S. Geol. Swvey Prof. Paper, 85 tFPed pages,15 illes-traticas.
Ease, M.F., Peterson, D.L., and Sherums Eeward, Bouguer gravity any of northern and eastern Maine, submitted for publication as a map with text in the GP series.
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.~~ '
SUMMARY
OF ENGINEERING CE0IAGY OF THE PROPO. SED NUCI2AR
. POWER FIANT ON BODEGA HEAD, SONOMA COUNTY, f
)
9 CALIFORNIA - s i, .
.v.
I
't by f
Julius Schlocker and M. G. Bonilla * ;
- i. ,.
, .e,mr .;., _
i 1
., . .,,r..- ,_. e ., '. , ' ! '*2 % U. S. Geological Survey .
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l CONTENTS
!s Page In troduc t ion ~ -------------- .- - -- - -- --------------- ~~ ------ --- .
1 . 2.
, Ts unam i ha zar d -------- ---------- ------------------------------- 2a ;:
. . l
- w. - . . Geo lo gic s e t t ing------------------- ------------ ---------- ------ - 3 ,,_ . ,
. . c. ~ -
. Granit ic rock of Bodega Head---------------------------------- 3 .'- j!
t Joints an d faul ts ---------------------------------------- 4~
'{:
We a t he r in g------ ------ - ---------- --------------- ---- ----- 7 f Pleis tocene and Recent deposits-------------------------------- ' 7 Fos s il s an d a ge-- ------ --- -- -- - --------- -------- -- ----- 8 Tilting of sediments and its significance to the site--- 9
% .y . j S ha f t Fa u l t -- ------ - -- -- -- - ----- - - ------ - -- --- - -- -- -- -- - ----- -- -
11
, .w., - . . ~ . .
i Origin o f S ha f t faul t ----------------------------------- 12 - Magnitude of movement of Shaft fault in sediments-------- 14 Age of movement of Shaf t fault in sediments------------- 18 l l i . Surface ruptures west of San Andreas fault zone---------------- 22
*l
! Significance to Bode ga Head s ite------------------------ 27 l Shaf t fault and San Andreas fault zone ----------------------- 32 ,
. Significance of Shaft fault and future faulting in granitic
- a i
- rock of reactor foundation shaft and vicinity---------- 34 jj
~
l t i e
-l - ' Re f e r e n c e s ----- ---~ ~~ -- --- ---- - - ------ - ~~------------ 40 j- *
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['- 3.
. LIST OF TABLES Table 1. Branch surface ruptures, San Andreas fault zone, formed during 1
earthquake of April 18,.1906, and described in the 1908 report
~
t
. , % -u.of the State Earthquake Investigation Ca==4asion. .
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,; ' 9 if Summary of engineering geology of the proposed nuclear power plant ,
i f 4 f i 4 on Bodega Head, Sonoma County, California. ;j 1
- 3 By J. Schlocker and M. G. BonillaN , U. S. Geological Survey ,1 s ,
. . L ,, , ., INTRODUCTION f=
- w. - -
. . [,
i The purpose of this report is to answer pertinent questions [. P asked by the U. S. Atomic Energy Commission staff in connection {
] . .
1
. with an application by the Pacific Gas and Electric Company for a ,
- l. -
License to build and operate the plant. Additional background and !
/ ,
detailed geologic data is given in U. S. Geological Survey Reports
'_-! c. .; &
el 0 ;m.p.c . E I TEI-837 (Schlocker, Bonilla, and Clebsch,1963, part I; Eaton,1963, - part II) and TEI-844 (Schlocker and Bonilla,1963). I i The main aspect of engineering geology that will be discussed
.l .
.1 here is the one relating to sudden permanent displacement by rupturing s
- i. a, d .. of the foundation zone of the reactor during an earthquake. The 6
. r aseismic design aspect, however, has not been neglected by the AEC
] 4 j .' briefly 1
staff and is discussed /below. From the brief historical record and l O This report was prepared by Schlocker at a time when Bonilla was , i in Alaska; it has not been reviewed by Bonilla. .
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from theoretical considerations (Benioff,1964, p.1,% it is bel.ieved that 2 to 4 episodes of severe shaking from a strong earthquake may , occur at the site ~in the nexc 200 years. The plant should therefore .
+
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, , ._ .' f be designsd to withstand damage from these seismic vibrations. We - '
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{ understand, however, that the accelerations, emplitudes, and frequencies >q s'
- 4. -
of seismic waves likely to be encountered at the site have been esti-mated by experts in engineering seismology, consulted by the AEC, and i' : l that the design criteria include consideration of resonant frequency and strength and flexibility of critical parts. . t.
. . s. _.
W ---> . ; v
~ " '
Ati the outset it should be made clear that the granitic rock . c foundation on the floor of the present reactor foundation shaf t is , generally capable of grting heavy loads. Ultimate, unconfined , ; 4 compressive strength /results range from 1,037 to 16,800 pounds per square inch. In our opinion most of the rock on the present floor u.-
., v of the shaft has strength properties in the upper half of that range. .veil Neverthele'es it is recommended th3a the b QS$
loundationgeparatio include
'h i"D L' i
" dental work" .to remove ,3.-
soft and plastic zones along faults in granitic h]
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a. l' i~ t . si - h TSUNAMI HAZARD
. s.
Tsunami effects on the shores of the site have not been investi-geted. The only data obtained was tentative information supplied by t the Chief of the U. 8. Coast Guard station located on Doran Beach, i i about 1 mile east of Campbell Cove. He reported by telephone that the j v P, largest tsunsai effect at Bodega Harbor,id in connection drop of seawith levelthe of Alaska 3 feet
-l relatively rap . . 1 followed by_a- s earthquake of March 27, 1964, caused afrelativdy in~p'id rise of 2 feet.
He suggested that more reliable information could be obtained from the
/ . t
' y F. G. & E.tida gauge located in Campbell Cove. The plant working level y
' . .. '.. ....m.., ,
.; s ..
[ of 25 feet above sea level is probably above the reach of most tsunamis l 9 s' that would enter Campbell Cove. The submarine ridge between Tomales j .
- i Point and Bodega Head would probably tend to prevent buildup of large .
t tsunami rise in Bodega Harbor. Nevertheless design of cooling-water l intake pipe should consider the possibility of strong stresses from ,[ u
} .
y
- rapid surges of tsunamis and also the possibility of temporary sea- i' '
. . t ..a .h. -
4 Icvels 5 to 10 feet below lowest reported low tide.,
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GE0I4GIC SETTING N site is adjacent to Campbell Cove on Bodeta Head, a granitic rock body that lies along the west border of the San Andreas "ault
^'
sone. N shaft for the reactor foundation is approximately 1,000 ,
, feet west of the zone. N granitic rocks are partly covered by k
- 5.
3 Pleistocene unconsolidated sediments consisting of interbedded near-shore marine, beach, dune, marsh, stream, and slope debris deposits that have a maximum thickness of 180 feet.
.W. , .
i N site is on a buried valley system that was eroded in granitic i !.
.. , . j'.$
rock by a surface semean and its tributaries, when sea level was > - TEI-8W ' relatively lower (pl. N. The valley was subsequently filled with ' marine and continental deposits. The main buried valley crosses Bode'ga Head in a more or less east-west direction. At its deepest 1 .. point, on the east shore of the Head at Campbell Cove, it is more [ . jj TEI-84 I than 80 feet below sea level (pl. 2). !. !!O .
. .i i n 1
GRANITIC ROCK OF BODEGA HEAD F .I j ' n. N granitic rock of Bodega Head is mostly a foliated coarse- s
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I J, WibG LOCATION OF FAULT.S, JOINTS, abo OlKES 4-t t . .., 't - a a
* *c" .
.u +. -: E . .. r. w.t v. e- . .k . % 5,, s i 4. .deM--. d'. .*c ..w. .w Q .v E t.- ..M,-... f .. .-.=-.~.-,- 5.5 . .w
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grained biotite-hornblende quartz diorite. ' Pegmatite and splite dikes
.f up to 7 feet in thickness, and dark granitic rock inclusions are common. .
' A leucodiorite dike with a maximum width of a foot cuts the granitic -
I t
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, rock of the shaft. ;
.u
. . ... , . . t 4 I
.. r Joints and faults y.
i , t Joints and faults are conanon, although they vary greatly in abundance from place to place. Closely jointed rock is cut - 4 or
- I
; more sets of joints and also by irregularly branching joints. Most rock i
i .
.is broken by joints and faults into blocks 3 to 5 inches wide, though j
- .l i
'.[~ ,
- 5. i
, the range in sizes is from less than an inch M 4, 0mn2Y in fault zones '
to 4 to 6 feet between some joints and faults. Faults and joints seen between elevations -66 and -73 feet on the perimeter of the reactor
~
foundation shaft are shown on plate 3, TEI-84 Traverses along the western and southern shore of the Head reveal
~
\'.
se 1,
.1 shear zones 3 to 10 feet in width in the granitic rock about every 150 kj to 300 feet of t9 averse, as well as a great abundance of narrower sones t ,
, , .of shearing or faulting. The wide zones consist of complex 1y inter-
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* * .'*'l related sonosf of plastic gough (clayey material of pulverized and *
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. ,.u #. c.- . ,
- i. . ,.
chemically altered rock) and breccia (coarsely broken rock), ..nd mylonite (pulverized, but firm rock). Breccia and mylonite in most shear sones is also altered chemically. All faults seen along the shore traverses are persistent in u . _. . . . . . . . 2. .. _ . . %. , , f l .,. lengthforatleast50to100 feet [inthewelinxposedrockyshore t
! n.
~ #
and adjoining seacliff, and those that are more or less parallel to , the shore, were followed for 200 to 800 feet. Faults in granitic . rock away from the shore and above the seacliff are not as conspicuous as those on shore because of theIover of vegetation, ' weathered rock l 4
.)
o ,.,
- debris, and other Pleistocene and Recent deposits. Stereoscopic study 4
of air photogritphs gives indications of lineations in such area that are l probably faults. Some of these can be traced on the photographs for hundreds of feet. I The fault zones in the granitic rock along the shore and in the r . ~v .o . ... , I i shaft are conspicuous zones within which the rock has been more. severely .
}
*1 l
,t l
i;; l- altered physically as well as chemically than the rock between these 1* l
; , zones. The magnitude of movement on the faults is difficult to measure , jl
, . - . .. 7
_ f
?
in some places because of the massive nature of the granitic rock. 5 n , s
- f
. ?. c 1 f
L
.' s jf
' '; , & r5%)cn@ y.s9;iQ.yQ V+.Fx ygf zg.-: ,,d ag. .
. L"$;$.1W1.. Q.2y"d_f@My@w
,. 9 p, WS en U; -NQ.-~fJd.n.SSO)..%.- . s-n ,w.-.m? ?.WG, 4.c I
^
)
- p....',...,',.a,. .w . . ., w
- c. .a ;..A;J., , a . , ,. t;,2;, ;,_, , ., c ,,',,j , . . . , ,; g,,. .,, ; .g
,g gl,j,.g.j -
, 2,
. ; . . . c.~ , ,,. ,
, ;+ 7 , .
+ . s ; L. . .~. . l Nevertheless, the dikes and the dark incluatons within the granitic ) I 1 rock serve as. markers, and where these are broken by faults, the broken j segments are separated from an inch or two to more than 20 feet.
, .o .
f,- .
.- ~ 8 hearing is also evident from microscopic examination of thin c
. y
-, sections of granitic rock collected at widely separated localities on ,
t
' the western and southern shore of the Head and at the reactor shaft.
/
Abundant shears on a microscopic scale cut the quarts and feldspar crystals. Shore traverses and examination of aerial photographs 1, . . 4 shew that trends of the largest faults are, in order of abundance, ;
. P*- ,.M g
.h , ,f v .l mostly northwesterly, northeasterly, and east-west. Ihandreds of ,
1
, J j measurements on faults exposed in granitic rock during the excavation of the shaft showed the dominant fault bearing is within the range of E
N. 70' W. to S. 80' W. and the predominant dip direction of faults of .. L _ n) e ,
'this bearing' range is 50' to 75's '
'.I' I
- i. .
- G
.s
( - g I- The abundance of faults, plastic gouSe zones, and microscopic.. ,, p
. ,u,
* - p shears in'the granitic rock of Bodega Head is considerably greater G
- - ~ . - -
, G H
"* - than that for'the vast masses of granitic rock in the Sierra Nevada. .
.x . . . h-
,1 i
7 v 6 $
^
} 3 ,
'.;- S4 , , . , ,, F .I b 'O : 5 j; ..[*
fy . Q WQ y "';ng.hM:)x%':
,c b';,9Q5.h iD y Yv xy ,
, 9.wky;,y ..+.--- .n..p,4;' m .. g% a.ww _ n.,m.., (;*af"'? y g.v.p~{w;,t, gtni[i t w %. w ,.
,- .ms;.e _,. g .; g at.g . S t;+"-gb5.f;.g.;A jg peyp.
~,.
p- .:j.t Q I.m . y ..%h.t. y ^ s ,.' ,:.l b ,4;,,; # ,;;. A g f., y .,...,s.;.g.i.w ,;;.,d c; 3 .-- G , M ., M . q g . , p+ g . . .. m
- 4. . .
- a. . ~ , . . .. ..,,. . . .. .. , . ,, . _ a . ,_ ,, , , , , , , , , _,,
l
' .y
. .y .Id I* ' '
, . . . , , j
. ., .y.g. , , j w. , . ,,;gq . .y . ,,
,.9 .
4' g 1 y' Weathering
. The granitic rock generally has a 5 to 30 foot thick mantle of l 4 weathered rock and soil.. The soil is a mixture of sand, clay, silt', and F
l
'6 ,
gravel. .
.a. 1 , . , ,
-.4.. ,,
4 F121STOCENE AND RECENT DEPOSITS .~.z:4 , r ?,
- e. . .
'A 'The'se deposits lie on granitic rock in the general vicinity of the -
.C o
'I
; site and are possibly thqinost extensive accumulation of such deposits on i
. > i
< i Bodega Head. They are thickest, more than 180 feet, over the main buried .
valley south of the shaft and wedge ost on the flanks of the partly-buried
. .n ,
s ;.
. s granitic rock hills north and south of the site at elevations of about 35 r
- D~.D ,j.7,,,7 ; G g,,;,g '. .gg , j ,_
, . } , y.
feet above sea' level. il
. I, One of the prominent sedimentary matedals in the shaft area is gray, t
I t, . i massive (unbedded), gravelly, sandy clay, that generally lies directly on i. 1 the granitic rock and reaches a thickness of more than 30 feet (plate 4). ;
, - ..e
, y 'L In many places the granitic gravel in the clay increases downward forming a , j w.
, 1n ii gradational contact with the underlying granitic rock. In the south part h t ,
1
- . ,s.
3
~. " of the shaft the gray, massive clay is interbedded with 0.1 to 1 foot thick 5 o j. , ' _ . -
- ;f d
.r,- sc.
j
%eds of sand and clay, probably of marine origin. All of these sediments i o . .. ..
. 1
., . ,e are covered by a thick beach or nearshore marine sand deposit that lies (
. 7 .
.w...n.
>, e s
e A
' , $hN h ,,!. . . . , . . . . . . .
T,MN rMCOMh ** *' .'b ? .. /3.~ 4.. , U.y~,y'digf>/g .Kk 2 m e n e[ m . _ .m e s%,ff'[ m m e,kn.gye,Mf.11. j,,,[ kT.;pl-% qw,.i+T3:egwg
s g.. sv s. . . . a. . . .a . .. . % w. 2.w ... ., ; . 4L;J.a;.A.. A& R &$.e.sa_J C .m a.,a,..;
.g b ;,. g. 3.w .,;.,,. s . m... . 6.,.~ . . . . - _ , . . , . , . _ , , , _ _ . . . . _ .. ;, _ . , ; -
, *e ... .
} ~nn. ..
.f m, -
'r -
i1 1l.e W au +1 , y
*in a small valley cut in the underlying ol/ der sediments. The end nn 1
thickens to more than 40 feet southwards towards the main buried valley. North of. the shaft interbedded sandy clays, clayey sands, and sands all
- 1
,g containing varying amounts of granitic gravel are exposed to elevations gZ, 'A.
d % ., . .. w.a . , , ,. ,, , y . - ': . v - . . . - l 7 t 5 i -
- Jof about ,'
85 feet above sea level.
.m s .. .. p
,}-
Fossils and age i F' g 1-
- The topmost 5 to 10 feet of sediments, mostly soil and wind-blown l t.
sand; are believed to have accumulated in the last 10,000 years or so and 1 l c...' [ are designated as Recent. . Fossil wood is abundant in the sediments be ow
.a v,y. o .. .; ..
~, . .- w.g.:
.i m those designated as Recent. Wood collected at elevations 77, 55, and 49
, c, . , ,
'. feet above sea level, all within 240 feet of the center of the shaft, ,
I i i j l s yielded radiocarbon ages greater than 42,000 years.. A study of the , fossil flora in the sediments 5 to 25 feet above sea level by Jack Wolfe,
,v Paleobotanist, U.S. Geological Survey indicates: .
,; : .e .
j ';
. }l m 1) The f1' ora is similar to the Pleistocene flora of the northeast shore of Tomales Bay and that both were deposited about the same time and in a ,
u
. pine forest' environment. Invertebrate fossils in the beds at Temales ,
o *
. .a. , : .:: .; ? . .
' Bay indicate an age younger than the folded early Pleistocene beds of
~
e the Merced Formation of the San Francisco Peninsula area. ( .
*j . ,.
8
's v
i *s. .A ;" . A,-s x sr s ~ a
. . . ----. m, i,
M,a ? Au m. _%swQ'b'* dT %I D ) 4d~,808p/e,s
.ow. o h#dt('TD y
- w. @.r5p,
$hD'-(d*h
... D-~nw it.wM.v d'% ,E g i[dE.
JUEoM, h !OI N y^r. m.f.
,ys6ey
_s,.0._4N..,%# h. jj'+,#7 4.. . m .... g Pi.*[*,SQ.E'i%WwA, 6
/,%:.w k
,~ ,. % m , . , , - , . . . _ . _ ~ .. .,_., . ., %._. m. ,u. . _s .
.,; . j w w . a .p...;
- u. u n, ,:n.a~.'ww,w.~nh-.z ~. w. . u -s.-- =.a-.w~au.--
j
.p....,;,-..~,-.-..-.m_... .. . . _ . . . . . . . . ~ . , . , , . ~ . . . . , - . . .
j y . - / '? ,
.,......9 J
.t s., . .: vy p. - .- ,. ,- * .- ..
. . 3, !
y i 1 lb . 2) Beds near' the ' northeast rim of the shaf t at an elevation of approximately
;t-1 4 7 feet, were probably deposited in a fresh water marsh.
7 J Louderback (1951, p. 86)' estimates that the folding of the Pleistocene .
,I :
. part of the Merced Formation took place from about 240,000 to 400,000 years l\
; 3-',. ...
;7 3. . .. ...n..
, 3 '
, ago. .Thus the sediments between these containing the wood ' at an elevation 1. 1 s
of 77 feet and those containing the fossil flora at elevation 5 feet are
, ' older than 42,000 years and probably yohnger than 400,000 years.
.i .
l. l Tilting of sediments and its significance to the site
"' 7' ' A ' general southeastward dip of the beds to as much as 8' is believed '
\
t
' ~. m. . , .
. . ~ . .:v. .
m.c. . re'x.;: ;;a.:c py, wG. a ,. . . . . . . . .t.
'; - to be caused by southeastward tilting of the Head. Incally dips vary from
'l ; zero to 15 degrees. Most are southeastward, though some are westward or
' L, i northward. Locally variations are believed to represent inicial dip of the sediments acquired when they were deposited. Evidence of tilting of I
. ' beds believed to' be of Recent age was not obtained because bedding is .,
.,~ . _ . . . _
.; ..m -
. s t.g .
- *" poorly developed in them. Thus evidence at hand indicates that the tilting
.l ,
, ' r .,
t
.e -. - .
' occurred some time after the depositten of sediments that are more than $
- ]I c .' ,
- ~ - . ;
y
- y. w g j ~ w :u42,000 and less than 400,000 years old. . i
' t I - . ~. . .. .,.;, .' -i1 Observations of the effects of the severe earthquakes in Chile in i i
1960, and in Alaska in 1899 and on March 27, 1964 indicate sudden tilting 3- . l
.5 ,.m'*;%}& Q . , % . , , 9,; -
4
., .,m 7 ...y. _2% . _ !
!~I$N kkbi b ,NNkhkhhIh hbhhkdii$MNi$hddfhMN
W
, ls -f .L;k.SO:.? ;1' uS & N
- Y:. ' ':%.L *.: h&O ' .~SJ '-.2w '.n 52 $ ~C.Ad 5 N.Y E 2
. g . e 7 . . r, . . . .,m ....~. m . .,. ~ ~ ... .._. .. -. - ..~. . . . - . . . . . . . , - . ;
t i
,9. ,...
fp ..o g- . . , - . ~ y
, y
? , .
; on a regional scale. In other places, however, it is believe.1 that tilting
\
.: has been gradual. Tilting is not considered a serious geologic hazard to 1: <
1 1 the plant because: (
'i
!- generally I
.' . .g; '[ J '. f,1)' Tilting /affects a wide area; 2) tilting may be gradual and its ji
. J. . .
t
. , q' effects in 200 years may be imperceptible or nearly so; 3) the .
.=
I probability of sudden tilting during the next 200 years is very
'l ,
j . . Iow. No significant regional tilting was detected in connection 1
'. with the severe California earthquake of 1906.
-- s 4
9.,.., ~
. L. SinFT FAULT
. . ..e, o . ^ ;;
. P'
~..c+ ,
*T yJ. ; l .1:; . e,s 1 s
.g i The Shaft fault, a major structure among abundant faults seen in the -
.Ii l
3 granitic rock of the reactor shaft area, is the only one seen there that i i
.e i- is accompanied by faults in the overlying Pleistocene sediments. The direct connection between the Shaft fault in granitic rock and in Pleisto-
. cone sediments is well . established on the south wall and on temporary j j
1 , a i floors of the Shaft. .Its general trend is N. 40' E. from the south edge !
. 1 .
l
, , , . .t,
, of the Shaft (For location, see pis. 2, 3, 4, TEI 844). Its dip in '"
. . .. e .,
F- *
,.q, +
,,~> -
. granitic rock is 65* to 85' W (dip is measured downward from a horizontal ~l I
, 9 3
- plane); in sediments it 'is variable (pl. 4, TEI-844). An en echelon branch !i 4
. i
. 11 >
L . t
-o; - ,
W = 9**"#*G f a
..** ; $~ . p .
5 s
**
- 1' '
~5 E.' - '
- L *?h' O *
- 5. .
y p., w. n.,u$y n., _ w S...G.oiW' 4_ ( M. w,%m6,,s,.ww' 4eQ 3. 4..
. a .s. .
r .m aM.,i.g,3.A'.gs,ss
. ~ _ . MM.J w. .ig_.
y2 g.. ,;@ g g i.ay_J(, Q S g. Q.., ._ __ . j@.
7 , w# . ,..d . a.i .n . a :, A .M.w-M 1. h~ m~.e.- -_.L.n . . .o --..a.w- ~, > w L.1 ^.- :-A u 4 . .%~a..--. D.
..._-,-.s.._..o.- . .. .. -
'u a : '..
-, , . - a.
j - t ,,s -- , - l
.n. *. ,
~
I
^
.. f .y . - # .m, .
.r
- f. ., . ' , , yr . 1:
'in sediments was followed from a point 2 feet from the Shaft, at approximate t
elevation -5 feet to a point 170 feet SW of the Shaf t at approximate. ele-i I
'] vation 21 feet. Though it did not terminate at this point it was not seen ,
- l .$.
j
;; .2 's a.M; in% crench
, .... . ., 3 hl.2,' TEI-844) at elevation 51 to 52 feet, 250 feet SW of
. . . ;, .. . m .. . . .n . . r .
.i -
w;, . e, ,,v . ,; . *E ..
.b I
,. ,r.
_ lcheShaft. .
., y e
The Shaft fault could not be seen in some places in the gray, massive,
, gro'ull'y sandy clay in exposures of this sediment on the south wall (pl. l 3
4, TEI-844), on temporary floors of the shaft in a belt about 10 feet
.i '
/
- j. wide on the south border of the granitic rock, and above tib'e Shaft fault
~
RO$ .. b
,. ' .' in ' granitic on the northeast wall', . At the last locality the fault splayed..
i ( I e out in a complex of small, intersecting faults 5 feet below the top of the granitic rock. The complex may represent the chaotic jumble of granitic blocks created by an ancient landslide. The Shaf t fault was not seen in - the embankments northeast of the shaft. .
- +
w
! . . . .# ,. ~ . .. . , .a t ,
u .i
. Origin of Shaft Fault .
. t ,
r'.
. The origin of the Shaft fault in the sediments is fundamentally
-p
'D' impodant in..o any evaluation of its significance to site acceptability and !!
4 t - plant design. Tectonic faulting is considered to be the most probable origin. .
. 12 '
S. L kk ' ~
'} Y *Y* . .t , , . . *** N? )
yn;a &s.; m.,. n.:,n.;m.n.w m. iL* .Y w:,wnu.~.mu. s'n.a.m.xm( 'n, ~ , l.f m., h j2,*n* *,A
-w -wwm; ,v.
a,-.g.pa:mww
.;~<n:vmsm:wsrw :' w. . me . . .ym ~~*#m mm m.
9 1
):.,L.ij 3.. h3 4:m , p
.u J m
. ..-w ..n
,. % ,. u: w &# ~.~.- -. --:zw&Ma .c.a~. J%, a M.:-f Mm.3&l.Oi'h*&u
. .. ~ .4..-.. .- - .- . . . . . - .
- - .lj
, - s.. .....-.;. 4
,; n .. ,& . . . .'
e; ,my , 3 gy.wf. .g e. - . m3 s . . , . - - 9 . . t Other mechanisms considered, but rejected are landsliding and subsidence from compaction of sediments. Lurching caused by earthquake vibrations
". l dF i wa's also considered, but this origin is fundamentally parte of the last
-l_ .
. {-
y .3 _ y
~' .
q two origins listed. . "4 3,. m. 4.. ,. . . m ..e - > '
-l
' y Faults other than the Shaft fault were found in sediments and may be caused
\
.i
'l.; 2.
k by. landsliding. 'One, located about 35 feet south of the south rim of the
- y. l shaft, trends N. 70* W. and several interrelated faults are located about 100 feet northeast of the northeast rim on the south cut of the ramp leading
/ .
-to the shaft, trend about N. 55' W.
l . ,, .- a .+.e & .% . .- - 1 I{ . Tectonic faulting is used here for rupturing fundamentally related to crustal stresses, such as those that produced the 1906 earthquake. The j Shaft fault in granitic rock is obviously tectonic. The broken segments i; - { of the leucodiorite dike exposed on the final floor of the shaft suggest
. F,. . ,.n .
.i
, t that the cumulative horizontal component of movement on the Shaft fault was
^A'.. j probably at least 24 feet.in a right lateral sense, that is, the dike southeast
.- 1 e
* . i
-t . -
of the fault is found' 24 feet southwest of its location on the other side of 'i I
-i y .a. 4
.s Ji s
3-*
-. .. ' ,, i ,s
' this fault (see attached additional data for Pl. 3, TEI-844) . Two small faults
.s ..
5 , 4
'?.
shown on plate 3'about 2 to 6 feet west of the main part of the Shaft fault g
. 13 ,!
.x .
,g s..T * 2 .
N.. . . ..
^"
, ? 5h $ihk h' . h . . ?lW* f$ $YD'$ NY fY . c:!u m. m%_$;?$ V g.'.?.*'Uh's5_f. _u.,.m_.m
- 1 w ,ae~: .ar .ymmgi M _1__www@;__ap_%:ww.s-wl _ ., 'h:Del .\D: %,T;f-l;;{ s.,Q * -_e._ .v.zu
_. s. .s:
, #y,-
? N %. ~ ,~w, .m.g :. . .. .:. u : n .a w., i.4 z .z.s.:.. .. ..- u .: 2 .a:x. i w . w 2 c c. 2. a _ ,L , ... ~ ..
.. . ...._..,...,._,,......__..,._s.,a,. . _, ., .. - .,. _ ._ ,
1c ... . ,s 2 ..,i. <. < .
, 1
- .f ,
$ b a g ;
.]
r . (' offset the dike, also .in a right lateral sense, more than 3 feet 2 .] ( ! The ~ unbroken extension of the Shaf t fault into the. overlying Pleisto-l cene sediments and the close coincidence in trend of the Shaft fault in
'4 granitic rock with the Shaft fault in the sediments within the shaft as
. .m -
m ,,, r. , ...
$ .well' as 'along the en echelon extension fo'r at least 170 feet southwest 1of
)
the shaft indicate that the displacements measured in the sediments along 1 1
- 1 this fault are also the result of tectonic activity. . j HAGNITUDE OF SHAFT FAULT IN SEDINENIS
/
The greatest well-established vertical separation of beds across tha - f
; - . . . Q:- -). ,
. ~ , . .
x , ;+ . J . , . . . . . . .; Sho!c fault in the sediments, measured directly on the wall, was 14 inches. An ffset of 19 inches was measured between elevations -32 and -29 feet, but this amount is funcertain because the correlation of beds across the fault was not clearly established. That the movement of the Shaft fr.;1t in the l
' sediments also had a horizontal component is suggested by: 1) differences
; . in thickness of beds and inability to match beds across the Shaf t fault as seen on temporary floors of the shaft, on the south wall of the shaft, and
' ~
.r . in trenches 1 and 2 and'the 20-foot embanianent between them; 2) changes in l
~
dip of the fault, particularly the right-angled bends of the easternmost < TEI-84 and highest branch shown on plate 4,/near vertical control line 39 at ,.
. . 14 g' n
' fhd.Ndfh2.';Ni*?,$**kN@(. yf,*N. g }s< &
~
.,. )2h5 'Q .n w;:,'s..j W.v: '.i G7;..z.Q; 3 **.. **'.q,'.f. - , . .
w&:WMy_yyt~< e. W 0. q!['.f%lg';[mb,Mflwp,*;%w ;
~ _ w m .~; + .*v.v, .
pgQ u.m4.ggl,,p;w. ,eq :s.Mf,U w %.ww.p, % -..-, . e -~, ~.- hu,.x,j.,_.yy:.9,;s, ~p;.4
.p. ~.mm c.g,.
- . e . _ r . _ . _ . . . __ _ . 2 ; ., u, g.,n . .. ,
; .,-.- p. . , ,,
. . . . - . . ~ , ~ .. . .. .. , ,. , . . ~ . _ . . , , , . , , , , , , _ . , , , ,
I ,
, . o.
elevation -14. Wholly dip-slip (vertical) movement would probably not 9 permit the sharp edges of these angular blocks to remain intact as they are now, but would break across them to form a smooth surface with no
- keyed-in interlocking projections and hollows along the dip direction ;
of the fault surface.
,' The difference in thickness of beds across the fault afiords a clue to the magnitude of the horizontal component, if we use data on the lateral -
change of thickness of the beds. Such changes of thickness of beds across
' the Shaft fault as from 8 inches to 5 inches, and from 2 inches to a range 1
u of zero to 1/2 inch suggest a ' minimum lateral component of fault movement of
~
4 to 6 inches, though the actual movement may have been much more. The principle used here is to choose a reasonable minimum amount of lateral distance along a bed that would show the safne change in thickness as shown across the fault. The unevenness in thickness of the unfaulted beds in the n walls of the shaf t makes this method of judging the horizontal component of fsult movement obviously unprecise. ,,
. An apparent vertical offset of beds can be produced by a wholly .
horizontal fault movement of beds, if the beds lie at an angle to the horizontal. Though the sediments across the Shaft fault generally dip , 15
-r -- .____.__ _ . _ ~#
2.[. - * * ~w:v,a.~g,, _ . ..w.- .. f c . , c ;, . ., ,. . j ;] r.j:, . .. . ; , , ,. ,4 a
.1,c . p l r,_
;y .-
( . .,. ,pf
.,'i%.,
n (. <~ S. .c ..a'- - WA47.,if-x .7,"r , . , . n.... . b '. ,' O bk:$*> h;s .AI? a . '* . s. . 3 f '. f 'Q- 'f'f ' ?" "4-
- s? .
a L a. ;;..; u .-...: & .v.h.3 4 M k.-.a: w. a. a. w .,u e. ..:s.u .. m m u.~ n. J' ~ t y.+ ,#.~, .a y.. ... . .. . .-j #, . - . . . . , . ,,. ... .s ...~. ,. :i
. . ;. ~
. e .. ...g ,
g.,.,.- . t.- ! . j i. $ sout- :.stward, we cannot use this method of calculating the horizontal component of movement because it involves the assumption that the vertical component of 4 , meverent.is sero. The actual movement in the Shaft fault may h.2 - been oblique
+
,,.in that it involved both horizontal' and vertical components of unknown magnituden..
. 4 .
,. y _ , , . o . .
- . ,5.. , ::.n ,, .
~
, Nevertheless, if the following assumptions are made 1: horizontal component of i
.l movement is 6. inches; 2) component of _ dip of beds along Shaft fault is 15 degrees; 1
l
. i
*1
- 3) movement is right lateral; 4) vertical separation of beds is 14 inches, then ;
.i ; ~
the vertical component of displacement on the Shaft fault in the sediments is i =
, calculated to be 12.4 inches, and the' total oblique-slip displacement is calcu-
.i ~~
i
'si. . *.. ..n . .. .
isted to be 13.'8 inches. .The following chart shows the calculated amount of oblique-slip displacements and the corresponding amounts of vertical component of displacement using various values for assumptions 1) and 2), but keeping the other assumptions the same as given above:
+
Horizontal component Component of dip of Vertical component Total oblique-of displacement (inches) beds along fault of displacement slip displace-(degrees) (inches) ment (inches)
, 6 15 12.4 13.8 12 15 10.7 16.1 12 .. , -
o 10 11.9 16.9 . t .
, fL .
12 C.A. .y . .
., ^ 55. - 13 17.7 j, l 6 . 5 ,
13.5 14.7 :. 6 1 13.9 15.1 < 12 1 13.8 18.3 45.4 10 6 45.8
- . .o .. *
... / (;, . , .;
' .i d . ,
.. J h1:O %?}:!*$!.*f[g&k'lL.g '.'~ c?TsY' <hE?fl.N s~$ .$ k? : ,'J k T;sa ~f. ., , , . Q "I y. . . .
. %W M.
- e. .,:he:m%2M%~m,.M; v:twWsy .Ar:rn: a g ag ur *4, % A -qe.+ q)hb, ym e)mi.. U+m.,.. )U. S,-.. 4 2.. u.,c m.;4. .sp; a;p,;.:
.Wmp. ~.4.A;.2.h',..'
M, ...s.. #...
&.;qA'? Ll m . . ,.,.,....
.- a . x az.xL.w.:~:hm.u..... --. a.a.:..:w w.... a. ~..w.-- . ~..-
.... . . . / y, ,,.. J uw.Oh M..a .r% #.w . # w <.q .w. ~ .
. , ~ - . :.~ ,4 4 .,
,, -... . n . . p
.n
.,. r,g.r v, . .o n .,y j ., **
- ICi "" M ". ' *"' $ 1 * .Ib((' . (...P Y,7 l ,
- It should-be emphasized that these total displacements are obtained by
- assuming a component of horizontal movement of only 6 or 12 inches, w hich demands a vert'ical component of displacement of about.one foot. If, for example, the vertical component of displacement is assumed to be only 6 8
~
',._ . g. J ' ;7, r' , ~7 mm- . ,-& ,
F- ., inches and assumption 2) is 10 degrees then the calculated horizontal component -
.4.,
..,, of displacement is 45.4 inches and the total oblique-slip displacement is f-
; 45.8 inches (see bottom row of chart). Thus a decrease in the vertical i
I component of only about.6' inches gives a substantial increase in the calcu-
'isted total movement. This emphasises 'the importance of having a reliable .
4 '
+
. ;. v *; - . . ,
l 4 .
. . .. w:s .. . . :. '
figure for the' vertical component before a meaningful calculation can be made ' : e of the total displacement. ' The calculations were made for l' dip to show that #
}
a the change in calculated vertical component and total displacement is relatively
- i small between 15' and 1*7and because the dip in the direction of the Shaft
. ,; 1' fault is believed to be between l' and 5' SW. -
,, j
. , w : ., .
)
In evaluating the fixed geometrical relations of dip of beds,' vertical .. [ . , ,
.e
', and horizontal components of displacement, the measured vertical offset of .
.i2d;!.
. . s. ,
f
. beds of 14 inches, and the geologic evidence for a horisontal component of
. - . y .
-I movement, Webelieve it is not unreasonable to surmise a total ' displacement
\
1 , of between one and three feet in the sediments. .
,p.
. . s .-
- c. :, ,... .
.y 1,. , . u- . 17 .,
4 r. . , , , , x , g,. . . . jp ;..:
,p m,. m , . , , . g,.,,,. ,
WW@@B@ssggngsygggggggggggg
.e . .m
- :.a4-.;a
. p4.
3..& )a_A.
.m . .. % ..ys.&:p . ,- .. s. .. ~.._. ..,.,.o.....-.,.....~ ~..sa ~ a m e.
~.a.- -.n
)
.4 .,,,,,.4 j r
l} b 4p ., l s
... . . ** , . * *l ~;f '. 7, n y. . . , .
3 I' . tJ Age of movement of Shaft fault in sediments ; f ne absence of the Shaft fault in trench 3 (pl. 2), located about . 250 fact southwest of the shaft can be attributed to 1) dying out of faulting i c. upward and/or laterally, or 2) deposition of younger sediments after faulting.
-a. L. m. ,m. . ~
a , . .- sectonic faults are characteristically discontinuous en' echelon, or , branching. Many examples of this can be found in the literature on the ~ t surface ruptures associated with the 1906 earthquake (see descr ' ions in Lawson and others 1908, p. 70-72 for the Woodville area 27 miles . southeast l 3 of th'e reactor site, and on p. 63-65 and map 3 in the atla's for the Fort .]
-- I .
l Ross area 18 miles north of the reactor site, also see Table 1 of present i report ) Surface ruptures, several hundreds of feet in length, are des-cribed for the 1906 ea'rthquake which show a few feet of horizontal offset in their central portion but no offset at their ends. Laws.on(1908, p. 53) describes the en echelon and branching nature of the 1906 ruptures as follows.
"The width of the zone of surface rupturing varied usually from a
~
. few feet up to 50' feet or more. Not uncommonly there were auxiliary cracks "
.)
., . ::: -:.:, , s -
L either branching from the main fault-trace obliquely for a few hundred feet , s', or yards, or lying subparallel to it ar.d not, sofar as disturbance of the soil
, indicated, directly connected with it.' Where these auxiliary cracks were 18
. sp>
.,6 a QX%.. ., fyQ.Rgy f;f.QigysyyjgT'i*:QWle qp.AC\
o;;ag4:h;W W fuwi;y&fdyquw;.r ,. apg:,x .y f G y.l2. Q :'f')f'yff.p4C g y,9 ,j Q.Lyg.; g pq %.g y ..~ .,,,,,.,nr.6.,q%m.,,..e,
;i .
w, . % _.. . . m.s %y m, .:,9_3yfm.. o m. ..f yg.#,;t., .p.y,.._swa.e. .e.M., oM.,.a._ ._.n,.i
. . ,._.,m,. ,.
1 pu.;w s . ~ u -.._.........s. w.a.a n:,. s.:u s :as.an.a. .a .u,w u . . ... w- :m.w . .s , ,
-,y w.,,._.:.....s.. . , . . .. - . . , . . - - . . .
a.~.L.a .x{. .
.[ ;, : p, _
.a... -
9 j .. ..# t,.m c - -: ..; a . er a w4 - 4 >' g. features of the fault-trace, the zone of surface disturbance which included
~
J them frequently had a width of several hundred feet. The displacements appear j l ) thus not always to have been confined to a single line of rupture, but to have . l i
. been distributed over c' sone of varying width." '
s
. ~ .#.c ,, . ,, .. w-..,..... ,
. . p e
. . . , . o -. ., . .y The discontinuous, en echelon nature of the 1906 ruptures can be 'I 9'
applied to the shaft area to explain the absence of the Shaft fault: 1) in ;) l ' l trench 3, at elevation 51 to 52 feet, 250 feet SW of the shaft; and 2) in , i the embankments, at approximate elevations 2 to 25 feet, 50 to 100 feet NE of I
/ .
1 the shaft, by upward and lateral dying out, rather than by being covered over. i l' . , , ;. ,, d ,'+;'...; M ., I M E ' - .
,- If so, then the last movement along the Shaft fault cannot be dated, from this ;
1
,' evidence, more precisely than any time following the deposition of the youngest
. 1 b e d.. i:. which it is found, that is, at any time between > 42,000 - 400,000 years ago to, say, a few years before the shaft was excavated. ,
i 1 The absence of the Shaft fault in sediments on the south wall between 1 l
- e. ... l u
ele -'tions -23 and -26 feet, and at some places on the floor of the' shaft, and above the agranitic rock on the northeast wall is attributed to the
~
-p . e .; . .
3 l massive, structureless, and plastic nature of the gravelly, sandy clay at ;
. {
the::c places. The clay may have been sheared but the visibic c.idence 19 s
. ' ~
f' c ; y. 7** .
, . . . ., . :-- -=, ,s' AM 3' .
'.gm
(*. .' 'k : ,, '"
- U *,. ., .
(< a
#[ ++ \.,h fa' . 'e 5/ ** ? #. [ i
- j.p4~..s% .q4,i.bm(N.y a g. t _.,
q M p,u,g; yj;:- xmpa,s,,s,,.%gi[r w ,,
..s9.,,..ssm.,ns,m g imsgMy,.e.a.u.iv.W,s,#aw.
gm , u. . cm.. .
@U'
., _.tQl3p'.g
)
>m.w .i. .
a u = ., w m .w. s & & w.v.2a. w h a: x = u s ...a.u n a.. . {
~.
.m. .. _ .m .r .g..
&.r. 3 ,.. c ..
_. . w. ~ , ,. . . 2 , . ..... . ..i.,..#. . . . . . . . . . . . a n ~.e c: ~ ." g;;cg t
.= , ' ~%:' p, tlyg, - ; , ; . .~ :
; , 3' s t' .
/*-.:'. ,
~ 1 g.
. for. shearing may have been concealed by subsequent "rehaaling" by re--
1
.,P.:-
distribution .of clay, or by the lack of marker beds in this structuraless material, or the stress may have been taken up by plastic deformation rather than by. shearing. l e> o.. . . . . . . . , .. . , g c. ,; . ,
;- j If the absence of the Shaft fault. in trench 3 is attributed to depo- .
- !)
.. i i sition of sediments after the last fault movement rather than to dying out,
{ i l 1 I then faulting of the sediments took place > 42,000 years ago, the age of the i i 1 unfaulted sediments according to radiocarbon measurement of fossil wood. i . The Pleistocene beds at the site are'probably younger.than a crustal dis-h
~
/
[ turbance that is' estimateIbiLouderback(1951,' p. 66) to have taken place from about 240,000 to 400,000 years ago. Thus under this assumption, the Sha . fault in the Pleistocene beds may have originated between>42,000 and 400,000 years ago. l I' The evidence afforded by iron oxide color-banding for age of the
'- . ,,, p.. . , ,,. .
g
- sh 't fault in the sediments is not very helpful because the banding is believed to be truncate'd by the ' fault. Thus it is older than the faulting. -
~ ~
. ,- - , ' x. . - . ,,
i
}
4 5- The reasons for this belief are:
,I
~
-A
- 1) The width of narrow bands is preserved to the fault its -if; i
e 20
- 4~: '
.y;
}-5 ~ . a.
, , . . . ,. ._ . - y
_n _ u* x m. m m *m'[.m..w m*mj" m* m" e!4fa.
~, ; h a a; .w.2 . .ur --su..;.aa...s :.n a ~ a. - a ww. ,, .. ..L. a- ~ -a u : * -- - u - aa-.2- .:~
. . . . . ,,., ., n .n ~. e, u. . -m. . . n . . . ..e . u n.. , , . .
.. . .. ;. , ,a.... ,
i k.1
~
.p.
y ./
- A '" f;1 ,i j
. 5,
.!)' Bands do not spread laterally along the fault as would be expected if the fault were a barrier to the migration of iron-rich solutions;
- 3) color bands do not cross the fault as would be expected at a ,
. . c , &, a.. u ,
m .
- few places along the fault where the fault is not a barrier to solutions;
- 4) color bands do not appear to represent oxidation in pisce of thin bearing beds, rich in iron /aineral grains. If they'did,the iron staining could have taken place before or after faulting.
- ..3
. . ,., ; . a
( .
>.c. -
Iron-staining in the fault-filling itself is paler, somewhat green in hue, and more diffuse than iron-staining and color banding adjacent to the fault. The explanation appears to be that color-banded sediments were cut by the fault and whatever chemical processes were active removed some iron i from the pre-faulting color bands and/or reduced part of it to the ferrous oxidation sta,te. The rate of this process cannot be judged because we know J l
, l
. .. nothing about the chamistry of the ground water that caused it. '
. .;. eJ
.. m
.,s
<j
'l
'." ' Thus the geologic evidence bearing on the age of the latest movement -
'of the Shaft fault is not especially useful in predicting geologic events );
s . that may occur in the next 50 to 200 years. What it tells us is that .
- , , ,- . 21 ;)
'17 , , W.*---+.~~.-*: ,y. ..
l
- l b[ 5 e . N 'bh,
* . , -[ -
(_
- N "- kI k.~~ ' Y '
- 4-
*If h *.sN h I o.Y,
- h N* ' . 'f[ ^ * u. (f i + /
- v -U j fb' ' X$$?$r'.N$$.'s ?%, '*J *$*U&s%%%b ( . ; ? d;&N',$&'!iVu~,.r. -
cl u : -M4l.}NU t ? 'N,0.,2$ :.$,\ st:*.'y. .ib' <h. hk' i&E llll,. .i _NOP"'IYt - ". _"'""*"MN''"*.W****+'-'""'"*""""'"~
"# ' F"' ""** ^* * * * **d" e l
- a.-..
, ~ . ~. :. : .v. : z.. ~ .a. - .a u.- .~.u.
w .a ...,~ ; ... a.~a.. m ...u. = n.. j .;. 2.; --.. a...n ......-,...n.~~g.,~...~,..a.-...a..... - , , . -. .. _.L.p.. . . ;f .
- .J .n .s., y x . s m @ , v; w : . .. . , - . .
. . , V
- either the last movement on the Shaft fault took place'1) more than ,
42,000 but less than 400,000 years ago; or 2)/between >[42,000 years ; 1 ago'and, say, a few years before the shaft was excavated. l
.v
.g ,
)
l' s v-,
. r.The
". Shaft, fault,in, ,the sediments may. represent
, ; only one epi.sode .l
-q ; ' ..; p .,
~l- + . . :~ .
y, .( , , , Lof faulting, the last one on the Shaft fault, though no conclusive field ,
, v.
i' I evidence for this belief was found. On the other hand, no conclusive {
.i .
evidence for ' repeated movements was found. If, as is aty best guess, only i ; ., one episode of faulting created the faults seen in the'sedimenc, we may
/ '. [ . S
, ': conclude that there has been only one episode of faulting in more than ,
t- ' ^', , .R ,
'l ;4 . .i h.s.* c
,c . .:.y .a .x,pe,x : . J.; g x., w; v ; .
I 42,000 years, or possibly in as long as 240,000 to 400,000 years. Note that this conclusion is valid if the faulting took place only a few years
. J ago. - 1 Surface ruptures west of San Andreas fault zone l
.t. . .. .. .
- Geologic evidence .
, - ,-m.
for faulting west of the San Andreas fault zone t .+ . W..g t . . h i; '
. was investigated to determine its genetic relation to the sone for use in
. ew. 's. .
. evaluating the probbili. ty of future surface rupturing at the proposed site
.w,;;.~ .-
w
. w ,e. .n.,..u..
. w. -
, ,y m..; .q..
G.on Bodesa Head. Some of. the most meaningful evidence was that related to . {)
. . . c.c .
- * ' M N' Surface rupturing created during the'1906 earthquake . l.
the 1906 earthquaka/and said to be of tectonic origin is described at many i 22 - g .. . k " *"
'#. % # *3,.
q g i
& * . [. w C-s.e.e e- . -
, . , ** rp,m-$ ' - 4fr* * * ' * * * * " * ~
***'*" 'Y
* .?*\bf {lf ' % f** lz \4 , hb . ' ^* a*-, .~ .
f*JI;** y 3 nm m,#qf.,.r,-.g.g a annw.az
}*
- ,e +w.n.Wl ,f."
)*. O *Lf o.g ;f y ,* / _s
,...e
.w.m .a
--. w. . ws, &, .u a . m. ._ .~,. ... _. .. ~ ..s._c.;n,4. .m.y.. .,s, ew,. m A a ..w.w .
; , q; ;, n L - . - _ _
= - -. +.i..a.Z;L d'M. .u : :~.,n . w -. ;.L.;..u.a .v. .uw., a :. : : -.... ' -
L' ' a . . a.m .
, . . ., a. t. .,..;-. . , _ . . , . , , . . . _ . , . . -
. . .. ph 3
<g. , s . , .m - ~ .. r '
t
- s
.A-,, Sq h . r . - -
.. P
, ' plac,es west"of' the San Andreas- fault zone. It is unfortunate , in light of f its obvious -imporcance to the evaluation of the site, that Bodega Head was not examined by a geologist for the 1906 State Earthquake Investigation
- g. . }
4 Me Consnission. Though it neglected Bodega Head, the record of events of the e a _ .. .. w ,,s.s., -ar g .;., , g n g. %, _ . , , , .L a a., a. . . , . ,. g
- . _4, 1906 earthquake is t}e only usefoi one we have, consequent.ly we must rely [ .
p
^! ; i .,
..}
.i heavily on it for cluis to future earthquake, phenomena, some of the'plac,es ,
.; zi
.; J '
( i described on Point ReyeA 7eninsula and 1*n the Santa Ctus Mountains southwest . r .i t . of u Gatos, at the site of 'the Morrell ranch, were examined by us .. Mpw6and, the ruptures at some localities appear
- to us to be of
~ %, , .e ;._.. , .~ -. .
, , . ( ,
. ..m
. m;. ., .
.,I.J ,
und:nbted tectonic. origin. . Of great significance is that some of t: hem arti * '
+ -
f fa vr away from the San Andreas fault sona than is the reactor shaft on( 1
+
i Bodega Head, r The State Earthqpake Investigation Commission' report (Lam :. , 1908)
, h cor.clins numerous description of rupturing outside o's the San Jreas
. . n. . +: . ., , . . . ~ , .. <
~y. ..
fault zone. Ruptures were ,tbundant at some of the localities. For example,e j
}
.. -) j
+
s q %.? Gilbert (Lawson, 1908, p. 75) says: " Bedrock cracks occurred at many point's #'
. ;+ 3 ~ .
- _w . w,- . :; : .. . . .
u , . s . .. a( .:t .
.2,[*with'in the 8,1ft, usually appearing as branches from the faults. They were
., . ?; , j j
j
. 1
_- 7 ; p .seen al.so at a number of points west of the Rift, their distribution reaching ' 1> f ,, ; , a ' ,.1 f 4 1 to the ocean in, the vicinity of Point Reyes,10 miles from the fault-tra,p,g ,
. M., m . - 4. g . . ..r 23 i d
- . . j , , .s ,+ . w .. . , :a w .
/ 1
.f :
.[ 5 ,'. . t3 2. * ,. *.=N *
[ *. F 3,( 1 's {** */;4 . Af'*. g / .. {.6 e ;8'
.k ,3 ' "I fi 3w %G 4wyW; , %:dx a, _::. % ;L:~.1. , .
i r.s ;:
;;;g ;
~K ,j.>Mw%%.%YGw.MW% , v e w w w %:
~-* v. m . #.,.% rw swg.. .m .
m .., m.: - .,, _, ,.. ..e. m . ,,,.. , n.y..~._ .,.i. A L
t
, ., ,.w .a. . a.... 3 ... %,.
s.
- . e._ t..~ .
. m ... . m. -, . .. .. .. ~~ .c~ . ,.:. , ,a..: .. .* .. .~ v.t. . -.
,..s.-.,y.;....... . . . = .;~., .a. . . . ae, v* .i- 9 w% .
n..
.g, . . .
.~<m
;. y g;.m { ,7 .y.6, m , ,
. -a,
, p., , ; , . .
~
.) , 9; '
' ]
At t h ... host remote points they were quite small, of ten barely discernible, l \
)
and no system of arrangement was discovereh" . They are peculi.. -y prominent along the summit of the ridge constituting the southwestern rim of the main i
. i m ..
NBolinas-Tomales ,_g, ,
- t. rough., , ._' This summit was visited on four lines of road, an'd ,,
. > . '. . w' ,
.; %, f5 y ,,
r ; ,, e i % - .
,,. sti '.,',- r
"*I4- .+
, at each lo dtty conspicuous crseks weg found. On the road from Inverness to I Point Reyes Post Office, about a mile in a direct line from Tomales Bay '
(that is, a mile from the San Andreas fault zone) a crack'was traced for more i
. . 1 than 800 feet. Its general crend is east and west, but its course is not
- straight and it has a branch diverging at 45*. Along this crack there iu a i
,-m..
c ~-.:: m, .y y ,p,.. .su,. ., . : ,,c.$ a.
~
. , + . . .rw < %,.; p,q v .q.u.. . f. . ..+.,.rm ,. f ., o 1.; <. .t-e.
e.u horizontal throw .e of from 2 to 6 inches- ". (tInderlining and parenthetical l note is oors). h n
/
Table 1 is a summary of all descriptions in the 1908 report of brancI t i faults outside the main San Andreas fault zone as well as some notable ones
.1 -
i within the s"eso. 'It shows that~.branch faults are ccaton in the zone and r o u .. . .r
, :s , . .
..j ..
, in some stretches near the zone. 'It' also'~ shows that. most branch faults were r, .
y %:.Johwa not adequately described'or- Tocated, and/a scarcity of adequately des .cibec
. . s.
. F. . . . w.- .
. . . . ~v.t. . . . ,:. .. - .
.P . . .,. ,C .
t e ,$ ., r ' .i 4,>. , , f. ' , f ' ./ :-
.' s, s
. o- examples of branch faults outside of the San Andreas fault zone. '
4 v . l l 24 .. i
/ 6
.g . ,% . 4 r
- . ze .o.t .a - . , ' . , 3 4{
- e 4 11..+ , 1** ,1 **g% , , , if *,,,,,,[. .p
} sp.stE'Q.y;%'"Qh,k;h.;1 Wth, -lf$'Nf*.7%iUQ';{f.'%fRQi, '].'??nhQ'q:: i
.;[ C a.: .q .% %gir : f.* /
*;b bi;t%.'.C n f i,U%D.u&.,p$h.1,4 Q !l M : & 'G f.;,.M 5 h & >'.% % t^3h D. m?k hl:i.&riw"T;86:SWrAW+~.W
-%.9 .~..,,n~. .
,,e 2a, ..s ~, . ., f.e . n- ,, , -w.w. -9. . m 4R^q
,y> . ..; _,..~ .. a . ,! _ .a_
.. .._,.A.m...
.-.__,....-...&.._ ._., . .... ., .w. . ... - , . .
~ . - . . . _ - . .
. _. a . u_ . 4 g ,
,.~ ,
2 o m . l,
. ' , . to 1i
> Gilbert's' . (Lawson,1908,p.76) opinion on the excent of bedrock v' l y Q i
~P '
fracturing in connection with widespread modification of flow of springs on f' Point Reyes Peninsula is expressed thusly: "Ihe spring phenomena and the
.y .
visible cracks way be grouped together as indications of bedrock fracturing,
- - - ,w - . . . . . , , _ . . , , . , , , , , -
e "
. . . !: . , . , q.~ ,
and their distribution indicates the regions in which the rocky foundation of the land was more or less shattered. That region includes the Rift and a J extends from it to the ocean. The phenomena diminish somewhat wLeh distance from the Rift, but the fracturing appears to have been important and general
/ .
- through a belt' 4 or 5 miles broad." In connection with spring flow modifi :,.
s - . ,.
. cat;
. ~ .ions . 3 east . .. fof the Jr .L .
-f -
.Lawson San Andreas fault zone he writes (QoCCogg,1908, p. 76) r 4
'"I heard of no changen in springs east of the fault-trace)., although a number of inquiries'were made." i e
In addition to ruptures created by the 1906 faulting, undrained
' topographic depres'sion features were seen at many places along a stretch ,
- . , . - - m a. .. , , . , ,
~
y of the San Andreas fault zone extending about 200 miles s.outh of Bodega He.- and as far as a mile west of the zone, that appear to be created by ,
. . . ~ .
,. ,tect.:nie movement suc.h as faulting or folding possibly in the last 20,000 .
pi ye " r. . Mud Lake on Point Reyes Peninsula (pl.1, TEI-844) is such a j fe tre. It is about 3,000 feet west of the San Andreas fault zone. , )
~
4- - 25 .
~
1 ' r . apeu.=A
- a. . - * . ,- - *w .*w jy e+.=r*, * % .
~-_
,y* _
..~.qyyc:/ tg.Q7iyqpp
.wp, m
_ __ e,a,;s y,,.
-___- . a m.,.s:.;.tyff4y*46,
..p.M,n:v,,,; ..y u , n . mv.,.r g w ,,
~ 'Hf3;f??"Q;wMc?>R:.p~~m%7..t+:,4
..u: my , aiwn;y, m.s,n.e.1 - , ~..., ,%
... . g,a
, . ,2;L'n.,p
,, ; ,. a. ,,n:c m. ,%m., ,.,. .g'.\
.. .. . . . -. l
.w ~
.r..w...
p.... .
. . > . . ~ . ,
.w ... .~ u s . . w : :
. ---:...----:u..--..--
' . - ~ *
.. , .r . . .. ~ w . - . .n . . , , . . - ~ .... . - , . .
# I y g a m .E g .-
m- m . .g m, .n c. .cw o.:. , .. ~ . .
, . , . t
, It lies in an elongate steep-walled depression probably formed by sub-sidence, estimated to be more than 40 feet, on a block bounded by faults.
Similar opinions on such features have been described by other
. geologists. Higgins (19614 p. 57) discusses the area between Point Arens
... . - . p . ., . . . . . , , .,
. .. . . . m. , f .g .y. . ,, , .. ., . ,
, {
, ~ . .a n. , . . , . v ., ,. .
"---numerous and Fort Ross',18 to 59;. miles IN of Bodega Head, as follows:
.n .
4 small ponds and depressions on the rolling sunnnit of the ridge west of the a 1906 faul: trace could only have been caused by small dislocations along faul.2 that are either part of, or closely related to, the San Andreas. J Yet' mnr of these ' depressions are ac'least half a mile southwest of the 1906
*3,
. c, z ,, a ., 2, . . , ,
, (./ Adj y. .gh y7. ; .,e -r 4t t,_, " .,
x ..'. ,s,, . .. ,:%. ;, +
- g. . ,
, l' faul'i Crace." , ./ ,a , , i
* . s, r: ,
~
0- - - y ,, , . . . . , .n. , . . . -
,c, u .
.+ . .n . .,
- ,. .' 4 .~ ;
7 I # 6 P
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s
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7
% *b , .C) ' A , h J
- t.3l ',#..,e'
- +-
4'
' 4. f. [t' - . , .
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=
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. 6 .' .f h' ^g , g 4 A- N e .
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, , ' * ,*- . 7F* . 4 , , ,U [ 1 ,. * ** .
mily'@ TA r@'"%'*:T+,6 Mi#eh. 774ipOg*j$% f.Wpl.M.g'. +;Fx/,';Q4 4.p,;c.i. g d.: ry ;rj ,. *..,s..- yyqqy, d
.. Q, w ,., 2m w.,w
- i e,%p. g
%., ,_a,, , .W;, ;;e..m. _%, . : .w ,., n. . - '
....n . m% e,.a %n :g.t,,.,.u, ug,r. ,4%_e.;,a;!g
.. . ., m ..,,, w 4.:.M. m ,, . 4.,. . . .. m........m.,m.,
.....-:- . a . . .. a. ' .: .; z., - - '-
d c . . , t.._.,.o,,,,,..,.rm,..;..,.._..._..._,,,..
- .~ .. :. ~c . . .. . :: a.~. ~ .. . -. .
. _ .. f . _.
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- v. . . .- .;., .wsu; ~ 5., -- ,
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Significance to Bodega Head site Eow do these observations relate to the question of the probability and magnitude of surface rupturing at the site during the' lifetime of *
...;,, e .n...:,~....
. . w ..,m . . . - . .. .. - n. .. . .. .
i L' . . the plant? Surface rupturing by tectonic faulting has occurred in 1906
. I on terrane geologically similar to that of the site and at localities that range from those that are closer, to those that are farther away ,
i from the San Andreas than is the site (Table 1). Table 1 shows that i en, ruptures were not reported for many stretches of the zone In general the abimilmm a and magnitude of the cracking and displacements increased . towards the San Andreas fault zona. They were seen as far as 10 miles I west of the San Andreas in the Point Reyes araa, but the ones farthest out were " barely discernible 7'j at a mile away, one had 2 to 6 inches of I horizontal displacement; and some at Inverness, about 2,000 feet from 1
. - . . . . 1, ,
the zona, had horizontal displacements of 2% feet. With respect to l I magnitude of displacement Lawson (1908, p.148-149) writes: Th e I
, .j a..
l
, . recognition of the/, distribution of the movement on auxiliary cracks, jl
>l 1
l some of which may not have appeared at the surface, and the deformation l 1 l 27
- I l
.g W %- ..u C AEf4 . 'iW% !,-rY-%
=
f W. _'.,m ._m q...a p % .h 4 d". j -@cm_ ~ - .
'@hW: -
.-MsW h
- W' W W:'iu Vi'WN$W k ,.oin
-.s.% mw&WW-w:t:." MMtr^L+1?"f&E-J
#. Ma: -- --
w\..W.m.m$_c:,w4
.. . ..: ... .:. ... < ... y. . _ . c. _ 2 ' ~ ; 1. 1 .. a. m . M u L L . a ~ 4 w m .s ,'....t,....
7 7............_......,........,..,..- , . _ , . . . . , . . . . . . . . . , . . . . . . , . . . m
. ' . . . . , , ,g
. i of the groimd along the zone of rupture, justifies the conclusion that, except under peculiar conditions--such, for example, as in the marsh at the head of Tomales Bay--the maxinnan figures obtained for the displace-
. . . . , , . . . . . , . , . . . , - , , . . . . .. .a. , . , , . , ,
.. .n ment by the measurement of offsets at the surface must be a mininann expression for the true extent of the movement in the firm, rock below."
?
The trend of the branch' faults showed great variability, though table 1 shows that most were generally, but not everywhere, aligned northwes terly.
' ' The 1906 ruptures,.both within and outside of the sone, generally followed scarps or sage which were believed to mark old lines of repeated faulting. That this tendency was not universal, however, is shown by Lawson (1908, p. 53-54) in the following statement:
" Thia differential vertical movement was made manifest by the
, , s
- c. ,s. f.. ., : :.#, . . :- . , . . , . ,
sppearance of low, abrupt fault-scarps, ranging from less than a foot up to 3 feet. Many of these occurred along the slope of somewhat j degraded fault-scarps due to former movesients, and served to revivify -
- - ,, ,y.;.
- , c , , ,
.l l thma. In other cases the new scarps have been developed on slopes where 28 e
% 't
- % b-if. - . , , 4.cp., a 2.s,yQ.; yygyg.f.s,, ,
,v, .
. . . .; . ? j.)
.x. .,; ye+: ,,s w m:.94.m.p-w.,9,,
~
+ n e: . .?s.g. 3.; v . .:
.:. .. m.,. .;,y.
w . . .~ . a
. .<.s
- 1. , . . . .
..s.g.,,,, .m .e , y s ,ms .. s,.g .r ..-...u.-
, . . .mp... . .y .n e 4....,.~, w ..
,..s_., _ ;. .. ._ s.~. . ,c.. c a _..: h : - .ha A .A Lw_ ..> . ^ : .a. . _1.u .
. . ~ ,. , ~ .. ,_ ..... . a . .. . .,.... , . . ... . . .
g.7, . .
, ~. .
., - . (
'6 . V9 ;~ e
.. p. ; < [,g8.eegA,.i j 8'g* ,hrg'J.r, f'
"( ,
r
.q no trace of a previous scarp can be detected. The low scarp which 1 \
formed on April 18 is by no means a continuous feature, but appears at a great many places not widely spaced along the fault-trace, extending f .
.77 . ;v . - .. - ; .. ,
, .. e.. . . %.m. y ,
,,,7,x .. m~, . . . .s . .,, ,,. . .y -o ,. ;.
l often for hundreds of yards at a ' stretch, with intervals where no , !
.c.
j abrupt scarp can be d ' etected. In the latter places is it probable that ) the differential vertical movement has been distributed over a sone of - 3 1 i some width, underlain by formations in which the deeper seated j fracture would be- taken up by plastic., deformation." .
/
p.~.. . . . ,!
"At Black Mountain near Palo Alto cracks were exceedingly abundant ,
i
~/.s for as far as # miles from the San Andreas fault sono in a wedge-shaped .
area between the sone and a 10-mile long, northwest-trending fault that intersects' it on the east, On the other hand, no ruptures are reported l i
,at many other places where large faults intersect the San Andreas at a
, ac -
similar angle. Thus, the geologic control for the location of many
)
ruptures is unknown. , 7.Only the most general application of these observations can be '
.@ n., p . w. ' r, ,. , . s ., . . b. : :-Q y . ,f.,. -
made to the site, because of our general ignorance of the geologie control for some of the 1906 ruptures, and especially because of our 29 s Is # 9 "".a ,
! t ,. ,,.r. . .,.3.., q. ,,, . ., _. -l
.i .Y. 2 . ab' *f k; h.' h.y (*'NdEd,DE #1 j ,.',7 'l ** , NP
/ , j. (
- i ,* '*f' h,[ f.id kyf
; i. w .w$N 'n . e,y
. . . , - r,.
.g%v o, y,-( ., e .[e w p . m m.s.t c
p....~,,,e.,.s w~ ., g .7,[2
.x 7,A.Ao m d, ..
,.w.4 r.i..% .
u . b, m_+, w,s.
~ i,w/4,....c ,q
+.s
.p.s.a w .;.. .n = . , - . . .a. :. 4 - i~.s. - . u. a.. .w ... .~. L. a n .a - ~ - '
.:'.,_.a,q..,a.._....,._..-,4.-....~:...~,
. . . , , _ . . . . -... .. ,,, ........,,.....y' 4
.e ,
'. 'I J! < % t. , ; ' . J; "'. , , . " w . .' ?.;., . .,s
. i 5
I general ignorance of the magnitude and direction of propagation of the ' energy which created the ruptures l )
- i 1
Tentative interpretations ares 'l a
. ;. ; ,]
s . ~ . , - .- .. m.e. % , ..- c . ./ ., , , .* ..,,;,.._ . , . (1 possibilityexists,howeverremote,thatastrong
. earthquake associated with faulting on the San Andreas 1
fault zone like the 1906 one, in magnitude and epicenter l j
- 1 l
location, may be accompanied by surface ruptures somewhere )
. ;on Bodega Head. j
.. g - . 3:. .
L _ (2) Because the site is about as close to the San Andreas
' ~
fault none as some 1906 ruptures for which substantial horisontal displacement was reported, if a surface rupture did occur on the site, in connection with a 1906-type earthquake, it may have a horizontal displacement as 1 .
.a.. 9
.,...~..,e :g .... , ,
. great as 1 feet. As is discussed later, the probability 3
1 l
. i of such a displacement is thought to be low, though the
...: , o. ,
- t. . .
possibility should not be ruled out. . 2
. .y . mu-. ,g. . ..
t . e e * * *
.I ).s . . . ~ , . .
- v. g .- .n , , . , .
ll ... . f d[ NSA t / *
- m % f'.i, f {.M,,, EY$ f lG;
- y i* ?{ad *,. ** ,g his.s , , ;, g a f ., 'I , ey * *:
- s u .v.w
- S+Aw?'.tOkiRA'Puw ddk [.' :. -. %ta M-;w...,w.c.t e g .;;,t.t. . g 6 b cq,14 t-n~~ e.-.~.
., c..,,
. - -W.a' r o- . . , , W , ,,w. v ;.w .' q s
s.,
,c .a .. .f.' ...y.. ..~ a: -.:. J J. =.A J - . z. .s . -. , - =-...~.2...' : w L- - - - . - 1 . A .-.* - -
L -w.2
. . . . + . . . . . . . , . . ~
_ . . 5-.
.. o , '4 .
i.. ;;.. f,;r w - ;
,-aw .'. , ,
c.
, 9 (3) Surface ruptures are more likely to follow existing northwest-trending fault zones, rather than those of other trends, like the northeast-trending Shaf t fault. The i =.
, . .. m s .m .. . ,. . . ...... . . .,
a; . 2 pattern of involvement of existing faults may be
- r ~ . n. -. :
.i slightly different if the epicenter of some future l il strong earthquake on the San Andreas is significantly .
different from that of the 1906 earthquake, which is thought to be some 30 to 40 miles southeast of the
.~
,e
.g
. ,. . ... ' + ..
. . . . - . L. -
r
' i. s n 4.. m , .-
site. 1 local epicenter may also give rise to greater . movement on ruptures than in 1906.
]
i
)
(4) Because many 1906 ruptures touched scarps and other
- s. .
1 1 I surface expressions of established faults, the scarp )
. or trough features on Bodega itead, especially the
. . . , . ~ . , . , , .
, ..n .
.... ..m. .
.. hv .'
low. northwest-trending troughs and bedrock sc'arps in the hilltop south of the site, should be considered
+ '
,a . .: . ,
- a. . ., .
,q- u - potential locations g. ,_ q ,
for ruptures, until it is proven ! 4 , .g q.
- a. _ ,
l
. . ~ , . . ... .
that they are not fault controlled. ,j S b 31
- s
,, ,Oe
, fe, , 'k . , **4,,,,
,w
,,,g . he- ,' y . g ,.,
i (( * [ .g It,', f .*'
'[.* '. $ ^ *
't .'
.M 4',,,., - : 'E .
- 4... - " #[
.'M w
4')
- f.
h ,..? sm.s: #. . . z+. _y . .h w s. . y
.... " s::a'.c.
.; 7% , O,x,,.nv w ., i s, %:, 4, c,,i, m ,W,
, , e',.m,:[&
v'.,- m._&.f)iw_k y,m,,,r:u gik(s'u[ ,.,_
.:l
.}4
( .-- . , -
.s...~,..
,. ... .:{a;L + . ~ a wa. .g z .a- . .: ,,- x.h . w.~ :.
m.a. s -. w- a ~ -lL a 'L.w w . Q c -
..%.~p..wr.m.~~.<*-.,.~...e+....e_.'........... . - . . . , . .
+ -
.,,,. ... .7 ,
. - 9,- r 6 4 raf;' ~,,, .qi,, 'f, .ay y ,. pgg ; ,, , , , .
s *i Shaft fault and San Andreas fault sone .
.1 .
1 The San Andreas fault sone, is a more or less vertical complex of o !. faults whose major omresents have !been right lateral. The stress field rz, . . . . . e.; s < .
**.',w- ..
uu. g mvy.--- 2
.i g.g ..w ,
f
., ..,. y j .7
. . . .y 4, m.
; g. . ., , %
,,,.3 : ,, . . ,,. . ,
_. ~ . 7 4. i that keeps the some active is located in a belt many miles, perhaps
, . ' N g.i N:, 3.;
, y % .
_, - m . . - . . hundreds of alles, wide along the sone and at a depth of many miles. From the orientation of the sone, N 37' W in the Bodega Bay area, the direction of the principal. stress is generally thought to be horizontal and oriented . e. nearly north-south, or,possibly a littla west of north.
... . m.. t...Dw n 7
< + .
- - The Shaft fault is oriented N 48 E, at a high angle to the San Andreas, ,e
.; .n e :n. ,
and dips steeply westward. The Shaf t fault probably also has right-lateral movement. The nearly north-south principal stress direction postulated for the San Andreas movement is inconsistent, by most shearing theories,
, ,, e .
, . # % 2 .,, ,. .1 , . . . .
.- 3 t' '
with the orientation and sense of umrament of the Shaft fault. Never-theless the Shaft fault does exist, is within the stress field of the .
. . , +. . 4.
2.y.3.. . :.: , : :,e y . . San Andreas fault mone, and the field evidence for its right-lateral
. :... . ,. w w ...w
.y:.. n .
, wu :.; . . - ~ . .;
movement appears reliable.' ' Furthermore, its activity at lasst mice
. 32 4
4 b h. *i 4 , 0 'l *
.. % . s a u s .w ..v.: . , . .. .,
,4 .('f. k'
** h [i[, 2 [y,h i - , .5 fdh.,$ *
, N9 b~' 4 ', ,5.* $ ;*;* ? ?i ' c , y . *,3 Nh,..# 'k. * ; ( .[' t.[c.',*k . = ' 'r[,.q jg
;.m, v m. .m~..w .w.wg.,,aa.n. nm'S'hd';,,
- 9[c me_a.w{ *s.. .w.i '; ym_.- _ _:. w{..m.._ .[.mm. ,n.w.sm 4 -
,_ ,.m. _
...,x.._.s..-..,.p.;. -
- m. . . _ . _ . 1 , . _ ,m . . _ . . - ..._m . -a
.a ;. ,x . . u. . . w.w ~ . .. . ..L m -- ; : 1. 4 .: t .. ...'.+ 3 .:. 1 .6 % :.: - A t - - ..- ,
,#a.,..y...-.--.-. _ - . . . . . _ _ . . , . ~ . .,z. . . . . , . . , . . .
.
- a
, n i,..' * ,*
, . H, s
- 3, .. s, <~ . g.'. n s j,~ r v.y.. _e ;y - , . ,
-0 ,
e during the last 240,000 to 400,000 years establishes its contemporaniety e and close genetic relation with the active San Andreas which is only a
.. , ._....,_,;,,w,_._-, . . .
short distance away and has been active for millions of years. Further , g,, 4 h J g support for the genetic connection between the two faults is the abundance of northeast-trending faults seen in the shaft sud stong the I shore, and northeast lineaments seen on air photographs, on Bodega Head - and along the San Andreas sone on Point Reyes Peninsula. This support
. . i V. . /
.. 4 ,
.1.. .J; c
is weakened, howeverl by lack of data on the direction and time of s.. ,.. .a : .m ,u.w. ..
-4
. .. ..,a. n movement along these faults. Inasmuch as the actual orientation of stresses in the crust in the Bodega Bay region is unknown it is possible that in the vicinity of the shaf t the local principal compressive stress I
axis is more northeast-southwest compared to the regional axis, which is l m, p : ,
- 4, .- w. r . .. , .
,{
theoretically nearly north-south. 'Jhe right-lateral movement on the ..
, y; . .
- 3. ;. ,
Shaf t fault can also be ' explained and correlated genetically with .the j
.,..+ . .
- y. , .
.*-t4/ %% f. a . 4.y $ ,. +
stress field on the San Andr'e as if the active part of the San Andreas !
.Lt.. .. p - . r -
\
,, .Jg.'cg,;gn q,r;. . . . ,
,j fault monahes s' bend to the northeast within the sone itself east of , l
( ,
\
the shaft. Rille (1963, p.174) gives an example of this from a locality -
)
i in Australia. l y 2 . e "
, . . . . * . . ,, , , , ., ~a. _o- . a
.l$.,if.
k %':] f . f Q G'Q Q
. . p ,%h,..n;y' j p g g 4 n ;~. u ' &, >
y., .{ j r. . , ,_', e t h,.D =i N 1E l d M s' % $ k32nMNi$$WM1 C M'de*yg,OWs". M,- , ,, n m 4. On ,
. q: e. q :.2--.2 > 4t : L.~x., : :. Wh winM %...d --:
..- .a-. .:~: ~_.w:. r---
.-u,.
..v.>,...-
-.--~s.., . .-.m,o._-. . , . - . . , . . "4.~. . v., . . . .
l^ . . . . a:~ u - . m 4. . e..
.. p
, .j, as.v.:m. w:'anw : ., . '; r~
c ;- , . . . ~ i
- Significance of Shaft fault and future faulting in granitic
- j. . rock of reactor foundation shaft and vicinity i.
Faults are abundant in the granitic rock of the shaft, however, one of the largest is the Shaft fault. The size and complexity of the 4
. -i.- '
. i l , n 7:,.. : Shaft fault in the granitic rock indicates that it has been the locus
.. . . , 4 m . -,3 :u r. .. ~ w,, .
. ., p..-.,.,...,,..,.-%,.. . . _ . ..! , , ,
~ -
- 7.. 4 . .w r 9 Jg., ,
w., t of strain relief at many times in the past. Offest of dikes indicates i . . . , , . . .
~9 ~
that its acrements have been primarily horizontal like that of the {. San Andreas. The ruptures in the Pleistocene sediments evidently forised t i during the latest movement along the Shaft fault. They, too, show l i 4 - *;, ,.g , j _. - evidence of.some horizontal component of novament. .
. m. .
+;s:. tzw,v. ;p..nc ,
m w.h v::~ , .-c c. .c, y e.n -. .N.- ..w , s. w; ,..
. . . .. g. . . .
,,"4 ~~~ n .
~. %.
.'.dw :he- 'stro.ng development of the Shaft fault indicates that local
~T s.; ,
l strain release in the vicinity of the shaft favored northeast-trending l faults though a more or less east-west direction is prominent for i I smaller faults (see figs. 1, 2, TEI-844). The ruptures in the'%' Pleistocene 1 l ., - ,
'j . : sediments,on the Shaft fault, especially in light of our uncertainty '
, - : , e .v.a o . . ~. ..n m ..e.: .e....- . . . , - . -
of the time of occurrence of the ruptures during the last 240,000 to . <
- a. .
400,000 years, point out the possibility of future significant tectonic g - x... ,, ,: ; .: n
-{. .
-..; og.;,.
4 ,, .3.
- s. , , .. . ;
t .w , .
... t- . t . .
. . . - . 1.#. a. 'f . ult ,, s movement west of the San Andress faul.t zone on Bodega Head.
, , , ., .. 3
, . ; .' s
,r l + ,
* . * " ., f;. i e-
- w i . s
, .. g. a
) ~
# 1
.h.
34
+ .- ,,,
s ., e .
, .4'. 44,.8 , ; h -' h . , ,. s ,. .,y, pg
+ "
; 1p . + e,. ; ah. *). . t Q au s ,,
4 y.4.e.4* g 1 w ..s,<.. .. . . . ...-.-o--. *=-~.-i.- . . . . . . ^ ' * ' .- = . .. - .. . ; h . bh h. 1 . ,. .. - e
'Ye. $f YA. [ s 7 5
,.h i* E'
- s mmw
,, as
(*i, t.m _ r*. W. qh ^. h:g;,.iuMy, - .m ~m h f N*:sQ:G W %' +p,ytig:p q; W t. _m..-- ..m
.; .,af._- --.
y ? ;; * *:d>;&y-!J.hgfEDRp,,y{
;i d ay.s w :._; w L w.._,-,-..u......
& J...Ls Ww.L. M
- a + .u.~. - : u--- :. . w-. :- ..~ .
..y,~,,_,. - , . . ~ . ; ., . . .g.p,__......t.,...
.m.7 ... _.. _.., ~.9_.(,;~..s
, . . , , .. 7 is " . - * *n - c; V lx ., +y. "-" s' -py . .t. *
, .!e-j Although the cumulative horizontal component of movement during .
i
'j' the lifetime of fhe' Shaft fault, which may be millions of years, is t .
possibly.a minimum of 24 feet, it has probably had only one large i ..- ., - my ,
. . pr . 3 'a .4 ,,, a . , - w pq , , , . ...
e .r., . . S v.p. ,17% n
*s'7 . ; , , , , . , , , . , .j.
1 ! .' movement,'.probably of 1 to 3 feet.of horizontal displacement in
. , i.
. ., the last 240,000 to 400,000, years.
;I -. It is tempting, then to say that the probability for a movement ,
~
of a similar magnitude on the Shaft fault during a 200-year occupancy of the site is between 200 chances in 240,000 and 200 1,n 400,000,
.,: . . ;, , u.
. m,. .
,~ ;jwhichgivesbetween1.chancein1,200chancesand1chancein2,000 , ,
a . , j chances. Such a probability calculation, however, is almost meaning-
, i I !
- less in light of our general ignorance of the local details of the 4 i
1 rate, magnitude, and pattern of strain accumulation in the crust below i
~
the shaft that ultimately leads to fault movement and earthquakes.
~
, , .i w . . na .-c v .. .. ; . ,. . m - ,. ,, . ;
'. Indeed our k' nowledge of the regional strain buildup anywhere along the San Andreat fault' sone itself is very inadequate and is
; , c. .
.+a 8 4 w '4
-.A. -,, , "A 8 0
'h
- h m .
- 64 q =,
, 'o *
~
t s e
.m A 4 . ' "*p*.. .' f )'. f ,' F .
g e , 9 e. t 35 i r e [r # , s 4 5 '- .%.. J- g t
.. g - . , , j ,
f q
- 4- :-..w. ,e. .m - ,- ,. . - --
__ s
- .. *[p 3I .'~1 ,
8+' k n ?[ % M T k+1 % 5d. N )[i*fjf h Mf) .
*%'[s}?.,[A. hka; .*h,ga.y3.a3g:JgsQ*g; . '* t .
q
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.-..,v 7. ;yy.g ,./. /; 4 .p p 9 g .;w 3 h y p p g.7;pg m3 * ~ %. e.t.tr.a.Th+ Lu4ppC!i.pfpyd.A.;,;$ yap, ,gcf..eu.pM;g t .g.;g/,.;'.c._.-.1. .%~_,.
% wy. . ~ . . . .,.., . ,,.,.._.y _. _ .._,..,_. . Q.
i.p;4:.~.L... u , .a.../.a w.:..ik A & & M :. a. .a. . ; . a - ~ :. a-.g:~ ..: ~ --
- % ,,, ,u..f . . .,. . ...s .e. #M~ .A m i .. , 44. ~ . c.e ~ . .
.m ,. , . . m b,,.. ~ . .. . . <. ... . . . . .
. ry.;,; .
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.y v
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- c. .
.n.
W:Q.;; W i.f v y n 9.:.L : w g yL @ :c2 y g ,:g. y , m (.; . ,, wu : - ~ 4: 'refJected.in our inability to predict the time,' magnitude, or
.; epicenter of. earthquakes along the sone. .The inference that
. . only one episode of significant displacement occurred on the j.
i l, ' 8 haft fault-in 240,000-to 400,000 years does not permit us to
+ ye m ...g. . . . .. . , . c .;
. .,ce 4.gg, , , ;j ygy ,, m.., ca, _,.,, ., , , , , ,
ry, ;.;; . . g
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. . n.3.7.y, ; ~. ,. u.u a.. g s. , , . .
~
~ dismiss' lightly the possibility that a large movement mary occur
.+:;d k , : m.o g.
* ~
. _7 .n y:~y q.: -
- ' J l during the first year of reactor operation, nor does it support ,.
- .- or deny *the possibility that no movement or no large earthquakes * #
will take place during the next 200 years. y.0ur. opinion is that thbugh, the possibility 6f a movement i. j . ;. . , ,
~5 t , ;- , 4~n 9. , u p.i h.:.~ . , . ,
; ,. >. . . .; w.. .. , v : , . ~~c. .4.m
, . c my .
, . . .n
.s . . .
s n., . , .. .
.n , . .
, l ., o s:.
e ,, the Shaft fault from a1few' inches to a few feet should be 4
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. 2. .
anticipated during the. lifetime of the reactor, the probability
; a of such an event is low. This opinion is based, admittedly not 1
i very soundly, on: 1) The trend of the Shaft fault is nearly i I n -
- ~: r -perpend'icular to the. San Andreas and its
, .: :n, n ..
r, - - nmu n. .w . m , ; e , ,;i,. , , ,. . , , . , _ ,,, _,
,.
- pb.'g 3;
, .e
{ _.rght-lateral i movement is contrary to what ~
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I would be expected if it were a shear, conjugate a~ n s- , , , ., . .w . , .. . y an.;,w.,. r
, j , ..
. , . ,. 7 y.. ., . , , _
' . to the SanAndreas -n .
- w. x 3 3 . p i ," ,m. . ,, '. . a ;. ,,. ;, g.e4;7 ym _ , ,. , 3.;., 4 , ,;
~ f. a ~ :. ,
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' . . , 2)
. Though conclusive evidence was not found to ,
1 ,n .6 k p support it, we believe it is possible that only
~ ,
, 36
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, , ,, , j
, $ g * . 3rs' w & g g 4;.;y .g, - *g. r s, y=.}}