ML20118D296
Text
-
d e,w.,
UNITED STATES GOVExNMENT Memorandwn DATs:
February 26, 1964 Files To CKb Clifford K. Beck FROM :
Deputy Director of Regulation SEISH0 LOGY ON bODIXiA sengcT:
.Q ~A/ 4 he U.S. Geological Survey has already filed two reports, now public, on Bodega; one before the excavation and one subsequent to that.
Schlocker has since then made a ntsnber of statements on technical positions at variance with those in the reports.
Anderson holds positions on several key questions which differ from those of Schiccker.
We must have a futther report from Geological Survey, or as an alternative we might write a caref.ul analysis of the key geologic issues and conclusions e.s best we can interpret them from the ntanerous discussions a have i eard, then assemble our consultants for polishing up these intet.,retations and conclusions --
without a formal report from The Geologit.si Survey. Coast and Geodetic Survey would be in this same discussion becw a the issues seriously overlap.
De important questirns include:
1.
Aside from the question of an retive fault in the actual reactor site, can a structure at this location be adequately protected against the ground vibrations of expected earthquakes?
t l
a.
Does the tentatively stateo value of 1 g represent an upper limit of ground accelerations from another 1906 type earthnuake?
h h
b.
Is the proposed El Centro spectrum of vibrations an T
l PDR acceptable one?
l Note:
It is our impression that earthquakes along the St. Andreas fault of the magnitude of the 1906 event can be expected to occur each l
50 to 100 years; that earthquakes substantially greater than the 1906 i
one are not likely, though possible; that the surface rupture along the i
St. Andreas is likely to be along the same line as enat Lakeu oy the l
1906 quake (over a mile ea a oi me reactor site), though a different l
location within the fault zone is possible... - not closer (known) to the I
reacter than the f airly well defined vestern edge of the zone
( > 1,000 feet east =f the reactor site).
It is also our impression that ground vibrations generated by a large earthquake are attenuated and diminished in damaging potentiaa at large distances ( > 5-10 miles) from the strike line.... and beressingly so at larger distance, but that for areas near the strike line (less than 5 or 6 miles), ground vibration and damage potential may be about as severe at any location as at any others (since the - focal point of the vibration source is 20-30 miles deep, surface vibration
4 l
] ;
3 in the 0-5 mile zone is more influenced by what happens there and only secondarily influenced by the actual ground break along the strike line).
Our impression is that there is difference of opinion and little in either direction other than conjecture, on the significance of " fling", i.e.
net lateral displacement along the strike line, on structures located near the strike line.
If the total displacement occurs by a multitude of short jerks and stops, as seems to be the case, the significant impact-on 2
the building is the accelerations, de-accelerationrand vibrations. On the other hand, if there should be a large displacement ~ in one movement, the inertial ef fects en the structure could be significant. Our impression i
is that the latter is not highly probable.
We tend to conclude then that a site nearby but defin.tely outside the i
f ault zone is neither better nor significantly worse than one a few miles further from the strike line insof ar as building vibrations and protective structural safeguards are concerue3. Arywhere in this zone l
a building would have to be protected against the upper limit of ground acceleration; and vibrations expected anywhere in the zone.
i nence, our question: would the tentative value of 1.0 g maximum acceleration employed tdthin the vibration patterr represented by the " averaged" El Centro (1940) spectrum be an acceptable basis for protective design within the "new" zone of St. Andress, and, in particular, at the Bodega site? (aside itom the question of f aults) or is 1.0 g too high?
What is the likelihood that f aults, ground offsets, or dif ferential displacement would occur in the proposed plant site area in case of future earthquakes along the St. Andreas fault of the 1906 type and what magnitude would these have?
What is the nature of general expectation and magnitude of a.
faulting within 0 to 2 miles of the surf ace strike line of a major earthquake?
i 4
b.
What is the significance of (1) general bedrock faulting and (2) the sediment fault in the shaf t excavation on Bodega.
What is the relevance of the Pt. Reyes observ tions?
c.
(liote: It is our impression that faulting of any significan:e i.e., over an inch or so,outside of the main f ault zone generally does not occur; it is a rare occurrence.
2 It is further our impression that, should f aulting occur outside the main fault zone during a major earthquake: (1) similar faulting in another earthquake would likely occur, and (2) the probability is high that tho l
'j <
l l
}.
i f aulting outside would take place along the same strike line as in earlier i
- cases, i
It is our impression that all the bedrock faults observed on Bodega j
(all being outside the main fault zone) are very old; no recent ones have i
been observed. Further, that the sediment fault in the excavation, though probably due in major part to tectonic disturbance, is associated with an old and inactive bedrock fault underneath, i.e., no movement of bedrock or sediment has occurred in at least 1,000 years; and probably not in over 40,000 years, during Wich many, many major earthquakes along the nearby St. Andreas hsve occurred.
i i
i It is further our impression that the tectonic surface ruptures of 1906 i
w Pt. Reyes outside the main St. Andreas zone are in each case associated with topogri,hically evident f ault sass, scarfs, or other evidence of a-pattern of sinilar, previous ruptures. On Bodega, no reord or evidence of similar surf ace ruptures exists (which, of course, does not indicate that none ocettred which have since been obliterated) but, more importantly, there are no gt.elogic or topographic features such as those on Pt. Reyes along which one would expect ruptures to occur.
l Thus, from the observable situation, one could conclude that faulting j
on Bodega would not occur in the event of future 1906 type earthquakes.
i There is then lef t the general and well-known possibility that outside faulting might occur; and a knowledge of the highly unpredictable and-l erratic nature of earthquakes in general. How likely is the unpredictable, random occurrence of an outside fault, where no recent f aulting has taken l
place? How large might such a fault be? Can building structures be designed against it?
i i
i 4
a 4
6 e
y
,.,,.-,.,--r.
-r
,-.-y
-~.
s.m.
m
4 a-w.=.
UNITED STATES GOVERNMENT Memorandum DI 1964 To
- Files DATn:
FROM : John F. Newell, Chief, Site-Environmental Branch, Division of Licensing and Regulation SUFHARY OF MEETINGS ON JANUARY 29 AND 30,1964, WITH USGS susper:
AND PC6E CONCERNING GEOLOGY OF THE PROPOSED BODEGA BAY REACTOR SITE On January 29 and 30, 1964, meetings were held in Room 107 at the Bethesda AEC building to discuss the report prepared by Julius Schlocker and Menuel G. Bonilla of the U. S. Beological Survey entitled " Engineering Geology of the Proposed Nuclear Power Plant Site on Bodega Hea,d, Sonoma County, California" and Amendment No. 5 of the Pacific Cas and Electric Company's Application to construct a reactor plant on Bodega Head. The USGS report rumnarizes and interprets geological ot.servations made in connection with excavation of the proposed reactor pit on Bodega Head, arvi the PCM Amendment No. 5, summarizes the findings of the PG&E consultants in geology and seismology based on observations of the same area. These reports reflect signi-ficant differences in the interpretation of certain observations.
The discussions on January 29th was centered on the report submitted by USGS and 'sas not attended by PG&E, though some of the differences with tha PGE report were discussed. The meeting
~ "
- ~~-
- U e
u_. _ _. _.
..mm.
4 ou January Mth was attended by both USGS and PCM and the discussion was centered on the PG M report and the differences with USGS interpretations. Attendees at the meetings were as V, lows 1 Janusn 29 and 30. 1964-January M. 1964
?
U. S. Geoloalcal Survey PG6E Dr. Anderson C. C. Whelchel Julius-Schlocker.
F.~Mautz Manuel Bonilla P. Crane Al Clebsch Dr. Bentoff (Consultant)
Dr. Tocher -(Consultant)
U. S. Coast and Geodetic Survey Mr. Mar 11 ave (Coneuttant)
Leonard Murphy USAEC
[
~
ACRS Dr. Kouts Mr. Rogers Dr. Geyer Mr. Wilcox USAEC
.11. L. Price C. K. Beck M. Mann R. Lowenstein E. Case R. Bryan N. Watson G. Hadlock L. Kornblith J. Newell The discussions during both days covered many details of the geological c'oservations most of which are described in the reports 4
S
I 4
l 3
l submitted by both PG&E and USGS. The following is a topical I
f summary of the discussions f or the two da5 s.
1.
Fracturina and f aultinz in the bedrock That the quartz-diorite bedrock is highly fractured and f aulted was verified by the shaf t excavation. There appeared to be general agreement between USGS and PG&E that this condition was a combination of tectonic activity and coolin.
s USGS observed that the size of quartz-diorite blocks appeared to be smaller at the bottom of the pit excavation that at tha upper bedrock elevations in the pit. The PG&E geologists did not disagree with th19 observation - nor did they agree.
USGS and PG&E appear to be in general agreement that the zone of faults (called the shaft fault in the USGS report) was produced by tectonic action.
Schlocker and Bonilla of USGS believes that slippage has occurred along the ruptures in this fault zone on several occasions. They stated that evidence in the quartz-diorite formation was not available for making a cunclusive determination as to the extent of slippage, although they observed that sharply dippin8 dikes (one pegmatite and one g
leucodiorite) are of fset by the shaf t f ault in a manner indic&t-ing possible horizontal covement of several f eet. They described observations on the two dikes as indicating possible lateral movement of several feet, though they emphasized the e
a
. unreliability of these observations for predicting the magnitude of any novement.
They stated that their interpretation of observations connected with the pegmatite dike indicated lef t lateral movement along the fault in the bedrock, while their observa-tions of the leucodiorite dike indicated the possibility for lateral movement in the opposite direction. USGS and PG&E vere generally in agreement that the extent of lateral sovement could not reliably be determined by the meager evidence available in the bedrock.
PG&E (Mar 11 ave) believes that movement in the shaf t fault has been no more than an inch. He believes the numerous fractures in the bedrock were caused by stresses induced by cooling and seismic action, that the hactures have relieved the stresses in
'the rock formation and, hence, the possibility for large movement during an earthquake. Bentoff stated that he has calculated the maxinum movement that could occur in a lault on Bodega due to a slippage of 20 feet (1c06 earthquake) at Bodega Bay along the active part of San.Andreas (which is near the eastern edge of the fault' sone) to be less than one inch. Sch?ocker believes that the evidence indicates movement in the shaf t f ault has been on the order o' ftet.
O e
1
, 2.
Of f sets in the sedite.ents USGS believes the offsets in the sediments over1 bag the bedrock to be directly related to slippage in the bedrock and that these offsets could have occurred during one tectonic event. The USGS conclusion in this regard is based on observations of these offsets in the southwest vall of the shaf t and the ability to trace f aulting in the sediments for sonw 150 feet beyond the southwest vall of the shatt. A maxiomm of 14 inches vertical separation was observed in the sediments on the shaft wall, and USGS believes that the reversal in directions of dip of the fault observed in this wall, the diff erence in thickness of sedimentary beds and the general lack of matching sedimentary beds on opposite sides of'the f ault al'. suggest that horizontal movement on the fcult has l
occurred. With respect to the reported ' measurements showing a maximum vertical separation in the sediments of 14 inches /
and Bonilla tngny believe that horizr.atal movement accounted for at. least part of the " apparent" vertical offset.
In this regard, they stated that calculations show a horizontal movement of about 13 feet would be necessary to-account for the entire:14 inches-of vertical offset.
PGfmE believes that offsets in the sedimen'.>. sere caused by 1
l landslides and subsidence because none were found in the sediments overlying t) t bedrock at the northeast vall of the shaf t, sad r,.
reg,m.
~-
m.
-s%,
e
+-...
.....*c.
e rws
.-~.e
-L-..
j 6-i f
of f sets were not observed in the sedirents overlying the f
bedrock f ault zone within the pit beyond a distance of about fif ty f eet as ressured from the southwest vall of the pit.
In addition, efforts to locate the fault in sediments easterly j
from the pit were not successful. Also, PGb1 contends that gross slippage of the shaf t f ault would have ruptured the sediments clear to the ground surface. The extension of the sediment fault in the voutVsest vall of the pit could not be seen above elevation of about minus 16 feet in the first trench constructed vest of the pit. The second f ault found in the wall of this trench, about eight or nine f eet from the shaft fault alignment, was traced by both PGkE and USGS for a distance of about 150 feet at the plus 25 foot elevation. This f ault was not found at the plus 50 feet elevation.
PGkE does not l
consider this f ault to be related to the shaf t f ault.
Since the sediments immediately overlying the bi rock in the eastern part of the pit consisted of a thick layer of clay, USGS attributed the lack of evidence (offsets) on the northeast i
vall to plastic deformation of the clay during tectonic movement along the shaft fault.
In connection with the observations in the trench, Schlocker and Bonilla believe that f aulting in the sediments " died out upward" 4
9 A
i.
also that the "second" f ault observed in the trench that is alout eight or nine feet from the alignment of the shaf t favit, is related to the shaft fault by "en echelon" faulting.
They stated that tectonic faults of lateral movement are characteristically " discontinuous," "en echelon," and
" branching" and that surf ace ruptures observed during the 1906 earthquake illustrated these characteristics.
{
Bonilla stated that the f ault in the sediments goes up over a bedrock ridge and the orientation of this ridge would have required a landslids to be bphill, or in a direction opposite to the slope of the bedrock.
Because of this, both Bonilla and Schlocker believe it highly unlikely that the sediment f aults were caused by landslide or subsidence.
PG&E (Tocher) stated that the clay seam which truncates the of feet in the sediments observed in the trench west of the pit indicates that off sets occurred before the clay seam and the overlying sediments were deposited, and therefore, if the of f sets were caused by tectonic activity they would have occurred considerably more than 42,000 years ago, based on the carbon 14 dating of wood found at elevations between plus 50 and plus 75.
Schlocker and Bonilla are not in agreement with the PG6E theory since they believe it more likely that the faulting died out upward and the clay seam did not rupture because of its capaciti for plastic deformation.
I
, 3.
Geolostic Ata USGS and PG&E vere in general agreement on the ages of rocks and sediments.
Quartz-diorite Bedre 80 mill un years.
Bottum of pit is in be rock at elevation minus 73 (below Ik e-sea level).
kpf,[3 ]4]f Fault in sedi nents found at plus 25 but not found at y
{g plue 50.
b g(.
The mininum age of the younger (upper) sediments was pieced at shout 42,000 years. The older sediments were estimated to a
rante in age from about 300,000 years to 800,00A years.
l There was genwal agreement between USGS and PGk t no ev...
- e was presented ad :c, observations in the be,
- k in t.>
shaft that vould be u cfa.1 hr dating the shaft fault.
Dr. Anderson of USGS does not believe that any evidence pre-i sented to date would support " recency" of movement along the shaf t f ault, but believes the last tnovement ceuld ha s occurred "in the order of centudes" ago.
There vs.s also general agreement that available evidence does not provide a basis for dating the sediment f aalts with ag degree of precision.
I J
4.
Relevancy of Point Reyes Schlocker and Bonilla reported that surface ruptures occurred in the vicinity of Point Reyes during ti.e 1906 ear % quake.
These were described by Gilbert (a geologist} following the
=
---.a.-
. - _ ~ _. _ - - _. -. -- - - - - - - - - -
I 9
i 1906 event. According to the report by Gilbert, ruptures Inverness is occurred at Inverness and at Mount Wittenberg.
4 i
I about 2,000 feet west of thewstern limit of San Ardreas, and the lateral r~;ement at Inverness according to Gilbert, was approximately 2-1/2 feet.
Schlocker and Bonilla found what they believed to be the rupture area described by Gilbert with assistance from a resident of Inverness.
l Schlocker and Bonilla believe the evidence at this location l
confirmed that a surf ace rupture occurred in 1906 Tocher stated his belief that "old" faults exist which have been "recently" active, and that f aults at Bodega Head have have not been recently active. Tocher also stated that he 4
believed the bedrock moved at Inverness in 1906, but questioned i
whether it moved two feet. Marlieve stated that the sediments moved two f eet or more due to landalide but the rock moved "very little."
Schlocker and Bonilla stated that the description by Gilbert, who was a coupetent geclagist that made the observation following the 1906 earthquake, does not confirm Mar 11 ave's and Tocher's beliefs.
At Mount Wittenberg, which is about one alle west of the San Andreas Fault Zone, neither USGS nor PG6E could locate the break i
described b, Gilbert. Se'1ocker and Bonilla stated that the faulting crossed a ridge at about right angles in this area and there was evidence that this was a fresh break in 1906.
e e
e.
4
..,y w-
....a.-e-
(
/
They stated that aerial photos show many lines in this crea I
which are faults and zones of weakness.. PG&E consultants suggested that faulting in the sediments at Mt. 'Alttenberg was due t:
.b. ping instead of gross movement in the bedrock.
Based on the information in the Point Reyes af ea, which showed about two feat or so movement in f aults about the same distance from the San Ancesas as ths
>dega reactor stic, Schlocker stated he would expect movement of this magnitude could occur at Bodega. Tocher agreed that he would expset movement in the Point Reyes exea, but said there is no evidence of recent slippage at Bodega. He stated that he "will not deny that it is possible,
~
but believes it is unlikely at Bodega," he would not recommend loca-I tion of a reactor at Point Reyes but he believes-that the evidence on Bodega Head shovs' that no slippage has occurred for thousands of ye.rs.
Schlocker and Bonilla stated that Bodega l
dead has nos been examined in sufficient detail to establish that lataral movement has not occurred along any faults on Bcdega Head.
In this regard they believe that weathering and lack of (:rees and oth*r cover together v;th grazing of the area would have obliterated any surface signs of faulting in 1906. Also they do not believe l
that probabilities of rupture can be determined for Bodega Head based on present1y available data. Tocher said that the probability for movement at Point Reyes area is higher than for movement at i
Bodega. Schlocker believes there is no difference between the two locations in this regard.
~
i i
13 I
5.
Miscellaneous observations concernitut San Andreas Fault '
Zone and Boders Head 1.conard Murphy of U. S. Coast and Geodetic Survey comented briefly about the San Andreas as follows3 only three or four major earthquakes have occurred along the San Andreas in recent times (150 years or so) and-their positions are ot known within a few miles, and the exact position of the 1906 earthquake is not known. The San Andreas earthquakes occur at a depth of 15 to 25 miles.
It cannot be assumed - that energy f rom an earthquake is transmi'eted vertically to the surf ace -
there is only the observation of what happens on the surface.-
The Hypocenter usuelly disagrees by several miles with surf ace f
effects. In California there have been innumerable small earth-
{
quakes off the f aults, but the major ones are located along the l
fault systems. There is one earthquake per day felt in California on the average. Those of a magnitude of 6.5 to 7 and above are i
located on or close to the major known faults.
i.
l There was general consensus between USGS and PC6E.that-the Bodega l-j reactor plant location _is approximately 1000 feet west of the i
" western boundary" of the San Andreas. fault zone, and that fault---
t ing existr outside_ of the comonly accepted zone boundaries.
In thf e regard, Dr. Benioff stated his belief that the San Andreas f ault zon ss from 100 to 260 miles vide if a definition of the i
4 4
M ' Te
- WBe
'f*d*uuthem g -
p se ey-
- -a w,
4
+gi
.._.-- - - - ~
i j
a i
12 -
i
-fault zone would include all faults'that have occurred along l
the San Andreas.-
1 j-Schlocker stated that his observations along the San Andreas i
indicate that abundance of f ractures and f aults increases as l
the San Andreas'is approached, and that the liklihood of 4
l' rupturing and lateral movement is. greater. adjacent'to the fault l
zone'than it would be somewhat further away.
Mar 11 ave and Tocher-indicated that any area within five to ten i
miles of the San Andreas fault, zone would be highly faulted and-f-
there would be no significant difference in hazard at five to ten 4
l-miles thara at tne distance of the Bodega site from the zone.
I Bentoff stated that the vibratory motions from an earthquake would be less adjacent to the fault than at che. greater distance, although
.there would te a shock of short turation and the " fling" due-to the i
sudden movement on the San Andreas.
d i
cci-R. L. Price i
C. K. Beck M. M. Mann h,G.Hadlock l
R. ?
,1 4ein
~
. R. Bryan
- N. Watson E. G. Case a
0 i
e j
M rm
-*-mim-ee-*-e-e V
- -.. -=
_e.ma we,m,.
e
+
j TDR 9ws
[i
?. b % [ 6q f
M u; s%T l
UNITED STATES
^
j DEF/ RTMENT OF THE INTERIOR OFFICE OF THE SECRETARY 4
WASHINGTON. D.C. 202. )
b
_&.. N s l N 3 5W Dear Dr. Seaborgt.
t In response to the letter of May 23 signed by Dr. Robert B. Wilsen 1
as Astias Chaiman of _ the Atomic taergy Commission, I e new trans-mitting the enclosed report, GEOLOGIC Am SE!5NIC INyssTIGAT1015 0F I
A PROPOSED NUCLEAR POW 51R PLANT SITE ON B00BGA MEAD, _50MMA COWITY, j
t The seelegic phase of that investigation disclosed me posit.tve evidesee ef setive fmutta passina through the parta ef the site j
ensavated as of June 6,1MS.
f but our seismic hasards imstigster, Dr. J. P. Estes, sonatudes "I hileve that absence of demonstrably resent fam1tiu in these parts of the site sad Sedega Herd where. field i
relationships are reaseaably clear is set sa adequate l
ariterten for astablishing the safety of the site.
l Theesh aseessary, it is met sufficient. la the mese of i
and units and fractures sutting. the quarts diarite, j
siner neemt offsets seu14 be-easily overleekod. On portions of the Head where the quarts diarite+1aiste-l eens sentast is bedly weathered or_ ethanise abaeused small reenet offsets probably seuld met be traeed-from j
bedeeek into the sediasetary sever. The site smaavatian itself septas only a fraction of-the 'reglen la which fanating night prove disastrous to the plante i
"The sammen occurrence darias large earthquakes of offsets en a ember of mis,tr f aults in sympathy with a larse displasement as the causative fault cannet be disressaded.
Lisplacements in bedroek west of the Sea Andseat fanit se the Point Repos Peninsula af the tins of the 1986 eartb-l gaske ladiasse that faatting does esaur outside the San Andoeus fonts some in ayayashy with large displaeonesas within the came. The escurrense ff M offsets se Se4pe Mead during Antuse earthquakes is a d5 finite peesibility.
"homose peliability limits se any estimate of seLamia l
hasard to the 74x3 plant an se breed, the ststement 4
l qsynaw ye u
1 l
i l
j of tolerable risk must be very general. The magnitude' i
of possible human damage that worrid vesmit fnm the i
destruction of the plant by an earthquake suggests that it should be built only if there is no reaseeable doubt--
that it would survire any eershguake linely to occur an j
the nearby San Ardreas fault. It appears te me that the site does not meet this test end that fi is set an j
adequately safe -location for a nuclear powcr pisat.
"Few places on the earth are exposed to more certain l
earthquake risk than are these along the San Andreas Tault in northern and central California. The case
{
arguing the esfety of the Sodega llead site rests
-largely on the confidence that 'sranite' is a seed j
foundation material and that it minimises ground shaking due te earthquakes and on the judge int, sup-l perted but not proved by geologic investigations of sedega Head, that no fas1 ting has occurred - these during the past several thousand years. The case assinst the site stresses seisselegy's lack of detailed informaties 4
on events and conditions in the epicentral tract of a j
sajor earthquake. Because we cannot 1. rove that the l
worst situation will not prorait at the site, we must rece3nine that it might.
l i
" Acceptance of Bodega llead as a safe reacter site will establish a precedent that will make it exceedingly -
i difficult to reject any proposed future site em the.
j grounds of extreme earthquake riek."
- M s6 fladings de nothirs to allay, but only reinferee, the grave j
eencern expressed in my May 20 letter to you -- regarding the -
seismic dangers of this proposed Sedega Head location for a usjor i
meclear power plant.
l t
Sincerely yours, t
i j
{ pg(D Johti.t W e A
+
4 Secretary of the laterior l
Dr. G1 se h
l Chai t(
s l
Atsu
,5 si 1717 i
W 4
Washi
[
ncl i
'\\
w9
,,,,-a,~,,,--
, ~,.,..,...,.., ~.,., -
... ~ ~..,,. ~... - - -. _ - -. -........ -