ML20235F113
| ML20235F113 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Bodega Bay |
| Issue date: | 05/18/1964 |
| From: | COMMERCE, DEPT. OF |
| To: | |
| Shared Package | |
| ML20234A767 | List:
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| References | |
| FOIA-85-665 2686, NUDOCS 8709280420 | |
| Download: ML20235F113 (15) | |
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SEISMICITY AND TSUNAMI REPORT .
BODEGA HEAD, CALIFORNIA ,
The Division of Licensing and Regulation of the Atomic Energy Commis-l- -
aion, Wachington, D. C., requested the U. S. Coast and Geodetic Survey to I
report on the seismicity and tsunami condition of Bodega Head, California.
This report contains an evaluation of the seismic condition of Bodega Head as defined by the Pacific Gas .and Electric Company in numerous documents l- submitted to the AEC.
In addition,'coments are made on documents submitted by the U.S. Geologi-L cal Survey as the material portains to seismic hazards, m -- -
and by Dr. Pierre Saint-Amand who prepared a geologic and seismologic s
t study of Bodega Head under the auspices of the Northern California Associ-o +
ation to Preserve, Bodega Head and Harbor. The Survey also presents an in-N l
)- dependently determined earthquake frequency pattern along the San Sndreas fault, the most probable ground motions measured in acceleration and dis -
placement for a magnitude 8.2 on this fault near Bo'dega Head, and finally, an evaluation of the tsunami hazard at the same location. The Survey is in a unique position to perform this service because it has either the original documents or a complete file of historical data for earthquake soismology, engineering seismology, and tsunamis, and has made studies in these fields for approximately 30 to 40 years. 7' In this report g all other geologic and seismic reports,jsubmitted to the AEC relative to the proposed reactor at Bodega Head, frequent reference l l
t is made to geological faults and in particular, the San Andreas fault. This )
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2 is necessary in describing earthquakes because a fault is the only surface ,
manifestation of previous earthquake occurrences. Geologists refer to l 1
these faults or earth fractures as active or inactive, depending upon the recentcy of movements. Active faults are associated with recent earth-quake activity, such as the earthquake belt around the ' perimeter of the Pacific Ocean and across Asia and along the Mediterranean Sea to the Atlantic Ocean. An example of an inactive or relative inactive belt is I
the Appalachian system in eastern North America where there are extensive '
fault systems but only minor and infrequent tremors.
The San Andreas fault,which is of principal interest due to the prox-imity (within 1100 feet of the limits of the western zone) to the proposed i '
I sit of Bodega Head reactor, is considered by geologists and seismologists :
to be an active earthquake source. The fault extends southeasterly from a point under the ocean about 300 miles from the Oregon coast (approximately 450 north latitude and 1300 west longitude) to the lower limits of the Gulf of California. It intersects the California coastline at Point Arena i and continues in a nearly straight line (southeast) to the vicinity of Gorman where it curves somewhat eastward. A few miles south of Gorman the I e
i fault curves westward slightly to become parallel to its original direction. '
Southward there is some doubt as to whether the observed faults are geologi-ca?.ly extensions of the San Andreas, but the seismicity of southern and Gulf f
of California leaves no doubt about its lower extension.
The San Andreas fault, which is a right hand strike slip fault (i.e.,
motion is predominately horizontal) has been associated with two great '
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earthquakes in 1857 and 1906. Other faults trending nearly parallel to this master fault show evidence of right hand displacement. Faul'is with trends crudely at right engles to the San Andreas are predominately left hand type.
In California the chief left hand fault is the Garlock which exhibits tapo-graphic evidence of activity without clear indication of displacement in historic time. The White Wolf fault, associated with the 1952 Kern County i earthquakes, is roughly parallel to the Garlock fault. The evidence indi-cates principally dip slip displacement on the fault in 1952, but some left hand strike slip motion was also established, in southern California there is evidence for accumulated shift of s
about 25 miles along the San Andreas fault since mid-Tertiary time. Some investigators believe much more horizontal motion has taken place. The fault is easily-followed between 35o and 400 north latitude. Beyond these limits it is deflected and complicated by the Mendocino fracture zone to the north and the Murray fracture zone to the south. Movements measured along certain areas of this fault by the Coast and Geodetic Survey are approximately 2 inches per year. The relative motion indicates the west side of the fault is moving northward and the east side southward. The maximum horizontal shif t observed after the 1906 earthquake was 21 feet at _
The vertical motion during the same earthquake was no greater than 3 feet. This is typical of the earth motions resulting from California earth-quakes, i.e., much greater horizontal than vertical displacements.
l Even though California and specifically, the San Andreas fault, are con-sidered earthquake prone areas, they experience a surprisingly low number of *
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m magnitude 6 and greater earthquakes. According to Richter, there'have been two " great" earthquakes (1857 and 1906) on the fault and approximately 15, earthquakes from 1800 to 1950 with magnitudes 6 to 7aplus within 75 miles of this fault. Under magnitude 6 earthquakes are quite numerous and their distribution is shown on the earthquake history map of California.
l As noted in the report submitted by Tocher for earthquakes felt at or near Bodega Head, 1838-1960, nome of them were located at Bodega. Of the 58 listed earthquakes,14 were positively reported felt at Bodega or in Bodega Bay; two caused 1ittle or no damage and one in 1906 caused appreciable damage and scme surface fissuring.
1 Studies of the seismicity along the San Andreas fault for the past 57 years show that a magnitude 6 to 6.9 earthquake occurs every 7 years on the average and only,.one magnitude 7-7.9 earthquake occurs during this period.
This fits the pattern determined by Gutenberg in Seismicity of the Earth which predicts a magnitude 8 earthquake about once every hundred years. In discussing the frequency of high magnitude earthquakes, it should be noted that many reoccur in the same epicentral areas. Richter mentions three Honshu, Japan earthquakes of 1897,1898 and 1905 with magnitudes from 7.9 to 8.3. A number of zones in Italy, for example, Girifaleo (1626,1659,1783, 1905); Monteleone (1659,1783,1905); Gerace (1720,1784,1791,1907); ex- l l
perienced damaging earthquakes. According to Davis, Valparaiso, Chile was destroyed in 1822 and again in 1906. Skopje, Yugoslavia,ofrecentmemory, was totally or partially destroyed in 1963,1921,1555 and 518. I i
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y in crder to design and construct earthquake resistant structures.it is I'
necessary to'know not only the above mentioned seismicity information about destructive earthquakes; but also the displacement, velocity and acceler-
' ation of ground motions and the response characteristics of structures to: I E
these motions. .Since 1933 the Coast and Geodetic Survey has made these ,'l j- -
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measurements of strong earthquakes in the Western United States and in
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Latin America. All. interested parties in this investigation are aware of l ' ,,
this.' work and the data collected have been used extensively by all. There is z
b, general uniformity in the interpretation of the direct recorded strong motion T data at El Centro, San Francisco and Seattle. However, there is some dis- ..
persion in the computed results when attempts are made to extrapolate from' .,
magnitude'6-7 earthquakes to magnitude 8.2 (San Francisco,1906). Computa-tions are necessary,since no magnitude 8 earthquakes have ever been recorded *
.by strong motion seismographs. It was hoped that such equipment might record at least one high magnitude earthquake aftershock in Alaska (1%4) but to
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date, not one has occurred. Such information, if available, would have been r ) aluable for this report.
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Using the seismicity and strong motion'information available for earth- '
quakes along the San Andreas fault and near Bodega Head, it is possible to
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define the vibratory motions produced by these earthquakes. The surface f' geology of Bodega Head is well defined due to the careful excavation that has
.been performed by the applicant and his excellent cooperation with all par- l ties studying the structure. The quartz diorite bedrock, even though frac- r
. t tured and crushed during geologic time, (probably more than 40,000 years ago) F
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is acceptable as good foundation rock for reactor support. The fab 1 ting
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j evidenced in the lower limits of the pit is a matter of some . concern; how- /
ever, according to geologists who have studied its character there is
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general agreement that it is_not of recent origin. I in determining ground vibrations generated by a magnitude 8.2 earth-quake on the San Andreas fault in the vicinity of Bodega Head, it is neces-m sary to evaluate (1) the intense shaking of the ground at the proposed reactor site caused by seismic waves propagated outward from the fault and also, from the actual permanent displacement (fling) along the fault of the site and (2) possible dislocations within the site due to rupture by the main fault, a branch of the main fault, a minor auxiliary fault, or other
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sources such as landslides, etc.
The Modified Mercalli intensity Scale has frequently been used to define earthquake motions. At best and only when the intensities are associated with estimated ground wave periods can these scale ratings be used for estimating accelerations. Consideringamagnitude8.2 earthquake,Tochj m s) '
7 and re ide estimate intensity V QI on the quartz diorite bedrock at the i
j site and an intensity X in the fault zone. They recommend the power plant structures should be designed to resist an earthquake of MM-Vill, or to provide a margin of safety MM-IX.
Saint-Amand suggests a minimum intensity of MM-IX on Bodega Head for a similar earthquake; MM-X if significant landslides occurred during the main earthquake; MM-XI if major faulting occurred on Bodega during the main earth-.
quake. His findings agree well with Richter's table of published relations '
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of magnitude and intensity. However, it should be noted that Richter states that the correlation is rough and applies to intensities on " ordinary ground." According to Neumann, who has made exhaustive studies of intensity ratings, magnitude determinations and strong motion smogram intensities on granitic basement rock (same as at Bodega Head) woul'd be approximately one grade lower or a maximum of MM-X.,. -
gp Eaton gives MM-lX as a reasonable estimate of the 1906 intensity at the site based on tha fact that the reactor would be sited on quartz diorite bedrock and that recorded maximum intensities of the 1906 earthquake near Bodega appear to be somewhat smaller than Richter's averages would suggest.
Using the Gutenberg and Richter (1942) semi-empirical relationship MM-Vill, IX, and X yield accelerations of .15 g, .32 g, an . respectively.
Neumann afjer exhaustive consideration of intensity and recorded strong motion data gives a range of .67 g to 1.0 g for a magnitude 8.2 earthquake on the San Andreas fault near Bodega Head. ~
e, Housner (Benioff and Tocher agree) employed the response spectrum. tech-I nique to determine the destructive action of the ground motion. Although /
this method is generally preferred to the intensity analysis, it has 7 specific 1imitaiions as the spectrum assumes a recorded earthquake acceler ation. Since no magnitude 8 shock has ever been recorded, the data must e extrapolated from a lower magnitude recording such as El Centro (1940),
Olympia (1949), etc.
Benioff in describing the motion at the fault states that it is effec-tively an uni-directional fling or pulse which radiates outward from the
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fault. "Although. the waves _ begin in the form of a ' single uni-dir'ectional
. pulse.they are quickly transformed into oscillatory forms by, reflections, )
refractions and change of type owing to the layering of the crust.and the-
- variations of wave speed with depth'. ~ Although th'e . vibratory wave amplitude
, is small at the fault it increases rapidly with distance from the fault so that from about 2 miles.to 12 miles, it is approximately constant, if the geology,is uniform......" .This' explanation does not agree with results -
of earthquake effects since' the larger intensities are indeed observed for larger. earthquakes. Moreover, as pointed out by Eaton from the very.defini-tion of magnitude and the seismologist's ability to compute magnitudes from T
relatively. short period body waves, there is good indication that the ampli-tude of. waves radiated from relatively small areas of the fault surface in-creases approximately ten times between magnitudes 6-7 and 7-8.
The Coast and Geodetic Survey having access' to 'these' reports and having evaluated independently the response spectrum and the intensity versus strong 4
motion data, recommends 2?--- 2/3 g (a, t periods from 0.3 see to 0.7 see for
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and 4 W g Relative to the possible dislocations in the site or adjacent parts of Bodega Head during a major earthquake, there is a scarcity of data upon which
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- to-~quote an accurate probable displacement. In considering the geology of >
the site, most of the observers (Schlocker, Bonelli, Tocher, etc.) believe that the site,is nafe" because of the quartz diorite formation ard the lack of evidence of recent faulting in the shaft. No major faults were found and' L
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the field evidence suggests that most, if not all, of the fracturing, shearing, and f aulting in the quartz diorite is very ancient. This is
, confirmed by the examination of the terrace deposits overlying the quartz diorite which failed to reveal any faulting in the terrace deposits. Even thou such evidence (lack of recent faulting in the shaft) was observed q in er .avating the shaft, it must be emphasized that this survey covered an infinitesimal segment of the geological structure associated with the ,
San Andreas fault. Therefore, it,is assume if such concentrated surveys were extended to other areas even very to the proposed site, that
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positiveevidenceofrecentfaulting(couldbefound.m ) Moreover, the fact that large earthquake.s of offsets on a number of minor faults in sympathy with a large displacement on thgcausativst. fault cannot be disregarded. '
Certainly in the. case of the Point Reyes Peninsula during the 1906 earth-quake the displacements in bedrock indicate that faulting does occur outside of the San Andreas fault zone in sympathy with large displacements within the zone. Such an occurrence of offsets on Bodega Head during future earthquakes is a definite possibility. Based upon the very likely existence of such faults, (he Surve7 believes)that displacements of at least 2k feet, similar to that experienced at Point Reyes, must be con- '
sidered likely at Bodega Head.
Another factor for consideration in evaluating Bodega Head as a possible r 3 _3 siteforareactoristhegprobabilitylor damaging} tsunami. It is well
, ~ -- a established that the San Andreas fault extends into the ocean along the northern coast of California. Since 1898 there have been two submarine '
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7 10 earthquakes 1alongthisfaultthatcouldhave[potentially] generated'atsunami.
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'Moreover, there_ 'is a possibility that the. next gre'at, earthquake of magnitude v
greater than 8 along this fault-could occur c.ff-shore.
Now, it might be in order to digress briefly and say something about tsunami causes and propagation since neither the applicant (PG&E) nor the -
consultants n- have discussed this matter in their documents. For the most part,
, tsunamis are generated'by submarine earthquakes or earthquakes located close to coastal areas. The causes .of tsunamis are not well established because only a small per.centage of submarine earthquakes generate measurable water waves. The most common explanation allsfor]thedisplacementofsubmarine
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p biocks of the. earth's crust. Since it has been observed on land that great af' rthq'uakes ea have caused uplifts of 30-50 feet and affected crustal blocks p.9 -
. ] /1, ' /) hundreds of miles long and up to a hundred miles wide, it is easy to con-ceive of such a crustal movement under the ocean generating a huge water wave.
Slides along the coasts are also throught to be the source of tsunamis.
Tsunamis frequently originate at great oceanic troughs where great masses. of unconsolidated material which, disturbed by an earthquake, may slide into the depths, displacing a great amount of water. Dr. Benioff, some years ago, suggestedApossible correlaQbetween tsunamis and n
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great surface wavesgith periods over a minute. This was remarkably con- j
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firmed during the recent Prince William Sound earthquake where waves of a few feet were generated in the Gulf of Mexico, in other large bodies of f water and in many swimming pools throughout the United States.
It is not surprising that the tsunami peril was not mentioned by PG&E t
and others because with the exception of a wave, reported generated by a 9
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] local earthquake on December 21, 1812., there is no record of a destructive.
tsunami generated along the coast of California.
The 1812 wave reportedly:
reached land elevations~.of 50 feet at Gaviofa, 30-35 feet at Santa Barbara,'
and 15 or more feet at Ventura.
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Inasmuch as historical records for locally generated tsunamis are so sparce, the' dimensions of tsunamis that have. been established through rela-tively frequent. occurrences in Japan should be considered, lida has done considerable work in establishing statistical relationships on the available Japanese data, using both earthquake magnitude and focal depth. His formu-las show a small tsunami will be generated for a shallow earthquake of maEnitude 6f-7. 'He shows disastrous tsunamis generated for shallow earthquakes with magnitudes of 7 3/4 or greater. The magnitude of 7 3/4 corresponds to a fault length of 120 km and a ground displacement of 5.4 meters.
Based on lida's formulas, a tsunami classified as destructive will have
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a height of about 10 meter _sgreater. The earthquake of March 3,1933, off k
Sanriku coast of Japan had a magnitude of 8.3 and was of shallow focal depth; the wave rose to heights of 23 meters on the . coast. The recent Alaskan earthquake had a magnitude of 8.4; maximum waves of 30-35 feet were reported at Kodiak and may have been exceeded elsewhere. Local waves of 15-20 meters were reported for the Chile tsunami of May 1960 (earthquake magnitude of 8} to 8t). These support lida's formula as being reasonable I
(even though far 'from being rigorous evidence) and suggest that his con-U' {
clusions for the Japanese area may apply approximately in other areas. '
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12 in confirmation of these facts, it is in order to tabulate s'ome sta-i tistica for a few major tsunamis generated in different geographical areas.
I Prince William Sound - March 28, 1964 - 610 N, 147.50 W, Magni tude 8.4.
Cordova 65 miles (Stat) 30 feet Kodiak 210 35 Seward 85 30 Sitka 495 23 Crescent City 1,620 13 San Francisco 1,890 7 Chilean earthquake - May 22, 1960 - 380 S, 73.50 W, Magnitude Bk.
Talcahuano, Chile 90 miles (Naut) *64 feet Valparaiso 312 ,E Antofagasta 875 S}
4 Crescent City 5 529 3 10.9 feet Hilo, Hawaii 5,704 35 Kanaisi, Japan 9,150 12.9 feet Aleutian earthquake - March 9, 1957 - 510 N, 1750 W, Magnitude 8.3.
Adak, Alaska 80 miles (Naut) 26(?) feet Unalaska 355 4.5 feet Kahalui, Hawaii 2,005 11.2 Valparaiso, Chile 7,384 6.7 Kamchatka earthquake - November 4,1952, 521 N,159 E, Magnitude St.
Attu, Alaska 460 miles (Naut) 8.0 feet Adak 893 6.9 Hi1o, Hawaii 893 7.9 San Francisco 2,265 3, 8.1 Talcahuano, Chile 8,420 Aleutian earthquake - April 1,1946, 53k N,163 W, Magnitude 7.4.
Scotch Cap, Alaska 100 miles 80 feet H ilo, Hawaii 2,280 35 (7)
San Luis Obispo, California 1,435 8}
Honshu, Japan earthquake - March 2,1933, 39to N,144}c E, Magnitude 8.9. l Sgoya, Japan 190 miles (Stat) 30 feet '
Tanohata 140 27 Koyatori 1 30 40 Ryor i S irahama 140 63 (Plus)
Hirota Atumari 145 77 -
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i 13 Even though little is known about tsunami generation and the propagation of the tsunami in open water where the velocities range up to 500 or 600 L.
miles per hour and the wave lengths may be a hundred miles long, there is certainly positive evidence that a potential exists for a tsunami along the California coast, particularly along the. San Andreas fault off the California co3st. In reviewing the wave heights generated by these and other submarine earthquakes, it would not be unexpected for an earthquake approximately 250 miles from Bodega Head to produce a wave height of 25 feet above mean sea
- 1. Therefore, the Survey recommends that adequate protection be provided for the proposed Bodega Head reactor site against a potential tsunami having a wave height of 25 feet above mean sea level.
1 Before summariz ions of report it i order to comment on the trendous amount of work that has been performed by the PG&E Company, its consultants. the scientists and engineers of.the AEC, etc., consultants v - _,
and the interested _publi;c_.
i Each one is aware of their great responsibility i
rin the decisions to be reached in the near future relative to either licensing or refusing a license for a reactor at Bodega Head, California.
This responsibility is explicitly emphasiced by the statement of the Honorable Chester Holifield of California "I feel that one large reactor incident i
would cause such great loss of life that it might preclude any further
' development in the industrial field if it should occur...."
Neumann states, "V/ nile there can be no quarantee that an earthquake greater than the.1906 shock will not occur in the Bodega Head area, the ;
1 history of ear 3qqkes in active seismic areas leads one to believe that this is no ively'.... Theoretical considerations lead one to believe that l
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'if certain tectonic processes are underway in the deep crustal rocks of th..
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' earth ' in a_ given region,' these processes will be repeated over very lon l' i periods of iime.....perhaps many centurles--before the pattern changm" 1 Eaton in his report succinctly and profoundly stated "Few places on
.' l earth are exposed to more certain earthquake risk than are those'along the i
San Andreas fault in northern and southern' California. Acceptance of p,
Bodega Head as a safe reactor site well establishes a precedent that will I make it. exceedingly difficult to reject any proposed future site on the grounds of extreme earthquake risk."
r The Survey, fully aware ,-- of ~ the exhaustive and comprehensive studies.
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.- by all participants, believes that the conclusions reached by'its
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i scientists are adequate and sufficiently complete so that the AEC may employ the7n in rendering a judgment.
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CONCLUS10NS l (1)
The seismicity study of the San Andreas fault area near the propo Bodega Head reactor shows the possibility of a magnitude 8.2 earthquake once every 100 years.
All actions relative to this site should be contingent
': upon the occurrence of a large magnitude earthquake during the lifetime of a reactor.
(2)
The characteristics of the ground vibrations tolerable at this site are:
acceleration of ground motions -Emmrr% g for periods of 0.3 to 0.7 V4 i
seconds
- t. o for which the structure and all of its elements should be designed
- 079 g for-the same period range is the limit for which critical elements 1 fail but not release fission material.
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15 (3) There is a definite potential for a tsunami to affect th'e Bodega Head site, it is therefore recommended .th...a.t any proposed reactor be so constructed that tsunami wave -
heights of 25 fe'et above mean sea level will *'
nothmpair its operation
_ , ) \nd the safety of the surrounding population '
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U. S. Coast and Geodetic Survey l Washington, D. C. 20230 {
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