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Sb - 2 c r FRANK NEUMANN "'"~~~~~....
S E t a M c Lc o is t, DEcLoav DEPARTMENT {*
- UNIVERSITY O F WAS HIN GTON 8EATTLE 5, WASHINGTON June 19, 1963.
1 Dr. Robert H. Bryan, l Division of Licensing and Regulation, Atomio Energy Comission, Washington 25, D. C.
Dear Dr. Bryan:
I
. There is rushed off herewith a report on the Bodega I Head case which is intended to conform with the plan mapped out .
at our conference on June 13th. One reference is still to be ad- I ded but it did not seem wotth delaying it further for this reason.
Perhaps with another review and possible discussion it will be possible to whip it into shape for a final draft. The illus-trations are obviously makeshif ts but if you think they should be drawn up in better form please let me know and I wili get one of the campus illustrators on the job imediately -- if they are not i all on vacation. '
Sincerely yours, K .n o s . 6 u .... - -
Frank Neumann. I l
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df Seismological Aspect's of Proposed Nuclear c& '
Power Plant on Bodega Head, California UgynaCG* j t
Introduction. - This report has been prepared at the request of the Division of Licensing and Regulation of the Atomic Energy Commission. Its purpose is to express the views of the writer regarding the seismic risk at the I Bodega Head site, to evaluate the most credible maximum earthquake inten .
sity likely to be experienced at the site and to estimate from available seismic data, the ground motions most likely to be assnciated with that intensity.
Much of the technical discussion vill center around findings that may be considered more in the field of research than in the category of text book information. Seismological data of engineering value were never systematienlly collected until the Coast and Geodetic Survey, early in the thirties, inaugurated a program that provided investigators with a vast amount of instrumental data on damaging ground motions and also descriptive information relating to intensity. It is from the analysis of these data that most of today's information on earthquakes and earthquake forces is o'otained.
The San Andreas Fault. - The rim of the Pacific Ocean is the world's most active seismic zone and California is an integral part of it. Seismic activity may therefore bo expected to continue as in the past. If there is a pattern of earthqu'ake frequency within the state it is not a simple one,; if one exists it vill probably take several centuries of observations to reveal it. While it may appear that a great shock occurs along the
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The San Andreas Fault is one of the earth's greatest active faults.
Its general trend is shown by the broken line in Fig.1. The maps are taken from reference (2) and show all important shocks in the California-Western Nevada area. At the northern end the fault apparently extends along the ocean floor to a zone off Cape Mendocino. It enters California near Point Arena and passes southeastward past Bodega Head to a point just off Golden Gate. It then crosses the coast again in San Mateo County and continues as shown down into the San Bernardino Mountains. South of here there is some doubt as to whether the observed faults are geologi-cally an extension of the San Andreas but the seismicity of Imperial County and Lover California leaves little doubt about the continued move-ment of deep crustal rocks in this area. The evidence from triangulation surveys (3) indicates very clearly that in certain areas the terrain on the southwest side of the fault is moving northwestward with respect to the northeast side at the rate of about 2 inches per year. In the epicentral l area of the 1906 shock there was an abrupt displacement along the fault of 15 feet in rock (h) .
Table I is a list of 25 shocho strong which apparently originated along the San Andreas Fault in approximately the last 150 years. The intensities were obtained from reference (2); the magnitudes primarily '
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from reference (5). Table II lists 11 strong shochs presumably originating L along the extension of the fault off the shores of Humboldt County. A 1
perusal of these data shows that in all areas the San Andreas is currently a very active fault. Sooner or later the Bodega Head vill be subjected to a damaging shoch, but no one can predict when it vill occur or where it vill center. Reports of the Coast and Geodetic Survey (6) show that since its canvassing program was inaugurated in the early thirties the number of weak shocks in the Bodega Head area are comparable with those reported from other active seismic zones.
Coast and Geodetic Survey's engineering seismology program. In the early
. thirties this bureau, the official earthquake investigation agency of the Federal Government, inaugurated a program of recordin5 stron6 earthquake motions on specially designed seismographs and collecting descriptive information on earthquake effects in all areas shaken by earthquakes (6).
The data were collected primarily to relate earthquake intensities to specific ground motions, and to provide the earthquake engineer with ground motion data from which he could estimate earthquakes stresses in a
structures. Table III is a list of 15 destructive earthquakes that have been registered on strong motion seismographs. Four of them represent strong shocks originating along the San Andreas Fault.
In subsequent paragraphs it vill be seen how both types of data, instrumental and non-instrumental, have been used to establish a relation-chip between earthquake intensity and related ground motion.
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Nature of earthquake intensity and intensity distribution. - The intensity l at pny point within a shaken area is rated according to the effect of the ground vibration on people and on inanimate oWeets such as bu13 dings, utility poles, trees, etc. The Modified Mercalli Earthquake Intensity i Scale (7) describes its 12 grades of intensity using critoria of this !
hind. The Coast and Geodetic Survey collects descriptive information on t
questionnaire card forms for all Widely felt shocks' sad evaluates the intensity at cach town by correlating the information thus furnished with
'that enumerr.ted bi the intensity scale. In California thes',e evaluations e
, are reviewed and confirmed by, seismologists at the University of Ca'_.i'lornia (Serkeley) .?od at the California hatitute of Technology (Pasadena) before
.i being published (6) . '
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f lover curve on the chart may be interpreted as indicating the attenuation of intensity on basemont rock for this shoch. If the curve is drawn on semi-log paper, as in the lover portion of Fig. 2, it beco:nes a right lina shoving that the attenuation rato is exponential in chcracter.
Further details concerning other basement rock intensity attenuation grrephs vill be found in reference (C).
. In Fig. 3 are shown the basement rock attenuation graphs for the l
Imperial Valley *.arthquake of May 18,19% and the Kern County earthquake ot' July 21, 1952. These graphs ciffer in slope from the Puget Sow 1d graph (probably due to differences in focal depth) but it is also apparent i
that the great mass of sedimentary rock that underlies the Central Valley area constitutes a secondary basement rock feature that changes the pattern of the basement rock graph in that area. The plotted points show that out to 100 miles this sedimentary rock layer evidently serves as a minimum intensity basement; beyond that the minimum intensities were uniformly one crade of intensity lover due presumably to the absence of the sedi.
, mentary basement. The lower values beyond 100 miles represent a co-called granitic rock basement (as in Puget Sound). It vill 'oe shown later how the granitic basement graph can be tied in empirically with the (Richter) i magnitude of an earthquake. Further study of the problem shows that while intensity attenuation in California is complicated by the presence of two typee of basement it is clear that the sedimentary basement always produces
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1 basement areas. (Later discussion of instrumental data vill reveal that )
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this means close to a doubling of the motion on the sedimentary basement)
The validity of this concept of basement rock intensity distribution thAt is, in the Puget Sound area, substantiated by the fact /the circular char-acter of basement rock intensity attenuation affords a new means of a e locating earthquake epicenters and these epicenter cry well with instrumental epicenters (9). It is found, however, that basement rock l intensities are not only often greatly increased on various kinds of overburden and surface formations, but there are timec and limited areas where, presumably because of major variations in the basement rock itself, observed surface intensites vill drop below the values expected for basement rock. Such " barriers" have been found in studies of micros 6 ism propagation (10) and in the writer's opinion do not vitiate the validity of the overall basement rock attenuation concept.
Gutenberg and Richter (11) years ago developed, for California earth-quakes, a relationship between magnitude and what they called maximum inten-sity; it is shown in Fig. h. Because the exact nature of intensity varia-tions was not too clear at that time this may be considered a rather loose concept of maximum intensity based only on a broad acceptance of the fact that local geology was a large factor in controlling intensity.
If this relationship were applied without reservation to the 1906 earth-quake the maximum intensity, presumably in the epicentral area, vould be IHT-115 (14cdified 14crealli scale). Such high intensity has never been suggested by any one discussing the Bodega Head problem. Ilowever, the basement rock intensity attenuation graphs provide a means for utilizing l
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Fig. 3 shows the magnitude " intensity equivalents" of Gutenberg and Richter indicated as ordinates along the intensity graduations for the Imperial Valley shock of thy,19h0, the Kern County shock of July,1952 and the California shock of 1906. From the evidence in Fig. 3, and from other evidence not detailed in this report the following conclusions are reached: (a) At a 1-mile epicentral distance the intensity-equivalent ordinate determines the position, or provides an anchor, for an intensity attenuation graph for granitic basement rock, (b) at two miles the intensity equivalent ordinate provides a similar anchor point for a sedimentary basement rock (graph) which is consistent with the observed intensity attenuation; (c) at three miles epicentral distance the intensities in-dicated along the various attenuation graphs correspond to intensities actually observed in the epicentral areas. In the 19h0 shock IN-9 corren-ponds closely to the na::1 mum reported intensity; in the 1952 shock cn intensity between 9 5 and 10 is consistent with the intensities reported although in this case the sparsely settled epicentral area did not provide the best type of information for evaluating intensity. In both cases the graphs and other evidence indicate that the intensity in the granitic base-ment rock underlying the sedimentary basement is very close to one grade lever than in the sedimentary basemen..
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Earthquahe intensity and related ground motion. - The maximum vibrational acceleration registered on a seismograph is sometimes used as a measure of earthquahe intensity. ' Fig. 5 s'iovs the very vide range of accelerations I
t obtained for earthquakes of different intensity and type. The one important outstanding fact is that for earthquakes of the same general tyme accelera-tion increases exponentially with respect to intensity; for each increase of one grade of intensit,y (up to grade IN-0) the acceleration is doubled.
Beyond IE-8 it seems very probably that a common ratio of 15, instead of 2.0, vould yield more probably values of acceleration with a maximum of one or two c (acceleration of gravity) for a maximum intensity of MJ-12.
H instrumental recordings have been obtained for intensities above 1312.
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-g-The four carthquake types indicated in Fig. 4 may be classed as follows: (a) close-up blast-like shochs of very short duration; (b) average types of da laging earthquake motions registered within roughly 35 miles of an epicenter - adopted as the type in which earthquake engi-neers are primarily interested; (c) average of all types of shocks; (d) shocks registered in marginal areas,' generally of very long duration.
It is seen how acceleration and duration combine to control the observed intensity of a disturbance.
Vibrational acceleration alone is inedequate for engineering use unless the related periods or frequencies are provided. This relates the acceleration to definite vibrational velocities and amplituden.
Fig. 6 shovo very approximately the periods associated with the various earthquake types for an intensity 41-6 earthquake. The h-vay log chart automically shows the vibrational velocities and displacements associated
- , with any vibration or wave of known period and acceleration. On this )
l chart h.5 cm/sec is taken as the best average velocity to indicate an I intensity m-6 shoch of the type of special interest to earthquake engineers. The possibility of vide deviations from this average are very evident. For higher or lover intensities the set of four graphs vould need to be raised or lovered to conform with the intensities indi-cated.
Because maximum ace,elerations limit the use of recorded frequencies i
to those in the high frequency range, and because waves of lover frequency and acceleration can also be very damaging, Fig. 6, which also shows the I spectrum of perioda and amplitudes in the El Centro record of 19h0, reveals l
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why vibrational velocity is a more practical measure of earthquake intensity than acceleration. This conclusion is supported by the fact that the a
hinetic energy of a vibration (a property analogous to intensity) is a function of vibrational velocity rather than acceleration.
'Possible ground motions of a 1906 type e'arthquake centered close to Bodeco
_ Head. - In the case of Bodeco Head the problem is to determine what ground '
motions vould be expected in case a shock similar to that of 1906 centered within a few miles of the proposed plant. It was previously estimated that the intensity would be at least M4-9 5 If reference is made to Fig. 5 and the suggested lover values of ground motion are used in the higher rances of intensity then all of the ground motions indicated by the El Centro spectrum in Fig. b should be multiplied by 1.4 yielding a maximun acceleration of 0 5 g. If the greater rate of increase of ground i
motion vith increase of intensity is assumed, the El Centro readings should be multiplied by 2 3 yielding a maximum acceleration (around 0 3
, sec. period) of 0.8 g.
In viev 'of the deviations of various hinds mentioned in the preceding paragraphs (especially the creator accelerations that might be involved in a near-by blast-type shoch) and other uncertainties inherent in the entire process of estimating possible ground motions the vriter feels that doubling all the El Centro readings (yielding an acceleration of 0 7 g) vould be on the safe side if Dodego Head should some day find itself in the epicentral area of another 1906 type earthquake.
The deduced increase of intensity in the 1906 epicentral area as j compared with the intensity at El Centro in 19ho is amply substantiated in f
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dairymen and their cattle were all thrown down by the violence of the groundnotion(h). Nothing approaching this was reported in the Imperial Valley shock of 19ho (6).
Hate on the intensity-ground motion relationship. - Uhen ground motion is
.i expressed in the form of period-acceleration graphs the graphs become a measure of intensity that is not restricted by earthquake type, epicentral distance, duration or other complexities. The top portion of Fig. 3 ,
shows such a graph superposed on an intensity grid from which it is often feasible to read not only the surface intensity but also the basement rock intensity. The different wave types traversing these media are evidently distinguishable on the seismograph record. Further details vill be found in reference (8). This item is mentioned because it helps substantiate the general concept of basement rock intensity attenuation. Unfortunately, I
there seems to be no feasible way of utilizing period-acceleration Graphs i in formulae that serve engineering purposes. i I
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, 12 Table I - Lict of stronger shocks in California originating on or very near.the San Andreas Fault (
Year Date County II4 Intensity Magnitude (3) 1800 Oct. San Benito --- Very large 1038 June San Mateo X Outstanding 1852 Dec. 17 San Luis Obispo VII-VIII v 1C57 Jan. 9 Ventura X-XI outstanding 1865 Oct. 8 Santa Cruz VIII-LX Very large 1063 May Riverside Very large 1885 Apr. 11 Monterey VII-VIII 1890 Apr. 24 Monterey VII Very large 1893 Apr. h Los Angeles VIII-IX 1898 Apr. 14 Mendocino VIII-IX 75I 1901 Mar. 2 Monterey VII-VIII 1906 Apr. 10 Marin XI 63 19C6 Apr. 18 Iraperial VIII 6+
1907 Sept. 20 San Dernardino' VII 6 1915 June 23 Imperial (2) VIII 61/h 1916 Oct. 23 1:ern VII 6 1922 Mar. 10 San Luis Obispo IX 61/2 1930 Feb. 25 Imperial VIII (less than 6) 1930 Mar. 1 Imperial VIII "
1934 June 7 M'onterey VIII 6.0 1940 lby 10 Imperial X 71 19h8 Dec. 4 Riverside VII 65 19h9 thr. 9 San Benito VII 1950 July 29 Imperial VIII ( Less than 6) 1957 Mar. 22 San Inteo VII 53 0
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Table II. - Stronger offshore shocho probably originating on northwestern ex-tention of San imdreas Fault.
Year Date County 141 Intensity Mar;nitude 1901 oct. 20 Humboldt VIII 6+
, 1910 July 15 VI 61/2 1922 Jan. 31 VI 76 i 1923 Jan. 22 "
VII-VIII 73 1932 June 6 "
VIII 6.4 19h1 Feb. 9 VI 6.6 1 1941 May 13 "
V 6.0 1941 oct. 3 "
VI-VII 6.4 1945 May 19 V 6.2 1951 oct. 7 "
VII 6 1956 oct. 11 V 6 (1) Shocks S.E. of the San Bernardino Mountains and into Imperial County are considered as being in the f3an Andreas Fault system even though this is not necessarily true.
(2) Refers to Modified Mercalli Scale of 1931. Data taken largely from U.S.
Coast and Geodetic Survey publication " Earthquake History of the U.S. '
1 Part'II",1960 edition I (3) Data largely from C.F . Richter's " Elementary Seismology", 1950 ;
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14 Table III. Strong earthquake ground motions registered on strong-motion seismographs of U.S. Coast and Geodetic Survey (1932-1957).
All places in California unless otherwise stated.
Year Date Place No. of records Acceleration (fraction of gravity) 1933 I4ar. 10 Long Beach, Calif. 3 .25 ;
1933 Oct. 2 Signal Hill, Calif. 7 .17
- 193b Dec. 30 Imperial Valley 0 .18 1935 Oct. 31 Helena,140ntana 1 .12 1930 Sept. 11 Off !!cndocino Point 2 .09
- 1940 11ay 10 Imperial valley 6 33 19h1 June 30 Santa Barbara 6 .17 19h1 Oct. 3 off !!endocino Point 2 .12
- 19h9 thr. 9 San Denito Co. h .19 19h9 Apr. 13 Puget Sound, Wash. 2 .24 1952 July 21 Kern Co. 24 .13 1954 Dec. 21 Humboldt Co. 2 .23 1955 Sept. 4 Santa Clara Co. 7 . 12 1957 Imr. 10 .Ventura Co. 5 .17
- 1957 14ar. 22 San 11ateo Co. 9 .12
- Earthquakes originated along San Andreas Fault or its extensions.
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- 1. Earthquake Investigations in California, 1934-1935 . U.S. Coast and )
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Geodetic Survey Publ. S.P. 201. i
- 2. Earthquake History of the United States - Part II, U.S. Coast and Geodetic Survey Publ. No. h1-1 (Revised 1960 edition) .
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- h. The California Earthquake of April 18, 1906, Report of the California l
Earthquake Investigation Corstission. In 2 Vols. and Atlas. Carnegie Inst. of Wash. 1908.
5 Elementary Seismology by C. F. Richter. W. H. Freeman and Co., 1958.
- 6. Abstracts of Earthquake Reports for the Pacific Coast and Western I Mountain Region. Quarterly reportsof the U.S. Coast and Geodetic Survey.
7 The !!odified Moren111 Earthquake Intensity Scale of 1931, by H. o. Wood and F. Heumann, Bull. Scis. Sco. Amer, Vol. 21, p. 277-203 j l
C. Earthquake Intensity and Related Ground Motion, by F. Heumann, Univ.
of Wash. Press.1954. !
l 9 Analysis of Earthquake Intensity Distribution :tps, by F. Heunann, fi Publications du Bureau Central Seismologique International, Serie A, Travaux Scientifiques, Fasciule 20, p. 213-222.
- 10. Symposium on Microseisms. Nat'l Acad. of Scier.ws. Hat. Research Council, Publ. Ho. '306.
- 11. Earthquake Magnitude, Intensity, Energy and Acceleration, by B. Gutenberg and C. F. Richter. Bulls. Seis. Soc. Amer. Vol. 32, p. 163-191 and Vol. 46, p. 104-145 1
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