ML20112G245
| ML20112G245 | |
| Person / Time | |
|---|---|
| Site: | 05000000 |
| Issue date: | 10/31/1984 |
| From: | Heaton T INTERIOR, DEPT. OF, GEOLOGICAL SURVEY |
| To: | NRC |
| Shared Package | |
| ML20105B688 | List: |
| References | |
| FOIA-84-462 NUDOCS 8501160259 | |
| Download: ML20112G245 (42) | |
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Northwest U.S. Subduction Zone Seismic Risk Assessment R
Proposal to U.S.G.S. research program for the U.S.N.R.C.
Project Chief: Thomas H. Heaton U.S.G.S., Seismology Branch Calif. Inst. Tech.
Pasadena, CA 91125 FTS 799-0267 Commercial 213-356-6822 Fundisg period: 01 October 1983 to 01 October 1984
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8501160259 840801 .
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. o j Statement of Problem Despite the fact that there is good evidenc.e of present day con-f vergence of the Juan de Fuca and North American plates, there has been remarkably little historic seismic activity along the shallow part of ,
the Juan de Fuca subduction zone. Although it is impossible to rule ~~
out the possibility of aseismic creep, we find that the Juan de Fuca subduction zone shares many features with other subduction zones which both have been locked and have experienced great earthquakes (Heaton and Kanamori,1983; included as an appendix). We propose to study the possible source characteristics and ensuing strong ground motions and Tsunami hazards for hypothetical great shallow subduction zone earthquakes off the coast of Washington and Oregon.
The first phase of the study will define the geometry and dimen-sions of potential rupture areas. We will also attempt to characterize the nature of rupture heterogeneity which can 'be expected. In the second phase, we will estimate the natue of ground motions which may j result by comparing the northwestern U.S. with other subduction zones for which strong motion records are available. In the third phase,'20 will synthesize ground motions for hypothetical great earthquakes by summing the responses of individual segments of the proposed rupture surface. The responses of individual segments will be approximated both by actual recordings of moderate-size'd earthquakes and also by numerical calculation of the theoretical response of layered crustal structure to point dislocations.
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! mportance I of the Prob 1cm to Program Goals
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-/ This research is directly motivated by the licensing procedure for
/ the Washington Public Power Supply System System Nuclear Project No. 3 located at Satsop, Washington. The ' possibility of large shallow subduc-tion zone earthquakes was excluded in the design phase of this facility. -
However, new study of the nature of the Juan de Fuca subduction zone indicates that such events may be possible. Estimates of ground shaking from large subduction zones earthquakes are of central importance in the licensing review of this plant. Furthermore, due to the nature of this problem, this research is relevant to earthquake hazard estimation through-out the entire western parts of Washington and Oregon. This includes the currently operating Trojan nuclear plant in Oregon.
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- 3) Work to be undertaken l
,, Work on this project falls naturally into three catagories.
l Characterization of the source In this phase of the work we will construct models of the feasible rupture parameters of shallow thrust earthquakes on the Juan de Fuca subduction zone. We will include para-meters such as fault length, fault dip, fault width, average stress drop, and rupture heterogeneity. Constraints on these parameters will be investigated by studying other subduction zones. That is we will assume that rupture characteristics of Juan de Fuca subduction zone events will be similar to rupture characteristics seen for other subduc-tion zones with similar physical characteristics. Physical characteristics which will be compared are; are of subducted lithosphere, rate of con .
vergence, fault dip, topography of the subducted plate, geometry of the accretionary wedge, nature of marine terraces, and temporal and spatial patterns of seismicity. There are good reasons to suspect that these physical characteristics are closely related to the rupture parameters of shallow subduction earthquakes (see accompaning paper by Heaton and Kanamori). If subduction zones with similar physical characteristics can be found, then the nature of rupture heterogeneity for events on these zones will be characterized by studying the teleseismic body wave radiation from these events.
Earthquake recurrence rates will be estimated using estimates of the plate ccnvergence rate together with estimates of rupture dimensions.
Estimation of strong ground motions We will use several procedures to estimate strong ground motion. The first procedure is described by Heaton et al. (1983). ' In this procedure a suite of strong motion records is constructed by collecting and scaling records taken at sites with simi-lar tectonic conuitions. Records are scaled with respect to site distance, earthquake size, and site conditions. However, it is desirable to collect records which require as little scaling as po'ssible. Once a scaled suite of records has been constructed, we can calculate the statistical mean.
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median, standard deviation, etc. of various strong motion parameters.
In this example, records An example of this procedure is given in Table 1.
from strike-slip earthquakes have been scaled to a distance of 50 km and earthquake magnitude of 61.- Recor'ds were chosen so that little scaling was The necessary. The suite' of scaled response spectra is shown in Figure 1. ~~
average spectrum, average plus one standard deviation spectrum, spectrum of the largest single record, and the spectrum which envelops all others are shown in Figure 2. Although the scatter may seem large, it is an accurate representation of the range of motions that have been observed at 50 km from magnitude 61 strike-slip earthquakes.
This same procedure will be applied to construct suites of strong These records are principally from motion records from subduction zones.
Japan. In Figure 3 we show a comparison of peak acceleration plotted as a function of dista' ice.and magnitude,for ground motions recorded in Japan and the western U. S.
We see that magnitude and distance scaling relationships seem to be similar in Japan and the western U.S. We also see that there is sufficient data to simulate subduction zone earthquakes with magnitudes up to about 71, provided that the distance is greater than 50 km. However for larger earthquakes and smaller source distances, the procedure described above is not appropriate.
Although no records are available for earthquakes of M > 8, we can make This synthetic ground motions by suming records from imaller earthquakes.
f type of sumation has been used with reasonable success by Hartzell (1978) and Kanamori (1979) on large strike-slip earthquakes. The technique has also been used by Heaton and also Kanamori to simulate ground motions for subduction zone earthquakes for use by Exxon Production Research Co.
The basic assumption in the synthesis procedure is that the motions from a large earthquake are a linear sum of the motions from smaller earthquakes.
Enough smaller earthquakes are sumed so that the sum of the seismic moments Timing delays of the smaller events equals the moment of the large event.
due to rupture and travel time dealys are included in the sumation process.
The details of the timing assumptions in this sumation process can, however, affect the nature of the final product. In order to discover appropriate timing assumptions, we will also construct synthetic teleseismic body waves
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for great earthquakes by suming body waves from smaller events. We will require that our models which produce strong motions also provide an adequate
/ characterization of observed teleseismic body waves.
We will also investigate the feasibility of using the theoretical re- ,
sponses of point dis. location sources as Green's functions for three-dimen-sional finite fault simulations of very large earthquakes. This technique may be useful if observed records are not available at desired source-
' station geometries. Such Green's functions would be calculated assuming a horizontally-layered earth structure. The Green's functions would then be integrated over the fault surface in order to produce motions due to a finite rupture surface. These techniques have been used with considerable sweess to model records from moderate-sized earthquakes (Heaton,1982; Hartzell and Helmberger,1982; Hartzell and Heaton,1983).
Evaluation of Tsunami hazard In order to obtain a rough estimate of
- the hazard due to local Tsunamis which may be generated by a great shallow subduction zone event, we will search for subduction zones with ocean bottom profiles and source geometries similar to that found in the Juan de Fuca subduction zone. Local Tsunamis generated by historic earthquakes in these other regions will be catalogued. These Tsunamis will then be scaled to
( account for differences in seismic moment to come up with estimates of the potential heights' of Tsunamis that might be expected along the coast of l
Washington, Oregon, and British Columbia.
- 4) Strateay and timetable Although the following work plan may evolve as we proceed into this project, we propose the following tasks and accompanying timetable. -
l Task I Characterization of source geometry. In this task, we compile physical characteristics of the Juan de Fuca subduction zone.
l Much of this background work has been done in the Final Safety l Acalysis Report of the WPPSS Nuclear. Project Number 3 (October l 1983) j .
. Task II Comparis:n with oth;r subducticn zen;s. This uill be
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primarily a literature search combined with interviews of knowledgeable colleagues. Cataloguing of physical features
- should allow us to select those zones with similar charac-teristics (October-No'vember.1983). .
Task III Estimate source dimensions and geometry of shallow Juan de Fuca subduction zone event. Models of source geometry and size will be constructed (November 1983).
_ Task IV Characterize rupture heterogeneity. This task ventures into an area not yet ,_ , studied. We intend to collect teleseis-mic time functions for large subduction zone events and to characterize the roughness of the time functions (December 1983 - Spring 1984). .
Task V Construct suites of scaled strong ground motions. Catalogues of strong motion records will be searched to find records '
which may be similar to those expected from a Juan de Fuca subduction zone event. (January - March,1984).
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Task VI Construct synthetic strong motion records by summing records from smaller events. Models will be checked for consistency with teleseismic recordings of other great subduction zone events (Spring 1984).
Task VII Estimate local Tsunami hazard. A catalogue of local Tsunamis
, with source geometrics and ocean bottom profiles similar to the Juan de Fuca subduction zone will be constructed. Tsunami heights will then be scaled using the results o,f Task III (Su. mer 1984). '
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7'tocation of proposed work
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This project will be conducted at the Pasadena, California, field office of the Office of Earthquakes, Volcanoes, and Engineering USGS. This office is locat'ed on the. campus of the California Institute -
of Technology. .
- 6) Other commitments or anticipated difficulties that will affect prooress or completion of the project Most computer codes to manipulate data and compute synthetic ground motions are written and working. However, these codes must be updated.
Furthermore, we expect to transfer our work from the Caltech Prime 750 computer to a new USGS VAX 11-750 computer in the Fall of 1983. Although we hope that this transition goes smoothly, there may be unanticipated delays caused by this. Digital recordings of ground motions from subduc-tion zones are presently available, but if a larger catalogue becomes
..! neces'sary, then collection of other records may delay our schedule.
Both principal investigato'rs in this project are also 1/2 time ccmnitted to work in the Seismology Branch project entitled. Southern California Cooperative Seismic Network Project. Their research in this project covers several areas, with the main emphasis in FY1984 being re-search into possible new directions for seismic networks. Since the Pasadena Field Office is a small office having many responsibilities, the occurrence of local emergency situations, such as earthquakes, may l
affect work schedules on research projects.
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- 7) Products 04/84 Preliminary report on nature of shaking from Juan de Fuca subduction zone earthquakes to the U.S.N.R.C.
. 10/84 Final report .
10/84 Scientific paper on 'the nature of seismic hazards associated I with the Juan de Fuca subductio,n zone.
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[g or facilities and eculement needed
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The major requirement of this project is conputer time. de presently
/ purchase computer time from Caltech on a Prirte 750 omputer. However, it
- I appears that a new USGS Vax 11-7,50 computer will become available for our use in Fall 1983. Thus our projected computer costs cover expenses for
- the Caltech computer which we feel will be necessary during the process . -
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of converting computers.
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j 9) Expected interaction with other projects and workers l
l There will be stror:g interation with Hiroo Xanarori at Caltech who maintains strong interest in the nature of subduction zone earthouakes.
He is presently working on similar studies under a research grant from I' Exxon Production Research Company. We also expect interaction from
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Doug Coats of Exxon Production Research Company and C.B. Crouse ,of i Earth Technology Corporation. Caltech graudate students, in carticular, l Anne Mori, will be encouraged to participate in the research. Due to the far-ranging implications of tnis research, we expect to interact .
1 frequently about the nature of our preliminary conclusions with research-ers at USGS-Menlo Park, Univ. of Washington, USGS-Denver, and the U.S.
N.R.C.
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- 10) Qualifications of principal investigators l The principal investigators in this project. Heaton and Startzell, have considerable experience .in the field of synthesizing both strong motions and teleseismic ground motions from complex realistic earthquake sources. They both also have experience in the problem of su rning l
records of smaller eartnauakes to simulate large ones. Both have ex-parience in the corrrnercial consulting field and Heaton has considerable j experience in the field of estimating ground motions at subduction zones. A full sunnary of the qualifications of the principal investiga-
! tors is contained in the resumes included with this proposal .
- M.Y. Effort Funding Requested 0.4 '. 40g
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,arences -
Hartzell,S.H.(1978). Earthquake aftershocks as Green's Functions,
_Geophys. Res. Letters, 5_, 1-4. ,
Hartzell, S.H. and D.Y. Helmberger (1982). Strong-motion modeling of .
the Imperial Valley earthquake of 1979, Bull. Seism. Soc. M., H. "
571-596.
Hartzell, S.H. and T.H. Heaton (1983). Inversion of strong-ground motion and teleseismic waveform data for the fault rupture history of t'eh 1979 Imperial Valley, California earthquake, Bull. Seism.
l Soc. M., in press.
Heaton,T.H.(1982). The 1971 San Fernando earthquake: A double event?,
Bull. Seism. Soc. M., H . 2037-2062.
Heaton, T.H., F. Tajima, and A.W. Mori (1983). Estimating ground motions using recorded accelerograms, manuscript. -
H:aton, T.H. and H. Kanamori (1983). Seismic potential associated with subduction in the northwestern United States, manuscript.
Jennings, P.C. and H. Kanamori (1983). Effect of distance on local magni-tudes found from strong-motion records, Bull. Seism. Soc. A_m_. ,H, 1645-1670.
Kanamori,H.(1979). A semi-empirical approach to prediction of long-period ground motions from great earthquakes, Bull. Seism. Soc. M.,
69, 1645-1670. ~
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Figure 1. Response spectra (31 damped) for horizontal components ,
of 15 records from strike-slip earthquakes which are
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scaled to a distance of 50 km and a magnitude of 61 Records description and scaling parameters are given in Table 1. Figure is from Heaton et al. (1983).
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Figurn 2. a) average spectrum, b) average plus one standard de-viation spectuna, c) specturm of the largest single record, d) spectrum which envelopes all others; based on spectra shown in Figure 1 (taken from Heaton et al.
, 1983). ..
Figure 3. Comparison of peak ground accelerations recorded in the western U.S. and Japan. Distance is approximately the l closest horizontal distance to the rupture. Dashed line is the modified local magnitude distance attenua-tion law of Jennings and Kanamori (1983). Figure is from Heaton et.al. (1983).
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1 2 3/11/33 Long teach L... Subway Ters. 6.3 42 0 6.23 2.38 *.15 18.0 1.38 29.5 22.6 l 3 12/30/34 L. Callfernia El Centre 6.5 61 0 6.30 2.61 *.15 S.32 1.32 16.0 21.8 4 10/21/42 Serrego Valley El Centre 6.5 . 46 0 6.38 2.44 *.15 12.3 .89 6.2 5.5 l l 5 12/21/54 Eureka Ferndale City Hall 6.5 40 1 6.38 2.35 0 10.72 , 1.82 - 31, 31.5 i
! 6 ,4/20/65 Japan Site #C8002 6.1 50 e 6.08 2.43 e.15 6.31 1.74 7.8 7.0 7 4/20/65 Japan Site #C3057 6.1 45 e 6.00 2.49 *.15 8.91 1.23 28.2 24.8 l
- 8 4/9/68 derrego Min. El Centre 6.6 65 e 6.45 2.65 *.15 a.91 1.23 29.2 24.0
] 9 10/15/79 leperial Valley Corre priete 6.4 39 2 6.3 2.33 .15 6.61 1.66 15. 24.9 !
10, 10/15/79 leperial Valley Seite 6.4 50 0 6.3 2.49 *.15 9.12 1.2 29.2 35.1 l
11 10/15/79 leperial Valley Victerla 6.4 60 0 6.3 2.5 *.15 7.00 1.55 18.2 15.8 j 12 10/15/79 layerial Valley Callpatria 6.4 41 9 6.3 2.37 +.15 12.02 .91 '13.7 12.4
) 13 10/15/79 leperial Valley $gerstitlen 6.4 42 0 6.3 2.39 e.15 11.48 .95 6.9 6.6 14 10/15/79 leperial Valley Plaster Clky 6.4 3e 8 6.3 2.32 *.15 13.49 .81 4.5 3.6 l 15 10/15/79 layerial Valley lilland 6.4 51 0 6.3 2.5 +.15 8.91 1.23 10.1 12.4 I
- Test Case 6.5 50 0 6.38 2.49 *.15 10.96 14.26 i S.5 17.87 i 9.
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Resume: Thomas H. Heaton
Title:
Geophysicist - U. S. Geological Survey Expertise: Seismology [ Earthquake Engineering -
Past Experience: -
1979-1982 - Geophysicist with U.S. Geological Survey at Caltech office. Strong ground motion studies and earthquake prediction studies 1978-1979 - Senior Seismologist with Dames and Moore.
Estimation of earthquake hazards for major energy facili-ties. Half-time visiting associate at the Seismological Laboratory at Caltech with emphasis on strong ground motion modeling 1977-1978 - Consultant to Dames & Moore--Seismic hazard studies 1974-1978 - Consultant to Converse, Davis, Dixon &
Associates--Fault hazard studies 1974- Converse, Davis, Dixon & Associates--Engineer-ing geology with emphas.is on fault hazard studies PROFESSIONAL , Seismological Society of American t
AFFILIATIONS American Geophysical Union ACADEMIC Chemistry and physics major, Bates College, 1903-1970 l BACKGROUND B.S. in physics with special interests in mathematics and geology, Indiana University,1972 Ph.D. in Geophysics, minor in Applied Mechanics, California Institute of Technology,1978 PUBLICATIONS Alewine, R.W., and T.H. Heaton, Tilts associated with the l Pt. Mugu earthquake, Proceedings, Conference on Tectonic Problems of the San Andreas Fault System, Geological Sciences, XIII, Stanford University,94-103, 1973.
Heaton, T.H., Tidal triggering of earthquakes, Geophys.
J.R. astr. Soc., 43, 307-326, 1975.
Heaton, T.H. and D.V. Helmberger, Predictability of strong ground motion in the Imperial Valley: Modeling the M4.9, November 4,1976 Brawley earthquake, Bull. Seism. Soc.
Am., 68, No. 1, 31-48, 1978.
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/ Heaton T.H. and D.V. Helmberger, A study of the strong ground motion of the Borrego Mountain, California, i*
earthquake, Bull. Seism. Soc. Am., 67 No. 2, 315-330 1977. - -
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Heaton, T.H., Generalized ray models of strong ground motion Ph.D. Thesis, California Institute of Technology, ~~ l 300 p., 1978. .
Heaton, T.H. and D.V. Helmberger, Generalized ray models of the San Fernando Earthquake, Bull. Seism. Soc. Am.,
- 69. No. 5,1311-1341,1979.
Anderson, J.G. and T.H. Heaton, Aftershock accelerogram recorded on a temporary array, in press U.S.G.S. Prof.
Paper on October 1979 Imperial Valley Earthquake,1980.
Heaton, T.H., J.G. Anderson, and P.T. German, Ground
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- failure along the New-River, in preparation.
McNutt, M and T.H. Heaton, An k aluation of the seismic window theory, California _Geolcoy, January 1981, pp12-16.
Amini, A., K. Moslem, J.G. Anderson, and T.H. Heaton, Aftershock accelerograms from the May 1980 Mammoth earthquake sequer.ce, in preparation.
Heaton, T.H., The 1971 San Fernando earthquake; A double event? BSSA, in Press 1982.
Heaton..T.
in Press, 1982. H., Tidal triggering of earthquakes BSSA, .
1 Heaton, T.H., F. Tajima, and A.W. Mori, Estimating l ground motions using recorded accelerograms, BSSA, submitted.
Liu, M.L. and T.H. Heaton, Array analysis of the
- ground velocities snd accelerations from the 1971 San Fernando earthquake, in preparation.
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. t First Quarter Report - FY 84 g
Northwest U.S. Subduction Zone Seismic 'Gsk Assessment Thomas Heaton Work is proceeding on schedule for the seismic risk evaluation of the Pacific Northwest and the estimation of the likely strong ground motion from a large, shallow, subduction zone event. If the total area of the Juan de Fuca - North America convergence zone were to rupture in one event (approximately 600 km by 200 km), a magnitude 9 earthquake would result. Some data, currently under evaluation, suggests that the plate boundary is segmented with different degrees of coupling on each segment. If two segments exist, and only on ruptures at a time, the maximum magnitude earthquake would then be 8.5.
As part of the determination of possible source geometries for the Pacific Northwest (Task I) and a comparison with other subduction zones (Task II),
trench bathymetry and the temporal and spatial patterns of seismicity have been studied. Based on trench bathymetry, seismic quiescence, and also plate age, Washington and Oregon compare most closely with the Nanka Trough in southern Japan, southern Chile, and perhaps northern New Zealand and parts of Mexico. Another aspect of trench seismicity which has been considered, is the rate of moderate sized earthquakes (magnitude 5.5 to 6.5). Moment release as a function of time has been plotted for dif ferent subduction zones for the given magnitude window. The objective is to test fore an inverse correlation between the maximum size earthquake in an stea and the moment release rate of j smaller events. The results do not show any systematic variations between subduction zones. However, nonuniform sampling may exist at the lower magnitude cut off. The results will be checking by using a magnitude window of 6.0 to 7.0. ,
t The characterization of the rupture heterogeneity (Task IV) is an important component of both the comparison of different subduction zones and the computation of response spectra for the Washington-Oregon area. After considering different data sets, the Caltech, 1-90 Benioff seisometer records were selected to characterize the rupture heterogeniety of large, shallow thrust earhtquakes from dif ferent subduction zones. The 1-90 instrument was i chosen because of its broad bandwidth and long history of operation. Records from the 60 largest, shallow, thrust earthquakes that have occurred in the
( circum-Pacific since 1938 have been collected and their P-waves digitized.
Time functions for 1/3 of these events have been computed to date using a constrained, least-squares inversion. When completed, this set of time functions will form a unique and valuable basis for the comparision of
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dif ferent subduction zones and the ground motion that may be expected frot subduction zones earthquakes.
The Japanese data set of strong motion records is perhaps the most appropriate (Task V) to use to construct ground motions for a Juan de Fuca subduction zone event. However, the final decision on which records should be used will be made at the completion of the time function analysis.
% 3
' Progress Report - 2nd Quarter, FY84 NOETHWEST U.S. SUBDUCTION ZONE Thomas H. Heaton SEISMIC RISK ASSESSMENT The purpose of this project is to access the potential seismic hazard due to great shall ow earthquakes along the Juan de Fuca subduction zone which is located along the coasts of Washington and Oregon. The work breaks naturally into two catagories: 1) estimation of potential source characteristics of a great northwest U.S. subduction earthquake, and 2) estimation of potential ground motions and tsunami excitation of such an earthquake. Work is progressing rapidly on the first catagory. Bathymetry and free-air gravity profiles for all major Pacific Ocean subduction zones have been compared. The Juan de Fuca subduction zone shares several characteristics with other subduction zones where very young oceanic crust is being subducted. We have also characteri zed and compared sei smi city along most major Pacific subduction zones. Although there are problems with the homogeneity of world-wide earthquake catalogues, we find that the present low level of seismici ty seen in the northwestern U.S. has been observed at the locations of several other very large subduction zone earthquakes.
In addition to comparing conspicuous physical features of subduction zones, we are comparing the nature of earthquakes that have occurred in those zones. To this end, we have collected and digitized broad-band (1 to 30 sec.) teleseismic body-wave recordings of 60 of the largest subduction zone earthquakes that have occurred in the last 50 years. Usi ng a linear least-squares inversion technique, we have computed fa r-fiel d time functions for each of these earthquakes .
Furthermore, we have computed Fourier power spectra for each of the P-wavetrains in order to investigate the nato e of spectral scaling relationships for very large earthquakes. Characterization of the teleseismic body waves gives vital information about source duration and complexity. This information gives important constraints on the way in which we construct models of strong ground motions.
Because of the need for baisc information about the nature of the source characteristics of great subduction zone earthquakes, we have concentrated our ef forts on the fi rst work catagory. Thus, our original estimates of a time schedule. for work on the actual estimation of strong ground motions has been significantly modified. We f' eel that this modification is necessary if we are to base our strong motion estimates on actual observations of great subduction zone earthquakes. We anticipate that the actual construction of strong ground motion models will be delayed until at least summer of 1984.
l PUBLICATIONS Hartzell, S.H., and T .H . Heaton (1984). Estimating the source parameters for a major subduction zone earthquake in the Pacific Northwest, Earthquake Notes, vol . 55, no.l.
Hartzell , S .H . (1984). The use of small earthquakes as Green's functions, EERI workshop on strong ground motion simulation and l
earthquake engineering applications, April 1984, Los Altos, Ca, l
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Northwes't D'.S. Subduction Zone s
Seismic Risk Assessment t
Proposal to U.S.G.S. research progras for the U.'S.M.'R.C.
Project Chief: Thomas H. Heaton U.S.G.S. , Seismolcgy Branch Calif. Inst. Tech.
Pasadena, CA 91125 FTS 799-0257 Comercial 213-356-6822 Fandf6g pertod: 01 October 1983 to 01 October 1984 e
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- 1) Statement of Problem Despite the facf. that there is good evidene.e of present day con-vergence of the Juan de Fuca and North American plates, there has been remarkably little historic seismic activity along the shallcw part of .
the Juan de Fuca subduction #zune. Although it is impossible to rule out the possibility of aseisinic creep, we find that the Juan de Fuca subduction zone shares many features with other subduction zones which both have been locked and have experienced great earthquakes (Heaton and Kanamori,1983; included as an appendix). We propose to study
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the possible source characteristics and ensuing strong ground motions and Tsunami hazards for hypothetical great shallow subduction zone earthquakes off the coast ,of Washington and Oregon.
The first phase of the study will define the gecmetry and dimen-sions of potential rupture area's.- We will also attempt to characterize the nature of rupture heterogeneity which can 'be expected. In the second phase, we will estimate the natue of ground motions which may result by comparing the northwestern U.S. with other subduction zones for which strong motion records are available. In the third phase, we will synthesize ground motions for hypothetical great earthquakes by suming the responses of individual segments of the proposed rupture surface. Tne responses of individual segments will be approximated both by actual recordings of moderata-sized earthquakes and also by numerical calculation of the theoretical response of layered crustal structure to point. dislocations.
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- 2) Imcortance of the Problem to Procram Goals
- l This research is directly motivated by the licensing procedure for i the Washington Public Power Supply System System Nuclear Project No. 3 located at Satsop, Washington. The possibility of large shallow subduc .
tion zone earthquakes was excluded in the design phase of this facility. - -
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However, new study of the nature of the Juan de Fuca subduction zone indicates that such events may be possible. Estimates of ground shaking from large subduction zones earthquakes .are of central importance in the licensing review of this plant. Furthermore, due to the nature of tr.is problem, this research is relevant to earthquake "??rd estimation through-out the entire western parts of Washington and Oregon. This includes the currently operating Trojan nuclear plant in Oregon.
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fl l Work on this pMect fhlls naturally into three catagories.
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Characterization of the source h!
- construct models of the feasible rupture parameters We will include of para-shallow thrust ll l 1 earthquakes on the Juan de Fuca sub' duction zone.
meters such as fault length, fault dip, fault width, average stress Constraints on these parameters will drop, and rupture heterogeneity. That is we will be investigated by studying other subduction zones.
assume that rupture characteristics of Juan .de Fuca. subduction bduc- zone y events will be similar to rupture characteristics seen for other su Physical characteristics tion zones with similar physical characteristics.
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which will be compared are; are'of subducted lithosphere, rate o ,
d t d plate, geometry of the !
vergence, fault dip, topography of the sub uc e l accretionary wedge, nature of marine terraces, and temporal. and sp '
There are good reasons to suspect that these patterns of seismicity.
physical characteristics are closely related ta the rupture d paramete of shallow subduction earthquakes (see accompaning paper by Heaton an If subduction zones with similar physical characteristics Kanameri).
can be found, then the nature of rupture heterogeneity for events on these zones will be characterized by studying the teleseismic body wa radiation from these events.
Earthquake recurrence rates will be estimated using estimates plate convergence rate together with estimates of rupture dimen We will use several procedures Estimation of strano ocound motions _The first procedure is describ to estimate strong ground motion.In this procedure a suite of stron Heaton et al (1983).
is constructed by collecting and scaling records taken at sites w Records are scaled with respect to site distance, lar tectonic conditions. However, it is desirable to collect earthquake size, and site conditions. Once a scaled suite records which require as little scaling as po'ssible.
of records has been constructed, we can calculate the statistical me 4
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m.edian, standard deviation, etc. of various strong motion parameters.
An example of this procedure is given in Table 1. In this example, records from strike-slip earthquakes have been scaled to a distance of 50 km and earthquake magnitude of St. Recor'ds.were chosen so that little scaling was l
necessary. The suite' of scaled response scectra is shewn in Figure 1. The '
. average spectrum, average plus one standard devi.ation spectrum, spectrum of the largest single record, and the spectrum which envelops all others are shown in Figure 2. Although the scatter may seem large, it is an accurate representation of the range of motions that have been observed at SG km from magnitude Si strike-slip earthquakes. ,
This same procedure will be applied to construct suites of strong motien records from subduction zones. These records are principally from Japan. In Figure 3 we show a c mparison of peak acceleration plotted as a function of distance,and magnitude, for ground motions recorded in Japan and the western U. S. We see that magnitude and distance scaling relationships seem to be similar in Japan and the western U.S. We also see that there is sufficient data to simulate subduction zone earthquakes with magnitudes up to about 71, provided that the distance is greater than 50 km. Howev.sr for larger earthquakes and smaller source distances, the procedure described above is not appropriate.
Although no records are available for earthquakes of M > 8, we can make synthetic ground motions by suming records from s'maller earthquakes. This type of su= nation has been used with reasonable success by Hartzell (1978) and Xanamori (<1979) on large strike-slip earthquakes. The technique has also been used by Heaton and also Xanamori to simulate ground motions for .
subduction zone earthquakes for use by Exxon production Research Co.
The basic ' assumption in the synthesis procedure is that the motions fr m a large earthquake are a linear sum of the motions from smaller earthquakes.
~
Enough smaller earthquakes are sumed so that the sum of the seismic moments' of the smaller events equals the moment of the large event. Timing delays due to rupture and travel time dealys are included in the sumation process.
The details of the timing assumptions in this sumation process can, however, affect the nature of the final product. In or' der to discover appropriate timing assu=ptions, we will also construct synthetic teleseismic bcdy waves
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for great earthquakes by suming body waves from smaller events. We will require that our models which produce strong motions also provide an adequate characterization of observed teleseismic body waves.
We will also investig. ate the feasibility of using the theoretical re-sponses of point dis, location- sources as Green's functions for three-dime'n-sional finite fault simulations of very large earthquakes. This technique may be useful if observed records are not available at desired source-
' station geometries.
Such Green's functions would be calculated assuming a horizontally-layered earth structure.
The Green's functions would then be integrated over the fault surface in. or' der to produce motions due to a finite rupture surface. . These techniques have been used with considerable su=ess to medal records from moderata-sized earthquakes (Heaton,1982; Hartzell and Helmberger,1987; Hartzell and Heaton,1983).
Evaluation of Tsunami haza In order to obtain a' rough estimate of -
the hazard due to local Tsunamis which may be generated by a great shallow subduction zone event, we will search for subduction zones with ocean bottom i profiles and source geometries similar to that found in the Juan de Fuca subduction zone. Local Tsunamis generated'by historic earthquakes in these other regions will be catalogued. These Tsunamis will then be scaled to account for differences in seismic mcment to come up with estimates of the potenthI heignts of Ts' unamis that might be expected along the coast of Washington, Oregon, and British Columbia.
- 4) Strateev and timetable Although the following work plan may evolve as we proceed into this project, we propose the following tasks and accompanying tiinetable.
- Task I Characterization of source geometry. In this task, we compile physical characteristics of the' Juan de Fuca subduction zone.
Much of this background work has been done in the Final Safety .
Analysis Report of the WPPS5 Nuclear. Project Number 3 (October-1983)
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Task II Comparison with other subduction zones. This will be primarily a literature search combined with interviews of -
knowledgeable ccTleagues. Cataloguing of physical features should allow us to select those zones with similar charac-teristics (October-No' vember,1983).
- Task III .
Estimate source diinensions and geometry of shallow Juan de Fuca subduction zone event. Models of source geometry and size will be constructed (November. 1983).
Task IV .,_ ..
Characterize rupture heterogeneity. This task ventures into an area not yet ,, , studied. We intend to collect teleseis-mic time functions, for large subduction zone ~ events and to characterize the roughness of the time functions (December 1983 - Spring 1984). '~ .
Task V _
Construct suites of scaled strong ground motions. Catalogues of strong motion records will' be searched to find records -
which may be similar to those expected from a Juan de Fuca subduction zone event. (January - March,1984).
j Task'VI Construct synthetic strong motion records by sunming records from smaller events. Models will be checked for consistency with teleseismic recordings of other great subduction zone events (Spring 1984).
Task VII Estimate local Tsunami hazard. A catalogue of local Tsunamis l with -source geometrics and ocsan bottom profiles similar to the Juan de Fuca subduction zone will be constructed. Tsunami he.ights will then be scaled using the results of Task III '
(Su. mer 1984). -
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- 5) location of prooosed work ..
This project will be conducted at the Pasadena, California, field office of the Office of Earthquakes, Volcanoes, and Engineering USGS.
This office is locate'd on
. -r the. campus of the California Institute
- of Technology.
- 6) -Other commitments or anticioated difficulties that will affect orceress or comoletion of the orefect Most computer codes to manipulate data and compute synthetic ground motions are written and working. However, these codes must be updated.
Furthermore, we expect to transfer our work from the Calteca Prime 750 computer to a new USGS VAX ll-75g comeuter in the Fall of 1983. Although we hope that this transition goes smoothly, there may be . unanticipated delays caused by this. Digital recordings of ground motions from subduc-tion zones are presently available, but if a larger catalogue becomes neces'sary, then collection of other records may delay our schedule.
Both principal investigato'rs in this project are also 1/2 time cannitted to work in the Seismology Branch project entitled, Scuthern California Cooperative Seismic Network Project. Their research in this project covers > several areas, with the main emphasis in FY1984 being re-search into possible new directions for seismic networks. Since the Pasadena Field Office is a small office having many responsibilities, the occ'urrence of local emergency situations, such as earthcuakes, may affect work schedules on research projects.
- 7) Products 04/84 Preliminary report on nature of shaking from Juan de Fuca subduction zone earthquakes to the U.S.N.R.C.
10/84 Final report e.
10/E4 Scientific paper on 'the nature of seismic hazards associated with the Juan de Fuca subductic,n zone.
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s The major requirement of this project is co.mputer time. de presently purchase computer time from Ca.ltech on a Prime 750 omputer. Hooever, it appears that a new USGS Vax 11-7,50 computer will become available for our use in Fall 1983. Thus our p.rojected computer costs cover expenses for
- the Caltech computer which we. feel will. be necessary during the process .
of converting computers.
- 9) Excected interaction with other orefects and workers There will be strong interation with Hiroc Kanacori at Caltech who maintains strong interest in the nature of subduction zone earthouakes.
He is presently working on~similar studies under a research grant from Exxon Production Research Company. We also expect interaction from Doug Coats of Eqcxon Production Research Cc=pany and C.B.'Crouse ,of Earth Technology Corporation. Caltech graudate students, in earticular, Anne Mori, will be encouraged to participate in the research. Due to the far-ranging imolications of tnis research, we exoect to interact .
frecuently about the nature of our preliminary conclusions with research-ers at USGS-Menlo Park, Univ. of Washington, USGS-Denver, and the U.S.
N.R.C.
- 10) Qualifications of orincioal investicators l The principal investigators in this project, Weston and Mart::all, l have considerable experience .in the field of synthesizing both strong moticns and taleseismic ground motions from complex realistic earthquake sources. They both also have experience in the problem of sunning records of smaller eartncuakes to simulate large ones. Both have ex-perience in the comercial consulting field and Heaton has considerable experience in the field of estimating gicund motions at subduction zones. A full sumary of the qualifications of the p'rincipal investiga-tors is contained in the resumes included with this proposal .
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- I _ References .
Hartzell,S.H.(1978).
Geochys. Res. Letters, 5_, 1-4 Eirthqua~ke aftershocks as Green's Functions, Hartzell, S.H. and 0.Y. Helmberger (1982). '
the Imperial Valley earthqua E~of 1979, Bull. SeismStrong-moti 571-596. ' . Soc. Am. , R, '
Hartzell, S.H. and T.H. Heaton (1983).
Inversion of strong-ground motion and teleseismic waveform data for the fault rupture h of the 1979 Imperial Valley, California earthquake, Bull. Seism Soc. Am., in press. .
Heaton,T.H.(1982).
The 1971 San Fernando earthquake:
Bull. Seism. Soc.Am.,R, 20_3.7-2062. A double event?,
Heaton, T.H. , F. Tajima, and A.W. Mori (1983).
Estimating ground motions using recorded acceleregrams, marilishript. - -
Heaton, T.H. and H. Kanamori (1983).
Seismic potential associated with subduction in the nort.5 4
Jennings, P.C. and H. Xanamori (1983).nvestern United States, man tudes found from strong-motion records, Bull. SeismEffect of di 1645-1670. . So c . A m. , 7_3,, 3 Xanameri, H. (1979). .
period ground motions from great earthquakes, 69, 1645-1670. .
. Soc. Am.,
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Figure 1. Response spectra (5 damped) for horizontal components ,
of 15 records f7ch strike-slip earthquakes which are
. scaled to a distince of 50 km and a magnitude of 61 Records description and scaling parameters are given in Table 1. Figure is from Heaton et al. (1983).
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Figure 2. a) average spectrum, b) average plus one standard de-viation specturm, c) specturm of the largest single record, d) spe.c_trum which envelopes all others; based on spectra shown in Figure 1 (taken frem Heaton et al. -
, 1983). .
Figure 3. Comparison of peak ground accelerations recorded in the western U.S. and Japan. Distance is approximately the closest horizontal distance to the rupture. Dashed line is the modified local magnitude distance attenua-l tion law of Jennings and Xanamori (1983). Figure is frem Heaton et,al. (1983).
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Resume: Thomas H. Heaton
Title:
Geophysicist - U. S. Geological Survey Excertise: Seismology / Earthquake Engineering -
Past Excerience: ,,
1979-1982 - Geophysicist with U.S. Geological Survey at Caltech office. Strong ground motion studies and earthquake prediction studies 1978-1979 - Senior Seismologist with Dames and Mccre.
Estimation of earthquake hazards for major energy facili-ties. Half-time visiting associate at the Seismological Laboratory at Caltech with emphasis on strong ground motion modeling 1977-1978 - Consultant to Dimes & Moore--Seismic hazard studies 0 '
1974-1978 - Consultant to Converse, Davis, Dixon &
Associates--Fault hazard studies 0
1974- Converse, Davis, Dixqn & Associates--Engineer-ing geology with emphasis on fault ha:ard studies PROFESSIONAL Seismological Society of American AFFILIATIONS American Geophysical Union ACADEMIC Chemistry and physics major, Bates College, 1968-1970 BACXGROUND B.S. in physics with special interests in mathematics and geology, Indiana University, 1972 Ph.D. in Geophysics, minor in Applied Mechanics, California Institute of Technology,1978 PUBLICATIONS Alewine, R.W., and T.H. Heaton, Tilts associated with the Pt. Mugu earthquake, Proceedings, Conference on Tectonic Problems of the San Andreas Fault System, Geoloaical Sciences, XIII, Stanford University,94-103, 1973.
Heaton, T.H., Tidal triggering of earthquakes, Geochys.
J.R. astr. Soc., 43, 307-325, 1975'.
i Heaton, T.H. and D.V. Helmberger, Predictability of strong ground motion in the Imperial Valley: Modeling the M4.9, November 4,1976 Brawley earthquake, Bull. Seism. Sec.
An. , 68, No. 1, 31 -48, 1978.
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- Heatoii, T.H.cand D.V. Helmberger, A study of the strong ground motion of the Borrego Mountain, California, earthquake, 1977. -
Bull. Seism. Soc. Am.
- ~
- , 67, No. 2, 315-330 ,
i
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Heaton, T.H., Generalized ray models of strong ground
i 300 p.,motion, Ph.D. Thesis, California Institute of Technology 1978.
Heaton, T.M. and D.V. Helmberger, Generalized ray models 69, No. 5,1311-1341,1979.of .-
the San Fernando Earthqu
~
~~
Anderson, J.G. and T.H'. Heaton, Aftershock accelerogram recorded on a temporary, array, in press U.S.G.S. Prof.
Paper or October 1979 Imperial Valley Earthquake,1980.
Heaton, T.H., J.G. Anderson, and P.T. Gennan,. Ground
.
- failure along the'New. River, in preparation.
McNutt, M and T.H. Heaton, An evaluation of the seismic window theory, California _Geolocy, January 1981, pp12-16.
Aftershock accelerograms from the May 1980 1
earthquake sequence, in preparation.
Heaton, event T.H., in 7 BSSA, The 1971 San Fernando earthquake; A double Press,1982.
Heaton, in Press, .T. 1982. H., Tidal triggering of earthquakes,- BSSA,
~
Heaton, T.H., F. Tajima, and A.W. Mori, Estimating submitted. ground motions using recorded accelerograms, BSSA, Liu, M.L. and T.H. Heaton, Array analysis of the
- ground velocities and accelerations from the 1971 San Fernando earthquake, in preparation.
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,a Enclosure (4)
Safety Evaluation Vit atory Ground Motion - Trojan As a result of regional research investigations perfonned since the issuance of the OL-SER for the Trojan site in October 1974, the knowledge of the seismicity and tectonics for this region has been greatly enhanced, and several issues are presently being debated. The most significant seismologic issue involves the seismogenic potential of the subducting Juan de Fuca plate beneath the Pacific Northwest, see for example, Heaton and Kanamori (1983, 1984) and Weaver and Michaelson (1983). These authors points out some of the features consistent and inconsistent with other subduction zones. They emphasize that there exists " sufficient evidence to warrant fu'rther study of the possibility of a great (magnitude greater than 8.0),' subduction-zone earthquake in the Pacific Northwest" (Heaton and Kanamori, 1984).
The United States Geological Survey, National Science Foundation and the Nuclear Regulatory Commission are all supporting seismologic and geologic investigations to assess the possibility of whether or not a great earthquake is likely or even credible. The staff is well informed as to the progress of this ongoing research, and will continue through the NRC Office of Nuclear Regulatory Research sponsored research .
activities to maintain this awareness. This ongoing research is complex and incomplete and conclusions emanating from it are highly speculative at this time. As a result, we conclude that there is no reason to alter the seismic design basis for Trojan represented by a modified Housner response spectrun anchored at a zero period acceleration of 0.25g, approved during the CP and OL reviews. If and when in the course of these research activities substantial results are produced which lead to any modifications of this conclusion, appropriate notification will be made at that time. Until then, this information should be viewed in the context of ongoing research of a generic nature relative to the Pacific Northwest in general and should not be considered site-specific in any way.
Date:
References Heaton, T. H. , and-K. Kanamori,1983, Subduction in the Northwestern United States; Seismic or Aseismic? Transaction of the American Geophysical Union, N. 64, No. 45, p. 842.
Heaton, T.H. and H. Kanamori, 1984, Seismic Potential Associated with Subduction in the Northwestern United States, preprint, submitted to Seism. Soc. Amer. bull.
/ Weaver, C.S., and C.A. Michaelson,1983, Segmentation of the Juan de Fuca Plate and Volcanism in the Cascade Range, Transactions of the American Geophysical Union, V. 64, No. 45, p. 886.
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A; UNITED STATES
- g NUCLEAR REGULATORY COMMISSION 3 masameTom,n.c.2 ossa .
f
% . .. [ MAR. 5 115 4
. 50-344
- Docket l Mr. Bart D. Withers Vice President Nuclear Portland General ETectric Company 12I S.W. Salmon Street PortTand,. Gregorr 97204
Dear Mr. Withers:
At the American Geophysical.. Union meeting of Decenber 12-16,1983, a number of presentations were given regarding subduction of the Juan de Fuca Plate in the Paciffe Northwest and the potential for a great (mag -
nitude greater than 8.0) earthquake along the subduction interface.
In particular, a paper presented by Weaver and Michaelson on the segmentation of the Juan de Fuca Plate would put the Trojan site near the potentially seismogenic segment, and a paper presented by Heaton concTuded that the Juan de Fuca. Plate shares many of the characteris-l tics of subduction zones which have had. great earthquakes.
4 Although at this time concTustons r.v=41ng. the seismogenic potential of the Juarr de Fuca zone are not complete,. ft. appears. as if this issue may eventuaTTy have ta her addressed by utilities in the Pacific Northwest.
We are enciosing four: documents reTated. to this issue for your informa-tion: 1) NRC staff questions on the Washington Nuclear Project #3 site;
- 2) NRC Draft Safety Evaluation report air the Washington Nuclear Project
- 3 site; 3) the accepted NRC. research proposal on the subduction zone which is being undertaken by. the United States Geological Survey; and
- 4) NRC current safety. evaluation of this matter for Trojan.
We conclude that presently we see na reason to alter the seismic design basis approved for Trojan during the CP and OL reviews.
Although we are. not requesting a response to the enclosed material at this
, time, we strongly reconnend that you keep abreast.of this issue and request i
that you inform us of' any significant findings relative to the Trojan site.
Sincerely, ,f
/?.c . N
, James R. Miller, Chief Operating Reactors Branch #3 Division of Licensing
Enclosures:
- 1. WNP#3 Questions -
- 2. Draft SER-WPN!3
- 3. Research proposal
- 4. Trojan SE , , , _ . , _ ,
cc: See next page uys otm -
- r. t o
- Portland General Electric Company eg.* Gary Johnston, Resident Inspector U. S. Nuclear Regulatory Commission Trojan Nuclear Plant P. O. Box 0 Rainier, Oregon 97048 Robert M. Hunt, Chairman Board of County Commissioners Columbia County -
St. Helens, Oregon 97501 Donald W. Godard, Supervisor .
Siting and Regulation -
Oregon Departnent of Energy Labor and Industries Building Room 111 Salem, Oregon 97310 Regional Administrator Nuclear Regulatory Commission, Region V Office of Executive Director for Operations 1450 Maria Lane, Suite 210
' Walnut Creek, California 94596 f
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