ML20105C712

Northwest Us Subduction Zone Seismic Risk Assessment, Proposal to Research Program

ML20105C712
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Site:	05000000, Satsop
Issue date:	01/20/1984
From:	Heaton T INTERIOR, DEPT. OF, GEOLOGICAL SURVEY
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Froposal to U.S.G.S. research program for the U.'S.N.R.C.

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Project Chief: Thomas H. He'aton U.S.G.S., Seismology Branch' Calif. Inst. Tech.

Pasadena, CA 91125 FTS 799-0257 Comercial 213-355-6822 Fondf69 pertod: 01 October 1983 to 01 October 1984 e

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tatement of Problem Despite the fact that there is good evidenc.e of present day con-vergence of the Juan de Fuca and North American plates, there has been remarkably little historic seismic activity ilong the shallow 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 zcne shares many features with other subduction zones which both have been locked and have experienced great earthquakes (Heaton and Xanamori,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 areah 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

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staning the responses of individual segments of the proposed rupture surface. The responses of individual segments will be approximated both by actual recordings of moderate-sized earthquakes and also by numerical calculation of the theoretical response of layered crustal structure to point. dislocations.

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2) Imoortance of the Problem to Procram Goals 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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Wark to be undertaken-W Work on this project falls naturally into three catagories. -

In this phase of the work we will ll Characterization of the source jj construct models of the feasible-rupture We parameters will include of shallow thrusti para-U carthquakes on the Juan de Fuca subduction 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 characteri. stics of Juan de Fuca. subduction bduc- zone events will be similar to rupture characteristics seen characteristics Physical for other su tion zones with similar physical characteristics. f  ;

which will be compared are; ari'of subducted lithosphere, frate the o . con .  ;

vergence, fault dip, topography of- the subducted plate, geometry tial o l accretionary wedge, nature of marine terraces, and temporal and spa i There are good reasons to suspect that these patterns of seismicity. ,

physical characteristics are closely related to the rup.ture d paramet of shallow subduction earthquakes (sce accompaning paper by Heaton a If subduction zones with similar physical characteristics Kanamori).

can be found, then the nature of rupture heterogeneity for events on j 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 dimens We will use several procedures Estimation of strono around motions _The first procedure is describ to estimate strong ground motion.In this procedure a suite of strong Heaton et al. (1983).

is constructed by collecting and scaling records taken at sites Records are scaled with respect to site distance, lar tectonic conditions. However, it is d'esirable to collect earthquake size, and site conditions. Once a scaled suite records which require as little scaling as po'ssible. i l mean,

-of reccrds has'been constructed, we can calculate the statist ca i

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median, standard deviation, etc. of various strong motion parameters.

I 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 Si.' Reco5fs were chosen so that little scaling was necessary. The suite' of scaled response spectra is shown in Figure 1. The

. 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.

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This same procedure will be applied to construct suites of strong motion records from subduction zones'. These records are principally frem Japan. In Figure 3 we show a ccmparison of peak acceleration plotted as a function of distance.and magnitude, for ground motions recorded in Japan and the western U. 5. 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. Howevsr 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 frem imaller earthquakes. This ,

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 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 frcrn 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 aporopriate 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 i

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- i

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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 success to model records from moderate-sized earthquakes (Heaton,1982; Hartzell and Helmberger,1987;' 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 potenttal heights of Ts' unamis that might be expected along the coast of Washington, Oregon, and British Columbia.

4) Stratecy 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 gecmetry. 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 WPPSS Nuclear. Project Number 3 (October l .

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l Task II Comparison with other subduction zones. This will be primarily a literature search combined with interviews of

• knowledgeable colleagues. Cataloguing of physical features l i

should allow us to select those zones with similar charac-teristics (October-November,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 heterogeheity. This task ventures into an area not yet,,, studied. We intend to collect teleseis-mic time functio,ns, 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).

Task"VI Construct synthetic streng motion records by surrming 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 gecmetrics and ocean bottem profiles similar to the Juan de Fuca subduction zone will be constructed. Tsunami heights will then be scaled using the results of Task III (Su. mer 1984) . -

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5) location er 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; located pn the campus of the California Institute

• 1 of Technology.

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6) _0ther comitments or anticipated difficulties that will affect orocress or ccmoletion of the project

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Mostcomputercodestomanipulatedat$andcomputesyntheticground motions are written and working. liowever, these codes must be updated.

Furthemore, we expect to transfer our work from the Caltech Prime. 750 computer to a new USGS VAX ll-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 necessary, then collection of other records niay delay our schedule.

Both principal investigato'rs in this project are also 1/2 time ccrmitted to work in the Seismology Branch project entitled, Southern California Cooperativa 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 earthouakes, may affect work schedules on research projects.

7) Products .

04/84 Preliminaiy report on nature of shaking from Juan de Fuca

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subduction zone earthquakes to the U.S.N.R.C.

10/84 Final report

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10/84 Scientific paper on 'the nature of seismic hazards associated

{ with the Juan de Fuca subduction zone.

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1. Majorfacilitiesandeouiementneeded f The major requirement of this project is computer time, se presently

. purchase computer time from Caltech on a Prime 750 omputer. However, 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 projects and workers There will be strong interation with Hiroo Xanacori at Ciltech 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 Resea,rch Compary. We also expect interaction from Doug Coats of Exxon Production Research Cc=pany and C.B.iCrouse ,of Earth Technology Corporation. Caltech graudate students, in carticular, '

Anne-Mori, will be encouraged to participate in the research. Due to the far-ranging i:6clications of tnis research, we exoect to interact .

frecuently about the nature of our preliminary conclusions with research-2 ers at USGS-Menlo Park, Univ. of Washington, USGS-Denver, and the U.S.

N.R.C.

! 10) Oualifications of orincioil investicators

} The principal investigators in this project, Heaton and Martzell,

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have considerable exoerience .in the field of synthesizing both strong .

l moticns and teleseismic ground ' notions fecm complex realistic earthquake sources. They both also have experience in the problem of su=ning records of smaller eartnouakes to simulate large ones. Both have ex-perience in the conrnercial consulting field and Heaton has considerable experience in the field of estimating ground motions at subduction zones. A full summary of the qualifications of the .p~rincipal investiga-tors is contained in the resumes included with this proposal i M.Y. Effort Funding Requested 0.4 '

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f. _ References .

1 Hartzell, S.H. (1978).

Earthquake aftershocks as Green's Functions, Geochys. Res. I.etters, 5, 1-4. ,

Hartzell, S.H. and D.Y. Helmberger (1982).  ;

Strong-motion modeling of ,

the Imperial Valley earthqua(e'~of 1979, Bull. Seism 571-596. '~ ._ Soc. Am., 7_2,, 2 ~

Hartzell, S.H. and T.H. Heaton (1983).

Inversion of strong-ground motion and teleseismic waveform data- for the fault rupture history 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., 2, 2037-2052.

, A double event?,

Heaton, T.H. , F. Tajima, and A.W. Mori (1983).

Estimating ground motions using recorded accelerograms, mariuscript. . -

Heaton, T.H. and H. Kanamori (1983).

Seismic potential associated with subduction in the northwestern United States, manuscript.

Jennings, P.C. and H. Kanamori (1983).

tudes found from strong-motion records, Bull. SeismEffect of distance '

1645-1670. . Soc. Am. ,7_3, 3 Kanamori, H. (1979). .

! A semi-empirical approach to prediction of long-period 69, ground 1645-1670. motions from great earthq'uakes, Bull. .Seism. Am., Soc

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Figure 1. Responsespectra(3hdamped)forhorizontalcomponents ,

of 15 records f/bh strike-slip earthquakes which are

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scaled to a dista'nce of 50 km and a magnitude of 61 Records description and scaling parameters are given in Table 1. Figure i.s from Heaton et al. (1983).

Figure 2. a) average spectrum, b)' average plus one standard de- l viation specturm, c) specturm of the largest single record, d) spe.ctrum which envelopes all others; based on spectra shown in Figure 1 (taken from Heaton et al.

, 1983). ..

F.igure 3. Comparison of peak ground accelerations recorded in the western U.S. and Japan. Distance is approximately the closest ho~rizontal distance to the rupture. Dashed line is the modified local magnitude distance attenua-tion law of Jennings and Xanamori (1983). Figure is from Heaton et.al. (1983).

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$oll Calculated H,(if ' Energy A g Earthquake l scale Velocity Velocity [

Station available) Distance (km) Tyg N 'I'8 Ao E '

L s X Factor (cs/sec) (ca/sec) .

1 3/11/33 Long Beach Vernon CHO Oldg. 6.3 36 0 6.23 2.28 *.15 12.59 .87 23, 28.

2 3/11/33 tong 8each L.A. Subway Ters. 6.3 42 0 6.23 2.38 e.15 10.0 1.'10 20.5 22.6 3 12/30/34 L. Californla El Centro 6.5 61 0 6.38 2.61 *.15 8.32 1.32 16.0 21.1 4 10/21/42 Borrego Valley El Centro 6.5 46 0 6.38 2.44 *.15 12.3 .89 6.2 5.5 5 12/21/54 Eureka Ferndala City llall 6.5 40 6.38 1 2.35 0 10.72 1.02 '31. 31.6 6 ,4/20/65 Japan Site #C8002 6.1 50 0 6.08 2.43 4.15 6.31 1.74 7.8 7. 8 7 4/20/65 Japan Site 808057 6.1 45 0 6.08 2.49 *.15 8.91 1.23 20.2 24.8 8 4/9/68 Oorrego Mtn. El Centro 6.6 C5 0 6.45 2.65 *.15 8.91 1.23 20.2 24.4 9 10/15/79 leperial Valley Cerro Prieto 6.4 39 2 6.3 2.33 .13 1,66 6.61 15. 24.9 10 10/15/19 Imperial Vallef Delta f. 4 50 0 6.3 2.49 *.15 9.12 1.2 29 2 35.1 i:

11 10/15/79 leperial Valley Victoria 5.4 60 0 6.3 2.6 *.15 '

7.08 1.55 10.2 15.8 12 10/15/79 Imperial Valley Callpatria 6.4 41 0 6. 'l 2.37 *.15 12.02 .91 13.7 12.4 13 10/15/79 Imperial Valley Superstillon 6.4 42 0 61 2.39 e.15 14 10/15/79 leperial Valley Plaster City 11.48 .95 6.9 6.6 .I 6.4 38 0 6.3 2.32 *.15 ,13.49 .81 4.5 3.6 "'

15 10/15/79 Imperial Valley Niland 6.4 51 0 6.3 2.5 e.25 8.91 1.23 10.1 12.4

. , e Test Case 6.5 50 0 6.38 2.49 *.15 10.96 14.26 1 8.5 17.8719. ,

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i p- v Resume: Thomas H. Heaton

Title:

Geophysicist - U. S. Geological Survey Expertise: Seismology / Earthquake Engineering -

Past Exoerience:

0 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 emphasis on fault hazard studies PROFESSIONAL Seismological Society of American AFFILIATIONS American Geophysical Union ACADEMIC BACXGROUND Chemistry and physics major, Bates College, 1968-1970 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, X111, Stanford University,94-103, 1973.

Heaton, T.H., Tidal triggering of earthquakes, Geoohys.

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.

An. , 68, No. 1, 31 -48, 1978.

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.O Heatch. T.H.cand D.V. Helmberger, A study of the strongi graund motion of the Borrego Mountain, California, earthquake, 1977. -

Bull. Seism. Soc. Am. , 67, No. 2, 315-330 j

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-e u I Heaton, T.H., Generalized ray models of strong ground - l i

1978.

300 p.,motion, Ph.D. Thesis, California Institute of Technology, Heaton, T.H. and D.V. .Helmberger, Generalized ray models of 69,the No.San Fernando Earthquake, Bull . Seism. Soc. Am. ,

5,1311-1341,1979. -~~

,a 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

, - 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 ,

earthquake sequence, in preparation.

Heaton, event T.H.,inThe 7 BSSA, 1971 San Fernando earthquake; A double Press,1982.

Heaton,.T. H.,

In Press, 1982. Tidal triggering of earthquakes, BSSA, .

Heaton, T.H., F. Tajima, and A.W. Mori ground motions using recorded accelerog, rams, BSSA, Estimat submitted.

Liu, H.L. and T.H. Heaton, Array analysis of the ground velocities and accelerations from the 1971 l

San Fernando earthquake, in preparation. i l

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