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Long-period mechanism of the 8 November 1980 Eureka, California, earthquake

Lay, Thorne and Given, Jeffrey W. and Kanamori, Hiroo (1982) Long-period mechanism of the 8 November 1980 Eureka, California, earthquake. Bulletin of the Seismological Society of America, 72 (2). pp. 439-456. ISSN 0037-1106.

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The seismic moment and source orientation of the 8 November 1980 Eureka, California, earthquake (M_s = 7.2) are determined using long-period surface and body wave data obtained from the SRO, ASRO, and IDA networks. The favorable azimuthal distribution of the recording stations allows a well-constrained mechanism to be determined by a simultaneous moment tensor inversion of the Love and Rayleigh wave observations. The shallow depth of the event precludes determination of the full moment tensor, but constraining M_(zx) = M_(zy) = 0 and using a point source at 16-km depth gives a major double couple for period T = 256 sec with scalar moment M_(0) = 1.1 · 10^(27) dyne-cm and a left-lateral vertical strike-slip orientation trending N48.2°E. The choice of fault planes is made on the basis of the aftershock distribution. This solution is insensitive to the depth of the point source for depths less than 33 km. Using the moment tensor solution as a starting model, the Rayleigh and Love wave amplitude data alone are inverted in order to fine-tune the solution. This results in a slightly larger scalar moment of 1.28 · 10^(27) dyne-cm, but insignificant (<5°) changes in strike and dip. The rake is not well enough resolved to indicate significant variation from the pure strike-slip solution. Additional amplitude inversions of the surface waves at periods ranging from 75 to 512 sec yield a moment estimate of 1.3 ± 0.2 · 10^(27) dyne-cm, and a similar strike-slip fault orientation. The long-period P and SH waves recorded at SRO and ASRO stations are utilized to determine the seismic moment for 15- to 30-sec periods. A deconvolution algorithm developed by Kikuchi and Kanamori (1982) is used to determine the time function for the first 180 sec of the P and SH signals. The SH data are more stable and indicate a complex bilateral rupture with at least four subevents. The dominant first subevent has a moment of 6.4 · 10^(26) dyne-cm. Summing the moment of this and the next three subevents, all of which occur in the first 80 sec of rupture, yields a moment of 1.3 · 10^(27) dyne-cm. Thus, when the multiple source character of the body waves is taken into account, the seismic moment for the Eureka event throughout the period range 15 to 500 sec is 1.3 ± 0.2 · 10^(27) dyne-cm.

Item Type:Article
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URLURL TypeDescription
Lay, Thorne0000-0003-2360-4213
Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1982 Seismological Society of America. Manuscript received 24 July 1981. We appreciate helpful suggestions made by Terry Wallace and the anonymous reviewer. Research was supported by the Earth Sciences Section National Science Foundation Grant EAR 78-11973 and by the United States Geological Survey Contract 14-08-0001-19755. One of the authors, T. L., was supported by a National Science Foundation Graduate Fellowship.
Funding AgencyGrant Number
NSFEAR 78-11973
NSF Graduate Research FellowshipUNSPECIFIED
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Caltech Division of Geological and Planetary Sciences3662
Issue or Number:2
Record Number:CaltechAUTHORS:20140813-132438489
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Official Citation:Lay, T., Given, J. W., & Kanamori, H. (1982). Long-period mechanism of the 8 November 1980 Eureka, California, earthquake. Bulletin of the Seismological Society of America, 72(2), 439-456.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48513
Deposited On:14 Aug 2014 21:28
Last Modified:09 Mar 2020 13:18

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