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Seismic characteristics of earthquakes along the offshore extension of the western transverse ranges, California

Bent, Allison L. and Helmberger, Donald V. (1991) Seismic characteristics of earthquakes along the offshore extension of the western transverse ranges, California. Bulletin of the Seismological Society of America, 81 (2). pp. 399-422. ISSN 0037-1106. https://resolver.caltech.edu/CaltechAUTHORS:20140806-085628992

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Abstract

The short- and long-period body waves of five moderate (M_L 5 to 6) earthquakes that took place in the nearshore region of southcentral California between 1969 and 1981 are modeled to obtain the source parameters. Both regional Pnl waveforms and teleseismic P waveforms are used in this analysis. Four of the events are thrust earthquakes with strikes that rotate southwestward as the epicenters move southward; the fifth is a strike-slip event occurring on a fault subparallel to the San Andreas fault. The focal mechanisms for all five events are consistent with known faults in the source localities and suggest that the regional stress field is compressional in a north-south direction. At least three events have complex source time histories, suggesting that complex sources are common even for events of this size. The most exotic event started with a low stress drop subevent, ruptured bilaterally, and concluded with strong asperity ruptures at each end. Since Pnl waveforms for thrust events are particularly sensitive to crustal thickness, regionalized crustal models were developed. The crustal thickness appears to increase southward but may be a function of the distance of the event from shore rather than of latitude. Basin and range paths yield the thinnest crustal models, while paths crossing the Colorado Plateau and Rockies yield the thickest. We also examined amplitude variations with station and path. In general, the amplitudes seem to be controlled by the station site rather than the path.


Item Type:Article
Related URLs:
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http://bssa.geoscienceworld.org/content/81/2/399.abstractPublisherArticle
Additional Information:© 1991, by the Seismological Society of America. Manuscript received 22 August 1990. This work was supported by USGS Contract 14-08-0001-G1872. California Institute of Technology Division of Geological and Planetary Sciences contribution no. 4931. Hiroo Kanamori read an earlier version of this paper and made some suggestions that improved its quality. Lisa Wald also reviewed the paper and provided us with many helpful comments.
Funders:
Funding AgencyGrant Number
USGS14-08-0001-G1872
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Caltech Division of Geological and Planetary Sciences4931
Issue or Number:2
Record Number:CaltechAUTHORS:20140806-085628992
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140806-085628992
Official Citation:Allison L. Bent and Donald V. Helmberger Seismic characteristics of earthquakes along the offshore extension of the western transverse ranges, California Bulletin of the Seismological Society of America, April 1991, v. 81, p. 399-422
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48048
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:06 Aug 2014 16:54
Last Modified:03 Oct 2019 06:59

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