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Earthquake focal mechanisms in the Eastern Transverse Ranges and San Emigdio Mountains, Southern California and evidence for a regional decollement

Webb, Terry H. and Kanamori, Hiroo (1985) Earthquake focal mechanisms in the Eastern Transverse Ranges and San Emigdio Mountains, Southern California and evidence for a regional decollement. Bulletin of the Seismological Society of America, 75 (3). pp. 737-757. ISSN 0037-1106. http://resolver.caltech.edu/CaltechAUTHORS:20140902-154523973

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Abstract

Earthquake focal mechanisms obtained from P-wave first motions are presented for the Eastern Transverse Ranges and the San Emigdio Mountains in Southern California. The former region shows a predominance of strike-slip faulting whereas Quaternary faults in the region show thrust motion. We suggest that the observed strike-slip mode of deformation cannot continue indefinitely without the occurrence of more thrust faulting. Fault deformation in the San Emigdio Mountains inferred from focal mechanisms is in accord with displacements across Quaternary faults in the area. This study and a search of the literature has yielded 19 mechanisms with shallow-dipping nodal planes. Previous workers have interpreted such mechanisms as evidence for a regional decollement. If such a regional decollement exists, these data give some indication of its regional extent. Slip directions inferred from the focal mechanisms with shallow-dipping nodal planes show some regional consistency, but this pattern cannot be entirely explained with current tectonic models. A comparison of the stress drop of an event having a shallow-dipping nodal plane with an event with steeper planes gave inconclusive results.


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http://bssa.geoscienceworld.org/content/75/3/737.abstractPublisherArticle
Additional Information:© 1985, by the Seismological Society of America. Manuscript received 28 August 1984. We wish to thank W. L. Ellsworth of the USGS at Menlo Park for providing replays of FM tapes and Art Frankel for many useful discussions. Ed Corbett, Tom Hearn and Carl Johnson gave assistance in accessing the phase data which was collected by the dedicated Caltech and U.S.G.S. staff. Don Anderson, Art Frankel, Gene Humphreys, Jim Pechmann, Chris Sanders, Steve Wesnousky, and an anonymous reviewer provided useful comments on the manuscript. This study was made while one author (T. H. W.) was on a Study Award from the Department of Scientific and Industrial Research New Zealand at the California Institute of Technology, Pasadena. The research was partly supported by USGS Contract 14-08-0001-21210.
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USGS14-08-0001-21210
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Caltech Division of Geological and Planetary Sciences4131
Record Number:CaltechAUTHORS:20140902-154523973
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140902-154523973
Official Citation:Terry H. Webb and Hiroo Kanamori Earthquake focal mechanisms in the Eastern Transverse Ranges and San Emigdio Mountains, Southern California and evidence for a regional decollement Bulletin of the Seismological Society of America, June 1985, v. 75, p. 737-757
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ID Code:49156
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:03 Sep 2014 14:19
Last Modified:03 Sep 2014 15:55

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