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The 1971 San Fernando earthquake: A double event?

Heaton, Thomas H. (1982) The 1971 San Fernando earthquake: A double event? Bulletin of the Seismological Society of America, 72 (6A). pp. 2037-2062. ISSN 0037-1106.

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Evidence is presented which suggest that the 1971 San Fernando earthquake may have been a double event that occurred on two separate, subparallel thrust faults. It is postulated that the initial event took place at depth on the Sierra Madre fault zone which runs along the base of the San Gabriel Mountains. Rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km. A second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the Sierra Madre fault zone. The surface trace of this fault coincides with the San Fernando fault zone which was the principal fault associated with surface rupture. It is postulated that rupture propagated from a depth of 8 km to the free surface. The moments of the first and second events are approximately 0.7 × 10^(26) dyne-cm and 1.0 × 10^(26) dyne-cm, respectively. This model is found to explain the combined data sets of strong ground motions, teleseismic P and S waveforms, and static offsets better than previous models, which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth. Nevertheless, many features of the observed motions remain unexplained, and considerable uncertainty still exists regarding the faulting history of the San Fernando earthquake.

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Heaton, Thomas H.0000-0003-3363-2197
Additional Information:© 1982 by the Seismological Society of America. Manuscript received 22 December 1981. I wish to thank Paul Spudich and William Bakun for critically reviewing the manuscript. I also wish to thank Donald Helmberger, Charles Langston, Steve Hartzell, and Thomas Hanks for useful discussions. Although this study was completed while I was an employee of the U.S. Geological Survey, major portions of the work were completed when I was employed by Dames and Moore and also by the California Institute of Technology. Thus, I give special thanks to Arthur Darrow and Donald Helmberger for their support of this research. This research was partially supported by the National Science Foundation Contract PFR-7808813.
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Issue or Number:6A
Record Number:CaltechAUTHORS:20121205-081142449
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35803
Deposited By: Tony Diaz
Deposited On:05 Dec 2012 19:24
Last Modified:03 Oct 2019 04:31

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