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Seismological Studies of the San Fernando Earthquake and Their Tectonic Implications

Allen, Clarence R. and Hanks, Thomas C. and Whitcomb, James H. (1975) Seismological Studies of the San Fernando Earthquake and Their Tectonic Implications. In: San Fernando, California, earthquake of 9 February 1971. California Division of Mines and Geology Bulletin. No.196. California Division of Mines and Geology , Sacramento, CA, pp. 257-262. https://resolver.caltech.edu/CaltechAUTHORS:20190918-075239587

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Abstract

Improved hypocentral locations have been obtained for the San Fernando earthquake and its larger aftershocks through the use of data from portable stations installed in and around the aftershock area subsequent to the main shock. The main shock, at 14 00 41.8 GMT on 9 February 1971, is now assigned a magnitude (M_L) of 6.4 and a location at 34° 24.7' N, 118° 24.0' W, h = 8.4 km. Fifty-five aftershocks of magnitude 4.0 and greater had occurred through 31 December 1971. The lunate-shaped epicentral distribution of aftershocks is consistent with the idea of southward thrusting along a disc-shaped fault surface, and aftershock depths as well as aftershock focal mechanisms suggest that the thrust surface dips about 35° toward N 20° E. However, a distinct linear alignment of left-lateral strike-slip aftershocks parallel to the motion direction near the west boundary of activity suggests that the fault surface has a steep flexure along this line, down-stepped to the west, and both the planar distribution of aftershocks and the local geology support this concept.


Item Type:Book Section
Additional Information:© 1975 California Division of Mines and Geology. Manuscript submitted to the California Division of Mines and Geology January 24, 1972. Contribution No. 2124, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena. We are particularly indebted to many other agencies and persons for supplying data from their portable stations that have been used in our study: Earthquake Mechanisms Laboratory, NOAA (Don Tocher); National Center for Earthquake Research, USGS (Robert Wesson, Willy Lee); University of California at San Diego (James Brune); California Department of Water Resources (Paul Morrison). At Caltech, Gladys Engen, Mark Gaponoff, Jan Garmany, and John Nordquist read many of the records and carried out many of the computer solutions. This study was supported by the Caltech Earthquake Research Affiliates and by the National Science Foundation (Grant GA29920).
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
Caltech Earthquake Research AffiliatesUNSPECIFIED
NSFGA29920
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences2124
Series Name:California Division of Mines and Geology Bulletin
Issue or Number:196
Record Number:CaltechAUTHORS:20190918-075239587
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190918-075239587
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98707
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:18 Sep 2019 20:03
Last Modified:03 Oct 2019 21:43

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