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Source parameters of two M_L ∼ 5 earthquakes near Anza, California, and a comparison with an Imperial Valley aftershock

Frankel, Arthur (1984) Source parameters of two M_L ∼ 5 earthquakes near Anza, California, and a comparison with an Imperial Valley aftershock. Bulletin of the Seismological Society of America, 74 (5). pp. 1509-1527. ISSN 0037-1106. https://resolver.caltech.edu/CaltechAUTHORS:20140903-085950592

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Abstract

Strong-motion records were used to determine the seismic moments, source dimensions, and stress drops for two earthquakes near the proposed Anza seismic gap (Thatcher et al., 1975) along the San Jacinto fault: the 25 February 1980 (M_L 5.5) event and the shock of 15 June 1982 (M_L 4.8). Seismic moments determined for the two events were 2.5 × 10^(23) and 1.1 × 10^(23) dyne cm, respectively. The source radii were estimated from the displacement pulse widths using the source model of Madariaga (1976). Static stress drops for the 1980 and 1982 earthquakes were calculated as 110 and 100 bars, respectively. Stress drops determined from the rms accelerations using the method of Hanks and McGuire (1981) were 220 bars for the 1980 earthquake and 180 bars for the 1982 event. The long-period seismic moments for these events, derived from regional recordings of 30- to 40-sec Love waves, were a factor of two to three greater than the moments estimated from the strong-motion records. As a comparison to the Anza events, source parameters were also determined from strong-motion records for an immediate aftershock (M_L 5.0) of the 1979 Imperial Valley earthquake. The seismic moment of this aftershock was calculated as 4.2 × 10^(23) dyne-cm, and its static stress drop was 130 bars. Static stress drops calculated from the displacement pulse shapes for the three events studied in this paper, as well as for an aftershock of the Oroville earthquake reported by Fletcher et al. (1980), exhibit a relatively narrow range between about 100 and 180 bars. This result indicates that the stress drops of the two main shocks near Anza were not unusually high, relative to those of certain aftershocks in other tectonic settings in California.


Item Type:Article
Related URLs:
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http://bssa.geoscienceworld.org/content/74/5/1509.abstractPublisherArticle
Alternate Title:Source parameters of two ML ∼ 5 earthquakes near Anza, California, and a comparison with an Imperial Valley aftershock
Additional Information:© 1984, by the Seismological Society of America. Manuscript received 16 March 1984. I thank Hiroo Kanamori, Steve Hartzell, and Terry Webb for reviewing the manuscript and providing helpful comments. Joe Fletcher, Gerry Brady, and Peter Mork of the U.S. Geological Survey kindly provided strong-motion records for the earthquakes near Anza. Doug Given provided the fault-plane solution for the 1982 Anza event. I benefitted from discussions with Jack Boatwright and Joe Fletcher. Comments from an anonymous reviewer were helpful in improving the manuscript. The figures were drafted by Laszlo Lenches. This research was supported by the U.S. Geological Survey under Grant 14-08-0001-21210. The author was supported by a Bantrell Postdoctoral Fellowship.
Funders:
Funding AgencyGrant Number
USGS14-08-0001-21210
Bantrell FellowshipUNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Caltech Seismological Laboratory4066
Issue or Number:5
Record Number:CaltechAUTHORS:20140903-085950592
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140903-085950592
Official Citation:Arthur Frankel Source parameters of two M_L ∼ 5 earthquakes near Anza, California, and a comparison with an Imperial Valley aftershock Bulletin of the Seismological Society of America, October 1984, v. 74, p. 1509-1527
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49177
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:03 Sep 2014 16:20
Last Modified:03 Oct 2019 07:11

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