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Aftershocks and Triggered Events of the Great 1906 California Earthquake

Meltzner, Aron J. and Wald, David J. (2003) Aftershocks and Triggered Events of the Great 1906 California Earthquake. Bulletin of the Seismological Society of America, 93 (5). pp. 2160-2186. ISSN 0037-1106. doi:10.1785/0120020033.

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The San Andreas fault is the longest fault in California and one of the longest strike-slip faults in the world, yet little is known about the aftershocks following the most recent great event on the San Andreas, the M_W 7.8 San Francisco earthquake on 18 April 1906. We conducted a study to locate and to estimate magnitudes for the largest aftershocks and triggered events of this earthquake. We examined existing catalogs and historical documents for the period April 1906 to December 1907, compiling data on the first 20 months of the aftershock sequence. We grouped felt reports temporally and assigned modified Mercalli intensities for the larger events based on the descriptions judged to be the most reliable. For onshore and near-shore events, a grid-search algorithm (derived from empirical analysis of modern earthquakes) was used to find the epicentral location and magnitude most consistent with the assigned intensities. For one event identified as far offshore, the event's intensity distribution was compared with those of modern events, in order to constrain the event's location and magnitude. The largest aftershock within the study period, an M ∼6.7 event, occurred ∼100 km west of Eureka on 23 April 1906. Although not within our study period, another M ∼6.7 aftershock occurred near Cape Mendocino on 28 October 1909. Other significant aftershocks included an M ∼5.6 event near San Juan Bautista on 17 May 1906 and an M ∼6.3 event near Shelter Cove on 11 August 1907. An M ∼4.9 aftershock occurred on the creeping segment of the San Andreas fault (southeast of the mainshock rupture) on 6 July 1906. The 1906 San Francisco earthquake also triggered events in southern California (including separate events in or near the Imperial Valley, the Pomona Valley, and Santa Monica Bay), in western Nevada, in southern central Oregon, and in western Arizona, all within 2 days of the mainshock. Of these triggered events, the largest were an M ∼6.1 earthquake near Brawley and an M ∼5.0 event under or near Santa Monica Bay, 11.3 and 31.3 hr after the San Francisco mainshock, respectively. The western Arizona event is inferred to have been triggered dynamically. In general, the largest aftershocks occurred at the ends of the 1906 rupture or away from the rupture entirely; very few significant aftershocks occurred along the mainshock rupture itself. The total number of large aftershocks was less than predicted by a generic model based on typical California mainshock–aftershock statistics, and the 1906 sequence appears to have decayed more slowly than average California sequences. Similarities can be drawn between the 1906 aftershock sequence and that of the 1857 (M_W 7.9) San Andreas fault earthquake.

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http://dx.doi.oeg/ 10.1785/0120020033DOIArticle
Meltzner, Aron J.0000-0002-2955-0896
Additional Information:© 2003 Seismological Society of America. Manuscript received 18 January 2002. Many people have helped make this research possible or have helped significantly along the way. We would like to thank Tousson Toppozada of the California Division of Mines and Geology for sharing his thoughts, knowledge, and data, and we want to thank Bill Deverell (Caltech), Bill Bakun (USGS), Lucy Jones (USGS), Bill Ellsworth (USGS), Jim Dewey (USGS), Lori Dengler (Humboldt State University), and Hiroo Kanamori (Caltech) for their ongoing assistance, on our 1857 work, and now for 1906. We would also like to thank Nancy King (USGS) and Sue Hough (USGS) for their thoughtful reviews and very helpful suggestions on the open-file report, and we would like to thank Bill Bakun and Tousson Toppozada for their helpful reviews and insightful comments on an earlier version of this article. We are especially grateful to Bill Ellsworth and Paul Reasenberg (USGS) for their thorough reviews, which in many cases encouraged us to go the extra mile (kilometer?) and which markedly improved the quality of this article. We are indebted to all of you. We also wish to acknowledge the use of the Generic Mapping Tools software package by Wessel and Smith (1991) to generate all the figures in this report. This work has been supported by funding from Caltech’s Summer Undergraduate Research Fellowship (SURF) program, from funds awarded in conjunction with the 1998–99 Fritz Burns Prize in Geology at Caltech, and by funding from the U.S. Geological Survey.
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Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Caltech Fritz Burns Prize in Geology 1998-1999UNSPECIFIED
U.S. Geological SurveyUNSPECIFIED
Issue or Number:5
Record Number:CaltechAUTHORS:20140804-142949354
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Official Citation:Aron J. Meltzner and David J. Wald Aftershocks and Triggered Events of the Great 1906 California Earthquake Bulletin of the Seismological Society of America, October 2003, v. 93, p. 2160-2186, doi:10.1785/0120020033
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47920
Deposited By: Ruth Sustaita
Deposited On:04 Aug 2014 21:40
Last Modified:10 Nov 2021 17:51

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