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Comprehensive analysis of earthquake source spectra in southern California

Shearer, Peter M. and Prieto, Germán A. and Hauksson, Egill (2006) Comprehensive analysis of earthquake source spectra in southern California. Journal of Geophysical Research B, 111 (B6). Art. No. B06303. ISSN 0148-0227. doi:10.1029/2005JB003979.

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We compute and analyze P wave spectra from earthquakes in southern California between 1989 and 2001 using a method that isolates source-, receiver-, and path-dependent terms. We correct observed source spectra for attenuation using both fixed and spatially varying empirical Green's function methods. Estimated Brune-type stress drops for over 60,000 M_L = 1.5 to 3.1 earthquakes range from 0.2 to 20 MPa with no dependence on moment or local b value. Median computed stress drop increases with depth in the upper crust, from about 0.6 MPa at the surface to about 2.2 MPa at 8 km, where it levels off and remains nearly constant in the midcrust down to about 20 km. However, the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop. Spatially coherent variations in median stress drop are observed, with generally low values for the Imperial Valley and Northridge aftershocks and higher values for the eastern Transverse ranges and the north end of the San Jacinto fault. We find no correlation between observed stress drop and distance from the San Andreas and other major faults. Significant along-strike variations in stress drop exist for aftershocks of the 1992 Landers earthquake, which may correlate with differences in main shock slip.

Item Type:Article
Related URLs:
URLURL TypeDescription
Shearer, Peter M.0000-0002-2992-7630
Hauksson, Egill0000-0002-6834-5051
Additional Information:© 2006 American Geophysical Union. Received 4 August 2005; revised 20 December 2005; accepted 16 February 2006; published 13 June 2006. We thank the personnel of the USGS/Caltech Southern California Seismic Network who pick and archive the seismograms and the Southern California Earthquake Center (SCEC) for distributing the data; we especially thank Vikki Appel, who facilitated access to the database. We thank Susan Hough and Gregory Beroza for constructive reviews. Funding for this research was provided by NEHRP/USGS grant 03HQPA0001. This research was also supported by the Southern California Earthquake Center, which is funded by NSF Cooperative Agreement EAR-0106924 and USGS Cooperative Agreement 02HQAG0008. This is SCEC contribution 919 and contribution 9121 of Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
Group:Seismological Laboratory
Funding AgencyGrant Number
Southern California Earthquake Center (SCEC)UNSPECIFIED
Subject Keywords:earthquake source spectra; earthquake stress drop
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Souther California Earthquake Center (SCEC)919
Caltech Division of Geological and Planetary Sciences9121
Issue or Number:B6
Record Number:CaltechAUTHORS:20130219-133723415
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Official Citation:Shearer, P. M., G. A. Prieto, and E. Hauksson (2006), Comprehensive analysis of earthquake source spectra in southern California, J. Geophys. Res., 111, B06303, doi:10.1029/2005JB003979.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36987
Deposited On:20 Feb 2013 18:40
Last Modified:09 Nov 2021 23:26

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