A Caltech Library Service

Computing a Large Refined Catalog of Focal Mechanisms for Southern California (1981–2010): Temporal Stability of the Style of Faulting

Yang, Wenzheng and Hauksson, Egill and Shearer, Peter M. (2012) Computing a Large Refined Catalog of Focal Mechanisms for Southern California (1981–2010): Temporal Stability of the Style of Faulting. Bulletin of the Seismological Society of America, 102 (3). pp. 1179-1194. ISSN 0037-1106. doi:10.1785/0120110311.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


Using the method developed by Hardebeck and Shearer (2002, 2003) termed the HASH method, we calculate focal mechanisms for earthquakes that occurred in the southern California region from 1981 to 2010. When available, we use hypocenters refined with differential travel times from waveform cross correlation. Using both the P‐wave first motion polarities and the S/P amplitude ratios computed from three‐component seismograms, we determine mechanisms for more than 480,000 earthquakes and analyze the statistical features of the whole catalog. We filter the preliminary catalog with criteria associated with mean nodal plane uncertainty and azimuthal gap and obtain a high‐quality catalog with approximately 179,000 focal mechanisms. As more S/P amplitude ratios become available after 2000, the average nodal plane uncertainty decreases significantly compared with mechanisms that include only P‐wave polarities. In general the parameters of the focal mechanisms have been stable during the three decades. The dominant style of faulting is high angle strike‐slip faulting with the most likely P axis centered at N5°E. For earthquakes of M<2.5, there are more normal‐faulting events than reverse‐faulting events, while the opposite holds for M>2.5 events. Using the 210 moment‐tensor solutions in Tape et al. (2010) as benchmarks, we compare the focal plane rotation angles of common events in the catalog. Seventy percent of common earthquakes match well with rotation angles less than the typical nodal plane uncertainty. The common events with relatively large rotation angles are either located around the edge of the (SCSN) network or poorly recorded.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle Supplement
Hauksson, Egill0000-0002-6834-5051
Shearer, Peter M.0000-0002-2992-7630
Additional Information:© 2012 by the Seismological Society of America. Manuscript received 9 November 2011. This research was supported by the U.S. Geological Survey Grants G11AP20032 and G12AP20010 and was also supported by the Southern California earthquake Center (SCEC), which is funded by NSF Cooperative Agreement EAR-0106924 and USGS Cooperative Agreement 07HQAG0008. This article is SCEC contribution number 1512 and contribution number 10066 of the Seismological Laboratory Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena. We are grateful to the operators and analysts who maintain the USGS/Caltech SCSN, and who pick and archive the seismograms. We thank Jeanne Hardebeck for providing the HASH programs and useful discussions. We thank Carl Tape for providing the moment-tensor catalog with 234 earthquakes. We used the RFOC package (Graphics for Spherical Distributions and Earthquake Focal Mechanisms in R) provided by Jonathan Lees to visualize focal mechanisms. We appreciate Sarah Gordon, Shengji Wei, and Zhongwen Zhan for valuable comments. We appreciate associate editor Heather DeShon and two anonymous reviewers for constructive comments.
Group:Seismological Laboratory
Funding AgencyGrant Number
Southern California Earthquake Center (SCEC)UNSPECIFIED
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center (SCEC)1512
Caltech Seismological Laboratory 10066
Issue or Number:3
Record Number:CaltechAUTHORS:20120706-130911669
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32282
Deposited By: Tony Diaz
Deposited On:09 Jul 2012 21:34
Last Modified:09 Nov 2021 21:26

Repository Staff Only: item control page