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Evidence for Vertical Partitioning of Strike-Slip and Compressional Tectonics from Seismicity, Focal Mechanisms, and Stress Drops in the East Los Angeles Basin Area, California

Yang, Wenzheng and Hauksson, Egill (2011) Evidence for Vertical Partitioning of Strike-Slip and Compressional Tectonics from Seismicity, Focal Mechanisms, and Stress Drops in the East Los Angeles Basin Area, California. Bulletin of the Seismological Society of America, 101 (3). pp. 964-974. ISSN 0037-1106. https://resolver.caltech.edu/CaltechAUTHORS:20110613-105415659

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Abstract

We have synthesized the characteristics of the seismogenic zone in the east Los Angeles basin by analyzing earthquake data recorded during the past 30 years (1981–2010). The seismicity is distributed along the Whittier fault, with the majority of earthquakes located adjacent to the south side, in the depth range from 0 to 9 km, with b value of 1.1±0.05 and mostly normal and strike-slip faulting. Within the depth range of 9–12 km, the seismicity is scattered uniformly across the region, the b value is 1.0±0.05, and all three faulting styles are present. At the deepest depths (12–18 km), seismicity is sparse and primarily limited to a few clusters striking north; these deeper earthquakes primarily have reverse fault motion, and the b value is 0.78±0.04. Inversion of high-quality focal-mechanism data for the orientation of the regional stress field showed that the direction of maximum compressional stress rotates from N12°W at shallow depth to due north at the bottom of the seismogenic zone. Similarly, a depth dependence is observed in stress drops calculated from P-wave source spectra, which indicate stress drop generally increases from ~7 MPa at shallow depth (3 km) to ~53 MPa at the base of the seismogenic zone (17 km). Overall, our results provide new evidence for the vertical partitioning of styles of deformation and state of stress within this complex fault system in the east Los Angeles basin.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1785/0120100216DOIArticle
http://bssa.geoscienceworld.org/cgi/content/abstract/101/3/964PublisherArticle
ORCID:
AuthorORCID
Hauksson, Egill0000-0002-6834-5051
Additional Information:© 2011 Seismological Society of America. Manuscript received 9 August 2010. This research was supported by U.S. Geological Survey Grant G10AP00017 and by the Southern California Earthquake Center (SCEC). SCEC is funded by National Science Foundation Cooperative Agreement EAR-0529922 and USGS Cooperative Agreement 07HQAG0008. This article is SCEC contribution number 1444 and contribution number 10053 of the Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena. We gratefully acknowledge the Southern California Earthquake Data Center for providing the data set, Jeanne Hardebeck for providing the HASH and the SATSI programs and useful discussions, and Debi Kilb, Joann Stock, Iain Bailey, Peter Shearer, and Robert Yeats for valuable comments. We are grateful to the operators and analysts who maintain the USGS/Caltech Southern California Seismic Network and who pick and archive the seismograms.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
USGSG10AP00017
Southern California Earthquake Center (SCEC)UNSPECIFIED
NSFEAR-0529922
USGS07HQAG0008
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center (SCEC)1444
Caltech Seismological Laboratory10053
Issue or Number:3
Record Number:CaltechAUTHORS:20110613-105415659
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20110613-105415659
Official Citation:Yang, Wenzheng, Hauksson, Egill Evidence for Vertical Partitioning of Strike-Slip and Compressional Tectonics from Seismicity, Focal Mechanisms, and Stress Drops in the East Los Angeles Basin Area, California Bulletin of the Seismological Society of America 2011 101: 964-974
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23987
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:13 Jun 2011 20:29
Last Modified:03 Oct 2019 02:52

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