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Abundant off-fault seismicity and orthogonal structures in the San Jacinto fault zone

Ross, Zachary E. and Hauksson, Egill and Ben-Zion, Yehuda (2017) Abundant off-fault seismicity and orthogonal structures in the San Jacinto fault zone. Science Advances, 3 (3). Art. No. e1601946. ISSN 2375-2548. PMCID PMC5351979. doi:10.1126/sciadv.1601946.

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The trifurcation area of the San Jacinto fault zone has produced more than 10% of all earthquakes in southern California since 2000, including the June 2016 M_w (moment magnitude) 5.2 Borrego Springs earthquake. In this area, the fault splits into three subparallel strands and is associated with broad V_P/V_S anomalies. We synthesize spatiotemporal properties of historical background seismicity and aftershocks of the June 2016 event. A template matching technique is used to detect and locate more than 23,000 aftershocks, which illuminate highly complex active fault structures in conjunction with a high-resolution regional catalog. The hypocenters form dipping seismicity lineations both along strike and nearly orthogonal to the main fault, and are composed of interlaced strike-slip and normal faults. The primary faults change dip with depth and become listric by transitioning to a dip of ~70° near a depth of 10 km. The M_w 5.2 Borrego Springs earthquake and past events with M > 4.0 occurred on the main faults, whereas most of the low-magnitude events are located in a damage zone (several kilometers wide) at seismogenic depths. The lack of significant low-magnitude seismicity on the main fault traces suggests that they do not creep. The very high rate of aftershocks likely reflects the large geometrical fault complexity and perhaps a relatively high stress due to a significant length of time elapsed since the last major event. The results provide important insights into the physics of faulting near the brittle-ductile transition.

Item Type:Article
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URLURL TypeDescription Materials CentralArticle
Ross, Zachary E.0000-0002-6343-8400
Hauksson, Egill0000-0002-6834-5051
Ben-Zion, Yehuda0000-0002-9602-2014
Additional Information:© 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. Distributed under a Creative Commons Attribution Noncommercial License 4.0 (CC BY-NC). Submitted 16 August 2016; Accepted 9 February 2017; Published 15 March 2017. We thank H. Kanamori for helpful discussions. We also thank D. Shelly and an anonymous reviewer for their constructive comments. Figures were produced with the Generic Mapping Tools. Funding: The study was supported by the NSF (grants EAR-1550704 and EAR-1551411), by the U.S. Geological Survey (USGS)/National Earthquake Hazards Reduction Program (NEHRP) (grants G15AP00095 and G16AP00147), and by the Southern California Earthquake Center, which was funded by NSF Cooperative Agreement EAR-1033462 and USGS Cooperative Agreement G12AC20038. Author contributions: Z.E.R. performed template matching and derived the aftershock locations. E.H. relocated the templates and calculated the focal mechanisms. Z.E.R., E.H., and Y.B.-Z. contributed to the analysis and wrote the article. The authors declare that they have no competing interests. Data and materials availability: All of the raw waveform data are publicly available from the Incorporated Research Institutions for Seismology (IRIS) and the Southern California Earthquake Data Center. SCSN data were provided by the California Institute of Technology/USGS SCSN (doi: 10.7914/SN/CI) and the Southern California Earthquake Center (doi: 10.7909/C3WD3xH1). All other data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.
Group:Seismological Laboratory
Funding AgencyGrant Number
Southern California Earthquake Center (SCEC)UNSPECIFIED
Subject Keywords:Fault zone structures, damage zones, Seismicity, San Jacinto fault, fault geometry, earthquake detection, template matching
Issue or Number:3
PubMed Central ID:PMC5351979
Record Number:CaltechAUTHORS:20170403-082404597
Persistent URL:
Official Citation:Abundant off-fault seismicity and orthogonal structures in the San Jacinto fault zone BY ZACHARY E. ROSS, EGILL HAUKSSON, YEHUDA BEN-ZION Science Advances 15 Mar 2017: Vol. 3, no. 3, e1601946 DOI: 10.1126/sciadv.1601946
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75640
Deposited By: Tony Diaz
Deposited On:10 Apr 2017 16:23
Last Modified:29 Mar 2022 16:01

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