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Report on the August 2012 Brawley Earthquake Swarm in Imperial Valley, Southern California

Hauksson, Egill and Stock, Joann and Bilham, Roger and Boese, Maren and Chen, Xiaowei and Fielding, Eric J. and Galetzka, John and Hudnut, Kenneth W. and Hutton, Kate and Jones, Lucile M. and Kanamori, Hiroo and Shearer, Peter M. and Steidl, Jamie and Treiman, Jerry and Wei, Shengji and Yang, Wenzheng (2013) Report on the August 2012 Brawley Earthquake Swarm in Imperial Valley, Southern California. Seismological Research Letters, 84 (2). pp. 177-189. ISSN 0895-0695. doi:10.1785/0220120169.

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The 2012 Brawley earthquake swarm occurred in the Brawley Seismic Zone (BSZ) within the Imperial Valley of southern California (Fig. 1). The BSZ is the northernmost extensional segment of the Pacific–North America plate boundary system. Johnson and Hill (1982) used the distribution of seismicity since the 1930s to outline the geographical extent of the BSZ, defining boundaries of the BSZ as shown in Figure 1. Its north–south extent ranges from the northern section of the Imperial fault, starting approximately 10 km north of the United States–Mexico international border and connecting to the southern end of the San Andreas fault, where it terminates in the Salton Sea. Larsen and Reilinger (1991), who defined a similar geographical extent of the BSZ, argued that the BSZ was migrating to the northwest, which they associated with the propagation of the Gulf of California rift system into the North American continent. During the seismically active period of the 1970s, the BSZ produced close to half of the earthquakes recorded in California (Johnson and Hill, 1982; Hutton et al., 2010). However, for two decades following the 1979 Imperial Valley mainshock M_w 6.4 and its aftershock sequence, the BSZ was much less active. In general, the BSZ seismicity is indicative of right-lateral strike-slip plate motion accompanied by crustal thinning as well as possible associated fluid movements in the crust (Chen and Shearer, 2011). The 2012 Brawley swarm produced more than 600 events recorded by the United States Geological Survey (USGS)–California Institute of Technology (Caltech) Southern California Seismic Network (SCSN). Other monitoring instruments in the region, such as the Global Positioning System (GPS) network, creepmeters, and the Wildlife Liquefaction Array (WLA) also recorded signals from the largest events. In addition, Interferometric Synthetic Aperture Radar (InSAR) satellites collected images from space.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemArticle
Hauksson, Egill0000-0002-6834-5051
Stock, Joann0000-0003-4816-7865
Fielding, Eric J.0000-0002-6648-8067
Hudnut, Kenneth W.0000-0002-3168-4797
Jones, Lucile M.0000-0002-2690-3051
Kanamori, Hiroo0000-0001-8219-9428
Shearer, Peter M.0000-0002-2992-7630
Additional Information:© 2013 Seismological Society of America. We thank the personnel of the United States Geological Survey (USGS)–California Institute of Technology (Caltech) Southern California Seismic Network (SCSN) for picking the arrival times and archiving the seismograms and the Southern California Earthquake Data Center for distributing the data. TerraSAR-X data are copyright 2012 DLR and were provided under the Group on Earth Observation (GEO) Geohazard Supersite program project prlund_GEO0927. E. Hauksson and W. Yang were supported by the National Earthquake Hazards Reduction Program/USGS Grant 12HQPA0001. This research was also supported by the Southern California Earthquake Center (SCEC), which is funded by National Science Foundation (NSF) Cooperative Agreement EAR-0529922 and USGS Cooperative Agreement 07HQAG0008. This paper is Contribution 1678 of SCEC and Contribution 10083 of the Division of Geological and Planetary Sciences, Caltech, Pasadena, California. We thank K. Marty (Imperial Valley College) and S. Williams (consulting geologist from Imperial, California) for help with fieldwork. The high-rate GPS data were processed and provided by S. Owen from the Jet Propulsion Laboratory (JPL). Part of this research was supported by the National Aeronautics and Space Administration (NASA) Earth Surface and Interior focus area and performed at the JPL, Caltech. We thank G. Fuis and D. Hill for reviews and J. Hole for valuable discussions about the tectonics and velocity structure. J. Stock’s participation was supported by NSF Grant OCE-0742253. The University of California at Santa Barbara operates the Wildlife Liquefaction Array facility, with funding through the George E. Brown, Jr., Network for Earthquake Engineering Simulation program of the NSF under Award CMMI-0927178. Most figures were done using GMT (Wessel and Smith, 1998).
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
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Southern California Earthquake Center (SCEC)UNSPECIFIED
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Southern California Earthquake Center (SCEC)1678
Caltech Division of Geological and Planetary Sciences10083
Issue or Number:2
Record Number:CaltechAUTHORS:20130412-114502163
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Official Citation:Egill Hauksson, Joann Stock, Roger Bilham, Maren Boese, Xiaowei Chen, Eric J. Fielding, John Galetzka, Kenneth W. Hudnut, Kate Hutton, Lucile M. Jones, Hiroo Kanamori, Peter M. Shearer, Jamie Steidl, Jerry Treiman, Shengji Wei, and Wenzheng Yang Report on the August 2012 Brawley Earthquake Swarm in Imperial Valley, Southern California Seismological Research Letters, March/April 2013, v. 84, p. 177-189, doi:10.1785/0220120169
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37915
Deposited By: Ruth Sustaita
Deposited On:12 Apr 2013 21:37
Last Modified:09 Nov 2021 23:32

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