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The 2012 Brawley swarm triggered by injection-induced aseismic slip

Wei, Shengji and Avouac, Jean-Philippe and Hudnut, Kenneth W. and Donnellan, Andrea and Parker, Jay W. and Graves, Robert W. and Helmberger, Don and Fielding, Eric and Liu, Zhen and Cappa, Frederic and Eneva, Mariana (2015) The 2012 Brawley swarm triggered by injection-induced aseismic slip. Earth and Planetary Science Letters, 422 . pp. 115-125. ISSN 0012-821X. doi:10.1016/j.epsl.2015.03.054.

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It has long been known that fluid injection or withdrawal can induce earthquakes, but the underlying mechanisms remain elusive. For example, the 2012 Brawley swarm, which produced two strike-slip shocks with magnitudes larger than 5.3 and surface ruptures in the close vicinity of a geothermal field, started with earthquakes about 5 km deeper than the injection depth (∼1.5 km). This makes the causality between the injection and seismicity unclear. Here, we jointly analyze broadband and strong motion waveforms, UAVSAR, leveling measurements and field observations to reveal the detailed seismic and aseismic faulting behaviors associated with the 2012 Brawley swarm. In particular, path calibration established from smaller events in the swarm allows waveform inversion to be conducted up to 3 Hz to resolve finite rupture process of the Mw 4.7 normal event. Our results show that the 2012 earthquake sequence was preceded by aseismic slip on a shallow normal fault beneath the geothermal field. Aseismic slip initiated in 2010 when injection rate rapidly increased and triggered the following earthquakes subsequently, including unusually shallow and relatively high frequency seismic excitations on the normal fault. In this example, seismicity is induced indirectly by fluid injection, a result of mediation by aseismic creep, rather than directly by a pore pressure increase at the location of the earthquakes.

Item Type:Article
Related URLs:
URLURL TypeDescription
Avouac, Jean-Philippe0000-0002-3060-8442
Hudnut, Kenneth W.0000-0002-3168-4797
Fielding, Eric0000-0002-6648-8067
Liu, Zhen0000-0002-6313-823X
Cappa, Frederic0000-0003-4859-8024
Additional Information:© 2015 Elsevier B.V. Received 21 November 2014; Received in revised form 26 March 2015; Accepted 31 March 2015. The seismic data were downloaded from Southern California Seismic Data Center and strong motion data center ( We thank the Omar Company for providing the leveling data used in this study. We are grateful to Elizabeth Cochran and two anonymous reviewers for their insightful and constructive comments. Suzanne Donovan helped editing the manuscript. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Part of this research was supported by NASA’s Earth Surface and Interior and Geodetic Imaging programs (grant number 102443-281945. We thank the UAVSAR team and in particular Scott Hensley, Yunling Lou, Brian Hawkins, Naiara Pinto, and Yang Zheng for collection and processing of the UAVSAR data.
Group:Seismological Laboratory
Funding AgencyGrant Number
Subject Keywords:fluid injection; aseismic slip; high frequency waveform modeling; UAVSAR and InSAR; geothermal; finite fault model
Record Number:CaltechAUTHORS:20150429-104726958
Persistent URL:
Official Citation:Shengji Wei, Jean-Philippe Avouac, Kenneth W. Hudnut, Andrea Donnellan, Jay W. Parker, Robert W. Graves, Don Helmberger, Eric Fielding, Zhen Liu, Frederic Cappa, Mariana Eneva, The 2012 Brawley swarm triggered by injection-induced aseismic slip, Earth and Planetary Science Letters, Volume 422, 15 July 2015, Pages 115-125, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57087
Deposited By: Tony Diaz
Deposited On:29 Apr 2015 20:12
Last Modified:10 Nov 2021 21:07

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