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Published August 2014 | public
Journal Article

Assembly of a large earthquake from a complex fault system: Surface rupture kinematics of the 4 April 2010 El Mayor–Cucapah (Mexico) M_w 7.2 earthquake


The 4 April 2010 moment magnitude (M_w) 7.2 El Mayor–Cucapah earthquake revealed the existence of a previously unidentified fault system in Mexico that extends ∼120 km from the northern tip of the Gulf of California to the U.S.–Mexico border. The system strikes northwest and is composed of at least seven major faults linked by numerous smaller faults, making this one of the most complex surface ruptures ever documented along the Pacific–North America plate boundary. Rupture propagated bilaterally through three distinct kinematic and geomorphic domains. Southeast of the epicenter, a broad region of distributed fracturing, liquefaction, and discontinuous fault rupture was controlled by a buried, southwest-dipping, dextral-normal fault system that extends ∼53 km across the southern Colorado River delta. Northwest of the epicenter, the sense of vertical slip reverses as rupture propagated through multiple strands of an imbricate stack of east-dipping dextral-normal faults that extend ∼55 km through the Sierra Cucapah. However, some coseismic slip (10–30 cm) was partitioned onto the west-dipping Laguna Salada fault, which extends parallel to the main rupture and defines the western margin of the Sierra Cucapah. In the northernmost domain, rupture terminates on a series of several north-northeast–striking cross-faults with minor offset (<8 cm) that cut uplifted and folded sediments of the northern Colorado River delta in the Yuha Desert. In the Sierra Cucapah, primary rupture occurred on four major faults separated by one fault branch and two accommodation zones. The accommodation zones are distributed in a left-stepping en echelon geometry, such that rupture passed systematically to structurally lower faults. The structurally lowest fault that ruptured in this event is inclined as shallowly as ∼20°. Net surface offsets in the Sierra Cucapah average ∼200 cm, with some reaching 300–400 cm, and rupture kinematics vary greatly along strike. Nonetheless, instantaneous extension directions are consistently oriented ∼085° and the dominant slip direction is ∼310°, which is slightly (∼10°) more westerly than the expected azimuth of relative plate motion, but considerably more oblique to other nearby historical ruptures such as the 1992 Landers earthquake. Complex multifault ruptures are common in the central portion of the Pacific North American plate margin, which is affected by restraining bend tectonics, gravitational potential energy gradients, and the inherently three-dimensional strain of the transtensional and transpressional shear regimes that operate in this region.

Additional Information

© 2014 Geological Society of America. Received 25 March 2013. Revision received 18 March 2014. Accepted 25 April 2014. Published online 24 June 2014. This work was fi nanced by CONACYT (Consejo Nacional de Ciencia y Tecnología) grant 81463, SCEC (Southern California Earthquake Center) grant 1697, and National Science Foundation grant EAR-0529922; the GEER (Geotechnical Extreme Events Reconnaissance) Foundation provided funding for initial field work. S. Leprince was supported in part by the Keck Institute for Space Studies and by the Gordon and Betty Moore Foundation. Part of this study was sponsored by the National Aeronautics and Space Administration (NASA) Earth Surface and Interior focus area and performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Enlightening discussions with Paul Wetmore and Francisco Suarez helped refine ideas about tectonics of the Big Bend domain and the kinematics of faulting in the Colorado River delta, respectively. We thank John Galetzka, Kate Scharer, David Bowman, Roman Manjarrez, and Maria Oturno for help with field work. We also thank Jose Mojarro, Sergio Arregui, and Luis Gradilla for technical support.

Additional details

August 20, 2023
October 17, 2023