Superficial simplicity of the 2010 El Mayor-Cucapah earthquake of Baja California in Mexico

Nature Geoscience (Impact Factor: 11.67). 07/2011; 4:615-618. DOI: 10.1038/ngeo1213

ABSTRACT The geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation, propagation and arrest of seismic ruptures(1-6). The fault system that runs from southern California into Mexico is a simple strike-slip boundary: the west side of California and Mexico moves northwards with respect to the east. However, the M(w) 7.2 2010 El Mayor-Cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike-slip fault(7). Here we use geodetic, remote-sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake. We find that the earthquake produced a straight 120-km-long fault trace that cut through the Cucapah mountain range and across the Colorado River delta. However, at depth, the fault is made up of two different segments connected by a small extensional fault. Both segments strike N130 degrees E, but dip in opposite directions. The earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike-slip motion. We show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves. We conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone.

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Available from: Eric J Fielding, Jul 28, 2015
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    • "The northern Baja California peninsula has active normal and strike-slip faults originating from the transtensional limit between the Pacific and North America plates (Stock et al., 1991). In this limit, separation of the Baja California peninsula from the continental North America plate occurs and continues to the northwest through the right-lateral movement (Fig. 1 inset ) of the San Andreas fault system (Axen and Fletcher, 1998; Suárez-Vidal et al., 2007; Plattner et al., 2007; Suárez-Vidal et al., 2008; Armstrong, 2010; Wei et al., 2011; Oskin et al., 2012). Within our study area (Fig. 1), south of Mexicali Valley, the Cucapah and El Mayor mountain ranges are located northwest of the Gulf Extensional Province (Suárez-Vidal, et al. 2008). "
    Seismological Research Letters 01/2015; 86(1). DOI:10.1785/0220140007 · 2.27 Impact Factor
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    • "But for earthquakes in the Imperial Valley, the depths appear different because of the deep sediment basin. The southern San Andreas fault system has a long history of significant earthquakes including the recent 2010 M w 7.2 El Mayor–Cucapah event (Wei et al., 2011). The most recent burst of earthquakes occurred on 26 August 2012 with the largest one having M w 5.4. "
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    • "e synthetics are computed using the three velocity models in Figure 2a . Both data and synthetics are filtered to 0 . 02 ~ 3 . 0 Hz . The peak amplitudes of data ( first ) and synthetic ( second ) are shown . data prove particularly useful in defining the slip distribution for large complex ruptures such as the M w 7 . 2 El Mayor - Cucapah event [ Wei et al . , 2011 ] . Unfortunately , use of the static GPS data alone for the present analysis is problematic due to the accumulated deformation of the swarm activity , and the relatively small magnitudes of the swarm events . How - ever , combining the geodetic and seismic data in the analysis provides a powerful tool for examining the relative contrib"
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