Wei, Shengji and Fielding, Eric and Leprince, Sebastien and Sladen, Anthony and Avouac, Jean-Philippe and Helmberger, Don and Hauksson, Egill and Chu, Risheng and Simons, Mark and Hudnut, Kenneth and Herring, Thomas and Briggs, Richard (2011) Superficial simplicity of the 2010 El Mayor–Cucapah earthquake of Baja California in Mexico. Nature Geoscience, 4 (9). pp. 615-618. ISSN 1752-0894 http://resolver.caltech.edu/CaltechAUTHORS:20111006-084146589
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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. 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° 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.
|Additional Information:||© 2011 Macmillan Publishers Limited. Received 8 August 2010; accepted 23 June 2011; published online 31 July 2011. This work was financially supported by NSF, USGS, the Gordon and Betty Moore Foundation, NASA and SCEC. Regional seismic data were provided by SCSN and RESNOM. The Incorporated Research Institutions for Seismology (IRIS) Data Management System (DMS) was used to access the Global Seismographic Network data. The GPS analyses were obtained from the Earthscope PBO data products system and UNAVCO. Optical data were provided by USGS. Envisat data are copyright 2009, 2010 ESA and were obtained from the WInSAR archive and the Group on Earth Observation Geohazards Supersite virtual archive. ALOS data are copyright METI, JAXA and were obtained from the Alaska Satellite Facility Level 1 Data Pool. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. We thank CICESE colleagues J. Gonzalez and J. Fletcher for their support and interest, and we thank J. Hollingsworth for his suggestions to improve the figures. This is Tectonics Observatory contribution #172. SCEC is funded by NSF Cooperative Agreement EAR-0529922 and USGS Cooperative Agreement 07HQAG0008. Author contributions: S.W. carried out the modelling and edited the paper; E.F. carried out the InSAR and SAR processing and edited the paper; S.L. carried out the optical image and SAR cross-correlation processing; A.S. helped with the modelling and downsampled the InSAR and SAR data; J-P.A. conceived and supervised the research and editing of the paper; D.H. supervised the research and edited the paper; E.H. carried out relocation of aftershocks and foreshocks; R.C. carried out modelling of teleseismic data; M.S. provided InSAR data; K.H. edited the paper and provided geological interpretation; T.H. carried out the processing of GPS data; R.B. contributed to the tectonic interpretation.|
|Group:||Caltech Tectonics Observatory|
|Subject Keywords:||Structural geology; tectonics and geodynamics; Seismology|
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|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||06 Oct 2011 16:04|
|Last Modified:||26 Dec 2012 14:14|
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