SCEC Award Number 12129 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Postseismic relaxfation following the 2010 Mw7.2
Investigator(s)
Name Organization
Jean-Philippe Avouac California Institute of Technology
Other Participants Sylvain Barbot
Chris Rollins
SCEC Priorities 1e, 1b, 1d SCEC Groups SDOT, Geodesy, Seismology
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 The Salton Trough in northern Mexico may be an ideal site in which to use postseismic deformation to study the nature of sublithospheric ductile flow. Here the extensional component of relative Pacific-North American plate motion has thinned the lithosphere and brought the asthenosphere up to within ~40 km of the surface [Lekic et al 2011], while the transform component of relative motion produces large strike-slip earthquakes above this shallow asthenosphere. The most recent such earthquake, the 2010 El Mayor-Cucapah shock, was the largest in this region since at least 1892 and occurred directly above shallow asthenosphere. We use continuous GPS data to constrain the transient surface deformation following the earthquake, then use a combination of kinematic inversion and forward modeling to infer which deformation mechanisms could have contributed to the transient. Preliminary findings suggest that asthenospheric flow did play some role in
postseismic deformation but may have occurred in concert with other mechanisms.
Intellectual Merit Our findings will shed light on the
rheology of the lithosphere and asthenosphere, with implications for the mechanics of fault loading and the evolution of seismic hazard over time. We will also be able to study the way that the states of stress along the Elsinore, San Jacinto and San Andreas faults may have
evolved in the time since the El Mayor-Cucapah earthquake, with important implications for seismic hazard in southern California and operational earthquake forecasting.
Broader Impacts We have presented preliminary findings
from this project at the 2012 SCEC Annual Meeting and the 2012 AGU Fall Meeting and plan to present
updated research at the 2013 SSA Annual Meeting. In addition, we plan to submit a paper detailing our
findings to the Journal of Geophysical Research in May 2013. There was widespread concern in 2010 that the El Mayor-Cucapah earthquake may have brought the Elsinore, San Jacinto and San Andreas faults closer to failure; we will be able to provide constraints on whether any appreciable stress transfer to those faults has occurred since the mainshock.
Exemplary Figure Figure 3. Modeled viscoelastic relaxation in the asthenosphere. a) Distribution of depths to the lithosphere-asthenosphere boundary inferred by Lekic et al [2011] and geometric model of shallow asthenosphere in the Salton Trough. Depths in purple are the top depths of the modeled asthenosphere. b) Simulated distribution of extensional vertical strain (red indicates extension, blue indicates compression) imparted by the Fialko et al [2010] slip model to an elastic halfspace at 50 km depth, near the top of the modeled viscoelastic asthenosphere in the Salton Trough. c) Cross section of displacements at depth in the section of the elastic halfspace corresponding to the Imperial Valley. The purple domain is the modeled asthenosphere in the plane of the cross section, extending up to within 42.5 km of the surface within most of the Imperial Valley. d) Comparison between data and synthetic cumulative one-year displacements produced by modeled viscoelastic relaxation in the asthenosphere. Black vectors and colored circles are extracted GPS displacements from figure 2a; green vectors are synthetic displacements at GPS stations; colored surface represents synthetic surface uplift and subsidence. Figure produced by Chris Rollins.
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