New fault slip distribution for the 2010 Mw 7.2 El Mayor Cucapah earthquake based on realistic 3D finite element inversions of coseismic displacements using space geodetic data

In this work we investigate the 4 April, 2010, Mw 7.2 El Mayor-Cucapah (EMC) earthquake. Existing studies modeled the EMC area as an elastic half-space in a homogeneous or vertically layered structure, which, along with differences in data and inversion methodologies, led to considerable variability in the resultant fault slip models. To investigate the EMC earthquake more realistically, we first examine how published coseismic fault slip models have approached the problem and what are their findings, then we select the optimal geometry and slip of one most recent and comprehensive coseismic fault slip model, obtained through analytical inversions, and adapt them in a three-dimensional finite element numerical environment where we assess the effects of topography and material heterogeneities. Numerically optimized slip models are obtained via joint inversion of GPS, interferometric synthetic aperture radar and subpixel offset datasets. We find the effect of topography to be negligible while the inclusion of material heterogeneities enhances the slip at depth, as might be expected where the medium has higher rigidity, and better fits the displacements at both near and far field, especially around the Salton Sea area. The match with geodetic data is significantly improved when the fault slip is increased at the fault planes close to the epicenter and deeper at the southernmost plane, with respect to the slip of the chosen analytical model. Our findings suggest that this earthquake was associated with a higher and more spatially concentrated slip than previously thought implying a greater stress drop at depth.

The research was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, and administered by Universities Space Research Association under contract with NASA, in collaboration with the Agenzia Spaziale Italiana (ASI).