El Mayor-Cucapah (Mw 7.2) earthquake: Early near-field postseismic deformation from InSAR and GPS observations

Alejandro A. Gonzalez-Ortega, Yuri Fialko, David T. Sandwell, Jose Javier Gonzàlez-Garcìa, F. Alejandro Nava-Pichardo, John M. Fletcher, Jose Javier Gonzàlez-Garcìa, Brad P. Lipovsky, Michael Floyd, & Gareth J. Funning

Published February 24, 2014, SCEC Contribution #6241

El Mayor-Cucapah earthquake occurred on 4 April 2010 in northeastern Baja California just south of the U.S.-Mexico border. The earthquake ruptured several previously mapped faults, as well as
some unidentified ones, including the Pescadores, Borrego, Paso Inferior and Paso Superior faults in the
Sierra Cucapah, and the Indiviso fault in the Mexicali Valley and Colorado River Delta.We conducted several
Global Positioning System (GPS) campaign surveys of preexisting and newly established benchmarks
within 30 km of the earthquake rupture. Most of the benchmarks were occupied within days after the
earthquake, allowing us to capture the very early postseismic transient motions. The GPS data show
postseismic displacements in the same direction as the coseismic displacements; time series indicate a
gradual decay in postseismic velocities with characteristic time scales of 66 ± 9 days and 20 ± 3 days,
assuming exponential and logarithmic decay, respectively. We also analyzed interferometric synthetic
aperture radar (InSAR) data from the Envisat and ALOS satellites. The main deformation features seen in
the line-of-sight displacement maps indicate subsidence concentrated in the southern and northern parts
of the main rupture, in particular at the Indiviso fault, at the Laguna Salada basin, and at the Paso Superior
fault. We show that the near-field GPS and InSAR observations over a time period of 5 months after the
earthquake can be explained by a combination of afterslip, fault zone contraction, and a possible
minor contribution of poroelastic rebound. Far-field data require an additional mechanism, most likely
viscoelastic relaxation in the ductile substrate.

Gonzalez-Ortega, A. A., Fialko, Y., Sandwell, D. T., Gonzàlez-Garcìa, J., Nava-Pichardo, F., Fletcher, J. M., Gonzàlez-Garcìa, J., Lipovsky, B. P., Floyd, M., & Funning, G. J. (2014). El Mayor-Cucapah (Mw 7.2) earthquake: Early near-field postseismic deformation from InSAR and GPS observations. Journal of Geophysical Research: Solid Earth, 119(2), 1482-1497. doi: 10.1002/2013JB010193.