Early postseismic deformation following the 2010 El Mayor-Cucapah earthquake from ALOS PALSAR and campaign GPS data

The 4 April 2010 M7.2 El Mayor-Cucapah earthquake ruptured approximately 110 km of the plate boundary zone in northern Baja California and southern California, including a previously unmapped section through the Colorado River delta. The event was unusual in that it had a longer rupture length than other recent events of the same magnitude, perhaps a manifestation of crustal thinning in the region, in the transition between transform motion on the San Andreas-Imperial fault system to the northwest and seafloor spreading in the Gulf of California to the southeast. Here we examine the ongoing postseismic deformation that has occurred in the aftermath of the event, using a combination of InSAR and GPS time series. In order to identify the spatial pattern of postseismic deformation, we process the full archive of ALOS PALSAR data held by the Alaska Satellite Facility's USGRC datapool, spanning a nine month interval from April 2010 to January 2011. We supplement these data with campaign GPS measurements made on a series of post-earthquake campaigns in Baja California by researchers from UCR, Scripps Institiute of Oceanography and CICESE, starting one day after the event. Preliminary indications suggest that the first year of postseismic deformation was marked by i) a narrow zone of ~10 cm of subsidence bounded to the north by the Colorado delta segment of the main fault rupture; ii) a secondary area of initial subsidence located a few kilometers to the northeast of the main subsiding zone that is recovered within ~6 months of the earthquake; iii) near-field right-lateral shear of ~5 cm across the Sierra Cucapah. The first two of these deformation signals are consistent with a combination of transient poroelastic deformation and the third with shallow afterslip. Preliminary models of predicted Maxwell viscoelastic relaxation do not appear to explain this early, rapid deformation.