Co- and post-seismic slip analysis of the 2017 MW7.3 Sarpol Zahab earthquake using Sentinel-1 data

The MW7.3 Sarpol Zahab earthquake that occurred in the Zagros Fold-Thrust Belt (ZFTB) of Iran on November 12, 2017 is the largest earthquake instrumentally recorded in the region. This earthquake provides an opportunity to investigate the slip behaviour and frictional properties of the fault, which is significant for assessing future seismic potential. In this study, we use Sentinel-1 images to map the co- and post-seismic deformation to invert for the fault slip. The result indicates that most of the coseismic slip is buried in the depth range of 11–17 km, and the maximum slip is about 3.8 m at a depth of 15 km. The coseismic slip induces an increase of Coulomb stress in the unruptured area of the seismogenic fault plane, driving the afterslip. Based on the stress-driven afterslip, we obtain a frictional parameter of (a − b) = (0.001 − 0.002) for the updip afterslip zone and (a − b) = 0.0002 for the downdip afterslip zone in the framework of rate-and-state friction. The constitutive parameter (a − b) of the fault is very small, suggesting that the fault segments are close to velocity-neutral and may experience coseismic rupture.