Early post-seismic deformation of the 2017 Mw 7.3 Darbandikhan, Iran/Iraq Earthquake on a flat-ramp-flat fault

Postseismic deformation is one of the few geophysical phenomena that can be used to obtain the rheological properties of the lithosphere and provide key information for understanding stress variations that are induced by the mainshock or aftershock. On November 12, 2017, the Mw 7.3 Darbandikhan earthquake struck the border between Iran and Iraq, causing heavy casualties and property losses. Here, we first use the multidimensional small baseline subset technique to obtain the 2D postseismic deformation field from Interferometric Synthetic Aperture Radar data within ∼228 days after the event. The 2D postseismic deformation field shows that the main deformation region exhibits westwards horizontal movement with a maximum displacement of 7.5 cm, while the maximum uplift and subsidence reach 8.2 cm and 4.7 cm in the southwestern and northeastern areas of the main deformation region, respectively. Then, we choose preferred faults of co- and post-seismic slip distributions by considering the distribution of co- and post-seismic slip, aftershock precision location results, data misfits, and the Coulomb failure stress change from previous studies and use a joint model to simultaneously estimate the afterslip distribution and viscosity of the lower crust in the Zagros Mountains. As a result, the joint inversion performed on the flat-ramp-flat fault (preferred fault) suggests that the lower bound of the preferred viscosity of the lower crust beneath the Zagros Mountains is 3 × 1018 Pa s, the afterslip is distributed both up- and down-dip of the coseismic slip region, and the maximum slip of 0.61 m is located up-dip of the coseismic rupture. The cumulative seismic moment caused by the afterslip is 2.97 × 1019 N m, which is equivalent to a Mw 6.94 earthquake. Moreover, the stability and reliability of faults and the joint model are verified through Monte Carlo inversions. •we use the multi-dimensional small baseline subset technique to obtain the 2 D post-seismic deformation field from InSAR data within ∼228 days after the event.•the listric fault and flat-ramp-flat fault are regard as the preferred faults of co- and post-seismic slip distributions.•we use a joint model to simultaneously estimate the afterslip distribution and the viscosity of the lower crust in the Zagros Mountains.