Midcrustal thrusting and vertical deformation partitioning constraint by 2017 m w 7.3 Sarpol Zahab earthquake in Zagros Mountain Belt, Iran

Abstract

We investigate the geodetic data set of Interferometric Synthetic Aperture Radar (InSAR) including Advanced Land Observation Satellite (ALOS)-2 and Sentinel-1A/1B satellites for inferring the fault model of the 2017 Mw 7.3 Sarpol Zahab, Iran, earthquake. The InSAR deformation fields show that the seismogenic fault does not reach the ground surface, but some shallow folds have been triggered by the mainshock. Our preferred faulting model suggests that the coseismic rupture occurs on a single planar fault surface with a strike angle of 337.5°. Two significant slip sources are determined by the geodetic data: one is located within the 11.8-to 13.5-km depth range with a peak slip of 4.9 m, and the other occurs at the shallower depth (10.5-12.5 km) with a peak slip of 4.5 m. Both of them are responsible for the primary deformation signals in the geodetic imagery. The significant fault slip concentrates at the 10- to 14-km depth within the Pan-African basement. However, most of the aftershocks have depths between 3 and 12 km in the shallow sedimentary section. We hypothesize that the Hormuz Salt section with a depth of 12-13 km detaches the high-slip zones from the aftershock cluster, by which the fault slip is not transferred through the intervening salt section to the surface. The predicted static Coulomb stress change by our preferred faulting model at a depth of 10 km could encourage the occurrence of aftershocks. Moreover, the triggered fault-related folding in the southwest of the seismic zone has a positive Coulomb stress change and aseismic slip caused by the mainshock. Electronic Supplement: Figures showing the geological and geo-dynamic map of the Zagros orogeny in the northwest Iran, the inferred curved faulting model of the 2017 Sarpol Zahab earthquake, and Interferometric Synthetic Aperture Radar (InSAR) interferograms. © Seismological Society of America. All rights reserved.