Co-seismic deformation and slip distribution of 5 April 2017 Mashhad, Iran earthquake using InSAR sentinel-1A image: implication to source characterization and future seismogenesis

Abstract

We analyzed interferometric synthetic aperture radar sentinel-1A-based observations to characterize the source of 5 April 2017 Mashhad, Iran mainshock (Mw 6.1), for the first time to understand the seismogenic potential of the source area using the estimates of co-seismic displacement and slip distribution on applying the steepest descent method (SDM). SAR pixel offsets (SPO) provided a deep insight into the co-seismic surface deformation of the entire source zone. Based on iterations of a total of 451 models, our analysis of sentinel-1A data from ascending and descending tracks revealed surface deformation occurred in an area of 40 × 30 km with a maximum co-seismic uplift of 10 cm. We estimated geodetic moment of 1.9 × 1020 Nm corresponding to the magnitude (Mw 6.0) of the Mashhad mainshock for which the rupture has a planner geometry with uniform slip dislocation in an elastic half-space with slip of 0.35 ± 0.1 m; strike of N313°E having dip of 48° of the thrust fault associated with oblique motion. The rupture length of 45 ± 3 km along-strike and 30 ± 3 km down dip has been estimated. The best-fit fault model geometry derived from SDM suggests that rupture occurred in the vicinity of the Kashafrud thrust fault, located west to the main Kopeh-Dagh Fault with its strike of 315°E. It is observed that a maximum slip of 0.35 m occurred at a depth of 8 km that extended to 10 km in the crust, which is found to be in unison to the Coulomb stress model that showed low-stressed zone is associated with the majority of events of lower magnitude (M ≤ 4.5) in NE–SW to the mainshock, whilst the EW zone to the mainshock found relatively highly stressed as a probable source for generating relatively higher magnitude earthquakes (M > 4.5) in the future. We infer that the estimates of co-seismic source attributes are essentially important for understanding the nature and extent of earthquake risks for Mashhad, Iran earthquake source area and of the areas of analogous geotectonic settings, elsewhere in the world.