Co-seismic And Post-seismic Deformation And Simulation Of The 2017 Mw 7.3,Iran Earthquake Inferred From InSAR Technology

The November 12,2017 Mw7.3 Darbandikhan earthquake in the northern Zagros Mountains of Iran-Iraq was the largest instrumentally recorded earthquake to date in this mountain belt.Moreover,the earthquake was the largest event recorded by instruments in the region and the focal mechanism solution was quite different from the previous earthquakes Therefore,geodesic means of co-seismic,post-seismic surface deformation observation and post-seismic mechanism simulation of the earthquake will not only help us to better understand the seismic fault of the earthquake but also help us to understand the seismogenic mechanism and seismogenic structure of the region.Here,based on InSAR and time series InSAR technique,we take the 2017 Iran Mw7.3 earthquake as the research object,and carrie out the co-seismic surface displacements observation,observations of surface deformation within one and a half years after the earthquake and simulation of postearthquake mechanisms..The main research contents and conclusion of this paper are as follows:(1)Based on D-InSAR technology,we derived the co-seismic interferograms from the Sentinel-1A/B data for different orbits and successfully described the surface deformation of the main seismic zone.The slant range shortening and lengthening signals of the ascending and descending tracks are completely different,indicating that the surface deformation of the Darbandilkhan earthquake is dominated by a vertical component.(2)Using the along-and across-track deformation fields of different orbits,we retrieved the three-dimensional deformation field,which suggests that the Darbandikhan earthquake may be a blind thrust fault close to the north–south direction and the seismic fault is located to the left of the deformation center.(3)Based on the InSAR co-seismic deformation field data and elastic disloaction model,we inverted the geometrical parameters of the seismogenic fault and the slip distribution of the fault plane.The results show that the source fault has an N-S strike and a northeast low dip angle.In addition,the Darbandikhan earthquake has an average rake of 135.5°,with the maximum slip of 1.8 m at 14.5 km depth.On the basis of the derived depth and the aftershock information provided by the Iranian Seismological Center,we inferred that this event primarily ruptured within the crystalline basement and the seismogenic fault is the Zagros Mountain Front Fault(MFF).(4)We used InSAR time series analysis to explore the 1.5 year of postseismic transient deformation.We inverted the interferogram network for the evolution of phase employing the Small Baseline method to obtain the SAR LOS average deformation rate field and the time series of cumulative post-seismic LOS observations.The shape of the displacement pattern shows an N-S alignment.The time series of ascending and descending track show displacement toward the different direction in LOS,which implies significant vertical movements,supplemented by horizontal movement.(5)We first investigate models of poroelastic rebound,afterslip,and viscoelastic relaxation individually and then attempt to resolve the trade-offs between their contributions by evaluating the misfit between observed and simulated displacements.The modeling results of the poroelastic rebound and viscoelastic relaxation show that these mechanisms can't satisfactorily explains near-and far-field postseismic deformation following the Darbandikhan earthquake.The kinematic inversions and stress-driven inversion of post-earthquake after-slip models can fit the observed InSAR post-earthquake deformation data well,which indicates that the deformation of the epicentral area within a year and a half after the earthquake is mainly due to the post-earthquake afterslip.(6)About one and a half years after the earthquake,the accumulated residual slip obtained by the simulation reached 0.9m,and the post-earthquake residual slip was mainly distributed in the area with strength-rate along the upward tendency direction of the fault co-seismic rupture,while no significant post-earthquake residual slip occurred in the area with enhanced fault velocity along the downward tendency direction.At the same time,the friction strength at the residual slip fault layer is low,which is speculated to be corresponding to the formation of the sliding layer in Zagros region by the Hormuz shale with weak mechanical properties.(7)We discussed the relationship between co-seismic and post-earthquake slip.Our inversions highlight a seismotectonic structure wherein both the crystalline basement and lower Phanerozoic cover of the Lurestan Arc and Kirkuk Embayment shorten seismically via slip on low and high-angle reverse faults,respectively,and that these two zones are decoupled by a low friction decollment that slips aseismically in response to co-seismic stress changes.