Coseismic slip model for 2020 Ghotor earthquake based on InSAR DATA

The Ghotor doublet earthquake happened on 23 Feb 2020 near Khoy and Salmas cities in west Azerbaijan province of Iran near Iran-Turkey border .The first large event with a magnitude of 5.8 Mww (USGS) happened at 5:52 UTC (9:23 AM local time) and followed by a second large event of magnitude 6.0 Mw (USGS) at 16:00 UTC. The second event inflicted most of the building damages. No surface rupture has been reported for the events. We estimated the areal extent of the surface displacement related to the 2020 Ghotor doublet earthquakes using three sets of C-band imagery from the European Space Agency Sentinel 1A and 1B satellites. Due to small ground displacement, we could not model the fault geometry of the first mainshock. The ascending and descending displacement maps of the second main shock are used to jointly invert the causative fault plane parameters. To obtain the source parameters, we first down-sampled the unwrapped LOS surface displacements by a quadtree algorithm and then inverted the unwrapped interferograms to infer the geometry of a single rectangular plane with uniform slip in a uniform elastic half-space. The fault geometry parameters are location (X, Y, and Depth), size (length and width), orientation (strike, dip, and rake), and uniform slip of the rupture plane. We assume the X, Y, and depth to correspond to the center of the top edge of the rupture plane. We used a nonlinear inversion method as implemented in the open-source software called Geodetic Bayesian Inversion Software (GBIS) released by Centre for Observation and Modeling of Earthquakes, Volcanoes, and Tectonics (COMET). We used Okada‘s (1985) displacement green functions to model the displacement field. The calculated optimal model illustrates a northeast-striking (N24°) left-lateral rupture plane dipping ~86° towards the west. Once the geometry of the fault plane with uniform slip was estimated, we expanded the rupture plane 20 km along-strike and 12 km along down-dip directions and divided it into 1291 individual patches to obtain the distributed slip on the rupture plane. Each patch has a fixed geometry according to optimal source parameters obtained from the nonlinear modeling, and the slip was allowed to vary freely on the fault plane. We used a modified version of the open-source software called FaultResampler 1.4 to apply the linear inversion for calculating slip distribution on the rupture plane. The coseismic rupture concentrates around a center depth of 3 km with a maximum slip of 97±8  cm. Assuming a rigidity modulus of 30 GPa, the geodetic moment is estimated to be 1.517E+18 Nm, equivalent to a moment magnitude of 6.05 Mw.