InSAR-based coseismic deformation, fault slip distribution, and Coulomb stress propagation of the 2023 Herat earthquake sequence

From 7 to 15 October 2023, four M (sub w) 6.3 earthquakes occurred in northwestern Afghanistan. These earthquakes occurred on the northeastern edge of the Arabia-Eurasia collision zone, within the fault transition zone formed by the Doruneh and Herat fault systems; this area is primarily influenced by compressional stress from northeastern Iran. We used Interferometric Synthetic Aperture Radar to obtain the coseismic deformation of the earthquake sequence. Coseismic surface deformation in both ascending and descending tracks moved toward the satellite, consistent with the characteristics of a thrust fault rupture. Based on the coseismic deformation field and elastic half-space model, we inverted the fault-slip distribution of the earthquake sequence. The results indicate that the earthquakes occurred on a north-dipping, low-angle (27 degrees ) reverse fault. The rupture length of the earthquake sequence was approximately 55 km, with the rupture not reaching the surface. Rupture primarily occurred at depths of 5-15 km along the fault plane, with a maximum slip of approximately 2 m; the slip direction primarily reflected the fault's thrust motion. Using the fault kinematics model, we calculated the Coulomb stress changes on the fault plane for this earthquake sequence. The first two earthquakes caused stress loading on the fault planes of the subsequent two earthquakes, with stress reaching approximately 3 bar, indicating that the first two earthquakes had a stress-triggering effect on the latter two earthquakes. The deformation results show that the eastern segment of the fault bends toward the northeast owing to obstruction by mountains to the east.