Co- and early post-seismic InSAR observations reveal complex rupture of the 2023 Herat earthquake sequence, NW Afghanistan

SUMMARY In October 2023, an earthquake sequence comprising four ~MW 6.0 events struck Herat Province in northwestern Afghanistan, causing severe casualties and property losses. The geometry of seismogenic faults and the mechanisms of the earthquake sequence are essential for regional seismic hazard assessment, but still remain poorly constrained. With Interferometric Synthetic Aperture Radar techniques, we extracted high-resolution co- and early post-seismic deformations of the events. Through a two-step inversion method, we inferred the geometry of the causative faults and the distributed slip models. The earthquake sequence ruptured two intersecting low-dip thrust faults, indicating that the complex geometry may have played a key role in controlling the propagation of the events. The ruptures of the four major events are clearly imaged at depths of 1–10 km without reaching the surface, showing a pattern of first spreading westwards, then jumping eastwards to the bend segment, and finally rupturing an adjacent fault. Post-seismic deformation further reveals reactivation of a secondary fault splay which underwent afterslip. Shallow afterslip up-dip of the coseismic rupture dominates post-seismic deformation during 10 months following the earthquake sequence. Relying on the evolution of afterslip, we infer that significant rate-strengthening property in the shallow bend section may have hindered further coseismic rupture propagation. Combining obtained results and the complex geological setting of the Herat region, we suggest that the earthquake sequence reflects N–S crustal shortening between two branches of the western Herat Fault System.