Nonoverlapped Sources of the Devastating 2023 Mw>6 Herat, Afghanistan, Earthquake Swarm Estimated by InSAR

Abstract The occurrence of the devastating 2023 Herat earthquake sequence shattered a 1200 yr period of seismic quiescence in western Afghanistan. In this study, we utilize Interferometric Synthetic Aperture Radar (InSAR) data to derive the surface displacements associated with this swarm, demonstrating a maximum coseismic displacement of 82 cm in the InSAR line of sight direction. The rupture models estimated from InSAR-mapped coseismic deformation suggest that the major slips in the seismic swarm are dominated by thrust faulting concentrated at a shallow depth of 4–6 km, characterized by low dip angles and corresponding to a sliding structure in a shallow layer. These unmapped blind ruptures manifest as isolated asperities, generally corresponding to the five major events. Given the spatial distribution of these slips, these five major events should be sequential occurrences due to a strong interaction, and a high-potential seismic risk should be still in the Herat fault system. Using the time-series satellite gravity change in the recent two decades, we find that prolonged drought in this arid region has resulted in a cumulative water storage loss of ∼200 mm, which can produce a Coulomb stress change of ∼1.4 kPa on the Herat fault and impact a positive stress effect to promote the occurrence of this seismic swarm.