Source modeling of the 2023 Herat earthquake sequence determined from InSAR observations

During 7th-15th October 2023, an earthquake sequence with four M W 6.2–6.3 occurred in the Herat region, Afghanistan, causing damage to buildings, fire, and loss of life. The co-seismic deformation induced by the earthquake sequence helps us invert the rupture model of these earthquakes to constrain the geometric characteristics of the Herat fault system, and estimate the future seismic risk at this fault system. In this work, we utilized the line-of-sight (LOS) displacements from Interferometric Synthetic Aperture Radar (InSAR) observations to determine the optimal fault geometry and slip distribution of the 2023 Afghanistan earthquake sequence through a two-step inversion method. Our results indicated that these four M W 6.2–6.3 earthquakes ruptured the western and northwestern segments of the Herat fault system, which are dominated by thrust motions. We identified two fault models from InSAR LOS displacement data, with two different strikes, and the same dip angle range of about 35–45 ° . The source model with the strike of 280.5 ° has a peak slip of about 2.2 m, a central rupture zone with about 25 km along-strike length, and a depth range of 5–10 km, corresponding to a M W 6.67 earthquake. The following source model with the strike direction of about 240 ° has smaller rupture length and width, and a peak slip of about 2.5 m, corresponding to a M W 6.65 earthquake. We also calculated the Coulomb Failure Stress of the Herat fault system around this rupture area caused by this earthquake sequence. Our results indicated that the stress loading at the western segment of the Herat Fault system is greater than the triggering threshold, suggesting that the future seismic risk in this area is at a relatively high stage. In summary, the rupture model of these earthquakes indicates that two unidentified thrust faults between the western and northwestern segments of the Herat fault system are in a compression-stress environment.