Coseismic Rupture and Early Afterslip of the 2023 Herat (Afghanistan) Earthquake Sequence: Insights From Sentinel-1 Radar Observations

Abstract

Between 7 and 15 October 2023, a series of devastating earthquakes struck Herat in northwestern Afghanistan, a region in which few historical earthquakes have been recorded, causing severe human casualties. In this study, we investigate the co- and post-seismic deformation mechanisms of the 2023 Herat earthquake sequence using Sentinel-1 radar interferometry. The 4-month postseismic deformation time series exhibits a significant, gradually accumulating, localized deformation in the south of the coseismic displacements. Coseismic slip is first modeled using a simplified planar fault geometry with multiple segments, then enhanced using a curved geometry based on the fault trace inferred from Sentinel-2 images analysis. Postseismic afterslip is the dominant mechanism of postseismic deformation, and mainly occurs in the down-dip of the coseismic rupture zone and an activated secondary fault, with a maximum afterslip of ∼0.3 m at 120 days. Co- and post-seismic slip behaviors seem to indicate that coseismic rupture mainly occurs on the north fault plane with spatially varying frictional properties, and then activated an aseismic secondary fault in the south. Additionally, we infer that structural complexity in fault systems (such as the complex fault network in the basin north of Herat) may act as barriers to rupture propagation, and static stress changes from extremely early afterslip may further promote rupture of subsequent events, both of which together cause the cascading rupture of the Herat seismic sequence.