Depth-Segmented Rupture of a Back-Thrust Fault During the 2022 Hormozgan (Iran) Earthquake Sequence

Between 1 July and 30 November 2022, four spatially adjacent shallow MW ≥ 5.7 earthquakes successively struck the Hormozgan province in southern Iran. This earthquake sequence offers a vital opportunity to clarify the subsurface seismogenic structure and rupture evolution in the eastern segment of the Zagros Fold-and-Thrust Belt (ZFTB). In the paper, we apply multi-temporal archived SAR images from the Sentinel-1 satellite to extract the high-precision coseismic surface deformation covering the July and November earthquake events, respectively, and further investigate the related seismogenic fault structure and slip distribution. Geodetic inversion results reveal that the cumulative coseismic slip of the three MW ≥ 5.7 earthquakes in July is distributed at a downdip depth of 5.5 to 8 km on a SW-dipping thrust seismogenic fault plane, while the coseismic slip of the November MW 5.7 earthquake is concentrated in the shallow downdip range of 1.5 to 6 km on the same fault, finely characterizing a partially overlapping depth-segmented rupture. According to a joint analysis of the regional topography and geomorphology, active fault distribution, and coseismic inversions, we conclude that this earthquake sequence nucleated on a secondary blind back-thrust fault of the Zagros Frontal Fault (ZFF). Coseismic Coulomb stress changes reveal that the July earthquake sequence triggered the occurrence of the November earthquake and that the shallow eastern segment of the Mountain Frontal Fault (MFF) and the eastern segment of the ZFF exhibit significant stress loading, indicating a high risk of future rupture.