Surface rupture from an aftershock: Remote observations from the January 2024 Wushi (Aykol), China, earthquakes

On 22 January 2024, a moment magnitude (M_w⁠⁠) 7.0 earthquake occurred in the southern Tian Shan region of western China, followed by an M_w 5.7 aftershock on 29 January. The M_w 7.0 mainshock occurred on a northwest‐dipping fault plane, at a hypocentral depth of 13 km. Both Interferometric Synthetic Aperture Radar (InSAR) and optical satellite imagery observations indicate a lack of surface rupture for the M_w 7.0 earthquake. However, mapping and subpixel correlation of high‐resolution optical satellite imagery and InSAR observations spanning the 29 January M_w 5.7 thrust‐faulting aftershock support the interpretation of fault surface rupture. We observed ∼4.8 km of discontinuous surface rupture associated with the M_w 5.7 aftershock. The surface rupture trace trends subparallel to the northeast–southwest bedding orientation within the limb of a syncline. Subpixel image correlation and digital elevation model (DEM) differencing indicate mean on‐fault offsets of 1 m, with a peak of ∼1.4 m, along the fault. Given these observations, we interpret the M_w 5.7 aftershock produced surface rupture on an unmapped flexural‐slip fault within a syncline in the hanging wall of the Maidan fault or on a back thrust associated with the Maidan fault. Pre‐existing fault features along the surface rupture trace in the landscape from pre‐earthquake DEMs indicate that the fault that ruptured in the M_w 5.7 aftershock may have ruptured in the past. Surface rupture only from an aftershock in a seismic sequence is a critical observation that highlights the need to understand secondary or distributed faulting in larger earthquakes for seismic and fault displacement hazard analysis.