Pre-, Co-, and Post-Seismic Temporal Deformation of the 2025 Mw5.8 Aheqi Earthquake and Its Blind Thrust Rupture Mechanism: Based on Pre- and Post-Seismic SBAS-InSAR Observations of the Aheqi Earthquake

On December 4, 2025, an M_W 5.8 earthquake struck in Aheqi County, Xinjiang. Its epicenter is located approximately 24 km southwest of the 2024 Wushi M_W 7.0 earthquake, and the seismic region lies in the hinterland of the Kalpintag fold-and-thrust belt on the western segment of the South Tianshan seismic zone. To clarify the seismogenic structure properties of this earthquake and its dynamic correlation with the strong Wushi M_W 7.0 earthquake, this paper constructs a time-series observation dataset covering 22 months before the earthquake to 5 months after the earthquake based on ascending and descending Sentinel-1A SAR images, and extracts the time-series deformation trend of Aheqi 22 months before the earthquake (after the Wushi earthquake) using the SBAS-InSAR technology. A step term is introduced into the time-series model to eliminate local unwrapping errors and residual atmospheric delays caused by severe convective weather in the summer of June 2025, so as to obtain a reliable interseismic creep rate. Combined with the co-seismic line-of-sight deformation field acquired by the two-pass D-InSAR method, a comprehensive study is carried out by integrating distributed fault slip inversion and Coulomb stress change simulation. The results show that: (1) The co-seismic deformation is dominated by uplift, with the maximum LOS deformation of approximately 5.0 cm for the ascending orbit and approximately 6.0 cm for the descending orbit. The deformation field presents a significantly asymmetric elliptical shape with no surface rupture, indicating that this event is a blind thrust rupture event; (2) The SBAS time-series analysis for the 22 months before the earthquake shows that after removing the observation disturbances caused by severe convection in June 2025, the tectonic rate of the hanging wall is approximately +26.9 mm/yr, that of the footwall is approximately +8.5 mm/yr, and the across-fault rate difference is approximately 18.4 mm/yr. After deducting the influence of post-seismic adjustment of the Wushi earthquake, it may indicate that the Aheqi fault was in a locked/strain-accumulating state before the earthquake, with continuous accumulation of elastic strain; (3) The inverted seismogenic fault has a strike of approximately 242°, a dip angle of approximately 40°, a slip angle of approximately 74°, a centroid depth of approximately 6.2 km, a maximum slip of approximately 0.2 m, and a moment magnitude of M_W 5.9. The rupture is dominated by thrust motion with a weak left-lateral strike-slip component, confirming that the Aheqi fault is the seismogenic structure of this earthquake; (4) The Coulomb stress calculation results show that the 2024 Wushi M_W 7.0 earthquake produced a static stress loading of more than 2 bar in the source region of the Aheqi fault, far exceeding the earthquake triggering threshold of 0.1 bar. Combining the pre-seismic locking characteristics, co-seismic slip distribution and Coulomb stress calculation results, it is considered that the Aheqi earthquake is a moderate blind thrust event triggered by post-seismic stress adjustment of the Wushi M_W 7.0 earthquake under the background of long-term tectonic loading. The results of this study can provide measured deformation constraints and reference for analyzing the seismogenic mechanism of the structural transition zone in the piedmont of South Tianshan and improving the regional seismotectonic model.