Fault model and slip distribution of the 2025 MW6.0 Chiayi earthquake in southern Taiwan, China, constrained by InSAR observations

On January 20, 2025, an M W 6.0 earthquake occurred in Chiayi County, southwestern Taiwan, China. In this study, we utilize Sentinel-1 data to investigate the coseismic ground displacement and fault slip model of this event. Here, we present the geodetic fault model of the 2025 Chiayi earthquake. While both east-dipping and west-dipping fault models can adequately reproduce the InSAR observations, the east-dipping model was found to better align with the quasi-east-west and quasi-vertical deformation fields derived from decomposing Interferometric Synthetic Aperture Radar (InSAR) ascending and descending orbits, the characteristics of interseismic deformation, and the tectonic features of the seismic region. The best-fitting east-dipping uniform-slip model shows that the seismogenic fault is characterized as a reverse slip striking 336.2°, dipping northeastward. The fault's upper boundary is buried at a depth of 8.0 km, with a dip angle of 27.6° and a slip angle of 61.6°. Calculations of Coulomb stress changes reveal that regions experiencing positive changes are primarily concentrated at the northeast and southwest extremities of the Chiayi earthquake rupture, as well as in the northwest and southeast lobes flanking the rupture zone.