Seismogenic Structure and Temporal Velocity Variations of the 2025 ML 6.4 Dapu Earthquake (Taiwan): Insights from Joint Inversion of Seismic and Gravity Data

The M_L 6.4 Dapu earthquake, which struck southwestern Taiwan on January 20, 2025, occurred in the western foothills belt, an area characterized by folds and thrust faults. The earthquake sequence exhibits intricate fault interactions, with recent observations suggesting a conjugate rupture pattern involving both east-dipping detachment faults and west-dipping basement structures. However, the detailed subsurface structure remains poorly constrained due to the lack of a high-resolution 3D velocity model in this region. To elucidate the seismogenic structure, we conducted a joint inversion of seismic arrival times and gravity data. We utilized a comprehensive dataset integrating: (1) long-term background seismicity recorded by the Central Weather Administration (CWA) from 2012 to 2020, (2) the 2025 Dapu mainshock and its aftershock sequence, and (3) dense gravity observation data in the study area. By incorporating gravity data, our model provides enhanced resolution for shallow crustal structures and density constraints that complement traditional seismic tomography. We focus on imaging the high-resolution 3D velocity and density structures to identify the specific lithological or structural boundaries governing the rupture. Furthermore, we investigate the temporal variations in seismic velocity structure before and after the mainshock to detect potential stress relaxation or fluid migration processes. In this presentation, we will demonstrate the correlation between the derived structural heterogeneity and the aftershock distribution, providing new physical constraints on the seismotectonics of the Dapu earthquake sequence.