Fast report: Coseismic source model of the January 2025 Mw 6.1 Dapu earthquake from geodetic data and its implications for seismogenic structures in Southwestern Taiwan

Abstract In southwestern Taiwan, the longstanding debate between thin-skinned and thick-skinned models is exemplified by the 2025 M w ~6.1 Dapu earthquake, especially considering its proximity to the 1964 Mw ~ 6.5 Baihe earthquake. Joint GNSS–InSAR analysis and early aftershock distribution reveal a predominantly east-dipping reverse fault, with high slip at depths of 8–15 km as a single asperity. The maximum coseismic of 40 cm is located at ~ 12 km depth. The estimated seismic moment release along the source fault is 1.49 × 10 25 dyne-cm equivalent to a M w 6.08 earthquake. Further, the subsequent seismic activity suggests that a west-dipping fault was also triggered, underscoring the complexity of conjugate fault systems extending into deeper levels of the fold-and-thrust belt. This geometry, defined by detailed seismic, geodetic, and focal mechanism data, indicates that basement-involved deformation occurs well beneath the traditionally proposed thin-skinned décollement, highlighting the importance of thick-skinned processes in regional tectonics. Coulomb stress modeling shows a 0.2–0.3 MPa stress increase contiguous to the coseismic slip area, suggesting the potential for future seismic activity on nearby faults. Meanwhile, high-pressure fluid zones at shallow depths may encourage aseismic creep, mitigating seismic hazards at the surface but shifting major rupture potential to deeper locked segments. These findings underscore the critical role of basement-involved faults in the tectonic framework of southwestern Taiwan and emphasize the need for continued, integrated geophysical monitoring to refine seismic hazard assessments.