Fast report: the 2025 M6.4 Dapu earthquake: preliminary field observation and surface deformation analysis

Abstract The 2025 M6.4 Dapu earthquake offers a crucial opportunity to investigate coseismic deformation and fault behavior in southwestern Taiwan. Despite the absence of surface rupture, remote sensing and geodetic analyses detected significant ground deformation, indicating subsurface fault slip and stress redistribution. This study integrates GNSS measurements, DInSAR data, and field investigations to quantify coseismic displacement. GNSS data from 38 stations recorded North displacement from − 12.24 to 24.56 mm, East from − 17.92 to 9.7 mm, and Vertical from − 8.53 to 50.05 mm. DInSAR analysis of Sentinel-1A data revealed relative LOS displacements of approximately 120 mm in the ascending and 80 mm in the descending, confirming widespread strain release. Field surveys documented liquefaction effects, including aligned sand boils along the Liuchia Fault and tensile surface ruptures along the Kouhsiaoli Fault. Slope failures and lateral spreading were observed, highlighting the role of site-specific conditions during the earthquake. A strong correlation between GNSS and DInSAR displacement fields validates the spatial consistency of observed deformation, improving our understanding of fault mechanics and strain redistribution. These findings contribute to seismic hazard assessment and risk mitigation strategies in southwestern Taiwan, emphasizing the importance of post-seismic monitoring to evaluate stress redistribution and afterslip effects, ultimately enhancing regional earthquake resilience.