Abstract
A magnitude 6.9 earthquake struck northern Cebu on 30 September 2025, with a shallow hypocenter at ∼5 km depth located offshore about 19 km NE of Bogo City. No active fault had previously been mapped within the epicentral region, raising questions about the earthquake source and the distribution of active deformation in the central Philippines. We investigated the causative fault, coseismic deformation, and associated impacts using seismicity, satellite-derived deformation, high-resolution geomorphic interpretation, and post-earthquake field observations. The datasets indicate rupture of an unmapped NE-trending, right-lateral strike-slip structure, herein referred to as the Bogo Bay Fault. Although the hypocenter was offshore, DInSAR and pixel-offset analyses, aftershock distribution, and the ∼8 km mapped surface rupture show that the fault extends onshore through Bogo City. Right lateral offset reaches up to ∼1.5 m. Along the Nailon–Siocon coastline, coseismic uplift reached ∼1.2 m, indicating a substantial vertical component of deformation that likely contributed to the minor tsunami. The earthquake also triggered liquefaction, landslides, sinkholes, and structural damage. Liquefaction was concentrated in coastal lowlands, marshes, and reclaimed areas, whereas landslides and sinkholes occurred mainly in karst terrains. Severe structural damage was concentrated in built-up areas underlain by soft, unconsolidated sediments, where liquefaction and amplification of ground shaking likely intensified damage. The spatial distribution of impacts reflects the combined influence of fault kinematics, local geology, site conditions, and land use. Beyond its local impacts, the earthquake reveals important aspects of active deformation in the central Philippines. The orientation and right-lateral kinematics of the Bogo Bay Fault indicate a stress orientation distinct from those inferred from previous earthquakes, suggesting spatial variation in the stress field across the Visayas region. Coulomb stress modeling further suggests that earlier earthquakes may have imparted small positive stress changes on portions of the Bogo Bay Fault, potentially bringing parts of the fault closer to failure. More broadly, the event shows that strain may be accommodated across a distributed network of interacting faults with long recurrence intervals and subtle geomorphic expression. The event underscores the importance of identifying and characterizing previously unrecognized active faults to better understand regional deformation and improve seismic hazard assessment.