Analysis of shallow structures and seafloor morphology in offshore western Luzon

High-resolution bathymetry and sub-bottom profiler data from the northern Manila Trench forearc region reveal two distinct morphotectonic features. The first set of features consists primarily of NW-SE trending faults, interpreted as offshore splays of the Philippine Fault Zone (PFZ). These faults are evidenced by offset submarine canyons, linear valleys, and fault scarps, indicating a dip-slip component likely resulting from complex deformation at the termination of the PFZ. The second set mainly comprises N-S trending normal faults, which are inferred to have been formed by forearc flexure caused by the partial subduction of the Scarborough Seamount Chain.

The NW-SE trending faults reflect tectonic deformation associated with the strike-slip activity of the PFZ, while the N-S trending normal faults highlight the impact of the varying seafloor topography of the subducting slab on the forearc region. However, the relationship between the forearc normal faults and the PFZ splays remains unclear due to observational limitations. Further investigation is needed to explore potential links between the normal faults and other nearby fault systems, including the Lingayen Gulf Fault System and the East Zambales Fault. This study provides new insights into the tectonic complexity of the northern Manila Trench forearc region, with implications for understanding the region’s broader tectonic setting.