Spatial variations of the crustal stress field in the Philippine region from inversion of earthquake focal mechanisms and their tectonic implications

This paper presents the spatial variations in the crustal stress field for the Philippine region. Based on the stress configuration, we divided the stress regime in the area of the Philippines into four parts: (1) Trench-perpendicular compressive stress axes (σ1) with an intermediate plunge were observed along the eastern subduction systems of the Philippine Mobile Belt (PMB), which suggests that the subduction of the Philippine Sea Plate (PSP) is the primary factor controlling the stress distribution. (2) Characterized by systematically rotated σ1 with very shallow plunge, the central-western portion of the Philippines appears to be largely affected by the collision between the Palawan Block and the PMB. (3) The σ1 distribution in the northern part of Luzon Island (north of 14°N) is compatible with the plate motion of the PSP, whereas the extensional axes (σ3) has a fan-shaped stress signature with N-S direction at the south and a more spreading direction to the north, which implies its north escapement. (4) Bounded by the Scarborough Seamount, the northern and southern portions of the Manila Trench reveal a very distinct stress pattern with a trench-parallel σ3 to the north and a trench-perpendicular σ3 to the south. This observation may infer a potential effect caused by the presence of the oceanic bathymetric highs on the behavior of the subduction process. In addition to the identification of the four provinces with different stress regimes, we suggest that the Philippine Fault Zone may play an important role to alter the stress state in the region of the Philippines.