Tectonic segmentation of the Manila subduction zone and its implication

Based on multi-channel seismic profiles, we have found that northern end of the Philippine Fault Zone (PFZ) is extended to the offshore area of Luzon Island. The northern terminus of the PFZ is terminated at the Manila Trench near ~119°E and ~17.5°N. As a result, the Manila Trench is segmented into two segments off the west Philippine. In fact, we can recognize four roughly NW-SE trending fault zones off west Luzon; the southernmost branch could be the offshore extension of the principal NW-SE trending PFZ in central Luzon. A new transform fault of ~40 km long has been formed to connect the northern and the southern Manila Trench segments. Because the slip along the PFZ was estemated to be 2 to 2.5 cm/yr, it implies that the age of occurrence of the PFZ is 1.5 to 2 Ma. Our age estimation of the PFZ is more or less coherent with geologic observation inland. However, the trend of the Manila Trench has changed ~35° counterclockwise from north to south. Coinciding with the NW-SE trending PFZ in central Luzon, the Manila subducting slab beneath central Luzon has been segmented as revealed by seismic tomography and seismicity. The northern subducted slab dips 40° eastward, while the southern slab dips 80° eastward. The segmentation of the Manila subduction zone along the NW-SE trending principal PFZ could predominate earthquakes, regional kinematics and crustal deformation.