Abstract

The plate convergence between the Philippine Sea Plate (PHS) and the Eurasian Plate (EP) is mainly located along the Ryukyu Islands, Taiwan, and the Philippines, displaying complex tectonics. The convergence cannot be described only by a simple rotation pole of PHS/EU. The PHS has subducted northward beneath the Ryukyu Islands. At the same time, the northern portion of the linear Luzon-Okinawa fracture zone has approached the Ryukyu Trench and shown its reluctant subduction. In contrast, in the middle of the Ryukyu Trench, a high gravity zone beneath the forearc has caused uplifted and extensive normal faulting in the forearc basin. Because of the strong plate coupling, a mega-splay fault occurs beneath the forearc region south of Miyako Island. As a consequence, a potential large tsunami is expected in the near future. In the westernmost Ryukyu Trench, the PHS/EU plate convergence becomes considerably oblique. The Southern Okinawa Trough back-arc basin has displayed intense rifting from the proto-Taiwan orogen since ~2 Ma. The backarc volcanism and hydrothermal activity are vigorous. Two right-lateral strike-slip faults have caused additional stress beneath the Nanao Basin and caused a risky cluster of earthquakes. In east Taiwan, the northwestward convergent PHS has split into a subducting part in the north and a colliding part in the south. The latter has caused several disastrous earthquakes.

Further south, The Manila Trench exists in the west of the Philippine mobile belt, while the Philippine Trench exists in the east of the Philippine mobile belt. In between, the Philippine Fault cuts through the whole Philippine archipelago. Large earthquakes have occurred frequently along the Philippine Fault. In the central Philippines, a plate collision occurred near Mindoro Island, where the Manila Trench vanished. The collision probably changed the motion of the middle and southern Philippine mobile belts, which became anti-clockwise against the EP instead of clockwise rotation. That is, another pole of rotation is located close to the south Palawan. The motion of the south Philippine Fault generally follows one of a small circle of rotation. Nevertheless, the motion of the north Philippine Fault seems to be affected by both two convergent behaviors.