|dc.description.abstract||The Eurasian Plate (EP) subducts beneath the Philippine Sea Plate (PSP) along the Manila subduction zone. The northern portion of this subduction system is located between the Taiwan and Luzon Island. Since the 2004 great Sumatra-Andaman earthquake, the tsunamigenic potential and the hazard risk of the Manila subduction zone has been underlined. Although some main tectonic structures of the area have been imaged based on geophysical approaches, the incomplete earthquake records caused by the poor seismic station coverage still limits our understanding for the seismogenic characteristics of the area.
In order to obtain more information about the seismotectonics of the northern Manila subduction zone, two temporal seismic arrays composed of 8 ocean bottom seismometers (OBSs) were deployed along the northern Manila trench from June 22 to July 12, 2016 and from June 27 to July 20, 2017, respectively. During this recording period, 1437 earthquakes were determined and relocated. Less than 15 earthquakes have been reported in the international or local catalogue for the same period, showing the efficiency and necessity of OBSs networks for the seismictoctonic studies for the marine area.
The result shows that the earthquakes appear to be segmented and divided into different groups. Furthermore, the hypocenters distribution reveals that most of the events occurred in the subducting plate to the west of the trench with depth shallower than 40 km and magnitude lower than 2, which infers the seismogenic behavior of the northern Manila Subduction system should be mainly controlled by the plate bending or/and the reactivation of tectonic structures in the subducting plate. Relatively less earthquakes are located to the east of the trench. Instead of spreading along the plate interface, they demonstrate a spatial concentration distribution. From the earthquakes relocation results, the earthquake events separate to three swarms. We suggest that the earthquake swarms in front of the trench are influenced by the plate bending in the subducting plate which could be observed by the seismic pattern. Furthermore, the composite focal mechanism inferred that these earthquakes are facilitated by strike-slip fault. The direction of the strike is parallel to Luzon Ryukyu Transition Plate Boundary, which is consistent to with the shearing feature in the southern end of Luzon Ryukyu Transition Plate Boundary. In the other hand, the earthquake swarm behind the trench is caused by local effect. We suggest that it is caused by the plate bending in the bottom of the subducting crust influence by compression stress or the loading of the buried seamount.