HR: 0800h
AN: S51B-0165    [Abstracts]
TI: Plate convergence along the northern Manila Trench, Taiwan-Luzon region
AU: * Ku, C
EM: jo@oc.gep.ncu.edu.tw
AF: Chia-Yan Ku, Institude of Geophysics, National Central University, Jhongli, 320 Taiwan
AU: Hsu, S
EM: hsu@oc.gep.ncu.edu.tw
AF: Chia-Yan Ku, Institude of Geophysics, National Central University, Jhongli, 320 Taiwan
AB: The Philippine Sea Plate overrides the Eurasian Plate along the east-dipping Manila Trench. From Luzon to Taiwan, the plate convergence evolves gradually from normal subduction to collision. Further north, the Taiwan orogen has been created. As evidenced by the earthquakes, the subduction-related earthquakes become diffusive close to Taiwan. The accretionary prism has also become wider toward Taiwan. To understand the transition of the plate convergence, we have collected 6 reflection seismic profiles across the Manila Trench between Luzon and Taiwan. The results show that the basement generally displays larger dipping angle in the south than in the north. The trench-fill sediments near the trench have larger quantity in the south than in the north. In the north, the trench-fill sediments have even been uplifted. Structural analysis shows that the crustal structures close to the trench area can be divided into two distinctive sub-areas: the normal fault zone and the proto-thrust zone. The normal fault zone is characterized by the distribution of numerous normal faults in the upper layer of the bent subducting plate. When the normal faults approache the trench, they are generally covered by trench-fill sediments. It implies that the normal faults occur at a maximum bending moment of the plate. Some normal faults resumes probably due to the strong plate convergence near the accretionary prism. The proto-thrust zone is located between the normal fault zone and the frontal thrust of the accretionary prism. Proto-thrust zone contains numerous blind-thrust beneath the trench area. The observation of the proto-thrust zone suggests two tectonic insights. Firstly, the compression of plate convergence comes from the base of the decollement and propagates upwards. Alternatively, the blind-thrusts come from the inheritance of the subducting normal faults.
DE: 7230 Seismicity and seismotectonics
DE: 8107 Continental neotectonics
DE: 7215 Earthquake parameters
DE: 1242 Seismic deformations (7205)
DE: 0930 Oceanic structures
SC: Seismology [S]
MN: 2004 AGU Fall Meeting