HR: 0800h
AN: S41A-0938    [Abstracts]
TI: The analysis and study of fault systems in the Southernmost Part of Okinawa Trough
AU: * Huang, Y
EM: M91860008@mail.ntou.edu.tw
AU: Tsai, C
EM: chtsai@oc.gep.ncu.edu.tw
AU: Lee, C
EM: leecs@mail.ntou.edu.tw
AB: Taiwan is located in the boundary between the Eurasian and Philippine Sea plates. Due to different subduction, two arc-trench systems in different direction were happened. One is Luzon arc-trench system in N-S direction; the other one is called Ryukyu arc-trench system in E-W direction. The Okinawa Trough is a back-arc basin which was formed by extension of Eurasian plate, and the tectonic setting in this area has a series of normal-faults and igneous bodies. According to previous studies, we know that Southernmost Part of Okinawa Trough (SPOT) have evolved at least two main tensional phases of Okinawa Trough, the first phase probably came up in early Pleistocene and struck in NE-SW direction; and the second phases occurred during late Pleistocene and Holocene changed the direction to E-W. In this study, we have used seismic data collected by R/V Chiu-Lien, Ocean Research I, and R/V L'Atalante to explain the normal-fault systems in the SPOT area. We integrate seismic profiles with corrected bathymetry to relocate these normal faults. Our results show these normal fault systems has two main strikes, respectively N$60\deg$E and N$80\deg$E. We find that most of N$60\deg$E faults are located in the northern slope of SPOT and landward to Taiwan. The N$80\deg$E faults are found in the southern slop and center area of SPOT. Compare with the faults and a new topographic map, we find there were a lot of faults around the canyon, such as North-Mienhua Canyon. We suggest that the origin of the canyon is probably due to these tectonic forces. The canyon is a weak area, and is eroded much fast than the surrounding continental shelf. Passing through a series of erosional processes, the canyon becomes what looks like today. We find a lot of graben structure located in the center of SPOT. This area is the extension axis of SPOT right now. We also find many possible igneous rocks in the seismic profiles, some of them are intrusions and the others penetrate the seabed along the weak zone and form the submarine volcanoes. We have found at least 68 volcanoes in the SPOT area. The interactions of submarine volcanoes, canyons, and fault grabens demonstrate an active tectonic episode.
DE: 8010 Fractures and faults
DE: 8109 Continental tectonics--extensional (0905)
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting