HR: 10:20h
AN: T42A-01    [Abstracts]
TI: 3-D Prestack Depth Imaging of the Nankai Subduction Zone off Shikoku Island, SW Japan
AU: * Park, J
EM: jopark@jamstec.go.jp
AF: IFREE, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Tsuru, T
EM: tsurut@jamstec.go.jp
AF: IFREE, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Sato, S
EM: satoso@jamstec.go.jp
AF: JGI, Inc., 1-5-21 Otsuka, Bunkyo-ku, Tokyo, 112-0012 Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: IFREE, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AB: The Nankai Trough subduction zone off southwest Japan is one of the best-suited convergent plate margins for studying large interpolate subduction-zone earthquakes as well as the formation of accretionary prisms. At this margin, the Philippine Sea Plate (PSP) is subducting beneath the Eurasian Plate (EP) to the NNW. The plate convergence rate is estimated to be 4 - 5 cm/yr. Large thrust earthquakes have repeatedly occurred along the Nankai subduction zone with a recurrence interval of 100-200 years. The most recent interplate earthquake was the Nankai earthquake (Mw=8.2), which occurred in 1946 off the Kii Peninsula. In order to figure out seismic structure and stratigraphy of the Nankai accretionary wedge off Cape Muroto of Shikoku Island, southwest Japan, we have conducted three-dimensional (3-D) multichannel seismic (MCS) reflection survey using R/V Ewing in 1999. We acquired the MCS data on 81 separate lines with 100 m line spacing, each 80 km long, producing 8 X 80 km 3-D seismic volume. To obtain the 3-D prestack depth migration images, we constructed and updated a 3-D interval velocity model using the CDP bin gathers for which preconditioning processings including amplitude recovery, deconvolution, and multiple suppression were applied. Miocene to Pliocene Shikoku Basin sediments underthrusts the overlying accretionary prism along a decollement as the PSP subducts beneath the EP. The oceanic crust of the subducting PSP is traceable over the entire inlines. Several imbricate thrust faults are observed in the overlying accretionary wedge. The decollement steps down on the top of subducting oceanic crust around ~30 km landward from the deformation front. We recognize several sigmoid, landward dipping out-of-sequence thrust (OOST) faults in the landward thick wedge package. Most of the OOSTs are apparently developed from the subducting oceanic basement to the seafloor in the forearc region, cutting both underthrust sediments and the overriding accretionary prism. In this paper, we will show and discuss recent results of the 3-D prestack depth migration, visualization, and seismic structural/stratigraphic interpretation.
DE: 3025 Marine seismics (0935, 7294)
DE: 3036 Ocean drilling
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005