HR: 1340h
AN: T53A-1115    [Abstracts]
TI: Preliminary Analysis of an Anomalous Bathymetric "Notch" Between the Kumano Forearc Basin and the Slope of the Nankai Trough Accretionary Prism
AU: * Martin, K M
EM: kylara@mail.utexas.edu
AF: University of Texas Institute for Geophysics, 10100 Burnet Rd Bldg 196 (R2200), Austin, TX 78758-4445,
AU: Gulick, S P
EM: sean@ig.utexas.edu
AF: University of Texas Institute for Geophysics, 10100 Burnet Rd Bldg 196 (R2200), Austin, TX 78758-4445,
AU: Bangs, N L
EM: nathan@ig.utexas.edu
AF: University of Texas Institute for Geophysics, 10100 Burnet Rd Bldg 196 (R2200), Austin, TX 78758-4445,
AU: Moore, G F
EM: gmoore@hawaii.edu
AF: University of Hawaii at Manoa, 1680 East-West Rd, post 813, Honolulu, HI 96822,
AU: Tobin, H
EM: htobin@wisc.edu
AF: University of Wisconsin-Madison, 1215 West Dayton St, Masion, WI 53706,
AU: Kuramoto, S
EM: s.kuramoto@jamstec.go.jp
AF: Center for Deep Earth Exploration, Japan Marine Science and Technology Center, 2-15 Natshusima-cho, Yokohama, Kanagawa, 237-0061, Japan
AU: Taira, A
EM: ataira@jamstec.go.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164- 8639, Japan
AB: A 12 km wide, 56 km long, three-dimensional (3-D) seismic volume acquired over the Nankai Trough offshore the SE Kii Peninsula, Japan images the Nankai accretionary prism, forearc basin and the subducting Philippine Sea plate. Preliminary analysis reveals an unusual, trench-parallel ~1200 m deep depression (a "notch") along the seaward edge of the Kumano forearc basin and the upper slope of the accretionary prism, just landward of the shallowest branches of the previously-mapped splay-fault system. The shape of this notch varies along strike, from a single, steep-walled, ~3.5 km wide notch in the northeast, to a broader, ~6 km wide zone with several shallower linear bathymetric lows in the southwest. We have interpreted the shallow notch area in detail and find a large degree of deformation and a number of faults with varying dips and lateral extents. Faults below the central axis (bottom) of the notch are almost vertical, though often sinuous or splayed and therefore may have a translational component. Off-axis faults often dip toward the central axis but most of these faults have no indication of the sense of slip. The Bottom Simulating Reflector (BSR) is strong throughout most of the study area but has distinct gaps beneath steep seafloor slope breaks, such as the landward (northern) edge of the notch. Interpretation below the uppermost 2000 m is hampered by poor imaging due to the complex topography, strong BSR and associated gas deposits, and structural complexities from extensive deformation and fracturing. The structures associated with the notch may become clearer with additional seismic data processing. Several possible causes for this feature include an axial strike-slip fault complex, a thrust or normal fault system or a current-incised channel. The presence of faults along bathymetric anomalies indicates some degree of structural control, but an interaction between structure and currents cannot yet be ruled out.
DE: 3025 Marine seismics (0935, 7294)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting