HR: 10:55h
AN: T52A-03    [Abstracts]
TI: Massive sediment underthrusting beneath the Nankai Trough splay fault inferred from 3D seismic reflection data
AU: * Bangs, N L
EM: nathan@ig.utexas.edu
AF: University of Texas Institute for Geophysics, PRC 196, 10100 Burnet Rd., Austin, TX 78758,
AU: Moore, G F
EM: gmoore@jamstec.go.jp
AF: Center for Deep Earth Exploration (CDEX)/JAMSTEC, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
AU: Pangborn, E M
EM: emily@ig.utexas.edu
AF: University of Texas Institute for Geophysics, PRC 196, 10100 Burnet Rd., Austin, TX 78758,
AU: Gulick, S P
EM: sean@ig.utexas.edu
AF: University of Texas Institute for Geophysics, PRC 196, 10100 Burnet Rd., Austin, TX 78758,
AU: Tobin, H
EM: htobin@wisc.edu
AF: Dept. of Geology and Geophysics, University of Wisconsin-Madison, 1215 W. Dayton St., Madison, WI 53706,
AU: Taira, A
EM: ataira@jamstec.go.jp
AF: Center for Deep Earth Exploration (CDEX)/JAMSTEC, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
AU: Kuramoto, S
EM: s.kuramoto@jamstec.go.jp
AF: Center for Deep Earth Exploration (CDEX)/JAMSTEC, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
AB: In April-May 2006, we acquired a 3D seismic reflection data volume across the Nankai Trough and Kumano forearc basin to image the mega-splay fault system that lies along this segment of the Nankai Trough subduction zone. These data were acquired by Petroleum GeoServices (PGS) using 4 streamers, each 4,500 m long, and a 3090 m³ source, and cover an area of 12 x 56 km². The data were processed by Compagnie Générale de Géophysique (CGG) to suppress seafloor multiples, and to migrate and stack the data using prestack time migration. The mega-splay fault system appears as a high-amplitude seismic reflection with polarity opposite that of the seafloor that lies 1-2 km above the top of the subducting ocean crust. It is a regionally significant reflection that extends from 8 km subseafloor, 50 km landward of the trench, up dip to the seaward edge of the Kumano Basin where it branches into 3-4 individual near-surface faults. Along strike the mega-splay reflection extends across the 12 km width of the 3D volume. We have analyzed this fault-plane reflection waveform in detail across the entire 3D survey area. The reflection from the deep branch of the mega-splay fault is nearly everywhere consistent with the properties of a simple single reflection interface with lower velocity and density below the splay fault rather than a thin fault-zone layer of locally low-velocity/density material. There appears to be a direct correlation between the amplitude of the splay fault and the amplitude of the top of the subducting ocean crust. We interpret this correlation to as being due to the low-velocities and low-densities within the entire underthust interval between the splay fault and ocean crust and not just within a thin interval beneath the splay fault. These results imply the entire 1-2 km section beneath the splay fault has been thrust beneath the overriding section. This massive sediment underthrusting carries significant quantities of fluid-rich sediment into the up-dip portion of the seismogenic zone, where it can affect fault zone behavior.
DE: 8010 Fractures and faults
DE: 8012 High strain deformation zones
DE: 8045 Role of fluids
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting