HR: 1340h
AN: T53A-1118    [Abstracts]
TI: Uplift and deformation of the Kumano forearc basin: Preliminary results from Nankai Trough 3D seismic imaging offshore Kii Peninsula, Japan
AU: * Gulick, S P
EM: sean@ig.utexas.edu
AF: University of Texas Institute for Geophysics, Jackson School of Geosciences, JJ Pickle Research Campus, 10100 Burnet Rd, Austin, TX 78759, United States
AU: Bangs, N L
EM: nathan@ig.utexas.edu
AF: University of Texas Institute for Geophysics, Jackson School of Geosciences, JJ Pickle Research Campus, 10100 Burnet Rd, Austin, TX 78759, United States
AU: Moore, G F
EM: gmoore@jamstec.go.jp
AF: Center for Deep Earth Exploration, Japanese Agency for Marine Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa, 237-0061, Japan
AU: Martin, K
EM: kylara@ig.utexas.edu
AF: University of Texas Institute for Geophysics, Jackson School of Geosciences, JJ Pickle Research Campus, 10100 Burnet Rd, Austin, TX 78759, United States
AU: Nakamura, Y
EM: saru@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo, 162- 8639, Japan
AU: Kuramoto, S
EM: s.kuramoto@jamstec.go.jp
AF: Center for Deep Earth Exploration, Japanese Agency for Marine Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa, 237-0061, Japan
AU: Tobin, H J
EM: htobin@geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W Dayton St., Madison, WI 53706, United States
AU: Taira, A
EM: ataira@jamstec.go.jp
AF: Center for Deep Earth Exploration, Japanese Agency for Marine Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa, 237-0061, Japan
AB: Forearc basins contain excellent records of tectonic events that influence the subduction zones they overlie. The Kumano forearc basin, offshore the Kii Penninsula, Japan, overlies the Nankai Trough subduction zone, accretionary prism, and mega-splay fault believed to have slipped during the 1944 Mw8.0 seismic event. In 2006, an academic 3D seismic survey acquired by Petroleum GeoServices (PGS) and processed through prestack time migration by Compagnie Générale de Géophysique (CGG) resulted in unparalleled images of the outer Kumano forearc basin. We map key unconformities and sequences within this basin to look for evidence of significant events in the geologic history of the basin that might yield clues as to the processes related to the formation or evolution of the mega-splay system. Sequence 1 noncomformably overlies seismically-opaque, accretionary prism lithologies, averages less than 0.5 s twtt in thickness, and is generally flay-lying. These strata may have been deposited in a slope basin environment and then uplifted to form the base of the forearc basin. The flat-lying geometry is in stark contrast to all strata above this sequence, which have a pronounced landward tilt. Sequences 2-6 total over 1 s twtt in thickness and unconformably overlie Sequence 1. The geometry of the deepest of these landward tiled sequences, Sequence 2, seems to suggest a seaward sediment source. Sequences 3-6 exhibit diminishing landward tilt, increasingly landward-shifted sediment depocenters, and onlap relationships. The unconformity that separates Sequences 2 and 3 may mark a significant tectonic event. The Sequence 2 sediments below this unconformity have undergone wholesale tilting and form a pronounced bathymetric high running parallel and proximal to the current outer-arc high. Sediments above this surface show infilling of the sediment trap created by the uplift of the seaward 15 km of the forearc basin. Numerous clearly imaged normal faults persist in both the older, highly titled strata of Sequence 2 and to a lesser extent in the younger sequences. Several different processes could account for the uplift recorded in the forearc basin including accretion of large volumes of sediment to the prism changing the prism taper, subduction of a seamount or ridge, and/or changes in the fault (mega-splay) architecture. The waning tilt in the uppermost sediments suggests that there is a transient nature to whatever process caused the uplift.
DE: 1209 Tectonic deformation (6924)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 3002 Continental shelf and slope processes (4219)
DE: 3025 Marine seismics (0935, 7294)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting