HR: 14:35h
AN: T43C-04    [Abstracts]
TI: Primary switch of plate boundary fault in subduction zone and its relationship to the up-dip limit of seismogenic zone and change in wedge taper
AU: * kimura, G
EM: gaku@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, Bunlyo 7-3-1, Hongo, Tokyo, Tok 113-0033 Japan
AU: Kitamura, Y
EM: yujin@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, Bunlyo 7-3-1, Hongo, Tokyo, Tok 113-0033 Japan
AU: Yamaguchi, A
EM: asuka@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, Bunlyo 7-3-1, Hongo, Tokyo, Tok 113-0033 Japan
AU: Okamoto, S
EM: shinya@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, the University of Tokyo, Bunlyo 7-3-1, Hongo, Tokyo, Tok 113-0033 Japan
AU: Shibata, T
EM: shiba47@cc.kochi-u.ac.jp
AF: Department of Natural Environmetal Science, Kochi University, Asakura, Kochi, koc 780-8520 Japan
AU: Ujiie, K
EM: ujiiek@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Natsushima 2-15, Yokosuka, kan 237-0061 Japan
AB: One of unsolved problems in subduction zone is what controls the up-dip limit of seismogenic zone. Several hypotheses have been proposed; 1) change in friction behavior from stable to unstable slip of clay minerals caused by thermally controlled transformation (Hyndmann et al., 1993), 2) increase of effective strength due to reduction of fluid pressure caused by decrease in dehydration rate of hydrous minerals (Moore and Saffer, 2001), 3) change in location of plate boundary fault into the basement basalts due to lithification and hardening of a-seismic decollement and underthrusted sediments (Matsumura et al., 2003), and 4) reactivation of roof thrust, which is once abandoned during underplating (Kitamura et al., 2005). Increase of dehydrated fluid pressure might trigger the reactivation. Former two hypotheses implicitly keep in account that the friction behavior of the same fault zone changes at the up-dip limit whereas the latter two emphasize that the location of the plate boundary fault changes at the up-dip limit together with change in their friction behaviors. Nankai accretionary prism is divided into three segments; frontal, middle, and landward ones in regions from the west to the east. These segments indicate different aspects of wedge taper, internal structure, and basal plate boundary fault. Frontal segment is characterized by narrow critical taper, in-sequence-thrusted prism and aseicmic decollement. The middle segment shows large critical taper with steep surface slope, out-of-sequence-thrusted internal structure, and duplexed decollement possibly involving oceanic basement. The landward segment represents of stable narrow taper, weakly deformed internal structure and basal seismogenic and/or tsunamic plate boundary fault. Trench slope break and oceanward margin of forearc basin is located at the landward edge of middle segment. These common aspects in the area of onset of seismogenic zone might be related to lithification of both accreted and underthrusted sediments, and onset of localized pool of fluid dehydrated from underthrusted sediments and oceanic crust. Deformation and its freezing-reactivation process recorded in exhumed on-land melange suggest a switch of the plate boundary fault beneath the accretionary prism.
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8150 Plate boundary: general (3040)
DE: 8163 Rheology and friction of fault zones (8034)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005