HR: 11:15h
AN: T32C-04    [Abstracts]
TI: Structural architecture of the active thrust systems in Japan, revealed by deep seismic reflection profiling
AU: * Sato, H
EM: satow@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Hirata, N
EM: hirata@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Iwasaki, T
EM: iwasaki@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Ito, T
EM: tito@earth.s.chiba-u.ac.jp
AF: Dept. Earth Sci., Chiba Univ., 1-33 Yayoi, Inage-ku, Chiba, 263-8522 Japan
AU: Ikeda, Y
EM: ikeda@eps.s.u-tokyo.ac.jp
AF: Dept. Earth & Planet. Sci., Univ. Tokyo, 1-3-7 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Kato, N
EM: naoko@ eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Abe, S
EM: sabe@jgi.co.jp
AF: JGI, Inc., 1-5-21 Otsuka, Bunkyo-ku, Tokyo, 112-0012 Japan
AU: Ikawa, T
EM: ikawa@jgi.co.jp
AF: JGI, Inc., 1-5-21 Otsuka, Bunkyo-ku, Tokyo, 112-0012 Japan
AB: In the central to northern Japan, active thrusts were developed by the subduction of the Pacific and Philippine Sea plates and the arc-arc collisions. Since the Kobe earthquake of 1995, the evaluation of earthquake risk has become an important problem. To reveal the geometry of active thrust fault systems, including deep geometry of source fault and connectivity of faults in a fault system, is important for the estimation of strong ground motions and the risk evaluations. Deep to shallow seismic reflection profiling were performed across the several active thrusts in the central to northern Japan, such as the Hidaka thrust system in the central Hokkaido (A), the Senya thrust system in the central northern Honshu and the Kozu-Matsuda active fault system associated with the subduction mega-thrust in the southern part of Kanto (Greater Tokyo) area (B). The geometry of active thrust systems is well presented by these seismic sections down to 15 km in depth. In this paper, we present the structural architecture of these active thrust systems based on the recent results of seismic reflection profiling. The deeper part of the above-mentioned thrust-systems shows relatively simple geometry. In the shallower part within the sedimentary wedge, thrust system shows flat-and-ramp geometry associated with fault-related folds and spray faults. Basin-ward migration of thrusting is common feature within the sedimentary layer. It is well demonstrated by geomorphological and geologic evidences. The structural architecture in the shallow part of thrust system is marked by wedge-thrust, emergent thrust and fault-related folds. Large scale wedge-thrust was found by deep seismic profiling in the deeper active thrust systems in the arc-arc collision zones (A and B). Arc block is collided into the mid-crust forming a "crocodile structure" associated with lower crustal delamination in the Izu collision zone (B) and the axial part of Hokkaido (A). Due to complex geometry and existence of spray faults in the shallow part of thrust system, the evaluation of seismic risk and slip-rate have to be performed based on the knowledge of the structural architecture of a whole thrust system.
DE: 9320 Asia
DE: 7223 Seismic hazard assessment and prediction
DE: 8107 Continental neotectonics
DE: 8150 Plate boundary--general (3040)
DE: 7200 SEISMOLOGY
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting