HR: 09:00h
AN: G41A-05    [Abstracts]
TI: Crustal block kinematics of the Kanto and the Izu regions, central Japan estimated from GPS and leveling data
AU: * Nishimura, T
EM: takuyan@eb.mbn.or.jp
AF: Geographical Survey Institute, Kitasato-1, Tsukuba, Iba 305-0811 Japan
AU: Sagiya, T
EM: sagiya@seis.nagoya-u.ac.jp
AF: Nagoya Univ., Furo-cho, Chigusa-ku, Nagoya, Aic 462-8602 Japan
AB: We develop a kinematic block-fault model (Matsu'ura et al., 1986) in the Kanto and the eastern Tokai and the Izu regions based on geodetic data including GPS and leveling. Tectonics in those regions are characterized by the subduction and the collision of the Izu-Ogasawara(Bonin) arc at the Sagami and the Suruga-Nankai Troughs and the northern Izu Peninsula, respectively. First, we estimated horizontal and vertical velocity at 173 GPS sites from April 1996 to May 2000 and vertical velocity in 605 leveling sections between adjacent benchmarks in late 90's. Then, the observed data are inverted to infer the poles of rotation of the crustal blocks, the degree of elastic strain accumulation on faults, and volumetric change of inflation sources beneath volcanoes in the regions, simultaneously. The data are explained by four distinct crustal blocks, namely, the Izu micro-plate, the Central Japan block, the Pacific, and the Philippine Sea plates. The Izu micro-plate rotates clockwise rapidly (9.4 deg/Myr) with the rotation pole just north of its northern boundary. The zone of the strong-coupled faults extends from the rupture zone of the 1923 M7.9 Kanto earthquake to its southeast extension in the subduction zone along the Sagami trough. The boundary between the Izu micro-plate and the Philippine Sea plate has a left-lateral motion with the rate of ~30 mm/yr at east and south of the Izu Peninsula. The most part of this boundary is completely locked and has a large potential of future earthquakes. Though the subduction boundary along the Suruga-Nankai Trough between the Central Japan block and the Izu micro-plate is completely locked, convergence rate (10-20 mm/yr) is slower than that of the other part of the Nankai Trough ($>$45 mm/yr). It suggests the Tokai gap hypothesis to anticipate an M~8 earthquake along the Suruga-Nankai Trough should be reconsidered because the hypothesis implicitly assume convergence rate does not differ along the Nankai Trough significantly.
DE: 8150 Plate boundary--general (3040)
DE: 8158 Plate motions--present and recent (3040)
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting