HR: 0800h
AN: T41C-1227    [Abstracts]
TI: Oblique Subduction of the Pacific Plate at the Kuril Trench and Lateral Movement of the Forearc
AU: * Tanabe, A
EM: tanabe@cc.kochi-u.ac.jp
AF: Department of Natural Environmental Science, Kochi University, Akebono-cho 2-5-1, Kochi, 780-8520 Japan
AU: Tabei, T
EM: tabei@cc.kochi-u.ac.jp
AF: Department of Natural Environmental Science, Kochi University, Akebono-cho 2-5-1, Kochi, 780-8520 Japan
AB: Northeast-southwest trending Kuril forearc in the northwest Pacific is formed by oblique subduction of the Pacific plate (PA) at the Kuril Trench. Its northwestern boundary corresponds to a volcanic front and southwestern front collides with the northeast Japan arc in the central Hokkaido. We estimate lateral movement of the forearc in two ways. At first we combine relative plate motion vectors with slip vectors of major interplate earthquakes at the southern Kuril Trench. Plate motion vector is evaluated at each epicenter using the most recent global model REVEL-2000 (Sella et al., 2002), and decomposed into two components: one parallel to the earthquake slip vector that is related to interplate earthquake cycle and margin-parallel residual that may be taken up by the forearc lateral movement. The residuals show that the southern Kuril forearc moves southwestward at a mean rate of 12mm/yr. In more detail, northeastern part of the forearc moves at a faster rate of about 20mm/yr, and the rate decreases to 10mm/yr at the southwestern front. This implies a deceleration due to the collision with the northeast Japan arc. Next we estimate forearc movement using crustal velocities from nationwide continuous GPS array though data are limited only in Hokkaido region. In horizontal velocity field the most dominant is a crustal shortening of the forearc in the direction of plate convergence, which can be modeled as an elastic deformation caused by back slip vectors acted on plate interface. We determine plate interface geometry referring to high-precision unified hypocenters by Japan Meteorological Agency and apply plate motion vectors from REVEL-2000 on the plate interface. Full plate coupling is assumed to a depth of 50km. After subtracting calculated elastic deformations from the observed velocities, residuals are nearly margin-parallel in the forearc and show drastic change at around the northwestern boundary. Mean of the residuals in the forearc is about 10mm/yr. The result is consistent with that of the first estimation.
DE: 8150 Plate boundary--general (3040)
DE: 8158 Plate motions--present and recent (3040)
DE: 1206 Crustal movements--interplate (8155)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting