HR: 0800h
AN: G21A-0111    [Abstracts]
TI: Dense GPS Array Observations Across the Nankai Subduction Zone, Southwest Japan
AU: * Tabei, T
EM: tabei@cc.kochi-u.ac.jp
AF: Department of Natural Environmental Science, Kochi University, Kochi, 780-8520 Japan
AU: Miyazaki, S
EM: s_miyazaki@stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305 United States
AU: Hashimoto, M
EM: hasimoto@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Uji, 611-0011 Japan
AU: Matsushima, T
EM: mat@sevo.kyushu-u.ac.jp
AF: Graduate School of Science, Kyushu University, Shimabara, 855-0843 Japan
AU: Kato, T
EM: teru@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, Tokyo, 113-0032 Japan
AU: Kato, S
EM: s-kato@ssken.co.jp
AF: Department of Civil Engineering, Shikoku Research Institute Inc., Takamatsu, 761-0192 Japan
AB: Interseismic deformation in an oblique subduction zone is a mixture of short-term crustal shortening in the direction of plate convergence and permanent margin-parallel movement of a forearc block. We have deployed two dense GPS traverse arrays across the southwest Japan arc to better illustrate strain partitioning in the Nankai subduction zone. In 1998 we constructed the first array that composed of 22 stations along a 200km-long arc-normal line. The second array with 15 stations was constructed in 2002 nearly parallel to and 120km west of the first one. Both arrays cross the Median Tectonic Line (MTL), the arc-parallel strike-slip fault system dividing the forearc block from the rest of the overriding plate. More than 100 crustal velocities from these arrays and the nationwide continuous GPS arrays are used for inversion analysis to estimate back slip vectors on plate interface, a rate of margin-parallel forearc movement, and slip deficits on the upper fault zone of the MTL. Plate interface and MTL fault plane are reproduced by multi-rectangular segments and inversions are conducted for various dip-angles of the MTL. The optimum model shows that strong plate coupling causes a margin-parallel forearc movement at a rate of 3mm/yr together with a crustal shortening of 0.3-0.4 micro strain/yr in the direction of plate convergence. Slip deficits on the MTL are nearly equivalent to the rate of margin-parallel forearc movement in the opposite direction, showing a full locking of the upper fault zone of the MTL. Moreover inversion result favors northward dipping fault segments of the MTL throughout from east to west than the vertical. The rate of margin-parallel forearc movement is consistent with the geological slip rate of the MTL in the late Quaternary.
DE: 8150 Plate boundary--general (3040)
DE: 1206 Crustal movements--interplate (8155)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting