Profiling of crustal deformation across the southwest Japan arc

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The main purpose of this study is to delineate detailed pattern of three-dimensional crustal deformation in the Nankai subduction zone, southwest Japan. Ongoing interseismic deformation in this region is a mixture of short-term crustal shortening in the direction of oblique convergence of the Philippine Sea plate and permanent lateral movement of the forearc block along the Median Tectonic Line(MTL). We constructed two dense Global Positioning System(GPS) networks in the eastern and western parts of Shikoku Island that extended from the Pacific coast to Chugoku district across the MTL. The networks have been configured so that both strain partitioning in the direction of plate convergence and slip distribution along the MTL can be detected. We determined crustal velocities at 36 sites together with those at the nationwide continuous GPS stations in the vicinity.In order to decompose the deformation field into short-term and permanent components, we explicitly model the plate subduction using multi-rectangular fault segments, newly determined plate convergence vector, and depth-dependent plate coupling estimated from thermal model. Residual velocity field after subtracting the crustal shortening caused by plate subduction shows a lateral movement of the forearc block at a rate of about 5mm/yr along the MTL. Closer inspection shows that fault plane of the MTL inclines northward and its upper part is strongly locked to the depth of 15km while stationary slip is occurring below 15km. Plate coupling at the Nankai Trough is estimated very strong in a shallower zone to the depth of 25km, gradually decreasing with depth, and almost disappears below 35km.We published papers in Earth, Planets and Spaces and made several presentations at the meetings of the Seismological Society of Japan, the Geodetic Society of Japan, the American Geophysical Union, and others.