Profiling of crustal deformation across the southwest Japan arc

这项研究的主要目的是勾勒出日本西南部南开俯冲带地壳三维形变的详细模式。该地区正在进行的震间变形是菲律宾海板块斜向会聚方向的短期地壳缩短和弧前地块沿中线构造线(MTL)的永久横向运动的混合体。我们在四国岛的东部和西部建造了两个密集的全球定位系统(GPS)网络，从太平洋海岸延伸到MTL的中部地区。网络的配置使得既可以检测到板块会聚方向的应变分配，也可以检测到沿MTL的滑移分布。为了将形变场分解为短期和永久分量，我们使用多个矩形断层段、新确定的板块会聚向量和由热模型估计的随深度变化的板块耦合来显式模拟板块俯冲。减去板块俯冲引起的地壳缩短后的剩余速度场表明，弧前地块沿MTL以约5 mm/年的速度横向移动。进一步观察表明，MTL断裂面向北倾斜，其上部强烈锁定在15公里以下，而静止滑动发生在15公里以下。据估计，南开海槽的板块耦合在25公里以下的浅层非常强烈，随着深度的增加而逐渐减少，在35公里以下几乎消失。我们在地球、行星和太空上发表了论文，并在日本地震学会、日本大地学会、美国地球物理联合会等会议上做了多次发言。

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.