A55. Sato, K., and P. Bird (2002) Numerical modeling of neotectonics of Japan with SHELLS (abstract), Eos Transactions of the American Geophysical Union, Western Pacific Geophysics Meeting Supplement, SE22A-03.

Japanese island arc is located in a region where two oceanic plates, namely the Pacific and Philippine Sea plates, subduct beneath continental plates. We have been performing numerical modeling of the long-term tectonic deformation within Japan using a 2.5-D thin-shell finite element program SHELLS developed by Kong and Bird (1995). The finite element grid, consisting of about 6800 triangular thin-shells, is as large as ~2700 km ´ 1200 km (along- and across-arc directions) which includes whole Japan. We incorporate lateral variations in topography and thickness of lithosphere at each node position. Topography comes from ETOPO5 data set. Crustal thickness is based on a published isodepth contours of the Moho, while the thickness of mantle lithosphere is determined considering the isostasy at the base. For forearc regions, in order to define the geometry of the model base, the isodepth contours of the upper surfaces of subducting oceanic plates are used. Based on published geological maps, we also include most of active or potentially active faults. Imposing boundary conditions based on NUVEL-1A and other recent plate motion models, we apply shear tractions caused by oceanic plates along the base of forearc regions. In the calculation, nonlinear rheology and heat flow are fully taken into account. In order to score each model and pick up an optimal model, we compare the calculation with observation using three data sets, namely GPS velocities, maximum principal stress directions, and geological slip rates of faults. These three data sets respectively comes from the GEONET (GPS Earth Observation Network) operated by Geographical Survey Institute of Japan, the WSM2000 (World Stress Map 2000), and published literatures. Preliminary results include the following: (1) Shear tractions caused by the Pacific and Philippine Sea plates in forearc regions should be less than ~15 MPa and ~10 MPa, respectively. (2) Optimal fault friction coefficient is as small as ~0.06, such that the strength of most faults is found to be quite low. These results are almost consistent with those of modelings for other regions such as Alaska and Asia.