Transient and permanent deformation of central Japan estimated by GPS: 2. Strain partitioning and arc–arc collision

Deformation of central Japan can be divided into two main components: elastic deformation due to the interseismic locking of subduction thrusts and deformation associated with intra-arc tectonics. In a companion paper [Henry et al., Earth Planet. Sci. Lett. (2000) this issue], we estimated an elastic deformation field based on the modeling of global positioning system (GPS) strain rates. In this study, we show that the corrected field (GPS minus predicted elastic deformation) is consistent with geological and seismological observations and should represent long-term plastic deformation. We use this corrected GPS deformation field to describe the kinematics of partitioning of the Philippine Sea plate/Amurian plate (AMU) convergence, in relation with the Izu-Bonin arc collision. About one third of the relative Philippine Sea/Amur motion is transferred to the central Japan crust, north of the collision front. This transfer induces high strain rates in southern Kanto and in the northern Japanese Alps. The latter region corresponds to the eastern boundary of the AMU. We propose that the independent motion of central Japan results from the delamination and the underthrusting of the Izu-Bonin arc lower crust and the upward bent oceanic slab.