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: elast ic deformation due to the interseismic locking of subduction thrusts and de formation associated with intra-arc tectonics. In a companion paper [Henry et al., Earth Planet. Sci. Lett. (2000) this issue], we estimated an elasti c 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 seismologi cal observations and should represent long-term plastic deformation. We use this corrected GPS deformation field to describe the kinematics of partiti oning of the Philippine Sea plate/Amurian plate (AMU) convergence, in relat ion with the Izu-Bonin are collision. About one third of the relative Phili ppine Sea/Amur motion is transferred to the central Japan crust, north of t he collision front. This transfer induces high strain rates in southern Kan to and in the northern Japanese Alps. The latter region corresponds to the eastern boundary of the AMU. We propose that the independent motion of cent ral Japan results from the delamination and the underthrusting of the Izu-B onin are lower crust and the upward bent oceanic slab. (C) 2001 Elsevier Sc ience B.V. All rights reserved.