Strain partitioning in the zone of transition from Nankai subduction to Izu-Bonin collision (Central Japan): implications for an extensional tear within the subducting slab

The Izu-Bonin ridge collision with Central Japan is a type example of collision of two island arcs in a subduction context. Based on the analysis of active faults, paleomagnetic data and recent seismicity in the northern tip of the Izu-Bonin are and the adjacent oceanic plate, we propose a tectonic schema of the Izu collision system and its transition to the Nankai subduction to the west. The dense GPS network deployed in Central Japan allows us to constrain the kinematics of the different blocks identified. This new kinematic model demonstrates the essential role of strain partitioning there. As the northward component of the Izu-Bonin are motion is locked in the collision zone, 30% of the convergence between the Philippine Sea plate and Central Japan is accommodated within the Philippine Sea slab, along the Zenisu-East Izu deformation system. We show that this pattern of deformation is related to an extensional tear of the Philippine Sea slab propagating southward along the volcanic are. We discuss the implications of this kinematic model on the seismogenic potential of the area and the dynamics of the Central Japan convergence zone. (C) 1999 Elsevier Science B.V. All rights reserved.