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 colli sion of two island arcs in a subduction context. Based on the analysis of a ctive 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 subduct ion to the west. The dense GPS network deployed in Central Japan allows us to constrain the kinematics of the different blocks identified. This new ki nematic model demonstrates the essential role of strain partitioning there. As the northward component of the Izu-Bonin are motion is locked in the co llision zone, 30% of the convergence between the Philippine Sea plate and C entral Japan is accommodated within the Philippine Sea slab, along the Zeni su-East Izu deformation system. We show that this pattern of deformation is related to an extensional tear of the Philippine Sea slab propagating sout hward along the volcanic are. We discuss the implications of this kinematic model on the seismogenic potential of the area and the dynamics of the Cen tral Japan convergence zone. (C) 1999 Elsevier Science B.V. All rights rese rved.