Deformation and stress localization at the Nankai subduction zone, southwest Japan

Abstract

Deformation observed at subduction zones provides direct information on kinematics/mechanics of plate interaction. Previous analysis of GPS (global positioning system) observations at Japan subduction zones mainly focused on the pattern of deformation or strain, and did not attempt to assess stress change associated with plate subduction. In this study, we use a kinematic model constrained by horizontal deformation and seismicity to simulate the motion of a subducted slab and estimate stress change at the Nankai trough, southwest Japan. The three-dimensional plate interaction model, which incorporates the effects of major tectonic forces (slab pull, ridge push and drag force), provides an overall fit to the horizontal deformation observed by GPS over the year 2001 at the landward portion of the Nankai subduction zone. The model predicts a stress concentration zone with an accumulation rate of ≥0.07 MPa/yr, which encompasses the locations of most historical earthquakes of ML≥7.0. The correspondence between the predicted stress localization zone and the rupture areas of previous large earthquakes indicates that the interplate earthquakes at the Nankai trough are a consequence of persistent stress localization caused by the subducting slab in the region. These results confirm the potential earthquake hazard at the Nankai subduction zone, which was previously inferred from long-term earthquake predictions.