Transient and permanent deformation of central Japan estimated by GPS: 1. Interseismic loading and subduction kinematics

We analyze continuous global positioning system (GPS) data to estimate the kinematics of the Philippine Sea plate subduction below southern central Japan. Using a back slip dislocation model, we invert the strain rate tensors derived from the GPS velocity field to obtain the velocity of the downgoing slab with respect to the Tokai and Kanto forearcs along the eastern Nankai-Suruga and Sagami troughs, respectively. In both cases, these velocities are smaller and slightly rotated with respect to the Philippine Sea plate subduction velocity in central Nankai. This result implies strain partitioning between the subduction thrusts and on land and/or offshore deformation zones in both the eastern Nankai-Suruga and the Sagami area. In southern Kanto, we predict ∼20 mm yr−1 of dextral shear, in agreement with motion observed along the Boso strike-slip fault. In the Tokai region, the slip deficit accumulated since the last earthquake (1854) ranges between 6 and 3 m. Considering the extent of the locked zone, it would correspond to a magnitude MW=8.15 earthquake, if the slip deficit were to be released now during a single event.