抄録
A three-dimensional finite element method is used to simulate the observed stress state in the Southwestern Japan, which has been inferred by SHIONO (1977). Two different types of model are presented here, one is a locked model and the other is a decoupled model, where the former preserves a tight contact between the subducting Philippine Sea plate and the overriding continental plate, while the latter has a weak zone between them. In these models three different types of force are applied;
(1) a negative buoyancy due to the density contrast between the subducting plate and surrounding mantle,
(2) a northwestward compressional force generated by the movement of the Philippine Sea plate,
(3) a westward compressional force due to the subducting Pacific plate.
It is found that the observed extensional stress parallel to the leading edge of the subducting Philippine Sea plate may be caused mainly by a negative buoyancy, suggesting that the plate seems to sink down into the mantle by its own weight. The observed E-W compressional stress field prevailing in the Inner zone appears to be closely associated with the subduction of the Pacific plate. The northwestward horizontal compressional force may be smaller than the westward compressional force, and seems to be less than 500bars. The present calculations suggest that a low velocity layer between the oceanic and continental plates gives appreciable effects on low-angled thrust faulting off the Kii peninsula and the Shikoku island.
