GEOPHYSICAL FEATURES OF THE NANKAI TROUGH SUBDUCTION ZONE AND THEIR DYNAMIC SIGNIFICANCE

The Nankai Trough is the zone where the Philippine Sea Plate (PSP) subducts beneath the Eurasian. The Trough is divided into the east and the west parts based on differences in free-air gravity anomalies, temperature distribution, oceanic heat flow, crustal structures and stress field. The eastern part is under the Shikoku and the Kii Peninsula, and the western part is beneath the Kyushu. PSP subducts along the Nankai Trough from south to north in the eastern part, whereas the direction changes to nearly EW in the western part. The thickness of the subduction zone is relatively thin in the eastern part, and the subduction is characterized by a low angle and shallow depth. But the subduction angle is quite large, and the subduction depth is also deeper in the western part. These diverse characters are caused by several times of rotation of the Pacific Plate and PSP, changes in direction of motions, and other factors.