日本南海海槽俯冲带的地球物理特征及其动力学意义

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

日本南海海槽是菲律宾海板块和欧亚板块俯冲消亡的地带,其东西两段俯冲带的空间重力异常、温度分布和海底热流、地壳结构、应力场特征表现出显著差异。东段四国-纪伊岛下的俯冲带表现出典型的热俯冲带的特征,菲律宾海板块俯冲方向为由南向北,总体特征为俯冲带厚度较薄、俯冲角度小和俯冲深度相当浅等;西段九州岛下的菲律宾海板块由南北方向的俯冲过渡至近东西向,总体表现为俯冲角度大、俯冲深度深、板内震源较浅等特征;这些差异可能是由太平洋板块和菲律宾海板块的运动方向和速率发生了数次的旋转和改变,以及四国海盆的扩张等诸多因素导致的。

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.