琉球海沟俯冲带是探究欧亚板块与菲律宾海板块汇集、俯冲、弧后扩张及俯冲过程中流体循环的理想区域。虽然琉球海沟俯冲带研究已取得了丰硕的成果，但是，许多科学问题仍有待深入研究，如①琉球海沟俯冲带岩石圈的物质组成及几何学特征缺乏精细的刻画；②由于缺乏岩石圈深部的电导率信息，俯冲带中流体赋存状态及循环模式不清晰。海洋大地电磁法（MT）是探测岩石圈电性结构和流体分布最有效的地球物理方法。海洋MT和地震数据联合反演解释已被证明是研究俯冲带流体分布的有效手段。本项目拟通过琉球海沟俯冲带海洋MT和OBS大断面的实施，充分利用主动源OBS对地壳探测的高分辨率、天然源OBS的岩石圈深部探测能力及海洋MT对流体探测的高敏感性等优势，通过联合反演解释，获得精细的电导率、速度及密度剖面，刻画琉球海沟俯冲带岩石圈结构，推断俯冲带流体赋存状态，解析板块俯冲过程中的流体循环，探讨板块俯冲过程及弧后扩张机制。

The Ryukyu trench subduction zone is an ideal area for studying the mechanism of the plate subduction, the development of the back-arc and the formation of the basin. The plate subduction drives the flow and fluids from deep slab dehydration and/or fluids brought down from the shallow to deeper mantle by convection. Although a lot of geological and geophysical investigations have already been conducted, many scientific questions have yet to yield convincing and satisfactory answers. Among them, ① the most fundamental features to the formation of the trench-arc-basin system which is related to the lithospheric geometry of the Philippine Sea plate subduction has not yet been mapped; ② Due to the lack of deep resistivity information of the lithosphere, the distribution, accumulation and migration pattern of the fluid in the subduction zone are not resolved. The marine Magnetotelluric (MT) method is the most effective geophysical method for detecting fluid distribution in the lithosphere. The joint inversion and interpretation of marine MT and seismic data have been proven to be a very effective way for mapping the plate subduction zone, and as well for studying the fluid distribution in the subduction area. This project proposes to implement a large-scale joint survey of marine MT and OBS (Ocean Bottom Seismometer) in the Ryukyu trench subduction zone, starting from the East China Sea crossing the Ryukyu trench to the Philippine Sea Basin. The study will combine the strength of several geophysical methods, fully utilizing the high-resolution to the crust of the active OBS, the ability of passive OBS to map deep lithosphere and the high sensitivity of the marine MT to fluids to detect the distribution, accumulation and migration pattern of the fluid. Through the joint modeling and inversion, we will finally map fine crustal–lithospheric - mantle structures for the Ryukyu trench subduction zone and obtain the distribution and circulation pattern of the fluid. And we will then carry out detailed studies for the mechanism of the plate subduction, the development of the back-arc and the formation of the basin.