全球所有九级以上大地震，以及众多七八级大地震，都发生在俯冲带弧前，俯冲板块与上覆板块之间的巨大逆冲断层带处。这些弧前大地震，分布不均匀，并具有一定周期性。造成这种不均匀性与准周期性的原因，即俯冲带板间逆冲型大地震触发机制，一直以来备受关注。为此，本课题将针对西太平洋东北日本俯冲带弧前地区，以新建成的S-net所记录到大量海底观测数据为基础，结合以往积累的弧前地震、地形和重力资料，采用以地震层析成像为主的深部构造研究方法，开展“东北日本俯冲带弧前深部构造特征及其对板间逆冲型大地震的影响”研究工作，旨在厘清东北日本俯冲带弧前精细三维构造特征，深入刻画弧前巨大逆冲断层带构造特征与大地震破裂过程的内在联系，系统探讨俯冲带板间逆冲型大地震触发机制，为防震减灾工作提供理论支持。

All the earthquakes of magnitude nine and above, and many earthquakes of magnitude seven to nine, have occurred in the forearc megathrust zone between the subducting and overriding plates. These megathrust earthquakes are unevenly distributed and have a certain periodicity. The cause of such heterogeneity and quasi-periodicity, that is, the causal mechanisms of megathrust earthquakes, has received much attention. This project will focus on the forearc of the Tohoku subduction zone in West Pacific. We will image the detailed three-dimensional deep structure of Tohoku forearc, with many geophysical methods including the seismic tomography and so on, using a large number of seafloor observations recorded by the new S-net and the accumulated seismic, topography and gravity data in the study area. We aim to clarify the detailed structure of Tohoku megathrust and its implications to the rupture processes of megathrust earthquakes, and explore the causal mechanisms of megathrust earthquakes, which will provide theoretical support for earthquake prevention and disaster reduction.