西北太平洋俯冲带及其深震活动

俯冲带是理解地球内部物质循环和能量交换、大陆岩石圈演化、地震和火山活动及矿产资源分布等的重要环节.本文聚焦于西北太平洋俯冲带，通过汇集多种地震观测研究结果，清晰地揭示了由日本海沟至中国东北的俯冲板片整体活动图像，即整个西北太平洋俯冲板片的主压应力轴一致地稳定在俯冲方向上，俯冲板片上深浅部的显著地震活动存在密切的关联性；俯冲板片深处的亚稳态橄榄岩楔形区及其周边是深源地震多发区，深源地震可能是由亚稳态橄榄岩楔形区内的相变断层开始破裂的；在410~660 km深的地幔过渡带内处观测到的俯冲板片上下界面，揭示了俯冲板片的层状组分结构和板块下侧的高含水量.为更好地约束日本海下方的俯冲板片结构和深入探讨西太平洋的俯冲动力作用，有待于在全球罕有的大陆深部不断发生深震的西北太平洋俯冲区，开展海陆联合的地球物理探测及岩石高温高压实验和地球动力学模拟等研究.

The Northwest Pacific subduction zone and its deep earthquake activity

The subduction process drives the material cycling and energy exchange between Earth's surface and its deep interior,and thus the subduction zones are pivotal for understanding the evolution of continental lithosphere,the subduction-related earthquakes,volcanos,ore deposits,etc. This paper focuses on the Northwest Pacific subduction zone and summarizes our present understandings of the subducting slab from the Japan Trench to Northeast China based on multiple seismic investigations. Stress inversion shows that the principal compressive stress axis of the slab is subparallel to the subducting direction,indicating a close relationship for the shallow and deep strong earthquakes associated with the subducting slab. A metastable olivine wedge (MOW) does exist within the subducting slab at the mantle transition zone (MTZ) depth,with most deep earthquakes occurred within and in the vicinity of the MOW,favoring the dual-mechanism hypothesis as the initiation mechanism of deep earthquakes. Seismic observations show the upper and lower boundaries of the subducting high-velocity slab at MTZ depths (410 to 660 km),suggesting a compositionally layered slab and high water contents beneath the slab. A better understanding of the slab structures and the dynamic processes of the Pacific subduction zone,which is a very rare region with intense deep seismicity beneath continents,requires the efforts of interdisciplinary teams to carry out joint sea-land geophysical investigations,high-pressure/high-temperature experiments,and geodynamic simulations for the Northwest Pacific subduction zone.