俯冲板块正断层形成及其地震动态触发机制研究：以汤加海沟为例

Subduction zone is the birthplace of the earth's largest earthquakes. Normal faults in the subducting plate provide fluid conduits for upper mantle serpentinization, and normal faulting earthquakes may induce large tsunamis. Thus, the formation process of normal faults and triggering of normal faulting earthquakes is of great significance to study the dynamic processes of subduction zone and protect the human life safety. This project aims to study the formation of the bending-related normal faults in geological time scale and mechanism for dynamic triggering of normal faulting earthquakes in the Tonga trench, where there are relatively good observations. The project will focus on the following three objectives: (1) Quantitative analysis of the relationships between the tectonic parameters and the normal faulting characteristics in the subduction plate at the Tonga trench. (2) Setup geodynamic models to simulate the formation of bending-related normal faults, and reveal the evolution of normal faults in the subducting plate in geological time scale at the Tonga trench. (3) Regarding the 2009 Mw8.1 normal faulting earthquake at the Tonga trench as an example, setup 3-D geodynamic models of the dynamic Coulomb stress triggering of earthquakes, calculate the temporal variations of dynamic stress on the fault planes, investigate the triggering sequence of the normal faulting earthquake in the subducting plate and the megathrust in the subducting interface and the rupture process of the normal faulting earthquake. We have a great deal of research experiences on this topic. The results of this project will significantly improve our understanding of the geodynamic evolutions of the subduction zones.

俯冲带是地球上最大地震的发源地。俯冲板块正断层为上地幔蛇纹石化提供通道，其地震可能引发大海啸，因此研究其形成过程及其地震触发机制对推动俯冲带动力学过程研究及保护人类生命安全都具有重要意义。本项目拟通过地球动力学模拟方法，以观测较好的汤加海沟为聚焦研究区，揭示俯冲板块正断层在地质时间尺度上的形成过程，探讨俯冲板块正断层地震的动态触发机制及其破裂过程。项目将聚焦三个主要内容:1）定量分析汤加海沟地质构造参数与俯冲板块正断层特征的关系；2）建立俯冲板块弯曲产生正断层的动力学模型，揭示汤加海沟俯冲板块正断层在地质时间尺度上的形成过程；3）以汤加海沟2009年Mw8.1级俯冲板块正断层地震为例，建立三维地震动态库仑应力触发模型，计算各断层面的动态库仑应力变化，确定俯冲板块正断层地震与俯冲界面逆冲大地震的触发顺序及破裂过程。项目已有丰富的前期研究积累，其成果将显著提高我们对俯冲带演化动力学过程的认识。

本项目通过地球动力学模拟的方法，结合已有观测结果以及其它构造参数，以汤加海沟为聚焦研究区，深入研究俯冲板块正断层在地质时间尺度上的形成过程，定量化地阐明俯冲板块正断层与地震特征受到俯冲带地质、地球物理与流体参数控制的关键机理。项目完满完成了所有的既定目标。项目在汤加-克马德克俯冲板片弯曲模拟、西太平洋俯冲板块正断层模拟对比、全球俯冲带板块弯曲模拟以及全球俯冲板变形及破裂区变化等四大方面取得了重要进展。项目实施期间，共发表标注项目资助的研究论文11篇，其中包括9篇高质量SCI期刊论文以及2篇中文核心期刊。项目团队培养了中国科学院南海海洋研究所4名硕士与博士毕业生。项目组成员在国内外学术会议上积极组织专题，包括美国地球物理联合会（AGU）秋季年会、地球系统科学大会等，通过口头报告、展板汇报等形式展示了项目最新的重要研究成果。并与国际一流科学家合作开展地球动力学模拟合作研究，通过合作开发先进的地球动力学模拟方法，促进了项目研究的顺利完成。本项目的完成对于提升全球俯冲带动力学的认识具有重要意义。