基于密集台阵的福建及其邻区地壳地震波各向异性结构成像研究

Fujian and its adjacent areas are near the junction point between the Eurasian, Filipino and Pacific plates. The multiple crustal movements made complex tectonic structure in this region. Several destructive earthquakes occur in the past hundreds years and the probability of destructive earthquake is still high in the future. Therefore, it is need to analysis the seismogenic fields in this region, especially the stress field. Due to the poor coverage of available data, the resolution and coverage of the existing studies on the tectonic stress field are limit. The Fujian earthquake agency conducted many explosion and large-volume air-gun with dense array experiments in past years. Those experiments provide massive high quality data and make it possible to conduct high-resolution anisotropy imaging in crust that helps to understand tectonic stress field. Therefore, we propose to employ the P anisotropy tomography and shear wave splitting technique to image the crustal anisotropy structure, and comprehensive analyze the tectonic stress field with the seismic anisotropy structure, earthquake focal mechanism，crust deformation field, and geological information. The results are useful in the mid- and long-term earthquake hazard analysis and provide input data for the geodynamic study.

福建及其邻区邻近欧亚板块，太平洋板块和菲律宾板块的交汇处，多次地壳运动改造后形成复杂的构造体系，历史地震活动性较强，存在发生破坏性地震的可能性，因此有必要开展地震构造背景场研究，为中长期地震危险性分析提供参考。福建地区的现有构造应力场研究成果，限于可用数据的空间覆盖率不足，仍存在较大空白。近年来福建省地震局开展了一系列人工爆破和大容量气枪激发实验，以及密集台阵观测，提供了大量高质量数据。拟利用人工震源信号和天然地震记录，分别采用P波初至波各向异性成像方法和S波分裂分析方法，开展各向异性结构成像研究工作，获取高分辨率的P波三维和S波二维各向异性结构。综合各向异性结构，地震震源机制解以及地壳形变场和地质构造等信息，推断区内构造应力场，为地震危险性评估提供参考，也可为区内地球动力学研究提供基础数据。

福建及其邻区邻近多个板块汇聚边界，地质演化过程复杂，区内大型断裂发育，曾经发生过多次强震，地震风险性高。通过开展地震各向异性成像有望厘清区内构造背景场，为中长期地震安全性评估提供参考。搜集整理了研究区内2016年和2017年的固定地震台网连续数据，在此基础上综合采用偏振分析、噪声互相关函数非对称性等方法分析了连续记录中面波信号的来源方向，发现冬季主要源自北太平洋、北大西洋和南大洋，夏季主要源自西太平洋及福建近岸区域。反演构建了福建地区三维S波速度结构，揭示了大埔-政和断裂和邵武-河源断裂下方的中下地壳低速层，三个主要地块间的显著差异, 壳内呈现负径向各向异性。基于接收函数发现福建地区地壳呈现东南薄，西北厚的趋势，断裂带附近地壳Vp/Vs值偏低，东南部Vp/Vs整体偏低。