安宁河－则木河断裂带高分辨率三维地壳参考速度模型构建

The velocity structure of the fault zone plays an important role in controlling the earthquake rupture process, seismic wave propagation and energy radiation, inter- and post-earthquake deformation, and pattern of seismic activity. The Anninghe-Zemuhe fault zone is the important boundary of the eastern part of the Chuandian fragment, which is the likely risky segment for potential large earthquake (M≥7.0). In this proposal, seismic data recorded by the Xichang array, the Western Sichuan array and the permanent stations will be used to construct high resolution reference velocity model of the Anninghe-Zemuhe fault zone, including mapping the lateral variation of the Moho interface and Poisson's ratio with P-wave receiver function H-k stacking and CCP imaging, determining 1~60 s Rayleigh wave phase velocity maps with ambient noise tomography and teleseismic surface wave tomography, obtaining 3-D S-wave velocity structure using joint inversion of receiver function and surface wave dispersion, obtaining 3-D P-wave velocity structure using joint inversion of fault zone head wave and direct P-wave to enhance the accuracy of imaging in the northern section of the Anninghe fault. We then will construct high resolution 3-D crustal reference velocity model of the Anninghe-Zemuhe fault zone using joint inversion of body wave arrival time of local earthquake and surface wave dispersion data on the basis of the initial 3-D Vp and Vs velocity model obtained above. This project will provide velocity model and observation data for China Geophysical Reference Model. The results will be of great significance to understand the deep dynamic mechanism of strong earthquakes in the north and south seismic zones and the dynamics of the Tibetan Plateau.

断裂带的速度结构对地震破裂过程、地震波传播与能量辐射、震间和震后变形，以及地震活动模式都有重要控制作用。安宁河－则木河断裂带是川滇活动块体的东部重要边界，是未来发生7级以上地震的重点危险区。本申请使用西昌台阵、川西台阵和固定台站的数据，利用P波接收函数H-k叠加和偏移成像，确定莫霍面和泊松比的空间分布；应用噪声层析成像和远震面波成像获得1~60s的相速度分布；采用P波接收函数和面波频散联合反演，获得三维S波速度结构；联合使用断层带首波和直达P波进行成像，获得三维P波速度结构，重点提高安宁河断裂北段的成像精度。以上述研究获得的三维P波和S波速度结构作为初始模型，采用近震体波走时和面波频散联合反演，构建安宁河－则木河断裂带高分辨率的三维地壳参考速度模型，为中国区域地震学参考模型构建提供速度模型和观测数据。相关结果对认识南北地震带强震活动的深部动力机制和青藏高原动力学研究都有重要意义。

本项目以安宁河-则木河断裂带为主要研究区域，充分利用研究区的固定和多期流动观测数据，采用远震体波接收函数、背景噪声成像和体波走时成像等多种方法构建了安宁河－则木河断裂带及周边地区高分辨率的三维地壳速度模型。本项目取得的主要研究结果包括：（1）在安宁河－则木河断裂带完成了30个宽频带流动地震台站的观测，为项目研究提供了高质量的观测数据；（2）利用远震P波接收函数H-k叠加和偏移成像，确定了莫霍面和泊松比的空间分布；（3）采用噪声层析成像获得了研究区的三维S波速度结构，采用近震体波走时成像方法获得了研究区的三维P波和S波速度结构；（4）采用体波走时和面波频散联合反演，构建了安宁河－则木河断裂带高分辨率的三维地壳参考速度模型；（5）发展了基于深度学习的地震检测方法，对观测数据进行处理，获得了高完备、高精度的地震目录，探讨了安宁河－则木河断裂带的地震活动特征和危险性。本项目为中国区域地震学参考模型构建提供了速度模型和观测数据。相关结果对认识南北地震带强震活动的深部动力机制和青藏高原动力学研究都有重要意义。