基于程函方法的多数据联合反演海原大地震震源区速度结构

1920年海原地震是近代中国罕见的毁灭性地震之一,针对海原震源区深部精细结构的研究对于认识强震的深部构造背景和孕震机制具有重要意义。射线走时型地震层析成像技术是当前深部结构探测的有力工具之一，其中基于程函方程的成像方法，因可获得全局最小走时场，且具有无条件稳定性等优点，适用于三维非均匀介质反演中。Moho面、岩石圈与软流圈边界(LAB)等地球间断面的精确刻画，对于认识区域构造演化至关重要，而且可为高精度层析成像反演提供初始模型。所以本项目首先利用P波和S波接收函数联合反演Moho、LAB等间断面；然后结合程函方程的体波走时层析成像方法，发展区域地震与远震多震相联合反演地壳-上地幔速度结构算法；最后用宁夏及周边固定台和部分喜马拉雅二期流动台数据，反演出海原地震震源区地壳-上地幔速度结构。该研究不仅得到海原地震震源区地壳-上地幔的高分辨三维速度结构模型，也将发展一种有效的地震成像联合反演方法。

Haiyuan Earthquake in 1920 is one of the rare devastating earthquakes in modern China. It is of great significance to study the deep and fine structure of Haiyuan Earthquake area to understand the deep structural background and seismogenic mechanism of strong earthquake. Currently, ray tomography is one of the powerful tools to detect the deep structure of the focal area, among which, the imaging method based on the peikonal equation is suitable for 3D inhomogeneous medium inversion thanks to its advantages of the global minimum traveltime field and the unconditional stability. The accurate characterization of earth discontinuities such as Moho, lithosphere and asthenosphere boundary (LAB) is essential to understand the regional tectonic evolution, and can provide the initial model for high-precision tomographic inversion. Therefore, in this study, the P-wave and S-wave receiver functions are firstly used to jointly invert the Moho, LAB and other discontinuities, then in combination with the body wave traveltime tomographic method of the eikonal function method, the algorithm of joint inversion of crust and upper mantle velocity structure by regional earthquake and teleseismic earthquakes is developed. Finally, the data of Ningxia and its surrounding fixed stations and part of the Chinarray II seismic stations are used to perform the inversion of velocity structure of crust and upper mantle in the source area of Haiyuan Earthquake. This study not only builds the high-resolution 3D velocity structure model of crust and upper mantle in Haiyuan Earthquake source area, but also will develop an effective joint inversion technique for seismic imaging.