门源地区地壳三维体波速度结构及地震重定位研究

3D body-wave velocity structure of crust and relocation of earthquakes in the Menyuan area

本文使用甘肃、青海数字地震台网及中国地震科学探测台阵记录到的门源地区地震的P波和S波到时资料,应用双差层析成像方法联合反演了该地区的地壳三维速度结构和震源位置参数.结合地质构造背景,研究了门源MS6.4地震孕育发生的深部介质环境及该地区速度结构与地震活动性之间的关系.结果表明:反演之后地震的走时残差均方根显著降低,重定位后的地震在垂直方向上呈现出与断层位置有关的条带状分布.门源地区地壳速度结构存在明显的不均匀性,浅层P波和S波速度结构与地表地质构造及地形特征密切相关.研究区内地震活动性与地壳速度结构具有很强的对应关系,地震主要分布在高速异常区域及其边缘.门源MS6.4地震震中附近的P波和S波速度结构表现出明显的高速异常,且在震源区下方存在P波低速层,这种特殊的构造条件可能是导致此次地震发生的重要原因.

We used the double-difference tomography method and P-and S-wave travel time data recorded by the regional digital seismic network and temporary seismic array to invert 3D velocity structure and relocate seismic events in the Menyuan area.Combined with geological tectonic setting,we have studied the deep medium environment of the Menyuan MS6.4 earthquake and the relationship between velocity structure and seismic activity in this area.The results show that the root-mean-square residuals of earthquakes have been greatly reduced after inversion,and distribution of relocated earthquakes is obviously strip-shaped in the vertical section associated with faults.There is significant inhomogeneity of the crustal velocity structure in the study area,and the shallow velocity structure is closely related to the surface geological structure and topographic features.The seismic activity in the study area has a strong correspondence with the crustal velocity structure,and earthquakes are mainly distributed in high-velocity anomaly areas and their edges.The P-wave and S-wave velocity structures near the epicenter of the MS6.4 earthquake show obvious high-speed anomalies,and there is a low-velocity layer of P-waves below the source region.This special tectonic condition may be an important reason for the occurrence of the earthquake.