四川宜宾地壳浅部三维S波速度结构及方位各向异性

利用四川宜宾及周边地区布设的30个临时台站连续44天的波形记录,采用背景噪声互相关方法提取了周期为1—15 s的瑞雷面波相速度频散曲线,然后使用基于面波射线路径追踪的瑞雷面波直接成像方法得到0—10 km深度范围内三维S波速度模型,最后利用该模型作为初始模型采用相同的反演框架得到该地区的方位各向异性结构.结果表明:浅层...

Shallow shear wave velocity structure and azimuthal anisotropy in Yibin,Sichuan

Based on the 44-day continuous waveform data recorded by 30 temporary stations in Yibin and its adjacent regions, Rayleigh wave phase velocity dispersion curves in the period range 1?15 s are extracted by using the ambient noise cross-correlation method. Then the direct surface wave tomographic method with period-dependent ray tracing is applied to obtain the 3-D shear-wave velocity structure. Finally, by taking the inverted shear-wave velocity model as the initial model, we obtained the azimuthal anisotropic structure in the same inversion framework. The results show that the distribution of shallow shear-wave velocity is heterogeneous, and the degree of heterogeneity decreases with the depth. At about 2 km depth, high velocity is distributed beneath the Junlian-Gaoxian-Gongxian-Changning anticline, which may be related to the folding, uplift, weathering and denudation of the strata in this area. The northwest of Shizitan-Shuanghechang-Changning anticline shows relatively low velocity compared with the southeast with a depth deeper than 5 km. As we known, the medium with relatively low wave velocity are usually weaker compared with high velocity, so it may be one of the reasons for the northwestward rupture of the Changning earthquake sequence in 2019. Our results of azimuthal anisotropy show that near the Kongtan anticline, the fast wave direction is approximately parallel to the strike of the anticline, and the anisotropic strength becomes weaker with the increase of depth.We also found that the fast wave direction gradually converges to the north and spreads to the south, showing a brush-type structure. Under the influence of regional geological structure and stress field, the fast wave directions in some local areas show complex characteristics at different depths.