松辽盆地沉积层结构的短周期地震背景噪声成像研究

S-wave velocity structure of sediment in Songliao Basin from short-period ambient noise tomography

使用位于松辽盆地内部的NECESSArray台阵连续两年背景噪声数据,通过波形互相关和多重滤波方法提取到2~14s较短周期的Rayleigh波群速度和相速度频散曲线,基于快速行进(FMM)面波成像方法得到群速度和相速度成像结果,并采用最小二乘迭代线性方法反演获得了松辽盆地深至12km的三维S波速度结构.本文成像结果显示:松辽盆地内部S波速度分布的横向不均匀性与该区域的构造单元呈现出良好的空间对应关系.从地表至下方的6km深度,盆地北部比南部表现出更加强烈的低速异常,这一特征可能与盆地南北的沉积构造差异有关.中央坳陷区低速异常的边界与嫩江断裂走向相互平行,表明盆地基底断裂对盆地形成演化具有一定的控制作用.在垂直速度结构剖面中,2.9km·s^-1的S波速度等值线与地震反射剖面显示的盆地基底深度大致对应.基于S波速度模型和盆地基底速度(2.9km·s^-1),我们获得精细的松辽盆地沉积层厚度模型,结果表明松辽盆地的沉积层厚度分布呈现出中间厚、四周薄的特征,中央坳陷区的沉积层厚度范围大约在3~6km.

The ambient noise data of NECESSArray array located in the Songliao Basin were used to extract the Rayleigh wave and phase dispersion curves with short period of 2~14 sby crosscorrelation calculation and multiple filtering method.Rayleigh wave velocity and phase velocity distribution are obtained based on FMM surface wave imaging,three-dimensional S-wave velocity structures deep to 12 km in the Songliao Basin were obtained by the least square iterative method.The imaging results in this paper show that the lateral heterogeneity of the S-wave velocitydistribution in the Songliao Basin shows a good spatial correspondence with the tectonic units in the region.From the surface to 6 km depth,the northern part of the basin exhibits a more intense low-velocity anomaly than the southern part.This feature may be related to the difference in sedimentary structure between the north and the south of the basin.The boundaries of the low-velocity anomaly in the central depression area and the direction of the Nenjiang fault are parallel to each other,indicating that basin-basis faults have a certain control over the formation and evolution of the basin.In the vertical velocity structure section,the 2.9 km·s^-1 S-wave velocity contour roughly corresponds to the depth of the basin base shown by the seismic reflection profile.Based on the S-wave velocity model and the basin base velocity(2.9 km·s^-1),we obtained a fine sediment thickness model in the Songliao Basin.The results show that the thickness distribution of the sedimentary layers in the Songliao Basin is characterized by a thick middle layer and a thin surrounding area.The sedimentary thickness of the depression ranges from approximately 3 to 6 km.