利用面波和接收函数联合反演滇西地区壳幔速度结构

Using surface wave and receiver function to jointly inverse the crust-mantle velocity structure in the West Yunnan area

考虑到面波频散对介质S波速度、接收函数对界面深度的各自敏感性优势,综合利用面波和接收函数资料实现联合反演,求取滇西地区壳幔速度结构.本文利用适配滤波频时分析技术处理覆盖滇西地区的长周期面波资料,获得10.5～105.0s周期范围内的面波群速度频散,进而利用分格反演方法提取研究区内1°×1°网格纯路径频散;基于滇西地区宽频带三分量远震记录,经反褶积后得到台站下方的远震P波接收函数.联立面波纯路径频散信息和接收函数资料建立系统方程,利用阻尼最小二乘法实现联合反演,从而获得滇西地区壳幔S波速度结构.结果表明,滇西地区以红河断裂为界,东西两侧壳幔结构存在明显差异,断裂西侧约20km深度处存在一厚度为10km左右的低速层,而东侧并不明显;滇缅泰块体上的畹町、沧源一带属于上地幔低速区,而另一个地幔低速区则位于滇中块体上的康滇古隆起上,两处地幔低速区与大地高热流分布、强震活动具有较好的对应关系.

Because surface wave dispersion is well sensitive to S wave velocity and receiver function is sensitive to interface depth, respectively, we use surface wave and receiver function data to make a joint inversion to probe the crust-mantle velocity structure beneath western Yunnan Province. We apply the technique of matchedfilter frequency-time analysis to process long-period surface wave data covering western Yunnnan and obtain the surface wave group velocity dispersion in the period range 10.5 ～ 105.0s. Then we employ the grid inversion method to extract pure path dispersion in the grid 1°× 1° in the study area. Using the teleseismic broadband records of western Yunnan and the deconvolution method, we obtain the teleseismic P wave receiver function beneath the stations. Combining the information of surface wave pure path dispersion and the receiver function data, we perform a joint inversion by means of the damped least-squares method to determine the crust-mantle velocity structure beneath western Yunnan. The result shows that taking the Red River Fault as the boundary, the structures of the crust and mantle on its both sides are notably different. On the west side of the fault there is a low-velocity layer of ～ 10km thickness at depth - 20km, while this layer is not apparent on the east side of the fault. Beneath the Wanding and Cangyuan areas, which are geologically located in the Yunnan-Myanmar-Thailand block, the upper mantle has a relatively low velocity. Another low-velocity layer oI the upper mantle appears below the Kangdian palaeo-uplift in the Mid-Yunnan block. It seems that these two low-velocity layers of the mantle are associated with the distributions of high heat flow and major earthquakes.