滇西北三江并流地区地壳S波速度结构

Crustal S-Wave Velocity Structure in Three Parallel Rivers Region in Northwest Yunnan

对滇西北三江并流地区36个台站记录的远震波形数据进行处理,提取径向P波接收函数,基于中国地震科学实验场地区地壳剪切波速模型获取不同区域的初始模型,采用时间域线性反演方法和bootstrap重采样技术,反演各台站下方的S波速度结构。结果表明:1)研究区地壳S波速度结构整体以澜沧江断裂带和27.5°N为界,表现出明显的区域差异。在上地壳,S波速度在0~25 km深度范围内存在由地表向壳内延伸的低速层,但不同区域低速层厚度存在较大差异,27.5°N以北低速层较为发育,厚度在20~25 km之间;27.5°N以南,澜沧江断裂带东西两侧低速层厚度差异明显,断裂带以西在10~25 km之间,断裂带以东约4 km。2)在下地壳,S波速度在横向上以澜沧江断裂带和27.5°N为界,表现出NE与SW区域以相对低速为主,NW和SE区域以相对高速为主的分布特征;垂向上,怒江断裂带中南部和金沙江-红河断裂带北端附近局部区域25~45 km深度范围内存在低速体,与上地壳低速层相连。3)澜沧江断裂带为地壳厚度和S波速度变化的重要分界面,对滇西北三江并流地区的构造演化过程具有控制作用。

By processing the remote seismic wave profile data recorded by 36 stations in three parallel rivers region in northwest Yunnan,we extract the radial P-wave receiving function,and obtain the initial models of different regions based on the crustal shear wave velocity model of China Earthquake Science Experimental Field.We adopt the time-domain linear inversion method and bootstrap resampling technique.At last,the S-wave velocity structure under each station is inverted.The results show that:1)The S-wave velocity structure of the crust in the study region is divided by the Lancang river fault and 27.5°N,showing obvious regional differences.In the upper crust,there is a low-velocity layer extending from the surface to the interior of the crust in the range of 0-25 km in the S-wave velocity,but the thickness of the low-velocity layer varies greatly in different regions.The low-velocity layer is relatively developed north of 27.5°N with a thickness of 20-25 km,and south of 27.5°N with a significant difference in the thickness of the low-velocity layer on the east and west sides of the Lancang River fault.The fault is between 10 km and 25 km to the west and about 4 km to the east.2)In the lower crust,the S-wave velocity shows the transverse distribution characteristics of“the NE and SW regions are dominated by relatively low velocity,while the NW and SE regions are dominated by relatively high velocity,”which is bounded by the Lancang River fault and 27.5°N.There are low-velocity bodies in the mid-south of the Nujiang fault and the northern part of the Jinshajiang-Honghe fault at a depth of 25-45 km,which are connected with the low-velocity layer of the upper crust.3)The Lancang river fault is an important interface between crustal thickness and S-wave velocity,and plays a controlling role in the tectonic evolution of three parallel rivers region in northwest Yunnan.