云南地区地壳中上部横波速度结构研究

S-WAVE VELOCITY STRUCTURE OF THE MIDDLE AND UPPER CRUST IN THE YUNNAN REGION

根据云南地区的基阶瑞利波相速度频散资料 ,用面波层析成像方法反演得到该区域中上地壳S波速度结构 .给出了研究区域内在 4个深度上的S波速度水平分布图像和沿 10 0 .5°E、2 4°N、2 5°N、2 6°N及 2 7°N的S波速度 -深度剖面图 .结果表明 :在小江断裂与红河断裂围成的川滇菱形块体内 ,2 6～ 30km深度处的速度明显低于周边地区 ,其南段从地表到 15km深度均为明显的低速区域 .云南地区的强震 (M >6 .0 )震中位置与S波速度分布图像具有明显的相关性 ,主要分布于高速与低速的过渡区域 .

The dispersion data of phase velocities of the fundamental mode Rayleigh wave are used in this paper, the S-wave velocity structure of the middle and upper crust in Yunnan region is inverted. The horizontal distribution maps of S-wave velocities at four depths and S-wave velocities on profiles along 24°N, 25°N, 26°N, 27°N and 100.5°E in the study region are given. The results show that within the range of 26～30km depth, the S-wave velocity in the Sichuan-Yunnan rhombic block is obviously lower than that in surrounding areas; In the south rhombic block, there is a low velocity region to exist in the range from ground surface to 15km depth. The epicentral locations of strong earthquakes with M>6.0 in Yunnan region are closely related to the S-wave velocity distribution. They are mainly distributed in zones of transition between low and high velocities.