云南地区地壳厚度与泊松比变化及其意义

Tectonic implications from the distribution map of the crust thickness and Poisson's ratio in the Yunnan area

利用云南省＂十五＂期间建成的46个宽频带地震台2007年7月-2008年7月间记录的6级以上远震波形资料,提取各台站下方的P波接收函数,并据此计算和分析了云南地区的地壳厚度变化情况和泊松比的分布特征。得到的较前更高空间分辨率的结果表明,云南地区的地壳厚度总体呈现＂北深南浅＂的特征,最北部的中甸台地壳厚度是53.5km,而最南端的勐腊台仅为31.7km。红河断裂的边界作用较为明显,断裂以东的地壳厚度较大,以西的则较小;断裂西侧的地壳厚度变化较为舒缓,东侧则变化剧烈,且自东南向西北厚度逐渐加深。在川滇菱形块体及周围存在2个上地幔隆起,一个隆起的中心轴在楚雄-元谋一带,另一个隆起的中心轴在东川附近。从泊松比的分布情况来看,研究区内泊松比的分布是不均匀的,自南向北存在较大差异,北部的中甸台处达到最大0.289,而南部的景谷台处仅为0.146,与地壳厚度＂北深南浅＂的趋势基本相一致。泊松比在滇东块体内较低,在滇中块体内较高;北纬24°以北地区泊松比显然比以南地区要高。总的分布状态为：川滇菱形块体周围的泊松比属于中-高值（0.26≤σ≤0.29）。

We derived receiver functions under 46 stations of the Yunnan Seismic Network after the tenth ＂Five-year Plan＂from teleseismic P waves recorded from July 2007 to July 2008. We then used these receiver functions to calculate higher resolution crust thickness and Poisson ＇s ratio under this area. The result showed that the crust thicknesses in Yunnan are generally thicker in northern part than southern part,for example,the crust thickness under the Zhongdian seismic station in northwestern part of Yunnan is about 53. 5km,but only 31. 7km under the Mengla seismic station in the southeastern part of Yunnan. We also found that the crust thicknesses on eastern part of Red River fault is thicker and changes more gently than that in western part,so the Red River fault is an obvious boundary of the Yunnan area. Another clear result indicates there are two upper mantle rises in or nearby the Sichuan-Yunnan diamond block,one of the rise centers is in the Chuxiong-Yuanmou area,and the other is in the Dongchuan area. And the Poisson＇s ratio results reveal that they are lateral heterogeneous and different obviously from north to south. In north part,under the Zhongdian seismic station,the Poisson＇s ratio reaches 0. 289,but in south,under the Jingu seismic station it is only 0. 146. It seems they are in accord with the crust thickness feature. The distribution map also shows the Poisson ＇s ratio lower in eastern Yunnan block and in southern Yunnan from latitude 24°,but higher in mid-Yunnan block and in northern Yunnan from latitude 24° as well as the Sichuan-Yunnan diamond block is medium to high Poisson＇s ratio area.