秦岭及周边地区背景噪声Love波层析成像  

Ambient noise Love-wave tomographyin Qinling orogeny and surrounding area

作　　者：贺伟光[1] 陈永顺[1] 叶庆东[2] 安美建[3] 董树文[4] 

机构地区：[1]北京大学地空学院地球物理研究所,北京100871 [2]成都理工大学地球物理学院,成都610059 [3]中国地质科学院地质力学所,北京100081 [4]中国地质科学院,北京100037

出　　处：《地球物理学进展》2015年第1期47-56,共10页Progress in Geophysics

基　　金：中国地质科学院工作项目<中央造山带与南北构造带交汇区地壳深部地质调查>;科技部(2009AA093401-05);国家基金委项目(90814002)联合资助

摘　　要：和其它地震成像方法比较,背景噪声成像方法能够较有效的获得地壳以及上地幔的速度结构.本研究将PhaseWeighted-Stack方法应用到了互相关函数的叠加过程中,有效的增强了Love波信号,压制了获得的格林函数中的噪声.本文将这种技术应用到了北京大学与中国地质科学院合作布设在秦岭及其周边地区的(69台)宽频带流动地震台阵,利用台站的水平分量噪声记录提取的Love波频散曲线来获得台站间Love波相、群速度,进而得到了从6 s到30 s周期的Love波相速度二维分布图像.进一步进行了三维SH波速度反演,获得了研究区地壳和上地幔SH波3D速度结构,为研究该地区构造运动和上地幔动力学提供基础观测资料.一个重要的结果显示秦岭造山带以及鄂尔多斯块体外部西北方向在50 km深度呈现较强的SH波低速异常,这个连贯的低速异常带是否对应于青藏高原上地幔物质在鄂尔多斯块体和四川盆地块体之间的向东扩展流动而形成的温度异常或者部分熔融体还有待于进一步验证.Ambient noise tomography has become a powerful method to image the structure of crust and upper mantle with a better resolution compared to surface wave tomography.After pre-processing the seismic record,Phase-Weighted-Stack,which enhanced Love wave signal,was incorporated into crosscorrelation process,down-weighting noise in the resulting Green functions.This technique was applied to the data collected at a portable seismic array which consists of 69 seismic stations operated by Peking University and Chinese Academic Geological Science.Phase velocity distribution of Love waves at periods of 6 s to 30 s obtained by tomography is consistent with geological settings in the region.Further 3D SH velocity inversion was conducted from these phase velocity results to provide seismic observations for studying the tectonics and upper mantle dynamics in the region.One important observation is that there exists a low SH velocity zone beneath the Qinling oregenic belt at 50-km depth.Whether this low velocity zone was caused by the eastward extrusion of the Tibetan mantle between the Ordos block and Sichuan Basin is debatable and should be further investigated by other seismic imaging studies for this region.

关 键 词：LOVE波 Phase-Weighted-Stack SH波反演 背景噪声 

分 类 号：P541[天文地球—构造地质学] P315[天文地球—地质学]