湖北地区上地幔各向异性及其动力学意义  

Research on the upper mantle seismic anisotropy beneath Hubei and its geodynamic implication

作　　者：张丽芬[1,2] 姚运生[2] 廖武林[1,2] 李井冈[1,2] 王秋良[2] 王墩[2] 

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]中国地震局地震研究所,武汉430071

出　　处：《地球物理学报》2011年第1期35-43,共9页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(40730317);中国地震局地震研究所所长基金(IS200956052;IS200956011)共同资助

摘　　要：SKS波分裂测量是研究大陆地幔的形变特征、探索大陆动力学和演化过程的重要工具.本文选用湖北数字地震台网(HB台网)和中国数字化宽频带地震台网(CB台网)提供的三分量宽频带数字化地震资料,使用旋转相关法和切向能量最小法,计算得到了湖北地区20个地震台站下方上地幔各向异性参数.结果表明,快波偏振方向较为复杂:大别造山带内,呈平行于大别造山带构造走向的NWW向,且与绝对板块运动方向基本一致,反映印支燕山期扬子板块与华北板块南北向挤压碰撞造山的过程,而地幔流动则是造成这种南北挤压的力源.扬子板块内NWW向虽与绝对板块运动趋势一致,但比较离散,受地幔对流影响不明显,而NE向各向异性主要与燕山后期之后应力场的转变有关.分析认为,该地区的上地幔各向异性为地幔流动和固结在岩石圈中的"化石各向异性"共同作用的结果.根据上地幔各向异性方向与主要构造带的走向平行,可以作为地壳变形与上地幔连贯变形的证据.整个研究区域得到的分裂延迟时间在0.5～1.35 s之间,厚度在58～155 km之间.SKS wave splitting measurement is a powerful tool to characterize mantle deformation and study the dynamics and evolution of continents. In this paper, Hubei digital seismograph network and China Broadband Digital Seismograph Network are used to analyze the direction and extent of seismic anisotropy. We use the rotation correlation method and the technique of Silver and Chan to determine SKS wave splitting parameters at 27 three-component broadband stations in Hubei area, including the azimuths of fast polarization direction and delay times of split shear wave. The fast wave polarization directions beneath this area are divided into two groups： NWW and NE. The preferred orientation of NWW shows a good relation with the strike direction of the Dabie orogenic belt, and is parallel to the absolute plate movement. Combining with the structural evolution process, we infer that the preferred orientation of NWW maybe reflects the north-south-trending compression and collision of Yangtze block and North China block, and the mantle flow is the power source leading to this compression. And the preferred orientation of NE in Yangtze platform should have a certain relation with the change of stress field after the late-Yanshan stage. The upper mantle anisotropy can be explained by the combined effect of mantle flow and the so-called ＂fossil anisotropy＂ frozen in the lithosphere, which was caused by the Indosinian and Yanshanian orogeny. Delay times range from 0.5 s to 1.35 s. According to the relationship between time delay and anisotropic depth, we can infer that the fossil deformation may produce anisotropic structures at depths about 58-155 km.

关 键 词：上地幔 地震各向异性 SKS分裂 大别造山带 扬子地台 

分 类 号：P315[天文地球—地震学]