摘要
本文利用华北地震科学台阵、鄂尔多斯及周缘地震台网和区域地震台网记录的62736个远震P波走时数据,获得了鄂尔多斯块体中部与华北地区之间400km深度范围内的P波三维速度结构.考虑到研究区的复杂地质结构,本文采用FMM算法和子空间反演算法进行地震层析成像.成像结果表明:1)研究区的地壳速度分布与地质构造格局的相关性显著,随着深度的增加相关性减弱;断裂带多为高速异常区和低速异常区的分界线.2)研究区东部的速度结构与鄂尔多斯块体相比存在明显的不均一性,上地幔高速异常具有南北不均匀性.表明华北克拉通破坏时东、西部的岩石圈可能经历了不同的构造变形过程,东部岩石圈受到大规模破坏,破坏后的上地幔物质呈南北向不均匀分布,西部鄂尔多斯块体岩石圈保持着相对稳定的克拉通特征,不存在大规模破坏的证据.3)华北克拉通的岩石圈厚度由东向西整体逐渐增加.东部在100km深度附近出现大范围的低速异常,表明在该深度已进入软流圈,西部鄂尔多斯块体的岩石圈厚度约为250km.4)鄂尔多斯块体的东边界在黄河以东的离石断裂带.
We determined the 3D P-wave velocity structure down to 420 km depth beneath the central Ordos Block and North China Basin using 62736 teleseismic arrival times,which were recorded by 222 seismic stations in our study region.For adapting to the complicated structure,we used the FMM algorithm and Subspace Inversion method in our tomography.Our results show that：1）The crustal velocity structure of the study area is coherent with surficial tectonic though it attenuates with increasing depth.Most fault zones are the boundaries between the high-velocity zone and the low-velocity zone.2）Velocity distributions of crust and upper mantle beneath the eastern of study area are inhomogeneous both in horizontal direction and vertical direction,where high-velocity anomalies are strong lateral heterogeneous in NS direction;however,the heterogeneity in Ordos block is not obvious.It indicates that the North China Craton destruction of eastern and western lithosphere may experience different tectonic deformation process.The eastern lithosphere was subjected tolarge-scale destruction, which the upper mantle is inhomogeneous in NS direction. While,the Ordos block lithosphere maintained a relatively stable craton feature,which did not exist the large-scale destruction evidence currently.3）The thickness of the NCC lithosphere is increased gradually from east to west.There are extensive ranges of low velocity anomaly at 100 km depth,which indicates that the NCC had been into asthenosphere. The thickness of Ordos block lithosphere is about 250 km.4）The eastern boundary of Ordos block is Lishi fault zone.
出处
《地球物理学进展》
CSCD
北大核心
2014年第3期999-1007,共9页
Progress in Geophysics
基金
国家自然科学基金项目(41174070
90914005)资助
