华北地区三维地壳上地幔结构

本文用均等显示滤波频时分析方法分析了长周期瑞利面波资料,获得了路经中国大陆及邻区的238条混合路径的面波群速度频散,其周期范围为10.5-113s.用改进的分格反演方法从混合路径频散中提取出位于华北地区的12个4°×4°网格单元的纯路径频散并反演其地壳上地幔结构.所得结果表明,华北地区地壳上地幔结构横向变化显著;从东向西地壳逐渐变厚;位于华北东部的分格在地壳中20km深处普遍存在低速层,整个华北地区上地幔低速层埋藏较浅,一般为55-100km之间.各个网格上地幔低速层的速度不尽相同.     

Group-velocity tomography and lithospheric S-velocity structure of the South American continent

The lithosphere of the South American continent has been studied little, especially in northern Brazil (the Amazonian region). A 3D lithospheric S-velocity model of South America was obtained by first carrying out Rayleigh and Love wave group-velocity tomography, and then inverting the regionalized dispersion curves. Fundamental mode group velocities were measured using a Multiple Filtering Technique. More than 12,000 paths were examined and about 6000 Rayleigh- and 3500 Love-wave dispersion curves with good quality were retrieved. Checkerboard tests showed that our dataset permits the resolution of features 400-800 km across laterally in the central part of the continent from crustal to upper mantle depths. Our results confirm previous tomographic results and correlate well with the major geological provinces of South America. The 3D S-velocity model confirms both regional features of SE Brazil from P-wave travel-time tomography and continental-scale features of central and western South America from waveform inversion, e.g., lowest velocities in the Andean upper mantle; three parts of the Nazca plate with flat subduction; strong low-velocity anomalies in the upper-mantle depth beneath the Chaco basin. Furthermore, our 3D model revealed new features in the South American continent: (1) high velocities in the lower crust were consistently found in regions with high Bouguer or free-air anomalies; (2) the NE-SW trending TransBrasiliano shear zone was delineated by a NE-SW low-velocity belt at lithospheric depths; (3) the eastern Amazonian craton appears to have thicker lithosphere than the western craton; (4) in areas of Archean nuclei located in the northeastern Guaporé shield and southeastern São Francisco craton, high velocity anomalies were found down to 150 km.     

任意空间取向TI介质中体波速度特征分析

基于任意空间取向TI介质(简称ATI)中体波速度和偏振解析解,通过模型数值计算给出ATI介质中体波群速度和相速度的变化特征,说明TI空间取向与测线方位对速度的影响。研究表明,体波群速度图案和相速度图案相对TI对称轴固定,随TI对称轴倾角及其相对测线方位角的变化呈现出一定的对称性和重复性;可以针对ATI地区的地质情况,给出体波群速度和相速度变化图案,为进一步的理论研究提供便捷。此结果也可以直接用于VSP(垂直地震剖面)和井间地震资料的分析研究