川滇地区三维P波速度结构反演与构造分析

3-D P Wave Velocity Structure Tomographic Inversion and Its Tectonic Interpretation in Southwest China

根据205个区域台站记录的近60000条地震初至P波走时资料,采用层析成像理论与伪弯曲射线追踪方法,反演了川滇地区地壳上地幔的三维P波速度结构.结合区域地质构造以及地球物理背景,分析和解释了三维速度结构图像反映的川滇地区不同深度的介质结构与构造特征.结果表明:(1)沉积盆地、高山山地等主要表现出速度负异常的特征,有的高山山体负异常可深达下地壳与上地幔,反映了新造山带的强烈构造隆升与相伴的重力均衡作用;(2)川滇块体周缘大型活动断裂带附近的中下地壳内普遍存在低速层,它们的存在为调节断裂和块体运动提供了深部解耦条件;(3)根据对P波速度结构图像的分析,识别和推断出川滇地区若干主要活动断裂的深部构造特征及它们倾向与下延深度.

We have selected about 60 000 arrival times recorded by 205 regional stations, with the seismic tomography theory and three dimensional ray tracing method, to determine a detailed three-dimensional （3-D） P wave velocity structure of the lithosphere in southwest China. Then we present the medium structure and tectonic characteristics of different depth which are reflected by the 3-D P wave velocity image in this area, integrated with the previous geological features and geophysical data. The results suggest that deposit basins and alpine mountainous regions present as negative anomaly, with some montage negative anomalies even extending to the deep crust or the upper mantle, which reflects the sharp rising of the new orogens and the concomitant gravity equilibrium; low-velocity layers exist far and wide in the middle and deep crust under the large fault zones around the Sichuan-Yunnan block, which can be taken as the decoupling layer adjusting the faults and blocks movement; some deep structures related with the main active faults, and the trends and extending depths can be distinguished from the P wave velocity image.