北京地区上地壳三维细结构层析成像

Fine tomographic inversion of the upper crust 3-D structure around Beijing

利用三维不分块地震层析成像技术对北京东北部地区的三维人工地震莫霍反射波走时数据进行反演,得到了该区上地壳的三维P波、S波慢度及波速比结构图像,三种结构不同深度的切片图像揭示出慢度和波速比分布有呈北东向和北西向展布的特征.断裂活动引起沉积不均匀造成现今的速度分布,地震大多分布在波速比较低的块体内,说明地震不仅与断裂活动有关,有可能还与物质结构和性质相关;北京地区上地壳速度结构、断裂活动和物质性质三者之间存在密切关系.

Travel-time data from 3-D Moho reflection survey in 2002 are inverted using seismic tomographic method without blocks. The upper crustal 3-D structure of slowness of P, S wave and V P/V S around Beijing area are given. The slices of three structures in different depths reveal the NE and NW trends of slowness and V P/V S distributions. The upper crustal velocity images are resulted of the sedimental heterogeneity by active seismotectonics in the area. Most of regional earthquakes occurred in low-V P/V S zones, it indicates that earthquake activities are not only related to active faults and may be linked to crustal structure and its material property. There is a close relationship among velocity structure, active faults and upper crustal materials around Beijing area.