三峡水库坝址及邻区中上地壳S波速度结构

S-wave velocity structure of upper and middle crust beneath the Three Gorges reservoir dam and adjacent region

利用三峡数字地震台网记录的Sg波到时资料,采用地震层析成像技术,重建了三峡水库坝址及邻区中上地壳的三维速度图象,研究了地壳深部构造,主要结论是:①黄陵背斜的岩性具有固结程度高、岩体均匀完整、埋藏深度至少达14km的特征;②秭归盆地与边缘构造由于岩层一致,而速度结构相同;构造变形的强度决定了秭归盆地及周缘区域沉积层的厚度分布和速度结构特征;③中上地壳中存在上地幔部分熔融物质,主要分布在秭归盆地和培石附近下方;④结晶基底的构造不均匀,顶面和底面起伏变化大,厚度和速度变化较大;⑤速度梯度带与重力梯级带位置一致,重力梯级带成因需要考虑深部构造和介质因素.

A 3-D S-wave velocity structure of upper and middle crust beneath the Three Gorges reservoir dam and in adjacent region was reconstructed by means of the seismic tomography using the absolute Sg-arrivals from the earthquakes observed by the Three Gorges seismic network. Main research results of the crustal structure are as follows. ①The lithology of the Huangling anticline is highly solidified, with uniformity and integrity. Its buried depth is not less than 14 km. ② The rock strata of the Zigui basin are consistent with that of its marginal region, so their velocity structures are the same. The depth distribution and velocity structure characteristics of the Zigui basin and its adjacent areas depended on the intensity of the tectonic deformation. ③ The partially molten substances, located in upper and middle crust and intruded from upper mantle, mainly distribute beneath the Zigui basin, as well as nearby the Peishi region. ④The crystalline basement was constructed inhomogeneously, its top and bottom boundary, and the basement thickness and corresponding velocity structure, show significant regional variation.⑤ The velocity gradient zone is generally consistent with the gravitational gradient zone.