河西走廊中部地区三维速度结构研究  

A study of the 3-D Velocity Structure in Central Hexi Corridor

作　　者：董治平[1] 张元生[1] 

机构地区：[1]中国地震局兰州地震研究所,甘肃兰州730000

出　　处：《地球学报》2007年第3期270-276,共7页Acta Geoscientica Sinica

基　　金：地震科学联合基金项目(编号:504004;197025;106086)资助。

摘　　要：利用天然地震记录资料,对河西走廊中部地区三维速度结构与震源参数进行了反演,获得了该区的三维速度图像.分层速度结果反映出研究区深部结构的一些重要信息.①浅部沉积层的速度为5.00～6.15 km/s,垂直速度梯度接近0.15 km/s;结晶基底埋深约7 km,速度为6.15 km/s.②上地壳深达18 km,速度约为6.33 km/s;民乐盆地速度略高于祁连山和龙首山,阿拉善地块存在明显的向河西走廊下插的现象.③中地壳底部深约30 km,速度为6.58 km/s;较显著的速度变化区正位于北祁连与河西走廊过渡带.④下地壳厚度显示祁连山偏厚,莫霍面埋深为54 km;河西走廊稍薄,莫霍面深约为52 km;阿拉善地块莫霍面深53.5～53.0 km,介于祁连山与河西走廊之间.在34～42 km深度存在明显的低速层,速度约为6.5 km/s.研究认为,龙首山断裂带可能是逆冲性质的上地壳断层,昌马-俄博断裂可能是一条近直立的中地壳断层.The 3-D velocity tomography image of central Hexi Corridor was obtained by the joint inversion of 3-D velocity structure and focal parameters based on the S-P data of micro-earthquakes recorded by the digital seismic network. The inversed layering velocity structure does reflect some important features of the deep structure in the study area： ① The velocity of shallow deposition is about 5.00 ～ 6. 15 krn/s and the vertical velocity gradient is close to 0.15 km/s; the depth of the crystalline basement is about 7 km, with the velocity being 6.15 km/s. ② The depth of the upper crust is some 18 km, with the velocity being 6.33 km/s ; the velocity of Minle basin is slightly higher than that of the North Qilian Mountain and the Longshou Mountain. The Alxa block is obviously thrusting under the Hexi Corridor. ③ The bottom of the middle crust is about 30 km in depth with the velocity being 6.58 km/s, and the low-velocity zone is located just between the Qilian Mountain and the Hexi Corridor. ④ The depths of the lower crust imply that the Moho depth is 54 km in the Qilian Mountain, 53.5 - 53.0 km in the Minle basin and 52 km in the Alxa block, and that there obviously exists a low-velocity layer of 6.5 km/s at the depth of 34 - 42 km. The research results show that the Longshou Mountain fault may be a reverse one in the upper crust and the Changraa-Ebe fault is probably a vertical one reaching the middle crust.

关 键 词：河西走廊中部地区 三维速度结构 反演 低速层 

分 类 号：P315.31[天文地球—地震学]