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利用两条相互垂直的高分辨地震折射/宽角反射剖面和相应的非纵观测的多个扇形剖面取得的人工地震资料,研究天水和武都8级大震区的地壳和上地幔顶部结构和构造.二维剖面结果显示,地壳沿垂向可分为上地壳和下地壳两大层.上地壳中部存在低速层,层内介质速度比背景值低0.3～0.5km/s.莫霍面深度大约为46～48km.NE向的天水-武都剖面下地壳速度在横向上变化剧烈,NW向的成县-武山剖面,在礼县以西,Moho面和C界面有被上涌物质改造过的迹象.三维速度成像显示,在105°E附近,从7至11km的深度范围内,存在一条近NS向的断裂带,在该带的两侧速度结构有明显的差异,西侧为低速异常,而东侧为高速异常,这一近NS向的断裂带与二维剖面的下地壳深断裂在位置上很接近.该地区的几个8级大震均发生在105°E附近,并且呈一近NS条带.
Based on the data of two seismic vertical / high-resolution seismic refraction / wide-angle reflection sections and corresponding non-longitudinal seismic sections, the top structures of crust and upper mantle The results of two-dimensional profile show that the crust is vertically divided into two major layers, the upper crust and the lower crust, and the low velocity layer exists in the middle of the upper crust with medium velocity 0.3 ~ 0.5km / s lower than the background value. The depth is about 46 ~ 48km. The crustal velocity of Tianshui-Wudu section in the NE direction changes drastically in the horizontal direction. The NW-trending Chengxian-Wushan section is reconstructed with upwelling materials at the west of Li County, Moho and C interfaces .Three-dimensional velocity imaging shows that near the 105 ° E, there is a near-NS fault zone in the depth range from 7 to 11 km, with obvious differences in velocity structures on both sides of the belt and low-velocity anomaly on the west side , While the east side is a high-speed anomaly, and this nearly NS-oriented fault zone is close in position to the deep crust of the lower crust in the 2-D section. Several M ≥ 8 earthquakes in this area occurred around 105 ° E A near NS strip.