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2005年,跨西安坳陷完成一条NW方向,69km长的深地震反射剖面,首次获得该区域的地壳精细结构、主要断裂展布和深、浅构造关系图像.地震反射CMP叠加时间剖面显示,以反射事件C为界,地壳被分成上下两部分.上地壳由多组近水平反射带组成,具有分段连续性好、局部存在反射带明显错断或形态突变等特征,清晰地刻画出西安坳陷新生代沉积分层、坳陷底界、渭河断裂带、临潼—长安断裂带和秦岭山前断裂带的几何形态和关系.反射事件C是结晶地壳内宽度约0.5s的反射带,最深处位于桩号30km,底界约6.5s,向西北缓慢抬升至5.5s,向南东迅速抬升至5.5s.下地壳有两个明显的反射事件RA、RB:RB是位于桩号40～47km之间的局部反射团,而RA为宽度约2s、向坳陷倾斜的反射带.以桩号38km为界,反射Moho形态截然不同,而且出现了显著的错断:大桩号方向,反射Moho为位于双程走时11～14s水平的反射分段连续的过渡带,宽度约3s;小桩号方向,反射Moho为一宽度约2s、并向大桩号倾斜的反射分段连续的过渡带,其形态和反射事件RA相同.根据地震波速度资料,求得这几个反射带顶界的深度分别为:10.5～13.5km(反射带C)、20.3～21.5km(反射带RB)、16.8～34.3km(反射带RA)和32～36.7km(反射带Moho)左右.作者认为形态一致的反射事件RA和反射Moho很可能是古秦岭洋向华北地台俯冲的遗迹.此外,西安坳陷内错断新生界深达反射事件C的渭河和临潼—长安断裂带和莫霍错断的存在,表明该地区地壳现今活动性很强,是未来强震发生值得注意的地区.
In 2005, a deep seismic reflection profile of NW direction and 69km long was completed across the Xi’an Depression, and the crustal fine structure, major fault distribution and deep and shallow tectonic relational images were obtained for the first time in this area.Seismic reflection CMP superimposed time profiles show that with Reflectance event C as the boundary, the crust is divided into upper and lower parts of the upper crust by a number of sets of near horizontal reflection band, with good continuity of subdivision, the local existence of a clear reflection or sudden change in the shape of the characteristics of a clear delineation Xi’an depression The Cenozoic sedimentary stratification, the bottom of depression, the Weihe fault zone, the Lintong-Chang’an fault zone and the Qinling piedmont fault zone.The reflection event C is the reflection zone with a width of about 0.5s in the crystalline crust, the deepest It is located at about 30km from the station, with a bottom bound of 6.5s, slowly rising to 5.5s in the northwest and rapidly rising to 5.5s in the south. There are two obvious reflection events in the lower crust, RB: RB is located at 40 ~ 47km , And RA is a reflection belt with a width of about 2s, which is inclined to the depression.With 38km as the boundary, the reflected Moho morphology is quite different and there are obvious faults: the direction of the large stake, the reflection Moho is Located in the two-way travel time 11 ~ 14s level In the direction of small stakes, the reflection Moho is a transitional zone with a width of about 2s and a reflection section that is inclined toward the large number of stakes and has the same shape and reflection event RA. According to the seismic wave The depths of the top of these reflection bands are 10.5 ~ 13.5km (reflection band C), 20.3 ~ 21.5km (reflection band RB), 16.8 ~ 34.3km (reflection band RA) and 32 ~ 36.7 km (reflection band Moho) .The authors believe that the morphological reflection events RA and Moho reflection are likely to be the remnants of ancient Qinling ocean subduction to the North China platform.In addition, the fault of Cenozoic deep fault reflection in the Xi’an depression Weihe River And the existence of Lintong-Chang’an fault zone and Moho fault show that the crust in this area is very active nowadays and is worthy of attention in future strong earthquakes.