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在我国西北地区的柴达木盆地东部和甘肃地区,在距离炮点40互100公里处,能够接收到不少能量较强的地壳深界面反射波。另外还发现一种与一般反射波性质不同的波,其视速度特大,视速度随距离的变化不大,而且有较明显的终点;其吋距曲线与一般深界面反射波的时距曲线相交。根据它的特征可以判断地壳中存在具有速度梯度的高速夹层.求得的夹层参数为: 甘肃地区柴达木盆地东部覆盖层厚度 18.8公里 30.5公里覆盖层平均速度 5.5公里/秒 5.3公里/秒夹层厚度 6.0公里 3.2公里夹层速度 7.5—8.5公里/秒 7.5—8.0公里/秒夹层的上下界面均为强反射面,可以产生多次反射波。分別利用相邻两个反射波可以求得各层参数,并能避免射线折射的影响。甘肃地区和柴达木盆地东部的地壳厚度分別为51和52公里。地壳中有高速夹层的存在,可以更好地说明P~*速度分散的原因,而且也能够解释Lg波的传播机制。
In the eastern part of Qaidam Basin in the northwestern part of China and Gansu Province, at a distance of 100 km from shot 40, a lot of strong reflected deep-sea interface reflections can be received. In addition, a wave different from the general reflected wave is found. Its apparent velocity is very large, apparent velocity varies little with distance, and there is obvious end point; its displacement curve intersects the time curve of general deep interface reflection wave . According to its characteristics, it can be concluded that there is a high-speed interlayer with velocity gradient in the crust.The interlayer parameters obtained are as follows: 18.8 km in the eastern part of the Qaidam basin in Gansu Province 30.5 km Average speed of the cover 5.5 km / s Sandwich 5.3 km / Thickness 6.0 km 3.2 km Mezzanine Velocity 7.5-8.5 km / s 7.5-8.0 km / s The upper and lower interfaces of the mezzanine are highly reflective and produce multiple reflections. The parameters of each layer can be obtained by using two adjacent reflected waves respectively and the influence of the refraction of the rays can be avoided. The crustal thicknesses in the Gansu and Qaidam basins are 51 and 52 km respectively. The existence of high-speed sandwiches in the crust can better explain the reasons for the P ~ * velocity dispersion and also explain the Lg wave propagation mechanism.