岩石圈下部的速度结构

我们分析了中国华北平原以及沙特阿拉伯深地震测深的记录,发现P_n可以连续追踪到500公里以上,中间并无间断现象,而且在接收距离350-500公里之间,P_n后面有一到两个很强的续至震相,它们的速度与P_n相似,而能量比P_n更强。经与沉积层中薄层的野外实验结果以及室内超声波模型实验的结果相比较,我们得到这样的结论:岩石圈下部存在一至数个高速薄层,其厚度不超过一公里。地幔顶部物质的正常速度可能比薄层略低。岩石圈中薄层的存在对于岩石圈的演化过程具有重要的意义。

ON THE VELOCITY STRUCTURE OF LOWER LITHOSPHERE

Analyzing the records obtained from the deep seismic soundings in North China Plain and Saudi-Arabia, it has been noticed that the first arrival P_n can be correlated continuously without interruption up to a distance of 500 km from the shot point. No phase shift occurs at this interval. At a distance of 350-500 km from the shot point, there are one or two strong later arrivals, with the same velocity as P_n. In comparison with the results obtained from the field experiments in shallow sedimentary layers, it is concluded that in the region of lower lithosphere, one or two high velocity thin layers with thickness less than 1 km are embedded in a normal uppermost mantle medium of lower velocity. The existence of embedded high velocity thin layers in lower lithosphere may be of significance in the evolution of the lithosphere.