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转换波叠加和AVO分析要在共反射点道集即共转换点(CCP)道集中进行。我们可以准确地算出单一均匀层中PS或SP波的转换点座标,它是偏移距、反射层深度以及波速比(v_P/v_S)的函数。本文给出计算倾斜单层和一组平行倾斜层中转换点的近似方法。数值试验表明该近似方法适用于偏移距小于目的层深度的情况。水平层状介质中转换波的旅行时可展成为幂级数。偏移距较小时取级数的前两项就可达到较好的近似结果。只要对旅行时作些校正,这种近似结果也可用于倾斜反射层。校正量可由近似转换点坐标求得。
Converted-wave overlay and AVO analysis are performed on a common reflection point gating set, a CCP. We can accurately calculate the coordinates of the transition point of a PS or SP wave in a single uniform layer as a function of offset, depth of reflector, and velocity ratio (v_P / v_S). This paper presents an approximate method for calculating the transition point in a tilted monolayer and a set of parallel tilted layers. Numerical experiments show that the approximate method is suitable for the cases where the offset is less than the depth of target layer. Translated waves traveling in horizontal layered media can be developed into power series. When the offset is small, the first two terms of the series can achieve better approximation. This approximate result can also be used for the tilted reflector as long as some travel is corrected. The amount of correction can be obtained by approximating the coordinates of the transformation point.