横向变速介质中叠加速度误差分析

横向变速会使常规叠加速度分析产生误差。本文采用变速介质正演模拟算法，对具有不同类型的横向速度梯度地层的模型，模拟野外多次覆盖观测系统，计算出道集内时距曲线及常规叠加速度值，并与实际介质的均方根速度进行了定量对比分析，揭示了误差产生的原因及其变化规律。研究结果表明，在横向变速介质中，常规叠加速度不仅与共中心点处的速度及旅行时有关，而且还与速度沿横向的二阶导数有关。叠加速度计算误差的符号取决于排列长度内速度横向梯度的变化方向，误差的大小取决于排列长度内速度横向梯度的变化率。所得出的叠加速度误差变化规律有助于人们充分认识常规叠加速度分析的结果，进而可以采用行之有效的算法进行必要的误差校正。

Error analysis of stack velocity in the medium where velocity varies laterally

Lateral velocity variation causes error in stack velocity analysis. Applying for-ward modeling method for velocity variant rnedium,we simulate field multifold lay-out,and calculate CDP time-distance curve and stack velocity for the model havingdifferent lateral velocity gradients. The Stack velocity is quantitatively comparedwith mean square root velocity in real medium to discover the cause and regularityof the velocity error. It is shown that in the rnedlum where velocity varies laterally,conventional stack velocity is related to not only velocity and travel time at CMP butalso the second der1vative of velocity in lateral direction. The error sign of stackvelocity depends on the direction of lateral velocity gradient in a spread length,andthe error value depends on variation rate of the lateral velocity gradient in thelength. The error variation rate helps people to well know the analysis results ofconventional stack velocity and to rnake necessary error correction using effectivemethod.