压缩空间频率的分级偏移方法

CASCADED MIGRATION BY COMPRESSING THE SPATIAL FREQUENCY

地矿部第一海洋地质调查大队

Computer Centre of The First Marine Geological Survey Party wider MGMR

分级偏移(Cassade migration)可以减小有限差分波动方程偏移对于倾角的限制,提高有限差分波动方程偏移的精度.K.拉纳(K.Larner)等人首先对此作出了证明.但是,拉纳的证明必须假定每一次偏移处理的输入剖面都是正入射的几何图象.本文指出,这种假定的合理性需要进一步讨论.我们用波场的空间频率分析方法,首次证明了:在不考虑差分格式本身固有的色散效应的情况下,与陡倾角相关的有限差分波动方程偏移的频散问题,是偏移处理中使用近似波动方程,使被偏移数据体波场的空间频率畸变所致.有限差分波动偏移对于倾角的限制可以归结为是对数据体波场空间频率的限制.在室内对野外资料进行处理时,人为地加大地震道间距的数值可以压缩数据体波场的空间频率.在此基础之上,本文提出了压缩空间频率的分级偏移方法.这种方法对于被处理数据的几何特性无需作任何假定,完全以波动理论解释了分级偏移可以减少有限差分波动方程偏移对于倾角的限制,从而在理论上对分级偏移方法作了进一步的完善和补充.本方法已在国产TQ—6计算机系统上投入实际生产使用,效果是令人满意的.

This paper,having discussed K. Larner’s Cascade migration method in detail,points out that the assumption which considers the partially migrated data as new stack data is worth while further discussing. By means of the analysis method of the spatial frequency of the wave field,we have studied the cause which leads to the dispersion phenomenon in finite difference migration. In terms of the distortion of the spatial frequency of the data being migrated ,we explain how the dispersion phenomenon related to the structure dip rises. Consequently,the limitation to the structure dip in finite differenece migration can be considered to be the limitation to the spatial frequency of the wave field corresponding to the field data. The spatial frequency of the wave field can be changed through a linear trasform of the coordinate.Upon this point of view, we put forward the cascade migration of compressing the spatial frequency of the data. With the new method,we have perfectly explained why cascade migration can improve the accuracy of finite difference migration from the point of view of wave theory.The result of practical data is satisfactory.