起伏地表条件下偏移到多偏移距叠前时间偏移

Migrating-to-multiple-offset prestack time migration for irregular topography.

在速度横向变化比较缓慢时,叠前时间偏移是很好的成像手段。它可以作为复杂构造成像的一个关键的中间环节,对于提高最终的速度分析质量和深度偏移成像效果是至关重要的。由于时间域成像基准面选择困难,一般地,时间域偏移都是在一个水平的数据观测面(或浮动基准面)上进行的,非水平的观测面不宜作为时间域的成像参考面。提出一种新的成像方法,即引进一个随炮点和检波点变化的坐标,每次成像都是直接在该平面内进行,最后叠加到成像空间里。为了对来自非水平地表的低信噪比数据进行叠前时间偏移,引入Gardner提出的偏移到多偏移距的方法,把非水平地表叠前时间偏移方法与偏移到多偏移距的方法结合,可以较好地解决山地地震资料的叠前时间偏移成像问题。模型的初步检验证明,这种方法的确是可行的,且其计算效率较高。

Prestack time migration is a good way of imaging when lateral variations of velocity are gentle. It can act as an interim key step of imaging complex structure, which plays an important role for ensuring quality of velocity analysis and depth migration.Generally, time domain migration is implemented on a level (or floating datum), irregular observation surface is not applicable for time domain migration. This paper proposes an imaging method which ensures imaging in a plane and stack in the imaging space by introducing a coordinates changing with shot point and receiving point. In order to realize prestack time migration of low signal-to-noise ratio data from irregular topography, we adopted migrating-to-multiple-offset method pro- posed by Gardner, and take the advantages of irregular topography prestack time migration and migrating-to-multiple-offsct method to solve problems related to prestack time migration on data from mountainous areas. The correctness and efficiency of the method were showed with model data.