In chapter we discussed methods of imaging horizontal reflectors and of estimating velocity from the offset dependence of seismic recordings. In this chapter, we turn our attention to imaging methods for dipping reflectors. These imaging methods are usually referred to as ``migration'' techniques.
Offset is a geometrical nuisance when reflectors have dip. For this reason, we develop migration methods here and in the next chapter for forming images from hypothetical zero-offset seismic experiments. Although there is usually ample data recorded near zero-offset, we never record purely zero-offset seismic data. However, when we consider offset and dip together in chapter we will encounter a widely-used technique (dip-moveout) that often converts finite-offset data into a useful estimate of the equivalent zero-offset data. For this reason, zero-offset migration methods are widely used today in industrial practice. Furthermore the concepts of zero-offset migration are the simplest starting point for approaching the complications of finite-offset migration.