Aliasing can occur on the axes of time, depth, geophone, shot, midpoint, offset, or crossline. In practice, aliasing is the worst on the horizontal space axes. Figure 19 provides an illustration. Looking at that figure, you get confused about whether the dip is to the left or right.
Mathematical analysis has the same difficulty.
The effective dispersion relation of the wave equation when the horizontal axis is sampled. Frequencies are given for typical zero-offset migration. The problem of spatial aliasing begins when two circles touch each other, as shown at 20 Hz in Figure 19 . Another view of the spatial aliasing problem is that steeply dipping waves are suppressed by the geophone group. From this standpoint the limit past which spatial aliasing begins should be thought of in terms of angles at which energy is missing from the data.