When dealing with real data we almost never know what the true velocity of the subsurface is. Therefore it is important to understand the effects of velocity on our angle-gather time migration algorithm. To do this we simply created data for the dome model in Figure 4 at a fairly high velocity (3 km/s) and migrated it using a low velocity (1.5 km/s). The results are in Figure 11. For angles less than the maximum useful angle (), the angle-domain gather behaves exactly as the offset-domain gather does. Beyond the maximum useful angle, the events become even more curved and the amplitudes begin to change.

The behavior of the angle-gather migration is very similar to that of
offset-domain migration as long as the limitation of the maximum useful
angle is recognized. Therefore, we can probably expect angle-gather
migration to behave like offset-domain migration in *v*(*z*) media also.

Figure 11

4/20/1999