Effect of velocity on common-image gathers

Figure  illustrates the effect velocity plays on offset-domain common-image gathers. The three panels show CIGs produced by migrating the Marmousi synthetic dataset with three different velocity models: the correct velocity [panel (a)], a velocity that is too low [panel (b)], and a velocity model that is too high [panel (c)]. Interpreting patterns in the offset-domain CIGs is difficult; however, after transformation to the angle domain (Figure , standard residual-moveout patterns indicates the sign of the velocity error: events curving up meaning too low, and events curving down meaning too high.