Page 525 - Acquisition and Processing of Marine Seismic Data

516 11. SEISMIC MIGRATION

FIG. 11.25 Effect of migration velocity errors on the collapse of a theoretical diffraction hyperbola in a constant velocity
medium by Stolt f-k migration. Velocity of the zero-offset section is 1500 m/s.

Fig. 11.25 shows the collapse of a theoretical 11.5 REVERSE TIME MIGRATION
diffraction hyperbola in a constant velocity
medium by Stolt migration using different Reverse time migration (RTM) is a prestack
velocities. The effect of velocity errors on the or poststack two-way wave equation migration
migration outputs is quite similar to that for that can handle steep dips up to and beyond
Kirchhoff migration outputs: frowns with 90 degrees. It also produces superior results
undermigration occur for slower velocities, in the case of strong velocity contrasts in both
and strong smiles with overmigration arise for the vertical and lateral directions in areas of
faster velocities. Fig. 11.26 illustrates the effect complex geological settings, such as salt tecton-
of 10% lower and 10% higher velocity on the ics (Baysal et al., 1983). Although its name indi-
Stolt migration output of marine seismic data. cates a migration in time, RTM is actually
The response of Gazdag migration to systematic implemented either as a time or depth migra-
slow and fast velocities is quite similar to that of tion using the reverse time algorithm in 2D
Stolt migration. or 3D.