Velocity function

The migration algorithm was tested for the effect of distortion with the use of an incorrectly low or high migration velocity. For this purpose, testing was carried out on the zero-offset response of the dipping reflector shown in Figure 6, for a medium of constant velocity equal to 2000 m/s.

Figure 13 shows the result of migration using a velocity that is 20 percent lower than the true velocity. The reflector is only partly shifted updip and remains less steep than the true inclination of the model. Besides, diffraction events are still present at the edges.

Figure 14 shows the opposite effect on using a 20 percent higher migration velocity. Now the dipping reflector is overmigrated. It has in fact moved further updip than its true location, and the edges of the reflector are smeared. The edge effects now show up as ``smiles''.

 

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Figure 13 Undermigration of dipping reflector in Figure 6 (migration velocity, 20 percent lower than true medium velocity).

 

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Figure 14 Overmigration of dipping reflector (migration velocity, 20 percent higher than the true medium velocity).