new approach is presented for estimating the velocities of converted wave data that is based on prestack migration by equivalent offset to form common conversion point gathers. These gathers are used to form an initial estimate of the converted wave velocity Vc, that can then be used for the full accurate process of equivalent offset migration of converted wave data.

Equivalent offset common conversion point gathers are formed using the P-wave and S-wave velocities and the double-square-root equation. The formation of these gathers requires approximate values for the P-wave and S-wave velocities, but after their formation, accurate velocities can be picked and the prestack migration completed with moveout correction.

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