Page 440 - Acquisition and Processing of Marine Seismic Data

9.2 VELOCITY DETERMINATION FROM SEISMIC DATA 431

FIG. 9.6 Simple explanation of the theory behind the velocity spectra. (A) A synthetic CDP with only one reflection of
1500 m/s velocity, and its NMO corrected versions for different velocities (B) 1000 m/s, (C) 1200 m/s, (D) 1400 m/s,
(E) 1500 m/s, (F) 1700 m/s, (G) 2000 m/s. Corresponding stacked traces are also provided (traces with blue borderlines) next
to the NMO corrected gathers. (H) Stacked traces obtained from several different velocities from 1000 to 2000 m/s. A stacked
trace with the highest amplitude obtained for 1500 m/s velocity in (E) represents the optimal velocity to stack the reflection in
(A). If the amplitudes in (H) are contoured, a maximum enclosure is obtained at t(0) ¼ 640 ms and V ¼ 1500 m/s, which is the
stacking velocity of the reflection at 640 ms zero-offset time.