When the operator is applied to a gather, then the area
around the line t=x/vmin is susceptible to amplification.
From this, it follows that the low limit of velocity in velocity analysis
should not be chosen to be too small, otherwise this effect may distort
The low limit should not be chosen too high, either, because then hyperbolas
with lower velocities cannot be restored in a low number of iterations.
Thus the most convenient choice appears to be the lowest velocity in a
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