Choice of lower limit of velocity

When the operator ${\bf H^TH}$ is applied to a gather, then the area around the line t=x/v_min 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 data. 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 gather.