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Figure 8. Normal MoveOut (NMO) is a process applied to pre-stack data. Here the effect is shown on a single trace with one reflection event (left). NMO assumes the reflection comes from a horizontal interface in the earth (center). Using a velocity function supplied by the processor, NMO adjusts the original time (red) to that which would have been observed at the midpoint, marked S/R. The blue path is two-way time down and back, which must be less than the red path time. So NMO’s job is to move the reflection event up the trace (right). Note NMO operates on one trace at a time, which makes it inexpensive.