Normal moveout

In reflection seismology, normal moveout (NMO) describes the effect that the distance between a seismic source and a receiver (the offset) has on the arrival time of a reflection in the form of an increase of time with offset.

[1] The relationship between arrival time and offset is hyperbolic and it is the principal criterion that a geophysicist uses to decide whether an event is a reflection or not.

[4] According to W. Harry Mayne, inventor of the Common Point Reflection Method in 1950, in order to avoid the "smearing" of recorded seismic data caused by the use of geophone sensor arrays, I needed a very long array to attenuate the noise, yet each point of the array needed to represent the same reflection point of the subsurface.

For a non-dipping reflector, this meant that the source and receiver station would have to move the same distance-in opposite directions-from the reflection (or mid-) point.

Coupled with the normal moveout correction, Mayne stated, "the method was primarily intended to attenuate systematic surface noise, and to average out near-surface aberrations in travel paths.