seismic velocity

The rate at which a seismic wave travels through a medium, that is, distance divided by traveltime. Seismic velocity can be determined from vertical seismic profiles or from velocity analysis of seismic data. It can vary vertically, laterally and azimuthally in anisotropic media and tends to increase with depth in the Earth because compaction reduces porosity. Velocity also varies as a function of how it is derived from the data. For example, the stacking velocity derived from normal moveout measurements of common depth point gathers differs from the average velocity measured vertically from a check-shot or vertical seismic profile (VSP). Velocity would be the same only in a constant-velocity (homogeneous) medium.