(kor, ∂ lā’ sh∂n) 1. Identifying a phase of a seismic trace (or record) as representing the same phase on another trace (or record), indicating that the events are reflections from the same sequence of reflectors or head waves from the same marker. 2. The degree of linear relationship between a pair of traces; a measure of how much two traces look alike or the extent to which one can be considered a linear function of the other. The time-domain concept analogous to coherence in the frequency domain. See autocorrelation and crosscorrelation . 3. Determination of equivalence in stratigraphic position of formations; for example, in different wells based upon similarities in well-log character. 4. Geologic correlation involves determining structural or stratigraphic units that are equivalent in time (age) or stratigraphic position. 5. The matching of different well logs and other well data, either in the same well or in different wells.