**1. n. [Geophysics]**

The delay or difference in the arrival time of seismic events that can result from weathering of the rocks or variations in geologic structures in the subsurface.

**See:**
arrival,
event,
weathering

**2. n. [Geophysics]**

A term used in seismic processing to describe the interval between the zero-time of a crosscorrelation between two traces and the point of maximum correlation.

**See:**
crosscorrelation,
trace

**4. n. [Formation Evaluation]**

The distance between the static measure point and the dynamic measure point of a logging measurement. For nuclear logs and any others that must be recorded over a significant time period, there is a difference between the measure point with the tool stationary and moving. If the tool is moving during this period, the effective center of measurement will be a certain distance from the point at which the measurement started. This distance is the lag. The lag depends on the logging speed and the sampling interval.