1. The distance from the source-point to the center of a geophone group. Unless a particular geophone group is specified, the distance to the nearest geophone group center is implied; sometimes the distance is to an individual geophone. Often resolved into perpendicular offset, the distance at right angles to the spread line, and inline offset, the distance from the projection of the source onto the line of the spread.
2. The distance between transmitter and receiver in electromagnetic surveys.
3. In vertical seismic profiling, the horizontal distance between source and receiver. The distance from source to wellhead may be different if the well is not vertical.
4. Sometimes (in refraction work) the displacement (q.v.).
5. In plotting marine data, the stepback (q.v.).
6. The horizontal component of migration (q.v.).
7. The horizontal component of fault displacement, measured parallel to the strike of the fault.