1. Head-wave energy that has been reflected or diffracted back from a discontinuity in a refractor, such as a fault. See Figures R-7a, b, c.
2. A refraction multiple, involving head-wave energy that has been multiply reflected between reflectors. The extra travel may occur at any time during the travel along the refractor. The effect is to add cycles to the refraction arrival; see Figure R-7d.
3. Any of a number of travel paths that involve reflection at an interface as well as travel through a high-velocity refractor; see Figure R-7e.