In the seismic reflection method, a special type of multiple reflection. This is the reflection that takes place when the energy traveling upward from the shot is reflected downward by the base of the weathered zone or by the Earth's surface. The reflected pulse follows the primary downgoing pulse by a time interval determined by the depth of the shot below the weathering (or the free surface) and the velocity of the material above the shot. For normal shooting depths this interval will range from 0.010 to 0.020 s.