Definition - What does Direct Wave mean?
Direct wave is one of the seismic trace components generated during a seismic refraction test. Direct wave travels directly from the acoustic source to the geophone receivers without undergoing seismic reflection or refraction from a sub-surface layer.
The seismic trace components include direct wave, reflected wave and critically refracted wave.
Trenchlesspedia explains Direct Wave
Low-frequency seismic energy is produced by a seismic source on the surface such as a hammer plate, buffalo gun, explosion or weight drop, depending on the depth of penetration required. Geophones arranged at regular intervals of 1-10 meters detect these refracted seismic waves. The output data from the geophones is compiled and processed by a seismograph.
The first seismic wave to arrive at the geophone position is the direct waves. The travel time for a direct wave can be computed using the simple formula
t = x / V, where
t - time
x - distance from source
V - velocity