What Does Critically Refracted Wave Mean?
Critically refracted wave is a component of the seismic trace obtained during the seismic refraction test. It can be defined as the refracted wave propagating in a medium that does not emerge at the second layer but lies along the interface. A critically refracted wave travels along the interface of the two mediums and is refracted back into the upper layer at the critical angle.
The travel time of critically refracted waves is used to determine the seismic velocity and depth of sub-surface layers.
Trenchlesspedia Explains Critically Refracted Wave
The angle of refraction is determined using Snell's Law that gives the relation between the angle of incidence of a seismic wave passing through a boundary between two different mediums. If the wave travels from a medium of low velocity to a medium of high velocity, the wave is refracted away from the normal. On the contrary, if the wave travels from a high velocity to a low-velocity medium, the wave gets refracted toward the normal.
When critical refraction takes place in the second medium, the wave travels parallel to the interface, while radiating energy into the upper-medium. Seismic waves are generated from a source such as a hammer, buffalo gun or an explosion. The waves are picked up using geophone receivers arranged on the surface.