The seismic refraction method is based on the property of seismic waves to refract (or be bent) when they travel from one medium to another of different density or elasticity. The velocity of wave transmission changes as it enters another material with different elastic properties (Stein, 2003, pp. 120-128).
Seismic refraction calculations that allow the computation of layer thickness, are used for both natural energy sources such as shocks generated by earthquakes or volcanic activity, or subsurface exploration using man-generated shocks by use of explosives, weight dropping, sledge hammers, etc. The drawing above illustrates how refracted waves travel through a subsurface consisting of an overburden with a seismic velocity of 1,000 feet per second (305 meters/sec) over water-saturated overburden with a seismic velocity of 5,000 ft/sec (1,500 m/s) over bedrock with a seismic velocity of 15,000 ft/sec (4,600 m/s).
Typically, shallow earth materials have wave transmission velocities that increase with depth. The seismic refraction method is most effective (and accurate) when each successive layer has a higher transmission velocity than all overlying layers.
Some Useful Links
Following are some hyperlinks that can further assist with the evaluation and description of the seismic refraction method:
©1998-, Geologic Resources, All Rights Reserved