Seismic refraction is the geophysical principle governed by Snell's law (see Refraction). Used in the fields of engineering geology, geotechnical engineering and exploration geophysics, using seismic instruments and/or geophones, arrays and energy sources to perform seismic refraction traversals (seismic lines). Seismic refraction uses the refraction of geological layers and geotechnical units by seismic waves to characterize subsurface geological conditions and geological structures.
These methods depend on the fact that seismic waves have different velocities in different types of soil (or rocks): in addition, waves are refracted as they pass through the boundary between different types (or conditions) of soil or rock. These methods can determine the general soil type and the approximate depth of the stratigraphic boundary or bedrock.