Seismic refraction

Seismic refraction is a geophysical method that uses the travel times of refracted seismic waves to infer subsurface layer depths and seismic velocities. Its standard interpretation relies on waves traveling faster in deeper layers.

Snell's law: A law describing how a wave changes direction when it crosses a boundary between materials with different wave speeds. It governs the bending of seismic rays at subsurface boundaries.
Seismic wave: An elastic disturbance that propagates through or along the Earth. Refraction surveys measure the travel of these disturbances from source to receiver.
Shallow seismic surveying: Seismic investigation of near-surface structure, commonly for engineering, environmental, or geological purposes. Refraction is a standard method for estimating shallow layer thicknesses and velocities.
Seismic reflection: A seismic method that images subsurface boundaries from waves reflected back toward receivers. Reflection emphasizes returning echoes, whereas refraction emphasizes arrivals traveling along faster boundaries.
Critical refraction: Refraction at an interface where the transmitted wave travels along the boundary and radiates energy back into the slower medium. This boundary-hugging wave produces the refracted arrivals used in the method.
P-wave: A compressional seismic wave in which particle motion is parallel to the direction of propagation. Its speed commonly increases with depth, making it the principal refraction-wave type.
Bedrock depth: The distance from the ground surface to the top of competent bedrock. Refraction profiles often estimate this depth from the travel-time change at the bedrock boundary.
Seismic reflection and refraction: A field method that combines reflected and refracted arrivals to constrain subsurface structure. Joint interpretation can reduce ambiguities that arise when refraction data are used alone.
Travel-time curve: A graph of wave arrival time against source–receiver distance. Its slopes and intercepts encode layer velocities and depths.
Seismic source: A natural or controlled event that generates seismic waves. A known source location and time anchor the survey's travel-time measurements.

Linked from 13 pages