Commonly used for Bedrock mapping and water table surface. Compressional wave velocities of soil and rock (Vp).
Refraction was at one time the heart of the engineering applications because the most important element was bedrock mapping. Now it is done to accompany other techniques.
Measuring shear wave velocities of soils (Vs) and rock surface, determines seismic site class (Vs30).
1-D sounding for seismic site class or 2-D profile which is becoming more common for retaining walls and shoring walls or general mapping of bedrock.
Specialty devices for continuous images to 100 meters depth.