Seismic refraction is a geophysical principle (see refraction). In the fields of engineering geophysics , engineering geology and exploration geophysics , seismic refraction traverses (seismic lines ) are performed using a seismograph, geophone array and energy source. The seismic refraction method utilizes the refraction of seismic waves on geologic layers and rock/soil units in order to characterize the subsurface geologic conditions and geologic structure .