The seismic refraction method using compressional waves has been used in site investigation for many years to locate rockhead. Results from several surveys in northern England, where Quaternary glacial drift overlies Coal Measures, show that shear waves exhibit a large positive contrast in seismic velocity between overburden and bedrock, whereas the ranges of seismic velocity of compressional waves in overburden and bedrock are not clearly separated. Consequently, shear wave velocity is a more reliable indicator of lithology, and seismic refraction profiling using shear waves may be a better technique for estimating the depth of rockhead.
Unusually low compressional wave velocities have been measured over abandoned mine workings. If this is a subsidence effect, it may prove useful for locating old mine workings.