The propogation velocity of waves through ground has been used for many years in the
seismic surveys for the detection of underlying strata. From a knowledge of the percussion (P) and shear (S) wave velocities in different materials, together with their bulk densities, it is possible to derive dynamic moduli and properties, such as the shear modulus (G) and poisson’s ratio (n), which are essential in
 the solution of problems relating to dynamic earth pressure, soil structure interaction and the dynamic analysis of foundation strata relating to earthquake engineering. The principle involved in finding the wave velocities in ground materials is the same as used in finding velocities in any material. A simple wave form or pulse is generated at one point and the travel time to several other
 points is detected with suitable signal receivers.