Cores Drilling Technology, the coring process. The concept of rays are used to analyse the path of the seismic wave in the ground. This is an infinitesimally thin cone of the wave that is perpendicular to the wavefront. It depends upon the axial modulus and density of the rock. In general it can be thought of as being related to hardness.
Seismic waves travel faster through hard rocks and slower through soft rocks.
Gas in sandstone also slows down seismic waves. Interval Velocity is the Difference in Depth divided by the Difference in Time for ray paths to the same reflector from different source distances. The distance between one crest of a wave and the next. The frequency is the number of time is a second that a wave advances by one wavelength. Hz is the most useful.