BASIC PRINCIPLES OF GEOMETRIC SEISMICS
In a homogeneous and isotropic medium, the waves excited in the source propagate, so that the wave fronts form surface spheres.
In order to represent the wavefront in an inhomogeneous medium, the Huygens principle is applied, which indicates that every point of the wavefront can, at some moment, be considered as a source of a new wavelet. Around these points are formed elemental spherical waves of radius r = VΔt, where V is the speed of wave propagation in a given area, and Δt is the time interval that is small enough so the medium corresponding to that interval can be considered as homogeneous. The envelope of a large number of elemental wave waves gives a new position of the wavefront after the time Δt..