Translations:Diffraction/2/en

However, if an interface contains a sharp bend, special consideration is required. Suppose for instance that a body of material of velocity $v_{1}$ with a sharp edge is embedded in a uniform medium of velocity $v_{2}$, as shown in Figure 22. A ray BA incident on the sharp edge B, according to Huygens’ principle, will disturb point B so that it will act as a point source and emit energy in the form of an expanding circular wavefront. This wavefront is called a diffracted or scattered wave because the raypaths, as shown in the figure, are scattered in all directions with respect to the incident ray BA. Evidence exists on many seismic records that this process, which is expected on the basis of Huygens’ principle, is not merely hypothetical but is real and that the diffracted waves often carry very appreciable and measurable amounts of energy. The situation depicted in Figure 22 is in fact representative of a fault in a subsurface geologic stratum whose velocity is different from that in the surrounding strata. Prominent waves diffracted from the edges of faults often are observed on seismic records. We see from Figure 22 that diffracted rays do not have to obey either the law of reflection or Snell’s law of refraction.