Diffraction phenomena in seismic models

Summary. Refraction seismic profiles in the Alpine area occasionally show seismic 'shadows' which cannot be explained by a horizontal low-velocity channel. An example is demonstrated where the low P -velocity zone (Flysch) dips below a wedge of high P -velocity (the Calcareous Alps) which is a typical Alpine structure. This feature has been studied by means of a seismic model experiment. The corner of the wedge works as a source of diffracted P -, S - and Rayleigh-waves, when met by seismic waves. The diffracted waves can be distinguished from conventional waves by their amplitude–distance relation when the extinction coefficient is well known by an independent experiment.