Seismic Model Experiments on the Shape and Amplitude of the Refracted Wave

It has been known for many years from theoretical consideration that the first arrival part of a refracted seismic wave should have a waveform given by the time integral of the original wave (Jeffreys 1926). Quantitatively this is difficult to verify experimentally from field refraction records, although it is one of the causes of the “rounding” of the first part of the refracted waveform. However, by using seismic model techniques the experimental verification both of the wave shape and of the amplitude predicted by equation (I) becomes possible, and this note describes such experiments. Liquid media were used throughout the experiments. An electric spark immersed in the medium overlying the refractor simulated the seismic explosive source, and a lead zirconate transducer horizontally separated from the source by distance R (see figure) received the refracted wave. The receiver was designed to have a flat frequency response throughout the spectrum covered by the pressure pulse. The relationship between the received pressure of the refracted wave p,.(T) and the incident pressure po(t) referred to unit distance from the source is given in terms of the elastic properties of the media by