Seismic phases recorded in South Australia and their relation

The phases recorded from local earthquakes in South Australia are discussed. A simple single-layered crustal model, put forward by Doyle & Everingham (1964) from recordings of atomic explosions, has provided very consistent interpretations of all the prominent phases. The MohoroviCik discontinuity appears to be sufficiently sharp to produce the converted reflection S, P at frequencies near 24s. Normal super-critical reflections and a surface converted reflection sP, P are also regularly recorded. The converted reflections are very useful for the determination of focal depths; their recorded amplitudes give added weight to the hypothesis of almost constant crustal velocities. They illustrate the usefulness of later phases in studies of crustal structure and the advantages of using relatively long wavelengths, particularly for studying reflections. The amplitude data for P waves were found to give little useful information but satisfactory agreement was obtained between the observed amplitudes of S, S, S, P and sP, P and the amplitudes calculated for these phases using ray theory and plane wave reflection coefficients. 1