Spectrum, Phase and Group Velocities of the Theoretical Seismograms and the Idea of the Equivalent Surface Source of Disturbancet

Analyses are made of theoretical seismograms of torsional oscillation caused by a localized surface source for a homogeneous sphere and a homogeneous mantle with a liquid core. Special care is paid to the effect of parameters on the accuracy of analysis and the limitation of the applicability of various methods. At first, a simple description is given about the assumptions under which the theoretical seismograms were computed (Section I). Next, the spectrum analysis of the seismo-grams is carried on by the usual method of Fourier transform, giving useful information about how to employ the method. This analysis corro-borates recent similar analyses of the Chilean shock of May 1960 (Section 2). Group and phase velocities calculated by methods ordinarily employed show good agreement with theory. Calculations of initial phase also agree well with theory, giving confidence to similar studies using waves from earthquakes and explosions (Section 3). The idea of an equivalent surface source is proposed relative to the problem of the depth of the source within the Earth (Section 4). I