A quantitative evaluation of seismic signals at teleseismic distances

Body (P) and Rayleigh wave seismograms are computed for explosions and earthquakes using the expressions developed by Hudson; many of the features of observed seismograms are noted. For the earthquake source models used average Rayleigh wave magnitudes relative to P wave magnitudes are larger than for the explosion source models. This is true even for point sources; increasing the dimensions of the earthquake source only accentuates this difference in the relative excitation of Rayleigh waves. However the relative amplitudes are strongly dependent on the orientation of the observer relative to the fault plane of the earthquake owing to the radiation pattern of the P and Rayleigh waves. Where the observer is at an anti-node of the P radiation the relative amplitudes of the Rayleigh waves are not significantly greater than for explosions. A detailed study of observed P and Rayleigh amplitudes is now needed to see if the same effects of the P radiation pattern can also explain the observed differences in the relative excitation of P and Rayleigh waves by earthquakes and explosions.