Higher Modes of Rayleigh Waves and Upper Mantle Structure
The effect of the seismic velocity distribution of the upper mantle on the dispersion and amplitude of Love waves was studied in [1, 4, 7] by numerical experimentation. The main result of these investigations was the discovery of anomalous properties of the higher modes in models of the mantle with a low-velocity zone. The conclusions of [1, 4, 7] for a vertically inhomogeneous flat earth were later confirmed by calculations for a radially inhomogeneous spherical earth  and explained by an asymptotic theory in . Similar results for dispersion curves were obtained in . In the present paper, the same studies are continued for Rayleigh waves: the fundamental mode (the Rayleigh wave proper) and the higher modes (shear modes). The dispersion and amplitudes of the first three higher Rayleigh modes are calculated for a number of vertically inhomogeneous models of the earth. Combined theoretical seismograms for various models of the upper mantle and possibilities for experimental detection of waveguides from recordings of higher modes will be considered later.
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