Diffraction of Seismic SH Waves Caused by the Earth's Core

Abstract

The amplitude decay function of diffracted SH waves caused by the earth's core near the geometrical shadow point is explicitly derived from the Kelvin's stationary phase method with inhomogeneity parameters. Seismic SH waves from six intermediate and deep earthquakes are Fourier analysed by selecting suitable stations in the epicentral distances beyond 90 degrees. We empirically introduced the amplitude decay γ from the observed trend of the relation between distances and logarithmic amplitude spectra of the SH component. It is verified that the amplitude decay function is appropriate for interpreting γ in the first order. It is also suggested that a low velocity layer and lateral inhomogeneities might exist at the base of the mantle.