Inferences of a layered structure from S wave spectra -Part 3. SH and SV waves and some related problems

Abstract

An attempt is made to infer the crust-mantle structure in several regions of Japan and North America from the spectral amplitude ratio and the phase difference between SH and SV waves from deep shocks. It is found that the spectral behaviors of well-recorded S waves give support to some of the probable structures derived from P wave spectrum and some other information, suggesting characteristic differences in the tectonic structures; the possible existence of a rather thick intermediate layer having velocities between those appropriate to the lower crust and the normal mantle over three regions of Japan; and of a typical continental structure and oceanic crust in selected two regions of North America. The structures inferred for central and eastern Japan can explain satisfactorily the observed phase velocities of Rayleigh waves, but the Love wave velocities are significantly higher than those expected from the structures. If the high velocities of Love waves are not a result of higher mode contamination, the observed inconsistency may be accounted for either by anisotropic (transversely isotropic) mantle or laminated mantle models, but the spectral behaviors of S waves appear to favor the former model.