Crust-mantle whispering gallery phases: A deterministic model of teleseismic P/sub n/ wave propagation

Teleseismic P/sub n/ waves are modeled as a sum of whispering gallery waves, which propagate in a waveguide composed of a simple high velocity mantle lid underlain by a low velocity zone. This model is able to account for those P/sub n/ wave propagation properties that are not dominated by scattering, i.e., their apparent velocity and lack of long period energy. P/sub n/ apparent velocity data constrain the P wave velocity gradient in the upper 100 km of mantle to be low; dv/sub p//dz<0.001 s-1. The whispering gallery rays are shown to have significant amplitude (when compared to the direct P wave) and to have spectra that rapidly fall off at long periods. Yet this model cannot account for certain details of the observed P/sub n/ amplitude spectra. Most important among these is the spectral ratio of P/sub n/ to P, which the model underestimates by a factor of 10. Nevertheless, the model presents a useful framework for understanding some characteristics of P/sub n/ wave propagation and provides an estimate of the distribution of energy with depth in the P/sub n/ waves