1982 Theses Doctoral

Studies of the long range Pₙ phase

Menke, William H.

Long Range Pₙ waves are modeled first 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 Pₙ properties that are not dominated by scattering, ie. their apparent velocity and lack of long period energy. The low frequency scattering properties of rough interfaces are then studied analytically by extending a theory due to Biol (1968). Roughness on interfaces is shown to enhance the efficiency of the waveguide at low frequencies. An analogue model is then employed to examine the effects of scatterers at higher frequencies. Results indicate that scatterers near the turning point of the whispering gallery phases can lead to phases with coda of duration similar to that observed in the long range Pₙ phase.