The mudslide effect

Abstract

A novel range-dependent propagation effect occurs when a source is placed on the seafloor in shallow water with a downward refracting sound speed profile, and sound waves propagate down a slope into deep water. Small grazing-angle sound waves slide along the bottom downward and outward from the source until they reach the depth of the sound channel axis in deep water. They then detach from the sloping bottom and continue to propagate outward near the sound channel axis. This ‘‘mudslide’’ effect is one of a few robust and predictable acoustic propagation effects that occurs in range-dependent ocean environments. Consequently, a bottom mounted source in shallow water can inject a significant amount of energy into the axis of the deep ocean sound channel that propagates to very long ranges. Numerical simulations with a full-wave range-dependent acoustic model show that the Kaneohe experiment had the appropriate source, bathymetry, and sound speed profiles that allowed this effect to operate efficiently. This supports the interpretation that some of the near-axial acoustic signals, received near the coast of California from the Kaneohe source on Oahu, Hawaii, were injected into the sound channel of the deep Pacific Ocean by this mechanism. [Work supported by ONR.]