Low grazing angle reflection and shear-wave resonance on elastic-solid sediment

The low-grazing-angle reflection on elastic sediment seabed exhibits abnormally enhanced frequency characteristics, which significantly influences long-range sound propagation in shallow water. To study the influence of elastic sedimentary layer seabed environment on long-range sound propagation in shallow waters, we conduct a joint measurement of seabed and waveguide sound propagation in the Dongsha area of the South China Sea. The measurements show for the first time that the seabed resonance and the sound siphon effect occur simultaneously. Notably, this effect is different from the sound siphon effect observed in low-sound-speed seabed environments, as it exhibits smaller frequency intervals. By analyzing the low-grazing-angle reflection characteristics of the elastic seabed, we develop a theoretical model for the resonance frequencies of shear waves in elastic sediment layers under low grazing angles and investigate their influence on long-range sound propagation. The results indicate that under an elastic seabed model, the low-grazing-angle reflection modulated by shear waves induces resonance at specific frequencies within the sediment layer. This trap acoustic energy in the seabed, leading to the sound siphon effect. Furthermore, we analyze the sensitivity and coupling of key parameters related to the resonance frequency of shear wave. According to these findings, we develop an inversion strategy that integrates seabed and waveguide observations to estimate geo-acoustic parameters of the experimental area. The inversion results validate the mechanism by which the elastic seabed model contributes to the sound siphon effect in the water column.