A geoacoustic model based on sound speed characteristic of seafloor surface sediments of the South China Sea

The sound speed ratio R₁ of sediment to seawater and the sound speed ratio R₂ of compressional wave to shear wave are added up to the vertical gradient of sound speed geoacoustic model (GM) so as to achieve a more comprehensive and instructional GM in practice.Considering stress-strain relations of two-phase medium of sediment under the effect of heat and gravity,TFCMCM and DFCMCM models are established on the basis of Men-Chen model by introducing a freedom factor and considering coupled-frame elastic modular (FCMCM).Both models are used to adjust the seafloor surface sediment sound speed characteristic into the in-situ state,calculate and interpret the GMs.According to analysis of the existence of high-speed and low-speed types in seafloor surface sediments and the two kinds of porosity-depth states of constant and descent beneath the seafloor sediment (PDC and PDD),four representative basic geoacoustic models of sediments in the South China Sea can be expressed as low-speed PDC,low-speed and porosity-PDD,high-speed PDC and high-speed PDD.With the usage of combination of the four basic models,the Lu Bo and Liang Yuanbo’s three sound-speed structures of the South China Sea can be rationally explained as an example of the actual sedimentary acoustic state.The understanding of basic geoacousic models will benefit the seafloor inspection and classification of sea bottom regions with acoustic methods in the South China Sea.