Characteristics of sound speed in four seafloor sedimentary types in the South China Sea

The sound speed of sediments is significant in ocean engineering explorations, marine geophysics, and underwater acoustics. However, there are a variety of sediment types on the seafloor, and different sediment types have different pore structures and particle compositions, which can cause changes in the propagation of acoustic wave in the sediment, and thus affect the sound speed of the sediment. To accurately characterize the sound speed of seafloor sediment, four sedimentary types, i.e., silty sand, sandy silt, sand-silt–clay, and clayey silt, are selected to measure and analyze. The new regression relationships between the sound speed and physical properties (i.e., the porosity, density, and mean grain size) were established and compared with the previously built equations. The results confirmed that the trend of curves predicted show good agreement with our equations, but there is some inconsistency in the different sediment types. Moreover, this study also found that the porosity is controlled by packing in sandy sediments, the porosity in clayey sediments is primarily a function of compaction, and the porosity in silty sediments is affected of compaction and packing. However, the analysis of the impact of compaction and packing on the acoustic and physical properties in different sediment types requires further research.