Distributions and vertical variation patterns of sound speed of surface sediments in South China Sea

•The distribution of sound speeds is obtained in the southern South China Sea.•We establish 3 vertical variation patterns of sound speed in various geomorphic units.•We compare the sediments texture and sound speed properties from trough and slope.•Different key factors in different variation patterns contain porosity or grain size.

The distributions of sound speed show different characteristics in continental shelf, continental slope and Nansha Trough. The differences have closely related to the distributions of sediment physical properties in the southern South China Sea. According to the analysis of sound speeds and physical properties variation characteristics with buried depth, the vertical variations of sound speed are closely related to sediment texture, sedimentary environment, transport, erosion, compaction, consolidation, etc. The comparison results indicate 3 vertical variation patterns of sound speed: increasing model, invariant model and complicate variation model. The above 3 variation models represent the vertical distribution characteristics of sound speed in different depositional environments. Different variation patterns have different key factors which generally contain porosity or grain size. The calculated sound speeds with Buckingham’s theory of compressional waves in fluid-like marine sediments follows the trend of measured speeds accurately.