Understanding the Acoustics of Marine Sediments using Granular Mechanics

Understanding and predicting the acoustic behavior of water-saturated marine sediments (e.g., on the ocean floor) represents a fundamental technology issue for underwater sensing, navigation, and communication. Large collections of data collected from experiments and field measurements show a clear dependence on frequency for both the attenuation coefficient and acoustic wave speed. Existing theories can be fit to these data, but only by invoking multiple physical mechanisms involving parameter values that cannot be measured in situ. Here we focus on losses due to an inelastic component of normal compression at grain-grain contacts. This mechanism, although well established in granular mechanics, is not included in the existing models of sediment acoustics. Using theoretical analysis and DEM simulations, we show that this granular mechanics perspective, where forces are transmitted along lossy force chains, may be able to explain salient features of the acoustic properties of marine sediments