Geoacoustic models and bioturbation

Abstract

Two types of geoacoustic models are used to describe relationships between physical and acoustic properties of unconsolidated marine sediments: simple predictive, and theoretical models. Simple predictive models use the apparent correlation between physical properties of sediments (usually porosity, grain size or density) and acoustic properties of sediments to predict velocity and attenuation of compressional and shear waves. Theoretical models use elastic properties of sediments (rigidity, compressibility, etc.) to calculate acoustic properties. It has been shown that bioturbation by benthic animals profoundly affects the physical properties of marine sediments. Activities including burrowing, ingestion/digestion/defecation, tube building, biodeposition, cementation and metabolic activities modify porosity, grain size, density, fabric, rigidity and compressibility of sediments. We hypothesize that bioturbation by benthic animals alters acoustic properties of unconsolidated marine sediments. An example is provided for predicted effects of bioturbation on selected acoustic and elastic properties of a silty mud sediment. Knowledge of effects of bioturbation on unconsolidated marine sediments may increase our understanding of the relationship between predicted and measured acoustic properties.