Acoustics of Fine-Grained Marine Sediments

date January 29, 2016
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Friday, January 29, 2016 4:00 p.m. in ETC 4.150

Dr. Megan S. Ballard and Dr. Kevin M. Lee
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu

While the acoustics of granular marine sediment has been extensively studied, less attention has been paid to the physics of acoustic propagation in fine-grained muddy sediment.  Our research seeks to investigate the acoustics of fine-grained sediment through a combination of laboratory and field measurements.  A sampling of this work will be presented.

Laboratory experiments were undertaken to develop an understanding of the relationship between microscopic properties (e.g., flocculent structure) and macroscopic acoustic properties of muddy sediment.  Measurements of compressional and shear waves were performed in reconstituted mud formed from kaolinite and water.  A suite of additional measurements was also performed to characterize the physical properties of the model sediment.  These material parameters were used as inputs to various sediment acoustic propagation models including card-house theory and viscous grain-shearing theory for comparison with the acoustic measurements.

In another experiment, in situ measurements of compressional and shear wave speed and attenuation were collected below the water-sediment interface in Currituck Sound, North Carolina.  Two measurement locations characterized by fine-grained sand with different concentrations of mud were investigated.  At each site, grab samples were collected and later analyzed in the laboratory to quantify physical properties of the sediment, and acoustic measurements were performed in situ using a custom-built apparatus. Wave properties were extracted from the acoustic measurements and compared to predictions from two models originally intended for describing sandy sediment: the extended Biot model and viscous grain-shearing theory.