Abstract

Acoustic reflections from a lakebed provide valuable information about the dynamic boundary between water and the lakebed, where sediments and biota in the water column eventually settle. In this study, we present a comprehensive analysis of reflected sound wave amplitudes to gain insights into the physical properties of a water-sediment boundary. We decided to carry out this analysis within the unique ecosystem of the Mono Lake basin due to the fact that the Mono Lake, a meromictic and hypersaline waterbody is situated within one of the most active yet understudied volcanic regions in the United States. The fact that the upper boundary condition of the Mono Lake is well constrained with the existence of monthly water column temperature/salinity data, and that the bottom boundary condition offers a wide range of variability such as extreme changes in bottom sediment temperature, sediment type (tufa sand vs mud/silt), gases, and organics, presents a wonderful opportunity to study seabed reflectivity. We utilized a single-channel sparker source dataset acquired by the United States Geological Survey during the summer of 2009 to assess the variability in amplitude of the upper 1 meter of the Mono lakebed. Theoretical models were employed to understand the physical properties of the water-lakebed boundary, including the velocity and density of the water, and the lakebed sediment density and velocity, to assess how potential variations in physical properties impact the lakebed reflectivity.

Porosity, mineral composition, temperature, and pore fluid content were investigated to see how they drive variations in the physical properties of the water-lakebed interface. Our study reveals that among the numerous factors influencing the acoustic reflectivity of the seabed, porosity plays a primary role, varying the reflection coefficient of the lakebed by as much as 81% in a non-linear manner. Organic content, though less important than porosity, could potentially vary the lakebed reflectivity by 13%, assuming a mineral composition of 80% clay and 20% organics. This research represents a crucial step towards a better understanding of the complex geological processes at play in the Mono Lake basin and contribute to the general understanding of lakebed reflectivity.

Degree Date

Fall 2023

Document Type

Thesis

Degree Name

M.S.

Department

Earth Sciences

Advisor

Mathew Hornbach

Subject Area

Earth, Atmospheric and Marine Sciences, Physical Sciences, Physics

Notes

Seismic, Amplitude, Acoustic, Reflectivity, Lake, Lakebed, Porosity, Organics

Number of Pages

97

Format

.pdf

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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