Evaluating a Poroelastic Model via Pore Pressure Signals in Seafloor Sediments

Abstract

AbstractBelow a certain threshold of wave energy for a given depth, unconsolidated sediment should respond to wave action poroelastically. To this end, a generalized simple poroelastic model was applied to in situ data collected in coastal sediments near Oceanside, California. Pore pressure data were recorded by sensors attached to cylindrical unexploded ordinance surrogates, and water pressure sensors on bottom moorings. Orientation data were collected from inertial motion units attached to the surrogates, which were placed on the seabed and subsequently shallow buried during a high‐energy event on 13 February 2021. The model is characterized by two parameters. A consolidation coefficient controls the depth of diffusive flow, and Skempton's coefficient represents the ratio of the original signal into components transmitted by the sediment matrix and the pore fluid. The model assumes that the pore pressure signal is coherent with the seafloor signal; spectral coherence above 0.75 was used to select the frequency range from 0.05 to 0.2 Hz for the analysis. Spectral analysis methods were then applied to obtain averaged auto spectral densities of the pore pressure and bottom mooring signals over the coherent frequency band. Attenuation between sensor pairs was calculated. The results yielded burial depths over time for the surrogates that agreed with changes in significant wave heights, liquefaction, and recovery depths.