Oscillation-Modified Biot Framework Explains Rayleigh Wave Attenuation in Saturated Soils

Researchers have developed an oscillation-modified Biot framework to analyze Rayleigh-wave attenuation, velocity dispersion, and shallow displacement responses in saturated soils containing trapped nonwetting fluids. The theoretical formulation incorporates localized pore-throat-scale fluid oscillations that introduce additional energy dissipation in multiphase subsurface media.

In fluid-bearing saturated porous formations, Rayleigh-wave attenuation and shallow displacement dynamics provide critical information for geophysical characterization and dynamic-response assessment. However, classical Biot-based Rayleigh-wave formulations do not explicitly capture the energy dissipation caused by pore-throat-scale trapped nonwetting fluid oscillations, limiting the interpretation of dynamic responses in formations relevant to geothermal energy and geological resource development.

To address this mechanism, the authors introduced a frequency-correction function derived from a pore-scale nonwetting-fluid oscillation model into the fluid-skeleton drag term of Biot-type body-wave equations. From these modified governing equations, the Rayleigh-wave dispersion equation for a saturated porous half-space was derived.

Theoretical verification showed that the proposed formulation establishes a mechanistic link between trapped-fluid oscillatory dissipation and Rayleigh-wave behavior. When localized oscillation effects are neglected, the model directly recovers the standard Rayleigh-wave solution derived from classical Biot body-wave equations.

Numerical results demonstrated that trapped nonwetting-fluid oscillations affect Rayleigh-wave attenuation much more strongly than phase velocity. This attenuation response is especially prominent across the medium-to-high-frequency range.

The investigation further established that soil permeability, dissipation coefficients, and pore-throat geometry govern the locations and magnitudes of attenuation extrema, whereas nonwetting-fluid viscosity and density have secondary effects. In addition, displacement analysis indicated that the oscillation-induced wave modification remains predominantly confined to the near-surface region.

Subject of Research: Rayleigh-wave attenuation and displacement response in fluid-saturated porous soils

Article Title: Rayleigh-wave attenuation and shallow displacement response in saturated soils containing trapped nonwetting fluids: an oscillation-modified Biot framework

Article References: Deng, W., Yang, Y., & Qin, C. (2026). Rayleigh-wave attenuation and shallow displacement response in saturated soils containing trapped nonwetting fluids: an oscillation-modified Biot framework. Geomechanics and Geophysics for Geo-Energy and Geo-Resources. https://doi.org/10.1007/s40948-026-01240-5

Image Credits: AI Generated

DOI: 10.1007/s40948-026-01240-5

Keywords: Rayleigh waves, Biot theory, wave attenuation, saturated soils, nonwetting fluids, pore-scale oscillations, near-surface dynamics, geophysics, Rayleigh-wave, attenuation, shallow, displacement