ИСТИНА

Nonlinear effects in seismic wave propagation are observed even at very small strain levels, where classical elastic and viscous models predict linear behavior. For example, attenuation of seismic waves at low frequencies has been found to be independent of wave amplitude — an effect that cannot be explained by standard elastic or viscous dissipation mechanisms. Frictional sliding has been proposed as a possible amplitude- and frequency-independent mechanism, but it has proven inefficient in capturing observed attenuation. An alternative explanation is microscale plastic yielding, introduced by Yarushina and Podladchikov [1], which accounts for energy dissipation through irreversible deformation at grain contacts and defects. Their work demonstrated significant attenuation of compressional waves with quality factors in the range of Q = 12–20, though it was limited to low-porosity materials where pore interaction was neglected. Importantly, experimental studies have confirmed the presence of microplastic deformation under subcritical loading during seismic wave propagation, supporting its relevance as a physical attenuation mechanism [2]. In this study, we extend that model to account for both compressional (Vp) and shear (Vs) wave attenuation in elastoplastic porous media with interacting pores. Using finite-element modeling in CAE Fidesys [3], we simulate wave-induced stress cycling in a representative volume containing multiple pores. Plastic deformation initiates locally around individual pores and expands until plastic zones merge, resulting in distributed dissipation. Numerical averaging techniques [4] are applied to compute macroscopic attenuation, revealing a nonlinear dependence on wave amplitude. We further investigate the roles of strain amplitude, effective pressure, and porosity. The results reinforce microplasticity as a viable amplitude- and frequency-independent mechanism of seismic wave attenuation in preloaded, porous rocks. Keywords: Porous Rocks, Seismic Waves, Numerical Modeling References: [1] Yarushina, V.M. and Podladchikov, Yu.Yu. Plastic yielding as a frequency and amplitude independent mechanism of seismic wave attenuation: Geophysics, 75(3), 51-63, 2010. [2] Mashinsky, E.I. Quasy-microplastic processes and nonlinear seismic: Fizika Zemli, 2, 3–10, 1994. [3] Fidesys LLC official website: https://cae-fidesys.com/ [4] Yakovlev, M. and Konovalov, D. Multiscale geomechanical modeling under finite strains using finite element method: Continuum Mech. Thermodyn, 35, 1223-1234, 2023.