Elastic wave scattering and stress concentration effects in non-homogeneous poroelastic geological media with discontinuities

In this work, we investigate elastic wave propagation in complex geological media that exhibit material inhomogeneity in the form of depth-dependent material parameters and heterogeneity in the lateral direction. In addition, we consider a layered structure with non-parallel interfaces, free-surface relief, plus the presence of different type of discontinuities such as interface and/or internal cracks. The seismic load comprises incident, time-harmonic pressure (P) and vertically polarized shear (SV) waves, thus covering the plane strain case. Next, the computational technique developed herein is a hybridization of the semi-analytical wave number integration method (WNIM) with the boundary element method (BEM) cast in the frequency domain for solving 2D problems of elastodynamics. Transient response to this problem is recovered through standard Fourier synthesis of the frequency domain results. In essence, the present modeling effort interfaces continuum mechanics with linear fracture mechanics, since it focuses on wave scattering by cracks in complex geological regions. Material behavior is reproduced by the viscoelastic equivalent to Biot's poroelasticity. More specifically, by assuming saturated geomaterials, Bardet's model is introduced in the analysis as the computationally efficient viscoelastic isomorphism to Biot´s equations of dynamic poroelasticity, thus replacing the original two-phase material by a single phase one. Finally, the role of stationary cracks in poroelastic materials is investigated through an extensive series of parametric studies, whereupon these discontinuities act as both wave scatterers and stress concentrators. In sum, our simulations serve to quantify the sensitivity of the near field stress intensity factors (SIF) and of the far field free surface motions to incoming wave characteristics, surface and underground topography, and mechanical properties of the geological deposits.

► We investigate elastic wave propagation in complex geological media.
► The method of solution is a hybrid wave number integration/boundary element method.
► Poroelasticity is accounted for by using Bardet's model.
► Results are for near field stress concentrations and far field wave motions.