The IBIEM solution to the scattering of P1 waves by an arbitrary shaped cavity embedded in a fluid-saturated double-porosity half-space

Abstract

SUMMARY The double-porosity saturated medium is widespread in the Earth's crust, rocks and man-made materials. In this paper, we developed the indirect boundary integral equation method abbreviated as IBIEM to investigate the elastic waves scattering characteristics in a fluid-saturated double-porosity half-space with an arbitrary shaped cavity inside. First, the Helmholtz decomposition was utilized to derive the 2-D Green's functions for plane waves in a double-porosity half-space under fluid saturation. Then the scattered wavefield is constructed by line sources of compressive and shear waves located at a virtual surface near the cavity surface. After the verification of numerical accuracy, the scattering of plane P1 wave by an arbitrary shaped cavity in a 2-D fluid-saturated double-porosity half-space is solved and analysed. Numerical results show that: the displacement, hoop stress and pore pressure amplitudes are strongly dependent on incidence frequencies, porosities and boundary drainage conditions, etc. Displacement amplitudes usually reach their maximums under the dry condition, while hoop stress amplitudes obtain their peak values under the impermeable condition. The presence of matrix pore pressure and fracture pore pressure enhances the energy fluctuations of double-porosity media, which produces more complex seismic response.