Correlation of near surface fractures with seismic radial anisotropy: An approach for near surface fracture identification

Abstract

Fluid flow and solute transport in geologic environments are vital for natural systems, public well-being, and infrastructure that rely on understanding subsurface hydrology. Fractures strongly affect the hydraulic properties of rocks as they often serve as preferential flow paths for fluids. Therefore, the characterization of subsurface fractures is crucial to understand fluid flow in the geological environments and estimate the hydraulic properties of fractured-rock formations. Seismic radial anisotropy that is defined with respect to the difference between the velocity of a vertically polarized S-wave (SV) and one polarized horizontally (SH) can be used as a strong attribute for forecasting near surface fractures. We evaluate the correlation of seismic radial anisotropy with near-surface fractures. We obtain seismic radial anisotropy models at two sites with different bedrock geologies (one metamorphic-igneous and the other sedimentary) using dispersion analyses of the Rayleigh waves, for vertical polarization, and Love waves, for horizontal polarization. The seismic radial anisotropies at these two sites show a strong correlation with near surface fractures. We also perform a sensitivity analysis to obtain an optimum cut-off value to better interpret seismic radial anisotropy in terms of fracture probability.