Influence of Source Frequency on Shear Wave Splitting - An Experimental Approach

Elastic anisotropy due to aligned cracks has been the subject of many seismic physical modeling experiments. Different experimental approaches related to sizes, shapes and density of cracks has been taken into account in earlier investigations. In this paper we present a physical study of shear-wave splitting in anisotropy induced aligned cracked media. In this experiment, rubber discs were used as inclusions in a solid epoxy resin matrix. Pulse transmission measurements were carried out on a reference model (without inclusions) and two other models with different aperture of cracks and dissimilar crack densities. The seismic records were measured using three different S-wave source transducers with dominant frequency of 0.1 MHz (low frequency), 0.5 MHz (intermediate frequency) and 1 MHz (high frequency). Crack apertures to seismic wavelength ratio were varied from 1.3 to 13.3 in one model and 2.3 to 23.5 in the second cracked model. Our results show that effects associated with acoustic scattering, attenuation and velocity dispersion interfere directly in shear wave splitting, which in turn is a function of crack aperture and source frequency.