Measuring shear-wave splitting using seismic anisotropy

In this study, we investigate the feasibility of using microseismic data to invert for fracture density, fracture strike and fracture compliance ratio from shear splitting results. We simulate microseismic waveforms by propagating a moment tensor point source disturbance in a heterogeneous isotropic media using a finite difference program. The model heterogeneity is imposed by the inclusion of discrete fractures within an isotropic homogeneous background model. Shear-wave splitting due to wave propagation through the discrete fracture network is evaluated using an automated shear-wave splitting algorithm. The calculated fast directions and delay times are subsequently inverted using an effective media fracture model to invert for fracture parameters. For the particular geometry in this study, the results from the inversion are best for sub-horizontal ray paths, where wave propagation travels predominantly through the vertically fractured sub-volume. For larger fractures, the inversion under estimates the fracture density and larger error in fracture strike direction. The results indicate that acquisition geometry is an important factor in resolving fracture parameters.