The present invention provides a method for interpreting shear-wave seismic data to detect fractures in the subsurface of the earths crust. Seismic shear waves are acquired along medium symmetry planes and their corresponding AVO intercepts and gradients are estimated. The resulting AVO attributes are combined using a weighted least squares solution to estimate the change in splitting parameter and fast shear velocity, which are diagnostic of the presence of fractures. The method is also useful in assessing the porosity of the subsurface. Knowledge of subsurface fracturing and porosity is useful in locating, for example, oil and gas wells.