Birefringence parameters: Indicators of anisotropic symmetry systems

The difference in travel times between split shear waves (travel-time splitting) in anisotropic media depends on nine combinations of the density normalized elastic parameters (the birefringence parameters). These combinations are all zero in isotropic media, where there is no shear-wave splitting. The number of nonzero birefringence parameters increases with decreasing symmetry elements in the medium: from one in cubic media to nine in triclinic media.The birefringence parameters may be recovered from travel-time splitting observations. Their azimuthal behavior may then be interpreted in terms of crack orientation (strike and dip directions).