Spherical-wave AVO modeling in elastic and anelastic two-layer media

The AVO response of two-layer isotropic models for AVO Class I is investigated for P-waves and converted waves in elastic and anelastic media. Zoeppritz reflection coefficients and the Weyl/Sommerfeld-integral are utilized for the computations. Spherical-wave results for R-pp and R-PS are compared with plane-wave reflectivity. Depth dependence of spherical wave AVO is found to be strongest near critical angles of Class 1. There is a similar depth dependence between R-PP, and R-PS for Class 1. Anelastic effects are introduced via the constant-Q approximation. Anelasticity modifies the AVO response of two-layer isotropic models. However, when reflection amplitude losses due to attenuation are compensated for by unit reflectivity scaling, AVO characteristics similar to the elastic situation are found. Q-factor dependence of spherical-wave AVO is found to be strongest near critical angles of Class 1. This Q-dependence, to some degree, mimics depth dependence of elastic comparisons. Wavelet stretch of converted wave AVO reflection traces is observed in addition to a phase rotation of all anelastic trace examples when compared to the elastic situation. In summary, spherical-wave behaviour affects amplitude versus offset, both for PP and PS reflections in elastic and anelastic isotropic media.