Spherical-wave AVO modeling in elastic and anelastic media

Arnim B. Haase and Charles P. Ursenbach

ABSTRACT

The AVO-response of two-layer isotropic models for AVO-Classes 1 and 3 is investigated for P-waves and converted waves. Zoeppritz reflection coefflcients 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 some similarity between R PP and R PS for Class 1. Normalized Class 3 responses show no depth dependence. There is no similarity between R PP and R PS for Class 3.

Anelasticity modifies the AVO-response of two-layer isotropic models. 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. Normalized spherical wave Class 3 responses show a mild Q-factor dependence for the highest attenuation levels modelled at Q P1 = 100. 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.

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