AVO Is Not What You Think
Amplitude Versus Offset (AVO) was born in the late 1970s and early 1980s. The first major step came in 1979, when Aki and Richards proposed a linearized version of the Zoeppritz equations. Their aim was modest: distill elastic physics into a form interpreters could actually use. Then Shuey arrived in 1985. His two-term approximation was elegant, intuitive, and immediately became the common language of AVO. In 1994, Fatti et al. reframed the same physics into impedance contrasts, nudging AVO toward quantitative inversion. Three models, three decades, one underlying truth: they are all approximations of a deeper elastic reality . Forty years later, we still treat these approximations as if they were laws of nature. The Temptation of the Simple Equation Shuey’s expression: R(θ) ≈ A + B sin 2 θ is popular not because it is universally correct, but because it is easily interpretable . A is the zero-angle reflectivity, mostly ΔI p . B is the gradient, influenced by Δ...
