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A reflection coefficient (see [[Displaying seismic data#Polarity|seismic polarity]]) can be thought of as consisting of the sum of two components—an acoustic term and a [[shear]] term. The acoustic term depends only on the [[impedance]] of the two layers and the [[angle of incidence]]. The shear term depends on [[Poisson's ratio]] in the two layers and also on the angle of incidence.

A reflection coefficient (see [[Displaying seismic data#Polarity|seismic polarity]]) can be thought of as consisting of the sum of two components—an acoustic term and a [[shear]] term. The acoustic term depends only on the [[impedance]] of the two layers and the [[angle of incidence]]. The shear term depends on [[Poisson's ratio]] in the two layers and also on the angle of incidence.

An AVO response not only occurs from an interface characterized by a contrast in Poisson's ratio, but also from interfaces that are entirely acoustic—that is, the measured response is more than a simple contrast in Poisson's ratio.

An AVO response not only occurs from an interface characterized by a contrast in [http://en.wikipedia.org/wiki/Poisson%27s_ratio Poisson's ratio], but also from interfaces that are entirely acoustic—that is, the measured response is more than a simple contrast in Poisson's ratio.

[[file:amplitude-versus-offset-avo-analysis_fig3.png|left|thumb|{{figure number|3}}Gas sand model.]]

[[file:amplitude-versus-offset-avo-analysis_fig3.png|left|thumb|{{figure number|3}}Gas sand model.]]