AVO Theory for Large Contrast Elastic and Anelastic Targets in Pre-Critical Regimes

Innanen, K.A. (University Calgary)



Interpretable, easy-to-calculate corrective terms are added to first order (i.e., Aki-Richards type) approximate solutions of the Zoeppritz equations. The corrections quantitatively and qualitatively account for the influence of large contrasts and target anelasticity in the precritical regime. The formulation permits several observations pertinent to AVO to be made, regarding

1. The non-negligible importance of target VP to mode conversions, i.e., the angle dependence of RPS;

2.The importance of the number VP/VS = 2 to all elastic reflection coefficients;

3. Wave scattering from contrasts in QP and QS alone; and

4. The relationship between reciprocal quality factors and the frequency rate of change of anelastic reflection coefficients.

The basics of the approach are summarized and the above points are illustrated with AVO curves calculated from plausible large contrast elastic and anelastic media.