Nonlinear Seismic AVO in the Lab

The nonlinearity of the seismic reflection amplitude-variation-with-offset (AVO) response in the presence of large relative changes in acoustic and elastic medium properties is investigated with physical modelling data. A procedure for pre-processing reflection data, acquired using the CREWES-University of Calgary physical modelling facility, is enacted on the reflection from a water/plexiglas boundary. The resulting picked and processed amplitudes are compared with exact solutions of the plane-wave Zoeppritz equations, as well as R_PP(θ) approximations that are first, second, and third order in ΔV_P/V_P, ΔV_S/V_S, and Δρ/ρ. In the angle range 0-20 degrees, the third order plane wave approximation is sufficient to capture the nonlinearity of the AVO response of a liquid-solid boundary with V_P, V_S and ρ contrasts of 1485-2745m/s, 0-1380m/s, and 1.00-1.19gm/cc respectively, to an accuracy of roughly 1%. This is in contrast to the linear Aki-Richards approximation, which is in error by as much as 25% in the same angle range.