Seismic interface modelling: a physical approach to Zoeppritz Theory

Abstract

The analysis of a seismic wave impinging on an interface and the resulting distribution of various seismic waves is intrinsically related to amplitude variations with offset (AVO). This analysis is explained numerically by Zoeppritz Theory which governs the seismic wave partitioning at an interface. The application of physical modelling to understanding the Zoeppritz equations emphasizes the acquisition and processing considerations required for optimum AVO interpretation. The extraction of the true reflection coefficient for a seismic interface is not a simple procedure, due to a variety of factors affecting amplitudes. Physical modelling suggests that P-wave AVO studies are non-unique, since a similar signature can be obtained from different input parameters. SH-wave AVO data are considerably more definitive due to a controlled knowledge of directivity patterns, enhancing the opinion that shear-wave data can be a more useful tool in exploration seismology than is currently perceived. Zoeppritz equations of reflected and refracted energy partitioning in a physical model are generally stable until the incident angle approaches the critical angle (28°). Beyond this point, the equations do not hold due to rapid variations in reflected and transmitted P- and S-wave amplitude data. Similarly, at far offsets where shear-wave mode conversion predominates, amplitude measurements become increasingly unreliable.