Decomposition of Structural Amplitude Effect and AVO Attributes: Application to a Gas-water Contact

 — The structural amplitude effect, associated with focusing and defocusing due to the reflector curvature, importantly contributes to reflection seismic amplitudes. This paper develops a conciliatory approach for estimating the structural amplitude effect and the attributes of amplitude variation versus offset (AVO). The AVO attributes are extracted from raw amplitudes, in which the structural effect is taken into account explicitly based on a structural model reconstructed from travel-time inversion. One of the goals is to conduct the AVO analysis not just locally (per CDP) but also horizontally to see the global variation along the reflection. The lateral variations of AVO attributes are decomposed by the Chebyshev expansion. The method is demonstrated with an example of weak shallow gas-water contact appearing on a 2-D seismic profile of a site survey in the North Sea.