Previous work by others

Beyond the mere ``historical'' interest, previous work on defining and describing the FEAVO effect can help answer some potential objections to the proposed approach. For example, one objection might be that FEAVO effects are randomly distributed. Therefore, their expression in AVO pickings is the same as that of random noise, and can be treated the same way. () showed that focusing and defocusing caused by a random distribution of small velocity anomalies will not lead to the canceling of the FEAVO effects by each other. Moreover, they prove that even if the distribution of velocity anomalies is random, the probability that FEAVO effects appear is not randomly distributed with the distance from the shot. Therefore, FEAVO presence cannot be equated with random noise in AVO picking, since FEAVO-causing anomalies are not randomly distributed in real data. In the case of shallow anomalies the distribution is influenced by depositional patterns [the ``Rotten alligators'' in ()], and in the case of deep-origin FEAVO, by the presence of faults (). Besides, the amplitude of the FEAVO effects is often so large and spatially extended that it renders AVO analysis impossible.