In this work we do seismic modeling using typical rock properties from a real North Sea turbidite field. As is mentioned in Avseth et al. (1999), this field has been problematic because of complex sand distribution and non-reservoir sand anomalies. Two of the three most recent exploration wells failed to encounter reservoir sands in locations where poststack seismic amplitudes indicated reservoir sands. Avseth et al. (1999) suggest that AVO analysis in this field can help to discriminate sands from other lithofacies. However, because of the presence of complex velocity anomalies in the overburden, it is desirable to have a estimation of the uncertainty in the AVO response; in other words, how reliable is the lithology discrimination from AVO analysis given the presence of a complex overburden zone?
In this paper, we do forward modeling, simulating an earth model with an overburden that includes complex velocity anomalies. We generate several migration-velocity realizations by introducing coherent percentage velocity errors in the overburden zone of the original velocity model. We migrate the synthetic data using each velocity realization, and measure the variability in the resulting gradient and intercept AVO attributes that results from the velocity error.