Pitfalls in structural seismic interpretation due to subsalt multiples

A false structural interpretation can result from mapping coherent seismic events that are not primary reflections, but instead are multiples. It is well understood that mapping seismic events for structure is a process of tracking strong, coherent, and continuous seismic events. However, this is not a sufficient procedure for structural seismic interpretation because there can be significant coherent noise including converted waves, head waves, and multiples. These can appear strong, coherent, and continuous and so can be confused for true primaries as well as produce erroneous structural results. Subsalt multiples are an especially prevalent danger because the salt-sediment impedance contrast causes many unwanted reverberations. The pitfall of falsely mapping multiples as true structural events can be avoided using the following procedures: (1) understanding if the mapped events are structurally reasonable, (2) reviewing the geometry of stacked unmigrated time seismic sections, and (3) investigating the moveout of migrated prestack gathers.