TROUBLE WITH DIPPING REFLECTORS

The ``standard process'' is NMO, stack, and zero-offset migration. Its major shortcoming is the failure of NMO and stack to produce a section that resembles the true zero-offset section. In chapter  we derived the NMO equations for a stratified earth, but then applied them to seismic field data that was not really stratified. That this works at all is a little surprising, but it turns out that NMO hyperbolas apply to dipping reflectors as well as horizontal ones. When people try to put this result into practice, however, they run into a nasty conflict: reflectors generally require a dip-dependent NMO velocity in order to produce a ``good'' stack. Which NMO velocity are we to apply when a dipping event is near (or even crosses) a horizontal event? Using conventional NMO/stack techniques generally forces velocity analysts to choose which events they wish to preserve on the stack. This inability to simultaneously produce a good stack for events with all dips is a serious shortcoming, which we now wish to understand more quantitatively.