Analysis of mode conversions over high-velocity layers

Jitendra S. Gulati, Robert R. Stewart

A seismic model based on log data from northeastern Ireland is used to study seismic imaging problems over high velocity layers. Zoeppritz responses at the top and base of a high-velocity layer of the model are used to predict strong modal conversions for an incident P-wave Synthetic seismograms demonstrate that the presence of the various mode-converted (multimode) arrivals leads to complicated reflection events. Separation of various arrivals is important prior to interpretation. The P-S reflection equation is modified to a form which gives physical insight into the amplitude variation with offset of converted waves. Finally, this equation is shown to isolate the multimode arrivals and can be the basis of a modal filter.