Reverse Time Migration of Multiples

Multiple reflections have different wave propagation paths from primary reflections and thus can be used to complement the illumination where primary reflections from beneath the salt are not available. We propose to modify conventional reverse time migration (RTM) so that multiples can be used as constructive reflection energy for subsalt imaging. This new approach replaces the impulsive source wavelet with the recorded data containing both primaries and multiples and uses predicted multiples as the input data. In the RTM process, multiples recorded on the surface are extrapolated backward in time to each depth level, and the observed data with both primaries and multiples are extrapolated forward in time to the same depth level, followed by a cross-correlation imaging condition. A numerical test on the Sigsbee2B dataset shows that a wider coverage and a more balanced illumination of the subsurface area can be achieved by migration of multiples compared with conventional migration of primary reflections.