SUPPRESSION OF SEA-FLOOR SCATTERED ENERGY USING A DIP MOVEOUT APPROACH - APPLICATION TO THE MIDOCEAN RIDGE ENVIRONMENT

Multichannel seismic (MCS) images are often contaminated with in- and out-of-plane scattering from the sea floor. This problem is especially acute in the midocean ridge environment where sea-floor roughness is pronounced. Energy shed from the unsedimented basaltic sea floor can o bscure primary reflections such as Moho, and scattering off of elongat ed sea-floor features like abyssal hills and fault scarps can produce linear events in the seismic data that could be misinterpreted as subs urface reflections. Moreover, stacking at normal subsurface velocities may enhance these water-borne events, whose stacking velocity depends on azimuth and generally increases with time, making them indistingui shable from subsurface arrivals. To suppress scattered energy in deep water settings, we propose a processing scheme that invokes the applic ation of dip moveout (DMO) to deliberately increase the differential m oveout between sea-floor-scattered and subsurface events, thereby faci litating the removal of unwanted energy in the stacked section. After application of DMO, all sea-floor scatterers stack at the water veloci ty, while subsurface reflections like Moho still stack at their origin al velocity. The application of DMO in this manner is contrary to the intended use that reduces the differential moveout between dipping eve nts and allows a single stacking velocity to be used. Unlike previous approaches to suppress scattered energy, dip filtering is applied in t he common-midpoint (CMP) domain after DMO. Moreover, our DMO-based app roach suppresses out-of-plane scattering, and therefore is not limited to removal of in-plane scattering as is the case with shot and receiv er dip filtering techniques. The success of our DMO-based suppression scheme is limited to deep water (a few kilometers of water depth for c onventional offsets), where the traveltime moveout of energy scattered from the sea floor has a hyperbolic moveout with a stacking velocity that depends on the cosine of the scatterer steering angle in a manner analogous to how the moveout of a dipping reflector depends on the di p angle. The application of DMO-based suppression to synthetics and MC S data collected along the southern East Pacific Rise demonstrates the effectiveness of our approach. Cleaner images of primary reflectors s uch as Moho are produced, even though present shot coverage along the East Pacific Rise is unduly sparse, resulting in a limited effective s patial bandwidth.