USING MULTIPLE ELIMINATION TO IMAGE GEOLOGIC STRUCTURES BENEATH THE GAS HYDRATE STABILITY ZONE IN THE NORTHERN GULF OF MEXICO

Gas hydrates are well known for their capacity to change the physical properties of near-surface sediments and have been linked to massive slope failures on continental margins. As drilling in the Gulf of Mexico has progressed from shallow-water shelf depths (<200m) to deep-water slope depths (>1000m), wells now penetrate the gas hydrate stability zone. In order to understand the consequences of drilling through the hydrate zone, it is imperative to understand the geological setting in which these hydrates exist and to be able to estimate the distribution and concentration of gas hydrate deposits especially in the subsurface. In May 2003, the USGS conducted a 14-day cruise aboard R/V Gyre to collect high-resolution multichannel seismic reflection data and develop the geologic framework around two deep-water sites (near lease blocks Atwater Valley 14 and Keathley Canyon 195). Both may be drilled by industry in spring, 2004, to study gas hydrates in the Gulf of Mexico. The multichannel data from Atwater Valley, in 1300-m water, show many shallow unconformities, deeper dipping reflections, numerous diffractions, and substantial amplitude variations. A multiple elimination strategy, using a well-known subtraction technique, improves the strength and continuity of the deeper reflections. Results from this reprocessing of selected profiles around one of the vents/sea-floor mounds shows faulting and pathways that more clearly demonstrate the relations between the shallow and deeper structures.