Correlation between geological stuctures and gas hydrate amount offshore the South Shetland Island — preliminary results

Sediments of the accretionary prism, present along the continental margin ofthe Peninsula Antarctica SW of Elephant Island, are filled by gas hydratesas evidenced by a strong BSR. A multidisciplinary geophysical dataset,represented by seismic data, multibeam, chirp profiles, CTD and core samples,was acquired during three oceanographic cruises. The estimation of gas hydrateand free gas concentrations is based on the P -wave velocity analysis. In order toextract a detailed and reliable velocity field, we have developed and optimized aprocedure that includes the pre-stack depth migration to determine, iterativelyand with a layer stripping approach method, the velocity field and the depth-migrated seismic section. The final velocity field is then translated in termsof gas hydrate and free gas amounts by using theoretical approaches. Severalseismic sections have been processed in the investigated area. The final 2Dvelocity sections have been translated in gas-phase concentration sections,considering the gas distribution within sediments both uniformly and patchlydistributed. The free gas layer is locally present and, consequently, the baseof the free gas reflector was identified only in some lines or part of them. Thehydrate layer shows important lateral variations of hydrate concentration incorrespondence of geological features, such as faults and folds. The intensefluid migration along faults and different fluid accumulation in correspondenceof geological structures can control the gas hydrate concentration and modifythe geothermal field in the surrounding area.