Tomographic analysis and geological context of a bottom simulating reflector on the South Shetland

A scismic reficction tomographic analysis io identify spatial variations of wave velocity across a Bottom Simulating Reficctor (BSR) on the South Shetland Margin, in the northern tip of the Antaretic Peninsula is presented. Tbc resolving power of the acquired scismic data is quantified in order io evaluate the reliability of the velocity analyses performed. Wc show that conventional and continuous velocity spectra, as wefi as tomographic inversion of reficeted arrivals, support the hypothesis that the strong reflector is due Io the presenee of a gas hydrate layer overlying a zone of free gas. The hydrate layer is characierized by lateral variations of the average interval velocity over the range 2000 Io 2200 m/s. The gas-bearing sediments are identified in a continuous low-velocity zone of average interval velocity in the range 1500 m/s =E: 10%, between the BSR and the first detectable reflector picked about 80 ms below it. Tbc resolution of the acquisition system or of the tomographie inversion does noi aflow us io identify the actual thickness of the predieted gas-bearing layer. A geological framework for the South Shetland Margin and a general overview of the relevance of gas hydrates in geological processes are presented as an introduction Io the tornographie analysis.