Resumen
In this study one seismic section offshore Chiloé Island was analyzed to better define the seismic character
of the hydrate-bearing sediments. The velocity analysis was used to estimate the gas-phase concentration and relate it to
the geological features. The velocity model allowed us to recognize two important layers that characterize hydrate- and
free gas-bearing sediments above and below the BSR respectively: one located above the BSR, characterized by high
velocity (1,800-2,200 m/s) and a second one, below the BSR, characterized by low velocity (1,600-1,700 m/s). A weak
reflector at about 100 m below the BSR marks the base of the second layer. AVO analysis and offset stack sections
confirming that the reflector interpreted as BGR is related to free gas presence in the pore space. The velocity field is
affected by lateral variation, showing maximum (above the BSR) and minimum (below the BSR) values in the sector.
Here, the highest gas hydrate and free gas concentrations were calculated, obtaining 9.5% and 0.5% of total volume
respectively. A variable BSR depth (from 300 to 600 mbsf) can be justified supposing a variable geothermal gradient
(from 25 to 45 °C/km).