The distribution of gas and gas hydrate at natural seeps inferred from seismic data

The Naval Research Laboratory has conducted detailed seismic and acoustic investigations at natural methane hydrate seep sites at several locations worldwide. The seismic expressions of these features exhibit significant differences, such as bathymetric expression (mounds, pockmarks, pavements) and the positions of the faults that are likely acting as methane-supplying conduits. Similarities include the way in which the base of gas-hydrate stability, a pressure and temperature boundary is perturbed upward by the warm, upward advecting fluids that supply the seep. In all areas observed, massive, sediment-displacing deposits of gas hydrate on or within about one meter of the seafloor are consistent with a localized conduit supplying the methane, but also brings heat, thereby thinning the zone in which hydrates are stable. Although massive gas hydrates on the seafloor are one of the most visible types of gas hydrate accumulation, they appear to be very localized.