Hydrocarbon Seepage in the Deep Subsurface Inferred from Seismic Data in the Bering Sea

We infer the presence of long-lived hydrocarbon seeps in the Bering Sea, at water depths of about 3800 m. Images from reflection seismic data show lateral discontinuities extending from topographic highs in the crystalline basement all the way through the thick (>4 km) sediment column. At the seafloor these inferred conduits manifest as altered reflection amplitudes. The conduits are associated with stratigraphic changes (e.g. bed thinning), suggesting that they have been present throughout the deposition of this thick section. Within the sediment column gas phase methane manifests as anomalously low sounds speed, as well as either horizontally oriented high amplitude reflections, or vertically oriented low amplitude clouds. One such accumulation appears at the inferred base of gas (methane) hydrate stability (BGHS), a pressure-temperature dependent phase change. The BGHS here is broadly perturbed upward over the basement high suggesting higher heat flux at this location. In a few highly localized areas, the inferred top of gas implies a temperature that can only be achieved by advective fluid transport. The BGHS can be used to quantitatively constrain the time dependent heat flux, and by inference the fluid flux and methane carrying capacity of the advecting pore fluids.