Seismic stratigraphy, BSR distribution, and venting of methane-rich fluids west off Paramushir and Onekotan Islands, northern Kurils

Single-channel seismic recording, water chemistry determination, and sediment sampling were carried out off the northern Kuril Islands and the southern tip of Kamchatka. A bottom simulating reflector (BSR) was mapped in detail. The shipboard analyses of bottom water samples yielded methane concentrations up to 1000 nl/1. West off Paramushir Island, venting of methane-rich fluids from the seafloor into the water column is related to unusual trajectories of the BSR which emerges towards the seafloor. The destabilisation of gas hydrates and the origin of the vent site may correspond to anomalous high heatflow caused by recent volcanic intrusions into the sediment. No venting was found in the areas off the southern tip of Kamchatka and off Onekotan Island.