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 s ediment sampling were carried out off the northern Kuril Islands and t he southern tip of Kamchatka. A bottom simulating reflector (BSR) was mapped in detail. The shipboard analyses of bottom water samples yield ed methane concentrations up to 1000 nl/l. West off Paramushir Island, venting of methane-rich fluids from the seafloor into the water colum n is related to unusual trajectories of the BSR which emerges towards the seafloor. The destabilisation of gas hydrates and the origin of th e vent site may correspond to anomalous high heatflow caused by recent volcanic intrusions into the sediment. No venting was found in the ar eas off the southern tip of Kamchatka and off Onekotan Island.