The results of the cruise of R/V Akademik M.A. Lavrentiev conducted by the Pacific Institute of Oceanology, Far East Division of the Russian Academy of Sciences and the Shirshov Institute of Oceanology, Russian Academy of Sciences in August to September 2005 are considered. The aim of the works was to specify the tectonic structure, seismogenic potential, and tsunamigenic hazard of the central segment of the Kuril Island Arc. The complex studies involved single-channel seismic profiling, gravimetry, magnetometry, detailed bathymetry, dredge sampling of sea-floor rocks and sediments, and gas geochemistry. Geophysical and geological data are reported. It was demonstrated that the target area is an active tectonic destruction zone, the zone boundaries were outlined, and the main internal structural and compositional heterogeneities were identified.

Complex geological, gas geochemical and hydro meteorological studies were conducted to investigate the methane fields present in the bottom sediments and seawater of the Red River and Phu Khanh sedimentary basins. We demonstrate that the system of tectonic faults that formed the sedimentary basins of the Red River and the Phu Khanh (the eastern shelf and slope of Vietnam) created the necessary conditions for the generation and migration of endogenous methane into the bottom sediments and seawater. It is shown that dissolved methane in seawater can be transported by marine currents, which in turn can be influenced by seasonal and irregular synoptic processes. The research shows that part of the dissolved methane contained in the waters above the Ken Bau gas field can be transported to the south by the coastal Vietnamese current, which adapts to the conditions of the winter northeast monsoon. It is concluded that there could be at least two deep sources of hydrocarbon gas emissions in the Phu Khanh basin. The impact of Typhoon Nakri on the transport of dissolved methane in the water column of the Phu Khanh sedimentary basin has been investigated. The typhoon could create favorable hydrodynamic conditions for the movement of dissolved gases from oil and gas deposits near the coasts of the islands of Kalimantan and Palawan to the Phu Khanh basin. A possible route for this transfer has been identified.