2012 年 46 巻 4 号 p. 257-274
Chemical and isotopic compositions of seeping gas from the coastal area of Yagaji Island were measured. The gases composed mainly of methane. The δ13C and δD of methane suggest that the origin of the methane is thermal decomposition of organic matter. The δ13C of methane and CH4/(C2H6+C3H8) ratio in the gases suggest long distance migration from the sources. The 3He/4He ratios in the Yagaji gases suggest thermal decomposition of organic matter occurs in deeply-buried sediments. The Yagaji gases would be generated from marine organic matter in the Motobu group around 4 km below the ground.
