[M-IS32] Gas hydrate in environmental-resource sciences

[MIS32-P06] Characteristics of methane hydrate fields in the southwestern margin of the Yamato Basin, southern Japan Sea

*Naoto Ishida¹, Hidefumi Fujioka², Hitoshi Tomaru³, Takao Ebinuma¹, Ryo Matsumoto⁴ (1.Social Systems and Civil Engineering, Graduate School of Engineering, Tottori University, 2.Tottori Prefectural Fisheries Experiment Station, 3.Department of Sciences, Chiba University, 4.Gas hydrate Labratory, Meiji University)

Keywords:shallow-type methane hydrate, Yamato Basin, Japan Sea

The Yamato Basin is one of the methane hydrate fields located in the southern part of the Japan Sea. In the southwestern margin of the Yamato Basin, gas chimneys have been detected by the shallow-type methane hydrate survey conducted by METI. Subsequent researches by the Gas Hydrate Research Laboratory of the Meiji University and Tottori Prefecture revealed characteristics of the methane hydrate fields using sub-bottom profiling, piston and gravity coring, geothermal measuring, interstitial water analysis etc.

Geothermal gradient was measured at the southwestern slope of the basin as 71.33 mK/m and base of gas hydrate stability was estimated to be 138.6 mbsf. Several huge gas chimneys, hundreds of meters in width, were found in the northwestern slope of the Oki Ridge. Carbonate concretions just below the seafloor and shallow (<2.4 m) sulfate-methane interface (SMI) depths around the gas chimneys indicate high methane flux and strongly suggest large volumes of methane hydrate in the gas chimneys.