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[MIS16-05] Characteristics of BGHS in shallow methane hydrate fields of Oki Trough, eastern margin of Japan Sea
Keywords:shallow methane hydrate , BGHS, Oki Trough, Japan Sea
BGHS in the Oki Trough is mainly controlled by geothermal gradient. In the southeastern margin of Oki Trough, the geothermal gradient is comparatively high: 115–124 degrees C/km (e.g., Yasui et al., 1966, 1968). On the other hand, our geothermal investigation in the southwestern margin revealed the geothermal gradient as 71 degrees C/km. BGHS depths were estimated at the site in 727 m water depth in the southeastern margin and at the site in 763 m water depth in the southwestern margin to be 83 mbsf and 157 mbsf, respectively.
BGHS response to the 120 m sea-level fall during the Last Glacial Maximum was simulated. At the southwest slope of Oki Trough, the BGHS becomes 27 m shallower than present, while the variation at the southeast slope is 14 m. The response of BGHSs to the sea-level fall is prominently involved in methane hydrate disassociation, which makes the submarine ground unstable. This study intends to make reference to the relation between topographic deformation, like pockmarks and submarine slides, and methane hydrate disassociation in the Oki Trough.
This study was conducted under the commission from AIST as a part of the methane hydrate research project funded by the Ministry of Economy, Trade and Industry, Japan.