| 講演要旨(和文) | | SIPの一環として久米島西方沖の海底熱水活動域において海底重力探査が実施された。探査では独自開発の海底重力計OBG-3と海底重力計を着底させるための吊下げウインチシステムが用いられた。海底重力測定は2本の長さ600mの東西測線上を約100 m間隔で実施された。測線中央部で極大を示す重力差4mgalの明瞭な重力異常が両測線で観測された。2次元モデル計算の結果、周囲との密度差を2g/cm3と仮定した場合、観測データは、中央頂部がほぼ海底面と一致する最大層厚50mの三角形断面形状のモデルにより説明可能であることが分かった。これらの結果は、海底重力探査が潜頭性海底熱水鉱床の形状や密度の把握に有効であることを示す。 |
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| | 講演要旨(英文) | | An ocean bottom gravity survey using an ROV was carried out at the active hydrothermal area located off the west of Kume Island. A recently developed ocean bottom gravimeter OBG-3 and a multi-purpose hanger type survey system to landing the gravimeter were used for this surveys. The gravity measurements were conducted along two east-west trending survey lines 600 m in length. A distance between the measurement points was about 100 m. A clear positive gravity anomaly was observed on the both survey lines. The result of 2-D gravity modeling indicates that the anomaly can be explained by a north-south elongated simple high density block model with a triangular cross-section. The maximum thickness of the model is about 50 m on an assumption with a density difference 2 g/cm^3, and the top of the body locates near seafloor. These results indicate that the ocean bottom gravity survey can provide the shape of the SMS ore deposit under the seafloor as well as its existence. |
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