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| | Abstract | | 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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