Gravity measurement on the sea bottom is essential to detect the precise structure underneath the sea bottom and to estimate the density of sediment and bedrock.Measurement by use of on-land survey systems on board the deep sea submersibles SHINKAI 2000 and SHINKAI 6500 was carried out in the tectonically active sites:in the southernmost part of the Toyama Trough and the adjacent Toyama Deep Sea Channel,over the two small knolls located in the southernmost part of the "Fukaura Small Hills"off Oga Peninsula,in the WMARK area,western Mid Atlantic Ridge-Kane Transform intersection,etc.in these areas high-precision gravity anomalies higher than those expected from the surface-ship survey were obtained.Active tectonics occuring in these sites was discussed through the analysis of the obtained gravity data.
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