Detailed Gravity Anomaly Map in and around the Japanese Islands

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We compiled gravity data which were taken from various organizations in Japan. There are four groups of data source:The first is the data measured by ourselves during the last 15 years, numbering more than 10,000; The second is the data measured by the Geographical Survey Institute (GSI) and by the Hydrographic Department for geodetic purposes; The third is the data measured by university researchers for various academic purposes; and The fourth is the data measured by governmental exploration organizations such as the Geological Survey. The total number of data digitally compiled is about 500,000 points of which about 100,000 points are on land and 400,000 are at sea.Each data set is compared with the GSI's data set and both biases of gravity values and inaccuracy of gravimeter coefficients are examined. During these processes, incorrect or suspected data are either corrected or rejected from the data set. After these examination, all data are adjusted to the International Gravity Standardization Net 1971 (IGSN71) system.Using the data set thus obtained, we generate detailed gravity anomaly map in and around the Japanese Islands. The sap is prepared at a scale of 1:1,000,000 with a contour interval of 2 mgal. Colored (25 gradients) full size maps with an explanatory text and 30 transparent sheets which are indicating seismicity of the Japanese Islands has been published from the University of Tokyo Press.