Gravity surveys were carried out at 2570 points over the northern part of central Japan (35°40′-37°20′N, 136°-138°20′E) by means of the LaCoste & Romberg gravimeter (model G) No. 348. Based on 5800 data including 3230 data measured by several institutions in and around the surveyed area, a complete Bouguer anomaly map was drawn over the central and northern parts of central Japan (35°20′-37°30′N, 136°-139°E). All of the data were refered to the International Gravity Standardization Net 1971.
Terrain correction term was calculated for all data over 80km (40′NS×60′EW) around each measurement point using the 500 meter-mesh mean topographic data file. Density was assumed to be 2.67gr. cm-3.
The complete Bouguer anomaly map thus obtained involves a lot of geophysical and geological information. Descriptions and analysis of the results will be given in succeeding papers.
