CONSTRUCTION OF GRAVITY DATABASE OVER JAPANESE ISLANDS

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In the wide area of the geo-sciences, gravity data have very important meanings and play an important role. In the field of geodesy, for example, it is indispensable fundamental physical parameter for precise geoid determination. Therefore, it was impatiently longed to be accomplished nationwide gravity database in Japan. Recently, two large gravity databases have been published successively. One is the gravity database ; Gravity CD-ROM of Japan (GSJGDB) by the Geological Survey of Japan (present : National Institute of Advanced Industrial Science and Technology) published in 2000. The other is the gravity database in Southwest Japan (SWJGDB) that constructed by our gravity research group in Southwest Japan and published in 2001. Main frame of the gravity database in Southwest Japan was constructed by developing the achievement of former five projects (the same category of Grant-in-Aid for Scientific Research: No.01540331 in 1989-1991,No.04640400 in 1992-1994,No.07640552 in 1995-1997,N … More o.11440130 in 1999-2000 and No.13640428 in 2001-2003). By publications of those two large databases, circumstances of the gravity database in Japan have much progressed. By merging GSJGDB into our database, we complied a new one to cover whole Japanese islands (JGDB). As concerned to the data coverage of JGDB, there still remained some parts of blank or sparsely distributed areas especially in the Northeast Japan.Present project was planed and executed with two aims ; (1) to start construction of a developed high precition gravity database to cover whole Japanese islands, (2) to issue results obtained by the gravity database and to make it possible for public use. The results obtained are as follows. (1) During the period concerned, we performed an extensive gravity survey and the blank area in the west of Southwest Tohoku district had completely disappeared by more than twenty thousands of newly supplemented precise gravity data. (2) By utilizing this desirable condition, we publish a gravity atlas "Gravity Atlas of Japanese Islands--Southwest Japan and Central Japan--" from the Univ. Tokyo Press in 2004. Besides this, by dividing areas where the data are desirably distributed, we drew 1/75,000 scale of gravity maps. The area were divided into 7 regions, and 4 kinds of maps (a : station distributions, b : Bouguer anomaly, c : colored Bouguer anomaly, and colored Bouguer anomaly of the wavelength less than 125km) were prepared for each regions. Less