CONSTRUCTION OF A PRECISE GRAVITY ANOMALY MAP OVER THE EASTERN PART OF SOUTHWEST JAPAN,AND FORMATION OF GRAVITY DATABASE.

本研究是为了进一步发展日本西南地区重力研究的成果（科学研究资助(C), No.01540331,1989-1991）。两个目标；(1)建立高精度重力数据库；(2)构建覆盖日本西南部的精确重力异常图。我们通过收集20多个机构和组织的数据，创建了一个由85,000个组成的重力数据库。其中两万九千件是我们的原创作品。新增9600个数据，填补数据空白。通过对重力减小和坐标读数进行总修正，获得了1-0.5 mgal的高分辨率。在132e ~ Fossa-Magna数据密集分布的区域建立了大尺寸高精度的bouger异常图。地理调查所印发了两幅100万比例尺和200万比例尺的立体地形图。这些地图上描绘了非常有特色的重力剖面。识别出的因素有：1)沿主要地质构造线（如中构造线）和活动断裂（如阿特拉断裂）圈定了明显的线性线；2)从鹤河湾到四国东北部，形成了一条非常大规模的陡坡重力梯度带，经赤塔半岛形成了两条大弧。3)各地均有很强的中小尺度陡梯度重力带。在许多情况下，它们与活动断层有关。发现了许多迄今为止用其他地球物理或地质方法所不知道的线性。它们只在重力异常图上非常有特色地描绘出来。

Present study was executed to develop the achievement of the former work of gravity study in Southwest Japan (Grant-in-Aid for Scientific Research (C), No.01540331,1989-1991). Two objects aimed ; (1) to create a gravity database with high precision and (2) to construct a prcise gravity anomaly map to cover Southwest Japan were completely performed.We created a gravity database consisted of 85,000 by collecting data from more than 20 institutions and organizations. 29,000 among them are of our original. 9,600 data were newly measured to fill up blank area of data. By performing total revisions both for gravity reductions and coordinates readings, a high resolution of 1-0.5 mgal was obtained.A large sized precise Bouguer anomaly map was constructed and published in the area ranged from 132ﾟ E to Fossa-Magna where covered with densely distributed data. A couple of stereographic relief maps drawn in 1 and 2 million scales were issued from Geographical Survey Institute.Very characteristic gravity profiles are delineated on those maps.Factors recognized are : 1) Distinct linearments are delineated along major geological tectonic lines such as Median-tectonic line, and active faults such as Atera Fault. 2) A very large scale of steep gradient belt of gravity is running from Suruga Bay to north-eastern Shikoku through Chita Pneninsula by forming two large arcs. 3) Very strong steep gradient belts of gravity of middle to smale scale are found in various places. In many cases, they are associated with active faults. 4) There are founed many linearmaents not known so far by other geophysical or geological means. They are delineated only on the gravity anomaly maps very characteristically.