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

本研究是为了发展日本西南部重力研究的成果(科学研究补助金(C)，编号01540331,1989-1991)而进行的。完成了两个目标：(1)建立高精度的重力数据库；(2)建立覆盖日本西南部的高精度重力异常图。通过收集20多个机构和组织的数据，建立了一个由8.5万人组成的重力数据库。其中29,000个是我们原创的。新测量了9600个数据，以填补数据空白区域。通过对重力折减和坐标读数进行全面改正，获得了1-0.5mgAl的高分辨率。在132mgE到ﾟ-magna地区构建并发布了大尺寸精确布格异常图，该地区覆盖着密集分布的数据。美国地理调查局发布了两幅100万比例尺和200万比例尺的立体地形图，在这些地形图上描绘了不同特征的重力剖面。识别的因素包括：1)沿主要地质构造线，如中构造线，以及活动断裂，如Atera断层，划定了明显的线形。2)从苏鲁加湾到四国东北部，通过赤田岛形成了两个大弧线，形成了一个非常大规模的陡峭重力梯度带。3)不同地区存在中到斯梅尔尺度的很强的陡峭重力梯度带。在许多情况下，它们与活动断层有关。4)建立了许多其他地球物理或地质手段尚未发现的线性模型。它们只在重力异常图上非常有特点地被圈定。

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.