Construction of a Precise Gravity Anomaly Map over the Chubu and Kinki Districts, Central Japan, and Formation of Gravity Data-Base.

本研究是为开展名古屋大学1978年以来在日本西南部开展的重力测量工作而进行的。通过增加8800多个新数据，更新了我们原有数据的19555个点，并汇编了其他来源的数据，形成了一个由6万多个数据组成的重力数据库。这个数据库覆盖了日本全境的2/3，从38.5ﾟN开始的南部。其中，测点分布非常密集，分布范围从ﾟE到Fossa-Magna不等。对所有数据文件进行重力值折减和坐标读数的总修订。我们的数据库保证了1-0.5mgAl的综合分辨率，使绘制全范围内任何类型的非常精确的重力异常图成为可能。绘制了各种特征的重力剖面，并识别了以下因素：1)沿着主要的地质构造线，如中间构造线、Itoigawa-Shizuoka大地构造线等，以及活动断裂，如Atera断层，划定了明显的线性。2)一个非常大规模的陡峭重力梯度带通过赤田半岛从Suruga海湾延伸到四国东北部，形成了两个大弧形。这条腰带延伸到九州的麻生子墓地。3)不同地区存在很强的中小尺度重力陡坡带。其中最具特点的就是长达15公里的1984年长野县西部地震震源区沿线。4)Kinki三角标志着极具特征的强负异常。5)中央山脉无负低异常或负低异常太小。这表明它们的身体是由某种构造力支撑的，而不是均衡机制。

Present study was executed to develop the works of gravity survey in the Southwest Japan, conducted by Nagoya University since 1978. By adding more than 8, 800 new data, 19, 555 points of our original data were updated, and compiling ones from other sources, a gravity data-base consisted of more than sixty thousands of data were formed. 2/3 of whole Japan, the southern part from 38.5ﾟ N, were covered by this data-base. The area among it, ranged from 133ﾟ E to Fossa-Magna, has very dense distribution of measurement points. Total revisions both for gravity value reductions and coordinates readings on all data file were performed. Our data-base garantees 1-0.5 mgal of comprehensive resolution and makes it possible to draw any kinds of very precise gravity anomaly maps in the whole range.Very characteristic gravity profiles are delineated and following factors are recognized : 1)Distinct linearments are delineated along major, geological tectonic lines such as Median Tectonic Line, Itoigawa-Shizuoka Geotectonic Line and so on, 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 Peninsula by forming two large arcs. This belt extends to the Aso Graven in Kyushu. 3)Very strong steep gradient belts of gravity of middle to small scale are found in various places. One of the most characteristic among them is that with 15 km long along the seismic focal region of the 1984 Western Nagano Prefecture Earthquake. 4)The Kinki Triangle marks very characteristic strong negative anomaly. 5)Central Mountain Ranges have no or too small negative low anomalies. This suggests that their bodies are supported by some tectonic forces other than isostatic mechanism.