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タイトル: 24. Horizontal Secular Deformation of Land Deduced from Retriangulation Data. : 1. Land Deformation in Central Japan
その他のタイトル: 24. 三角測量結果から算出した土地の水平変動 : 1. 中部日本における変動
著者: KASAHARA, Keichi
著者(別言語): 笠原, 慶一
杉村, 新
発行日: 1964年12月25日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第42冊第3号, 1964.12.25, pp. 479-490
抄録: The Geographical Survey Institute conducted resurvey of the first-order triangulation net in central and western Japan during the period of 1948-1958. Comparison of the present data with that of the previous survey in 1889-1909 enables us to study the pattern of horizontal crustal deformation which occurred during the past several decades. The authors took the data from 86 triangulation stations in central Japan and computed various sorts of strain components, such as dilatation, maximum shear, rotation, and principal axes, where displacement and strain of the earth's surface were assumed to be continuous all over the district. Generally speaking, the total amount of strain accumulation thus obtained does not exceed 5・10-5 in every part of the district except the Mikawa Bay and Itoigawa areas. We may roughly say, therefore, that the average rate of strain accumulation is mostly less than the order of 10-6/year, although it is not certain whether the event did occur at a constant rate or not. There have been numerous large earthquakes in central Japan during the period between the two surveys. Naturally, the observed strain must be attributed partly to the crustal deformation appearing at the time of earthquake occurrence. This assumption is particularly likely on the large shear strain observed in the Mikawa Bay area, which is not far from the epicenters of destructive shocks in 1944, 1945, and 1946. The Itoigawa area is believed not to be affected so much by earthquakes and the large amount of strain (more than 10-4) observed there might be an indication of present activity of the tectonic belt that crosses the Japanese Island. Further field surveys are needed to make this point clearer. The mountainous part of central Japan shows contraction as much as 2~3・10-5. According to the results from repeated levellings, this area is subject to a general tendency of continuous upheaval, though its cause is not yet clearly understood. The abovestated information would be useful in clarifying the mechanism of the event. Other notable information is obtained through comparison of the principal axes of strain with the focal mechanism of shallow earthquakes in the same area. Direction of the compressional force at their origins, seismometrically determined by several authors, harmonizes well with the present data so far as the earthquakes in the coastal districts of the Japan Sea are concerned. On the Pacific side of Japan, such as the Kanto and Tokai areas, however,good harmony cannot be concluded.
URI: http://hdl.handle.net/2261/12167
ISSN: 00408972


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