地震発生前における異常地殻変動領域の拡大

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タイトル別名
  • Development of Area of Anomalous Vertical Deformation of the Crust before the Occurrence of an Earthquake
  • ジシン ハッセイ マエ ニ オケル イジョウ チカク ヘンドウ リョウイキ ノ カクダイ

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抄録

Study of crustal deformation before and after the Niigata Earthquake of 16 June, 1964, was the first case to detect successfully the anomalous vertical deformation of the crust as a forerunner of occurrence of an earthquake. This was already reported in 1964. But, at that time, only a few bench marks of levelling in the related area were used in study. At present, much more results of the first order levelling are available, because the Geographical Survey Institute carried out more levellings after the Niigata Earthquake and published the complete data after suitable “epoch reduction.”<br>The present author analyses the results of levelling on all the available bench marks and ascertains that the anomalous displacement of bench marks are, in all cases, in the sense of upheaval with no relation of sense of the secular change of bench marks. An area of the anomalous deformation is quite the same as an area of the crustal sinking at the time of Earthquake and also the same as aftershock area. These facts mean that the whole area of forerunner is nothing but the fractured region accompanied by the Niigata Earthquake.<br>By examining the results of frequently repeated levellings, we can estimate time of begining of the anomalous crustal deformation on the thirty bench marks. By drawing the contour lines which show time of begining of the anomalous crustal deformation, we can conclude that the more nothern part of Niigata area begins to move anomalouslly at earlier time, and area of anomalouslly deformed part of the crust developed gradually to the southern direction. Velocity of this development is about 2km/year at the nothern part and 6km/year at the southern part.<br>Finally the author suggests that the observed process of the vertical deformation of the crust may be nothing but the process of the creep fracture. As in the usual case of the creep fracture, three stages; transient creep, steadystate creep and accelerating creep, are acknowledged also in the actual case of crustal deformation accompanied by earthquakes.

収録刊行物

  • 地震　第２輯

    地震　第２輯 26 (1), 43-54, 1973

    公益社団法人 日本地震学会

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