1889年8月豪雨による十津川災害の再検討-とくに大規模崩壊の地質構造規制について-

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書誌事項

タイトル別名
  • REEXAMINATION OF THE TOTSUKAWA HAZARD IN AUGUST 1889 WITH SPECIAL REFERENCE TO GEOLOGIC CONTROL OF LANGE-SCALE LANDSLIDES
  • 1889ネン 8ガツ ゴウウ ニ ヨル トツガワ サイガイ ノ サイケントウ

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説明

The Totsukawa hazard occurred in August 1889 was triggered by heavy rainfall, and it isfamous at the report of the hazard published two years after the occurrence. The report consistsof 11 volumes, and the each contains the detailed description on characteristics of weather con-dition and landslides associated with the statistical tables. Reexamination of the record fromscientific point of view was carried out this time.The weather condition which brought this hazard was confirmed by the early weather maps.A small typhoon travelled the Shikoku and Chugoku districts from south to north slowly andcaused heavy rainfall at Kii Penninsula. Though measurement of precipitation had not beencarried out at that time in Nara Prefecture, it is speculated that the maximum daily precipitationwas at least about 1000 mm, by analyses of the data along the coast at that day and of the dis-tribution pattern of precipitation accompanied by recent typhoons which followed almost thesame course as in 1889.It is shown from quantitative consideration that the frequency of landslides is reciprocallyproportional to the logarithmic area of them. Data concerning the depth of landslides was col-lected too, and the regression line for area-depth relationship was obtained, by which estimationof the volume of landslides was carried out. The largest volume of landslides in this area haveorder of magnitudes over l0 7 m3. The large landslides often show a particular plan shape, namely, a rectangle considerablly close to a square.Sites of the largest landslides which damed up the river below are limited on the slopes facingnorth or northwest in this area. In relation to geologic structure, they have been occurred on dip-slope of layered mesozoic system. It is pointed out too that the situation like minor syncline onthe major fold flank, fault crossing the slope, or under-cutting of the slope by river has had theslide occur easier. Conclusively, it should be emphasized, in comparison to the other similarcase of landslides occurred in the terrain where Mesozoic layered rocks are distributed, that heavyrain is more important than earthquake as the trigger of large-scale mass-wasting of this type.

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