Morphological and Geological Features of Debris Flows caused by Earthquakes
地震による土石流の発生に係わる地形, 地質条件

Yoshiharu ISHIKAWA
1999 Journal of the Japan Society of Erosion Control Engineering  
The purpose of this study is to improve the understanding of morphological and geological features of debris flows cuased by earthquakes. Data of 24 slope movements which occurred in Japan after 1900 were collected from number of related literatures and investigated. The ratio of run-out distance of collapsed debris to the height of collapsed part is defined as a run-out ratio. The run-out raio and the degree of disturbance of deposited material were investigated. When the slope movements with
more » ... un-out ratio more than 7 and high disturbance, and with run-out ratio less than 4 and low disturbance are regarded as debris flows (fluidization occurred) and talus formations (fluidization did not occur) respectively, 8 slope movemets are debris flow type and 16 slope movements are talus formation type out of the 24 slope movements. The results are summarized as follows. 1) The obvious correlation was not observed between volume of collapsed debris and equivalent fiction coefficient, and the equivalent friction coefficients of slope movements at the volume of 104 106m3 order are relatively smaller than the values which are obtained in the past investigations. 2) Regarding the run-out ratio, the strong correlation was observed between the inclination at the downstream of collapsed part and inflow angle to the downstream of collapsed part. When the inclinations at the downstream exceed 0. 15 (about 9 degrees), the run-out ratios become more than 7 i. e. debris flows occur. When the inflow angles are less than 70 degrees, most of the collapsed debris change into debris flows. Moreover, the negative correlation was observed between the inflow angle and downstream inclination. 3) Regarding the transverse shape of slopes classfled into ridge, equilibrium and valley, the valley shape slopes are moreprone to debris flows compared with the ridge or equilibrium shape slopes. 4) Regarding the geology, the volcanic product area are more prone to debris flows compared with the tertiary or quaternary area.
doi:10.11475/sabo1973.51.5_35 fatcat:ggtthqk2lffnlceq3iqleqw6xy