11:00 AM - 1:00 PM
[HGM03-P01] The distribution of slope failure caused by past extensive heavy rain and its characteristics: A case of the Makurazaki Typhoon of September 1945 in Hiroshima Prefecture
Keywords:Makurazaki Typhoon, slope failure, Hiroshima Prefecture, GIS
Several heavy rain disasters occurred in Hiroshima Prefecture. In Particular, Makurazaki Typhoon in September 1945 caused severe damage in Hiroshima Prefecture (Iwasa et al. in press). However, the distribution of slope failures associated with Makurazaki Typhoon has only been revealed in a few areas (Kawata et al., 1992; Iwasa and Kumahara, 2020; Iwasa, in press). It is important to reveal the distribution of slope failures in a wide area and discuss the causes of such failures to consider the slope failure mechanism and future disaster prevention against slope failure. The aim of this study is to reveal the distribution of slope failures induced by the Makurazaki Typhoon over a wide area (9,624km2) in Hiroshima Prefecture and discuss their characteristics.
Based on the interpretation of aerial photographs, it is revealed that the number of slope failures induced by the Makurazaki Typhoon was 6,769. It is considered that the occurrence of slope failures and the amount of precipitation may be related. Furthermore, the density of slope failures increases with the amount of precipitation, with the highest density of 3.2 failures/km2 at 220-230 mm, suggesting that the amount of precipitation is related to the density of slope failure.
The density of slope failure is highest at 1,100-1,150 m in elevation and 25-30 º.
The relationship between geology and density of slope failure shows that 77% of the slope failures occur in the granitic areas. A comparison of the maximum 24-hour precipitation and the density of slope failure for each geology shows that the density of slope failure in the rhyolites is 1.1 failures/km2 when the precipitation is 180-190 mm, and the density is highest at 220-230 mm (3.6 failures/km2). On the other hand, in granitic rocks, the density of slope failure is 1.0 failure/km2 even with precipitation of 140-150 mm, and the density is highest at 220-230 mm (6.8 failures/km2). This suggests that the susceptibility to slope failure differs among geological formations even under the same precipitation. This suggests that the frequency of slope failure changes depending on the geology, even under the same precipitation.
Based on the interpretation of aerial photographs, it is revealed that the number of slope failures induced by the Makurazaki Typhoon was 6,769. It is considered that the occurrence of slope failures and the amount of precipitation may be related. Furthermore, the density of slope failures increases with the amount of precipitation, with the highest density of 3.2 failures/km2 at 220-230 mm, suggesting that the amount of precipitation is related to the density of slope failure.
The density of slope failure is highest at 1,100-1,150 m in elevation and 25-30 º.
The relationship between geology and density of slope failure shows that 77% of the slope failures occur in the granitic areas. A comparison of the maximum 24-hour precipitation and the density of slope failure for each geology shows that the density of slope failure in the rhyolites is 1.1 failures/km2 when the precipitation is 180-190 mm, and the density is highest at 220-230 mm (3.6 failures/km2). On the other hand, in granitic rocks, the density of slope failure is 1.0 failure/km2 even with precipitation of 140-150 mm, and the density is highest at 220-230 mm (6.8 failures/km2). This suggests that the susceptibility to slope failure differs among geological formations even under the same precipitation. This suggests that the frequency of slope failure changes depending on the geology, even under the same precipitation.