著者
寺田 秀樹 仲野 公章 浅井 健一 山越 隆雄 金子 正則 石井 靖雄
出版者
社団法人 砂防学会
雑誌
砂防学会誌 (ISSN:02868385)
巻号頁・発行日
vol.53, no.3, pp.52-57_2, 2000

An earthquake measuring 6.4 in Magnitude (M) on the Richter scale occurred at 16:02 on July 1, 2000, with an epicenter in the sea near Niijima and Kozushima Islands in the Izu island chain. It was followed by torrential rainfall caused by typhoon No.3 in July 7 and 8, and another earthquake measuring M 6.0 at 3:57 on July 9, with a hypocenter near the previous earthquake. They triggered many slope failures in Kozushima Island. The slope failures damaged some houses, and also produced a large amount of sediments on the beds of many streams.<br>In order to assess the risk of sediment-related disasters, the team of Erosion and Sediment Control Department in Public Works Research Institute has surveyed the state of slope failure deposits and erosion and sediment control facilities. The results of the surveys from July 4 to 6 and July 10 to 11 are as follows. 1) Slope failure sediments on the streambeds increase danger of debris flow disasters, because these streams have few erosion and sediment control facilities, except for Kozusawa. 2) Many slope failures and a few landslides were recognized in the surveyed area. Many of these failures occurred in the area of pyroclastic deposits. 3) The torrential rainfall by typhoon No.3 and the earthquake in July 9 widen the area of slope failure caused by the earthquake in July hand also caused new failures. It suggests that additional rainfall or earthquake will cause new failures and area extention of the failures which already occurred.