平成30年北海道胆振東部地震による斜面崩壊で発生した土砂・倒木量の推定

抄録

The 2018 Hokkaido Eastern Iburi earthquake on September 6, 2018 caused thousands of landslides, resulting in catastrophic sediment disasters which damaged lives, homes, agriculture, forestry and lifelines. To estimate the number, area and sediment volume of landslides caused by the earthquake, we conducted the elevation differential analysis with LiDAR data for 2 periods before and after the earthquake. We also estimated the fallen tree volume caused by landslides using forest register data. The number of landslides was found to be 7,142 across the four towns, Atsuma, Mukawa, Abira, and Yuni. 6,242 of them were shallow landslides on the slopes covered by highly-weathered tephra deposits and 900 of them were deep-seated landslides. Due to the limited LiDAR data available, the landslide depth was estimated for 509 shallow landslides and 35 deep-seated landslides by the elevation difference analysis, and the regression analysis with power-law function was conducted between landslide area and sediment volume. Using regression equations obtained, the sediment volume generated by each landslides were estimated. In results, the sediment volumes generated by shallow landslides and deep-seated landslides were found to be 64.7 million m³ and 80.2 million m³, respectively, resulting in the total of 144.9 million m³. The total amount of trees damaged by landslides were also estimated using forest register data before the earthquake, and found to be over 654,000 m³ in stem volume. These results can be fundamental data not only for the disaster prevention planning, sediment management and forest improvement planning in the local governments, but also for further research in sediment disasters and prevention in the future.