平成30年北海道胆振東部地震において発生した斜面崩壊の特徴

抄録

Large earthquake struck in the eastern Iburi prefecture, Hokkaido, Japan on 6^th September 2018. Several thousands of shallow landslides triggered by this earth quake with magnitude of 6.7. The earthquake victims from the earthquake rises 41 and 462 houses were totally and 14,170 houses were partially destroyed. In this study, we examined the characteristics of landslides caused by the earthquake on the area where thick pyroclastic fall deposits were covered in Hokkaido. By mapping landslides using high-resolution aerial photography and laser altimetry, 4,272 landslides were identified in Upper Atsuma river watershed. Field survey and statistical analysis show that shallow landslides were characterized as follows: 1) the tephra deposits on sedimentary rock (Neocene sedimentary rock) were translationally by the strong seismic shock, 2) shallow landslide layers were on the impermeable weathered tephra layer, 3) the most of shallow landslides occurred at relatively gentle slope (<30°), 4) Highest landslide ratio rises 35% at the Towa creek watershed 5) A large-scale deep-seated landslides occurred and resulted landslide dam.