[HDS09-P01] Fluidized landslides triggered by the liquefaction of subsurface volcanic deposits during the 2018 Iburi–Tobu earthquake, Hokkaido
Keywords:fluidized landslide, 2018 Iburi–Tobu earthquake, halloysite
To investigate the mechanism generating the landslides triggered by the Iburi–Tobu earthquake, we conducted a field survey at a typical landslide in the Tomisato area of Atsuma, and we found a distinctive occurrence of liquefaction in the field, which could be a precursive condition for the generation of the fluidized landslides triggered by the earthquake. In the scarp of the landslide, an altered halloysite-bearing volcanic layer is observed at a level almost coincident with the sliding surface. The layer is intensely undulating and can be divided into an upper clay-rich layer and a lower pumice-rich layer, suggesting that the altered layer had liquefied as a result of the strong coseismic ground motion. The layer had been soaked by heavy rainfall just one day before the earthquake and could have liquefied by interstitial fluid pressurization, producing a weak and slippery plane, resulting in the catastrophic landslides in this area.