Sediment-related disasters induced by the 2018 Hokkaido Eastern Iburi Earthquake

Abstract

On 6^th September 2018, a large earthquake (the 2018 Hokkaido Eastern Iburi Earthquake) with the magnitude of 6.7 struck the eastern Iburi region, Hokkaido and triggered numerous landslides. The landslides were distributed densely over hilly areas (400 km²) in Atsuma, Abira, and Mukawa Town, the total area of which reached 13.4 km². All landslides were shallow landslides except a large-scale deep-seated one generated in midstream area of the Hidaka-Horonai River. The area is covered by thick pyroclastic fall deposits derived from the Tarumae Volcano etc., and the strong seismic shock triggered shallow landsliding of them. Some shallow landslides occurred at a relatively gentle slope (<15°). Shallow landslides moving along a valley topography tended to travel longer than those moving along a non-valley topography. In catchments where shallow landslides densely occurred, the ratio of landslide area to the total catchment area was very large compared with past earthquake events, suggesting that the catchments became highly devastated. Based on these survey results, we propose viewpoints for preventing secondary disasters in the damaged area and for promoting countermeasures against and studies on earthquake-induced landslide disasters in volcanic regions.