[H-DS09] 地すべりおよび関連現象

[HDS09-07] Landslides caused by the 2018 Hokkaido Eastern Iburi Earthquake

★Invited Papers

*林 真一郎¹、小山内 信智¹、山田 孝¹、桂 真也¹、古市 剛久¹、柳井 清治²、村上 泰啓³、宮崎 知与⁴、谷岡 勇市郎¹、瀧口 茂隆⁵、宮崎 真由美⁶ (1.北海道大学、2.石川県立大学、3.国立研究開発法人土木研究所寒地土木研究所、4.株式会社シン技術コンサル、5.国土交通省、6.株式会社パスコ)

キーワード：平成30年北海道胆振東部地震、降下火砕物、表層崩壊、河道閉塞

The 2018 Hokkaido Eastern Iburi Earthquake struck the eastern Iburi region (epicenter: 42.691°N, 142.007°E, depth: 37.0km) of Hokkaido, Japan, at 3:07.59 JST, September 6, 2018 (18:07.59, September 5, 2018 UTC). Many shallow landslides and several large-scale deep-seated landslides, generating a landslide dam in the Hidaka-horonai River, were triggered by this magnitude 6.6 M_w (6.7 M_j) earthquake. The sedimentary rock in the affected area was covered by thick pyroclastic fall deposits derived from the Tarumae Volcano etc.. Landslides were densely distributed over hilly regions (elevation: 200–400 m) within an area of approximately 400 km² in Atsuma, causing 36 deaths, Abira and Mukawa, and representing the largest total area of earthquake-related landslides in Japan since the Meiji Era (1868–1912). The shallow landslides were characterized as follows: 1) pyroclastic fall deposits on sedimentary rock (basement complex) were moved by the strong seismic shock, 2) slip surface types included weathered tephra, weathered bedrock, and buried humus layers, 3) many occurred at relatively gentle slopes (< 30°), 4) shallow landslides moving along valley type topography tended to travel longer than those moving along planar slope topography, and 5) concentrated shallow landslides occurred in tributary catchments of the Atsuma and Abira Rivers. Large-scale deep-seated landslides were characterized as follows: 1) rare occurrence and 2) slip surface within sedimentary rock.