[H-DS05] 地すべりおよび関連現象

[HDS05-P19] On the initiation and movement of a deep-seated bedrock landslide triggered by the 2018 Hokkaido Eastern Iburi Earthquake

*王 功輝¹、巫 昇山²、土井 一生¹、古谷 元³、渡部 直喜⁴ (1.京都大学防災研究所、2.京都大学大学院理学研究科、3.富山県立大学、4.新潟大学災害・復興科学研究所)

キーワード：地震時地すべり、岩盤地すべり、地震動、せん断挙動、液状化

The 2018 Hokkaido Eastern Iburi Earthquake (M6.7) occurred at 3:08 on September 6, 2018, with a focal depth of 37 km. This earthquake triggered a huge number of landslides, resulting in several casualties. Although most of the landslides were shallow ones occurring on tephra slopes, some bedrock landslides had also been triggered. Among these bedrock landslides, a deep-seated one occurring in the Horonai area (termed Horonai landslide in this study) was featured by translational movement. The displaced landslide materials moved about 350 m along the gently sloped bedding plane (about 6 degrees). Post-event study on this landslide also indicates that the displaced landslide material also might have experienced high-speed movement. To examine the initiation and movement mechanism of the Horonai landslide, we installed seismometers at different locations of the landslide for understanding the possible seismic response of the slope during the mainshock of the earthquake. We made geological and geomorphological surveys on the landslide, took samples from the soil layers nearing the sliding surface, and conducted a series of undrained ring shear tests on the samples to examine their static/dynamic shear behavior. Based on the results, we discussed the initiation and movement mechanisms of this deep-seated bedrock landslide.