[H-DS05] Landslides and related phenomena

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

*Gonghui Wang¹, Shengshan Wu², Issei Doi¹, Gen Furuya³, Naoki Watanabe⁴ (1.Disaster Prevention Research Institute, Kyoto University, 2.Graduate School of Science, Kyoto University, 3.Toyama Prefectural University, 4.Research Institute for Natural Hazards and Disaster Recovery, Niigata University)

Keywords:coseismic landslide, Bedrock landslide, seismic motion, shear behavior, liquefaction

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.