Landslide Disasters Caused by the 2018 Eastern Iburi Earthquake in Hokkaido Japan and the Countermeasures to Completely Prevent the Similar Disasters in the Future

Abstract

AbstractThe catastrophic 2018 Hokkaido Eastern Iburi Earthquake triggered thousands of shallow liquefied landslides in pyroclastic fall deposits one day after the passage of Typhoon Jebi. The landslides were highly mobile and had long runouts. This study reports novel findings pertaining to distinctive properties of the widely distributed, weathered Plinian Ta-d tephra deposit from Tarumae volcano and their impact on the spatial clustering of the Iburi landslides. Distribution of the landslides is positively correlated with the spatial distribution of the Ta-d tephra. Liquefaction occurred in the weathered Ta-d pumice that has lower soil strength than other local pumice units, despite the absence of unconfined groundwater. The volumetric soil moisture content of weathered Ta-d pumice is very high (> 90%) and exceeds other soil layers, regardless of precipitation variation. The presence of hydrated halloysite was confirmed by X-ray diffraction. The halloysite enhances the shaking-triggered liquefaction because it maintains weathered Ta-d pumice in a highly saturated and exceedingly loose state, even in the absence of unconfined groundwater.