Landslides and Countermeasures in Western Japan: Historical Largest Landslide in Unzen and Earthquake-Induced Landslides in Aso, and Rain-Induced Landslides in Hiroshima

Abstract

This paper introduces three catastrophic landslide disasters on the tectonic orogenic belt in Western Japan caused by rainfalls or earthquakes and the countermeasures against them. The first case story is the mega slide of Unzen-Mayuyama of Quaternary volcanic rock due to the 1792 earthquake. The landslide and subsequent tsunami caused the worst Japanese landslide-induced disaster in Shimabara and Ariake Bay. The stone pillars installed after the disaster, indicating the arrival points of the tsunami will generate awareness of the tsunami caused by landslides for future generations. Secondly, the Kumamoto earthquake of 2016 has induced many shallow landslides on tephra-covered slopes and massive slope failures that disrupted highway and rail traffic. Unmanned construction to secure workers has been introduced to stabilize the slope failure early. There is an urgent need for research on the identification of hazardous slopes for landslides on tephra-covered slopes. Thirdly, the Hiroshima disaster in 2018 was characterized by landslides, mainly in the suburban residential areas in Hiroshima City, where heavy rains have caused landslides from the weathered soil, so-called “Masa,” of granitic rocks. Similar disasters occurred in 1999 and 2014 in Hiroshima. The restoration project has been carried out by adopting necessary structural measures such as Sabo dams and non-structural measures such as land use regulations and/or early warning systems based on the Sediment Disaster Prevention Act.