Geologic and Topographic Features of Slope Failure Sites in the Aso Caldera Wall Inducted by the 2016 Kumamoto Earthquake

Haruka SAITOU, Shin?ya KATSURA, Ryota UMETANI, Mio KASAI and Tomomi MARUTANI

Large-scale earthquakes can trigger slope failures. To effectively implement countermeasures to mitigate damage caused by slope failures, it is necessary to identify locations where the risk of slope failure is high. The geologic and topographic features of slope failure in the Aso Caldera wall induced by the 2016 Kumamoto earthquake were examined as a case study. The geology was roughly divided into three categories: pyroclastic flow deposits, andesite, and talus accumulation. The elevation, slope, and curvature were calculated using geographic information system (GIS) software and a digital elevation model (DEM) obtained before the earthquake; these parameters were then used as topographic indices. The analysis results showed that slope failures occurred most densely in the pyroclastic flow deposits. Within this geology, slope failure frequency increased proportionally with slope, and more slope failures occurred at sites with a positive curvature (i.e., convex slopes). There was no relationship between elevation and slope failure. We conclude that sites with these geologic and topographic features are prone to slope failure induced by large-scale earthquakes.

2018/1 117-122