5. Classification of the Geomorphology, Geology and Movement Types of Earthquake Landslides

Various types of landslides have been induced by the past earthquakes in Japan and outside of the country. This study aims to classify the geomorphology, geology, and types of movement at the sites of earthquake landslides including those of the 2011 Tohoku Earthquake. Earthquake landslides show common movement types with similar geological properties. They are (1) translational slides in ridges and cuestas with Tertiary–Quaternary well-bedded sedimentary rocks, (2) flows in areas with unconsolidated Quaternary volcanic sediments, (3) shallow rotational slides at ridges in areas of volcanic rocks, and (4) rock failures and toppling in areas of granite, accompanied by the flow of weathered granite. Many of the earthquake landslides occur within a 30 km distance of the epicenter for earthquakes up to magnitude 7. A magnitude of 8 and above can often induce rock slides at locations over 100 km away. Flow of unconsolidated volcanic sediment and rock failures of consolidated bedrock occurred at locations 200–300 km away. These indicate that magnitude 8 is the line of demarcation at which the relationship between the distance from the epicenter to landslide sites and the movement types changes significantly. The scale of the earthquake fault may be the cause of it. Many recent earthquake landslides have also been observed at residential embankments in Japan.