Earthquake risk assessments on fill slope instability in urban residential areas

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Recent destructive earthquakes in urban regions, such as the 1978 Miyagiken-oki earthquake and the 1995 Hyougoken-nanbu earthquake, have triggered instability in many of the gentle slopes in residential areas around Sendai, Nishinomiya and Kobe cities related to the urban development that has continued since the 1920s. The landslide risk maps with earthquake-induced slope-instability that has occurred is closely related to these artificial landform changes, especially with artificial valley fills (embankments) were made. These risk maps, 1/10000 Jiyugaoka, Musashi-kosugi, Tsurumi, and Shin-yokohama, show the potential of future landslide disasters. According to the maps, more than half of fills would be classified into a high-risk of instability group as the unstable fill slope following an earthquake in this metropolitan region. The geological aspects of all government developments plans should considered not only in terms of geotechnical engineering for surveying ground conditions, but also importantly in terms of providing information to residents.