Emergency Response to Sediment-Related Disasters Caused by Large Earthquakes in Japan - the Case of the Iwate-Miyagi Nairiku Earthquake in 2008 -

Abstract

Learning the lessons to be taught by large earthquakes of the past is one key to solving the problems of sediment-related disasters of the future, including slope failures, deep-seated landslides, and landslide dam (natural barriers formed by landslides). Our case subject is the Iwate-Miyagi Nairiku Earthquake in 2008 and the emergency response to disasters of Japan’s central government and other organizations. The earthquake occurred on 14th June 2008 and had a JMA (Japan Meteorological Agency) magnitude of 7.2 and a maximum seismic intensity of 6 upper on the JMA seismic intensity scale. The hypocenter in a mountainous area underlain by thick volcanic ejecta triggered over 3,000 slope failures, deep-seated landslides, and debris flows. The earthquake created 15 landslide dams which were expected to cause serious damage downstream if dams collapsed. Emergency measures taken included channel excavation and pumping of landslide dams. Moreover, emergency checking of potential danger sites immediately after the earthquake found 20 sites requiring emergency measures. The relationship between seismic intensity and sites of slope failure and deep-seated landslide showed that seismic intensity exceeding 5 upper caused such disasters and required emergency checking.