Some Recent Coseismic Landslides in Japan

Abstract

Earthquakes occur frequently in Japan, resulting in many casualties and great damage to properties. Landslides triggered by the earthquakes are a great threat to local properties and the lives of residents. In many cases, most of the casualties during the earthquake resulted from the coseismic landslides. In this report, we introduced those landslides triggered by some recent earthquakes that have occurred in Japan. A study of the 2004 Mid-Niigata Prefecture earthquake revealed that a huge number of landslides were triggered and most of the large-scale landslides are reactivated ones, but the displaced materials suffered long runouts and rapid movement. Rainfall preceding the earthquake may have favored the occurrence of landslides in large numbers and rapid movement of the displaced landslide materials. Some catastrophic landslides on tephra slopes triggered by the 2011 Tohoku Earthquake suggest that slopes that are undercut at the toe in part have lower slope stability, and that paleosols sandwiched on the tephra slopes favor the instability of the slope during earthquakes. Field monitoring of the ground motion indicates that the landslide area may have suffered very strong motion, although the seismic station nearby recorded motion weaker than other stations. Further experimental examination using the estimated ground motion during the main shock in the landslide area suggests that the ground motion of tephra slopes with different water moisture could be very complicated and further study on estimating the coseismic response of tephra slopes with high precision will be needed. The landslides triggered by the 2016 Kumamoto earthquake give another example showing the diversity of coseismic landslides; their initiation and movement are greatly dependent on the geological, geomorphological and also hydrologic features of the slopes Landslides in tephra slopes are probably not very large in size, but are normally catastrophic, because the displaced materials can be fluidized and undergo long runout and rapid movement, resulting great damage to local residential areas. This kind of disaster resulting from the landslides occurring on tephra slopes occurred again during the 2018 Hokkaido Eastern Iburi earthquake.