Tsukidate failure compared with the other flow-type failure during 2003 earthquakes in Northern Japan

Flow-type failures occurred at two sites during 2003 earthquakes in northern Japan. Two landslides are of similar magnitude and configurations, but of different material and failure process. One slope was a fill with pyroclastic sediments. The failure occurred during or immediately after the principal motion of the earthquake. It is considered that the unsaturated fill lost the initial shear strength and fluidized by earthquake induced cyclic shearing. The other failure occurred a few minutes after the principal motion of the main shock. Rainfall and multiple large shocks were important features that exacerbated the landslide. The upper portion of the fill lost shear strength, descended along the slope and spread on the rice field. The authors conducted site investigations and examined physical and mechanical soil properties of the failures, and discussed the causes of failures.