Dynamic properties of earthquake-induced large-scale rapid landslides within past landslide masses

During the 2004 Mid-Niigata Prefecture earthquake, thousands of landslides were triggered, among them two large-scale rapid landslides (Higashi Takezawa and Terano landslides) occurred within past landslide masses and dammed the river at the toe of the landslides, posing great risks for the society. Detailed field investigation was performed on these two landslides. To examine the triggering and movement mechanisms, samples were taken from these two landslides. By using a ring shear apparatus, real earthquake wave loading test and cyclic loading tests were performed on these samples. The test results revealed that those sand samples from both landslides can suffer from sliding surface liquefaction phenomenon with very low final apparent friction angles, while the silt sample from Terano landslide showed no liquefaction failure, indicating that the sliding surfaces of these rapid landslides must have been formed within the sand layer in the past landslide masses.