Landslide disasters triggered by the 2004 Mid-Niigata Prefecture earthquake in Japan

Synopsis During the 2004 Mid-Niigata Prefecture earthquake, thousands of landslides were triggered. Among them five catastrophic landslides were introduced in this paper. In addition, the influence of rainfalls in prior to the earthquake and the urgent response to prevent disastrous failure of landslide dams were also discussed and presented. Higashi Takezawa and Terano landslides occurred within past landslide masses and dammed the river at the toe of the landslides, causing great damages to the properties. Detailed field investigation was performed on these two landslides. To examine the triggering and movement mechanisms, samples were taken from these 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 lower final apparent friction angles, while the silt sample from Terano landslide showed no liquefaction failure, indicating that landsliding during this earthquake time was triggered within the sand layer above the silt layer in the past landslide masses. Finally, the movement of Higashi Takezawa landslide was simulated.