Morphometric analysis of relic landslides using detailed landslide distribution maps: Implications for forecasting travel distance of future landslides

This study analyzed the morphometry of relic landslides in four mountainous areas in Japan. Using detailed landslide maps issued by the National Research Institute for Earth Science and Disaster Prevention of Japan, the mobility of 338 relic landslides was evaluated based on the H/L ratio, i.e., the equivalent coefficient of friction. The H/L ratio strongly correlates with the initial slope, tanθr (R2 = 0.78–0.88). The H/L ratio and tanθr of recent disaster-causing landslides within the past few decades were also measured in each investigated area. The data of recent landslides correspond to the 95% lower prediction limit of the tanθr–H/L regression line for relic landslides. This result implies that morphometric analysis of relic landslides around an unstable mass allows for forecasting of travel distance of the unstable mass.