Estimation of Effect of Antecedent Rainfall on Coseismic Landslides

It is important to grasp the circumstances under which coseismic landslides occur as soon as possible for providing rapid initial response to these disasters. Though many factors are cited as reasons for coseismic landslides, only a few studies have focused on antecedent rainfalls or these have used only point rainfall data without two-dimensional extension, and instances of detailed quantitative evaluation have been low. Therefore, in this study, we estimated the effect of areal antecedent rainfalls on coseismic landslides. The Mid Niigata Prefecture Earthquake in 2004 was targeted for this purpose. We used random forest and classification and regression tree analysis for estimating the major factors that influence, and their effects on coseismic landslides. We found that antecedent rainfall had limited influence on the occurrence of coseismic landslides in this earthquake. However, the impact of antecedent rainfall on large landslides was greater than that on small landslides. In addition, the impact of long-term rainfall may be greater than that of short-term rainfall, at least for large landslides. This suggested that the accuracy of estimation of occurrence of coseismic landslides could be improved by considering the influence of antecedent rainfall.