2026 Volume 63 Issue 1 Pages 1-10
Although it is widely acknowledged that smaller-scale rainfall events can trigger slope failures after a large-scale earthquake, there has been limited research on the impact of a large-scale earthquake on the characteristics of rainfall-induced slope failure sites. In this study, we analyzed the characteristics (slope angle, general curvature, Topographic Wetness Index (TWI), slope aspect, and maximum acceleration of seismic motion) of slope failure sites triggered by a pre-earthquake rainfall event and two post-earthquake rainfall events in the Aso region, which experienced significant shaking during the 2016 Kumamoto Earthquake, using Hayashi's Quantification Method-II. The results indicated that slopes with aspects more susceptible to stronger shaking during the earthquake, inferred from the strike of the source fault, convex slopes presumed to have become more fragile due to amplified shaking effects, and slopes experiencing higher maximum acceleration were more prone to slope failure during the post-earthquake rainfall events. These earthquake-induced impacts on the characteristics of rainfall-induced slope failure sites persisted even two months after the earthquake. It is advisable to carefully consider the characteristics of seismic motion when identifying slopes potentially at high risk of failure due to post-earthquake rainfall events.
