Re-Estimation Method of Landslide-Triggering Rainfall Thresholds After an Earthquake with the Two Conceptual Models

Abstract

This study used two conceptual models to examine the effects of rainstorms on post-earthquake landslides: a tank model to calculate the soil water index and a process-based model employing a digital terrain model with 10-m resolution to calculate the regional potential for shallow landslides, based on the distribution of shallow infiltration water, Darcy’s law, and a safety factor estimated by infinite-slope stability analysis. The two models were applied to the Funyu Experimental Forest of Utsunomiya University, Tochigi Prefecture, Japan. In August 1998, a heavy rainfall event caused many shallow landslides in the study area, whereas other heavy rainfall events in 1994–2003 did not cause severe landslides. The two indices were closely correlated, confirming the validity of both approaches for the estimation of rainfall properties. Response analysis of the effect of earthquakes on soil strength parameters indicated that landslide-triggering rainfall thresholds varied with decreasing effective soil cohesion, implying that the relationships between effective soil cohesion and the soil water index derived from the two conceptual models were valid for the re-estimation of the influence of rainfall properties on post-earthquake landslide occurrence.