Key indicators describing the evolution of landslides in the Zhuoshui River Basin caused by the Chi-Chi earthquake in Taiwan

Abstract

This study selected the landslide caused by the 1999 Chi-Chi earthquake, which occurred once in a century, and analysed the spatio-temporal distribution of landslide evolution in the basin through the concavity, slope, and sediment delivery ratio (SDR) index of the landslide site. From the change in the determination coefficient of the relationship between the concavity index and the collapse rate, it can be shown that the strong earthquake and subsequent rainfall affect the basin collapse rate for about 8 years. The spatial distribution of landslide location types can be classified by the characteristics of slope and SDR into three categories, indicating that the evolution of landslide location types is gradually transforming from scattered off-bank landslides to concentrated near-bank collapses. Type 1 refers to the initial slope failure caused by the crustal uplift and Type 2 is the unstable slope caused by the earthquake and the subsequent rainfall-driven collapse. Near-bank landslides caused by the accumulated debris from Types 1 and 2 landslides are Type 3. Based on the huge and complex big data of the landslide evolution map, the focus of this research is to extract key indicators and build models to analyse the evolution mechanism of large-scale landslides caused by the earthquake. Highlights Topographic factors can be used as a criterion for judging the stream concavity of watershed. Concavity, slope, and sediment delivery ratio are key indicators, which can be used to extract sediment-prone areas for slope utilization and disaster prevention management.