Influence of typhoons and earthquakes on rainfall-induced landslides and suspended sediments discharge

The aim of this paper is to present data on the occurrence of landslides triggered by typhoon and earthquake events, and to discuss the basic earthquake triggering mechanisms involved. Four events of typhoon and earthquake triggered landslides in the Chenyoulan River catchment of central Taiwan during 1996 to 2004 were studied in order to identify their controlling factors. The landslides areas were measured by comparing aerial photos taken over the past 18 years, and sediment discharge was counted at hydrometric stations. Investigation results demonstrate that hillslope geomaterials that had been disturbed by strong seismic shaking induced expansion of landslide areas during subsequent events. Analysis of Normalized Difference Vegetation Index (NDVI) also registered the changes of uncovered conditions on the hillslope caused by landsliding. When flow discharge is lower than 100 m3 s− 1, post-seismic sediment concentration is roughly four times higher than pre-seismic concentration with the same flow discharge. This fate indicates that the amount of sediment discharge at normal flow discharge is affected by supplied sediment volume, which tends to increase with seismic activity.