Wen-Chi Lai

Rainfall-Induced Large-Scale Landslide Hazard Zonation in Taiwan

Open image in new window An evaluation method for large-scale landslide hazard zonation was proposed in this research. To set up a mitigation system, classification of risk areas is crucial. Hazard zones can be divided into the source area, main pathway, and deposition area. The source area can be identified with the high-solution DEM (Digital elevation model). The main pathway and deposition areas are identified by predicting the movement of the landslide. In this research, three types of zones within the main pathway and deposition area were defined: landslide, debris flow, and landslide dam. These definitions were based on volume, location, and the topography of the hill foot of landslides. There are two stages to hazard zonation. The first stage is a national survey of high-risk areas. At this stage empirical methods were used to evaluate the source areas, volumes, and movement patterns of potential landslides. Comparison of predicted movement patterns with hill foot topography allows the hazard zone to be effectively identified. Villages in the path of potential landslides are pinpointed and for those at high risk, numerical simulation was applied as a second stage. The proposed approach was proven effective through comparison with historical events for the first stage.

The Characteristics of Surface Ruptures and Landslides in the Chi-Chi Earthquake of September 21th, 1999

The Chi-Chi, Taiwan Earthquake provides an exceptional opportunity to study surface rupture of an earthquake fault. Detailed maps of the lateral distribution of fracturing adjacent to main traces show the different amount of offset and the slip rational in vertical to lateral. The maximum value of offset is up to 10 meters and it is much higher than documented in past studies of earthquake fault. Earthquake faulting also triggers the different types of landslide hazards, and these high-risk areas of landslides hazard should be treated immediately and carefully. Based on investigations on Nantou area, we observed lots of landslides located in tableland that composed by red soil around Puli basin. Lots of landslide debris filled ravines, they pose a continuing hazard from remobilization and flow during future intense, prolonged rainfall. Keyword: The Chi Chi Earthquake, Surface Rupture, Landslide