Landslides triggered by the 1999 Mw7.6 Chi Chi earthquake in Taiwan and their relationship to topography

The September 20, 1999 Mw7.6 Chi Chi earthquake and its aftershocks generated numerous landslides affecting at wide area of the foothills region of central Taiwan. This major seismic event provides a good opportunity for testing the idea that landslides triggered by major earthquakes and severe storms affect distinctly different parts of topography. In essence, seismically-triggered slope failures are concentrated at and near ridge crests, whereas heavy rains cause slope failure to concentrate in saturated, colluvial hollows further down slope. This insight into landslide mechanisms provides a framework for the development of regionally-based landslide hazard assessment tools. Two post-earthquake scenes of IRS 5m panchromatic data over central Taiwan constitute the primary optical remote sensing data used in the study. The two IRS scenes were co-registered to a 40 m DEM gridded in a UTM projection. When viewed in 3D perspective, it is clear from the merged IRS imagery and the DEM that landsliding does indeed appear to emanate from hilltops and ridge crests in agreement with our hypothesis for earthquake-triggered landslides