| dc.description.abstract | A large number of landslides were triggered by the Chi-Chi Earthquake (ML 7.3) on 21 September 1999. These landslides have been mapped from satellite images in this study. By using GIS (Geographic Information System) as a tool, we can construct a GIS table of landslides triggered by the earthquake and analyze their characteristics, including types, distribution, areas and numbers, …etc. The distribution and areas of landslides have been compared with the distance from the earthquake foci, rock types, faults, roads, rivers, hill slopes and slope directions.
There were 9272 landslides occurred during earthquake shaking within the area greater than 625 square meters and total area of landslides is 127.8 square kilometers. There were 8843 landslides located within the area of PGA value 250gal and above. These landslides were distributed in an ellipse-shaped region with the major axis striking NNE, coinciding with the trend of regional faults.
Statistics shows the following results: (1) Landslides almost located within the area that PGA greater than 250gal, especially within the area that PGA greater than 300gal. (2) A lot of landslides occurred within 20Km from the fault rupture plane. The longest distance from the rupture plane located at the interval of 60 to 70 Km. (3) the Toukoshan Formation, The Chinsui Shale and the Tachien Sandstone were more easily influenced by the earthquake shaking, especially at Huoyenshan Facies. (4) slopes with inclination larger than 100% involves more landslides. (5) At the hanging wall, most slopes collapsed at S and SE facing. At the foot wall, most slopes collapsed at S , SE and SW facing, whereas slopes facing to other directions were not so seriously damaged. It shows that the main movement of Chi-Chi earthquake is from SE to NW. | en_US |