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Comparison of Landslides Caused by Rainfall and Earthquake in Taiwan
In Taiwan, rainfalls and earthquakes are the two major incidents that trigger landslides in mountainous areas. This research compares the characteristics of landslides caused by rainfall and earthquake. Three watersheds, including two that suffered the Chi-Chi earthquake (ML 7.3) in 1999 and one far from the earthquake impact area, but damaged by heavy rainfall, were surveyed for landslide variations using 23 satellite images. The statistical method is used to analyze the slope and aspect of new landslides in the three watersheds. The result shows that the landslide slope can be presented using the Weibull distribution in earthquake-induced or rainfall-induced landslides. However, the mean landslide slope caused by earthquake is much greater than that caused by rainfall. The mean skewness of the slope distribution caused by earthquake is much smaller than that caused by rainfall. Furthermore, earthquake-induced landslides are usually located at the major aspect of peak ground acceleration. Rainfall-induced landslides are located mostly on the windward side of hills. However, landslides triggered by rainfall in earthquake damaged areas show a transition characteristic. They gradually vary from the earthquake-induced landslides to the rainfallinduced side. This result shows that the earthquake effects on landslides decay with time.