IMPACT OF EARTHQUAKE ON DEBRIS FLOWS - A CASE STUDY ON THE WENCHUAN EARTHQUAKE

This paper describes a study about the impact of earthquakes on debris flows with a focus on the Great Wenchuan Earthquake 2008 in China. The land form, precipitation, and source material are the three key factors for debris flow initiation in the Wenchuan surrounding area. Classifications and examples of four types of debris flow initiation triggering (gully triggering, slope triggering, liquefaction triggering, and gully erosion triggering) have been presented. The initiation mechanisms are attributed to hydraulic and geomechanical aspects. The actual debris flow cases linked with the Great Wenchuan Earthquake and other earthquakes in China have been used to illustrate the increased magnitudes of debris flows due to a large amount of loose materials created by the seismic actions. The critical precipitation for debris flows is reduced by the earthquake. It is predicted that the impact of the Great Wenchuan Earthquake on the local debris flows would be significant in the next 5-6 years, and much less in the following years (up to 20 years). Finally, the debris flow system will reach a relative stable stage. This prediction is based on the historical observations at other earthquake areas and the qualitative analysis on debris flow initiation mechanisms.