Numerical Simulation Analysis and Research of Huanglang Valley Ancient Landslide

Based on geological survey and mapping, large-scale ancient landslide occurred three times in Huanglangvalley. The landslide blocked the valley and formed a huge landslide barrier lake - Lake Mahu. A discrete element numerical analysis program, UDEC, was utilized to study dynamic response characteristics of a mountain as well as dynamic process of a "barrier" causing mountain collapse. Research results indicate that the stability state of limit equilibrium dynamical critical acceleration is 1.6 g while the "barrier" causing high-speed, long distance, debris flow starts at a critical acceleration of 2.4 g with a corresponding seismic intensity of less than XI. Therefore, it is inferred that a prehistoric intensity XI earthquake occurred along Mabian-Huangjingba fault zone where Lake Mahu is located. This intensity exceeded that from a modern Ms7.1 earthquake.