The Wenchuan （汶川） earthquake on 12 May 2008 induced a large number of landslides, collapses, and rockfalls along the Longmenshan （龙门山） fault. The landslide in Niujnau （牛圈） Valley （named Niujuan landslide）, close to the epicenter, is one that travelled a long distance with damaging consequences. Using QuickBird satellite images and GIS tools, the seismogenic mass movements are analyzed, and the movement phases, travel path, and post-catastrophic processes of Niujuan landslide are described and discussed. Image interpretation and a GPS survey showed that the mass movements denuded 37% of the research area. The Niujuan landslide moved 1 950 m along the Lianhuaxingou （莲花心沟） stream, transformed to a debris avalanche, and accumulated in the downstream bed of Niujuan Valley, where they formed a dam 30 m in height, blocking the Niujuan stream and creating a barrier lake basin with 0.11 million m3 storage capacity. Subsequent to the Ninjuan landslide, debris flowshave been more active in Lianhuaxingou and Niujuan valleys because of the accumulated mass of debris.
Debris flow is a kind of geological hazard occurring in mountain areas.Its velocity is very important for debris flow dynamics research and designing debris flow control works.However,most of past researches focused on surface velocity and mean velocity of debris flow,while few researches involve its internal velocity because there is no available method for measuring the internal velocity for its destructive power.In this paper,a method of temporally correlated shear forces（TCSF） for meas-uring the internal velocity of debris flows is proposed.The principle of this method is to calculate the internal velocity of a debris flow using the distance between two detecting sections and the time differ-ence between the two waveforms of shear forces measured at both sections.This measuring method has been tested in 14 lab-based flume experiments.
