Geo-hazards induced by the Wenchuan earthquake

The "5.12" Wenchuan Earthquake (Ms=8.0) generated tens of thousands of geo-hazards throughout an area of about 100,000 km2. By the field investigation and the interpretation of remote -sensing information after the earthquake, the distribution, seismic dynamic response and genetic model of geo-hazards triggered by the earthquake were analyzed. The conclusions were as follows: (1) Geo-hazards triggered by the earthquake showed the feature of zonal distribution along the earthquake fault zone and linear distribution along the rivers; (2) The slope steepness was a main factor which controlled the distribution of geo-hazards and a vast majority of geo-hazards were distributed on the slopes of 20 to 50 degrees; (3) The geo-hazards had a corresponding relationship with the elevation and micro-landform, for most geo-hazards happened in the river valleys and canyon sections below the elevation of 1500 to 2000 m; (4) Different lithologies determined the types of geo-hazards. Usually, landslides occurred in soft rocks, while collapses occurred in hard rocks;(5) Geo-hazards triggered by the earthquake has the following co -seismic effects: hanging wall and footwall effects, distance effect, snipping effect, direction effect and seismic intensity effect;(6) Under the horizontal inertia force of earthquake, the slope has back scarp and bottom shearing slide mechanism with the scarp destruction is the main part. This is different with the deformation mechanism with the main part is shearing destruction under ordinary gravity in nature. Slope shape, lithological association, site condition and elevation have different impact on the response to seismic dynamics. (7) The most basic and internal destruction pattern of landslides under strong earthquakes can be concluded as "tension fracture -shearing sliding movement". Large-scale landslides triggered by Wenchuan Earthquake have different genetic pattern such as: tension fracture-insequent sliding; tension fracture -consequent sliding; tension fracture -horizontal sliding; tension fracture -collapsing; tension fracture -shearing sliding.