"5.12" Wenchuan Earthquake (Ms=8.0) triggered tens of thousands of geo-hazards throughout an area of about 100,000 km2. The distribution of geo-hazards is definitely affected by the such factors as geomorphology, topography, lithology and human engineering activities, but the distribution of earthquake-triggered geo-hazards is mainly controlled by the co-seismic fault, for they present zonal distribution along the co-seismic fault. Through the studies of three geo-hazard concentration areas including Doujiangyan to Wenchuan Road, Beichuan to Anxian County area, and Magong to Hongguang area, it is found that Wenchuan Earthquake-triggered geo-hazards have the following co-seismic effects:
Wenchuan Earthquake is a thrust fault earthquake. The distribution of geo-hazards show marked "hanging wall and footwall effects", manifested by that the distribution concentration in the hanging wall of seismic fault is higher than that in the footwall and the former coverage is wider than the latter as well as that the scale of geo-hazards is larger than that in the footwall;
the strong development zones of geo-hazards are within the range of 7 km in the hanging wall of co-seismic fault. The ranges of 7 to 11km in the hanging wall and o to 5km in the footwall can be delimited as the middle development zones. A vast majority of large-scale landslides are distributed within the range of 5km from the fault, and large-scale landslides are unlikely to occur within the range of over 10km;
the transitional and staggered positions of fault are the concentration areas of geo-hazards and large-scale geo-hazards are likely to occur in these positions;
the preferred direction of landslide is NW-SE, basically vertical to the spreading direction of Yingxiu-Beichuan Fault. This may be because that Longmenshan Fault Zone has always been affected by the tectonic stress field of NW-SE extrusion area since Cenozoic Time;
the earthquake-triggered geo-hazards mainly occur in the zones of seismic intensity IX and higher. The concentration of geo-hazards in the seismic intensity zones XI is the same as that in seismic intensity zones X; the concentration in the seismic intensity zones IX equals to 1/3 of the abovementioned one; the concentration in the seismic intensity zones VIII is only 1/10 of the abovementioned one.
At 14:28 May 12, 2008(Beijing time), a great earthquake measured at 8.0 Ms according to the China Seismological Bureau struck Yingxiu Town (31.0°N, 103.4°E) of Wenchuanxian County, 70 km northwest of Chengdu, the capital of Sichuan, causing the frontal and central faults (Jingyou-Guanxian Fault and Yingxiu- Beichuan Fault) of the Longmenshan Fault Zone between the Western part of the Sichuan Basin and the eastern margin of the Qinghai-Tibet Plateau to rupture, resulting in the formation of an earthquake rupture zone of around 300km long(Huang, R.Q., et al, 2008, b; He,H.L.,et al,2008). The Wenchuan earthquake had a high magnitude and large energy release causing a strong destructive force and large area of influence. The epicenter of the strong earthquake was located in the medium to high mountain areas just West of Sichuan Basin, where the geological environment is quite weak.