FAULT EFFECT ANALYSIS OF GEO-HAZARD TRIGGERED BY WENCHAUN EARTHQUAKE

A great number of collapse and slide geo-hazards had been triggered by 512 Wenchuan Earthquake, covering 0.1M km2 or so. Undoubtedly, their distribution was influenced by topography and morphology, stratigraphy, people's engineering operations, and so on. But their distribution mainly was controlled by the faults triggering seism, and they distributed along those faults like a ribbon. Based on the study in three geo-hazards concentration regions, namely, from Dujiangyan to Wenchuan, from Beichuan to Anxian and from Magong to Hongguang, the following fault effects of geo-hazards in Wenchuan Earthquake were found: (1) Because the triggering-earthquake faults were reverse fault, the distribution of geo-hazards showed clear Upper plate/lower plate effect. In detail, compared with lower plate, the upper plate had higher distribution density, wider scope and larger scale; (2) Intensely developed region of geo-hazard ranged from 0 to 7 km in upper plate. Moderately developed region ranged from 7 to 11km in upper plate, and from 0 to 5km in lower plate; Vast majority of lager-scale landslides were about 5km away from faults; (3) The transition and stagger parts of fractures are usually the concentration zone of geo-hazards, and large-scale geo-hazards also frequently happened here; (4) The advantage orientation of sliding was NW-SE, which was nearly orthogonal to the extension direction of the fault of Yingxiu-beichuan. This was closed correlation to the fact that the propagation of earthquake wave was perpendicular to the strike of fault; (5) Earthquake geo-hazards mainly developed in these regions where earthquake intensity was equal to or above IX. The density of development was nearly the same in XI intensity zone and X intensity zone. The geo-hazard density in IX intensity zone was only one-third of the two former zones. Whereas, the development density in VIII intensity zone was only one-tenth of XI intensity zone or X intensity zone.