Risk Assessment Of Secondarily Geological Hazard Induced By The Wenchuan Earthquake

5.12 Wenchuan earthquakes have induced a lot of the secondarily geological hazard, which has brought a great hidden danger for the people's life and property and the sustainable development of social economy.Because of the secondarily geological disaster having the hysteretic nature, it is still the active phase in a very long time, the development trend of secondarily geological disaster is the one of main problems about post-disaster reconstruction. So, it is very important to carry out the risk assessment to the secondarily geological hazard by earthquake and provide the scientific basis for the prevention and control planning of geological disaster.I choose Wudu area in Gansu province as case study in this paper. At the foundation of summarizing and profiting from the predecessors' research results and through the field investigation after the earthquake with the detail analysis of the existing data about geological disaster, we verify the type and the essential feature of secondarily geological disaster by earthquake in the Wudu area and elaborates the distributed characteristic and forming reason of the geological disaster. Combined with the actual situation of study area, we introduces AHP-GIS technology into geological disaster appraisal. By mathematical statistics and expert experience, we determine the relationship and evaluation space of each factors, make thematic layers such as engineering geological petrofabric, fault density, seismic peak acceleration, slope, aspect, annual rainfall, rivers, roads and land use and so on, confirm the weight indexes of each factors and carry out the danger appraisal to the earthquake secondary geology disaster. According to the danger appraisal, the study area is divided into the high-danger, medium-danger, low-danger and safe area, the proportion was 12%, 24%,44% and 20%. The high-danger areas are mainly distributed in the Bailongjiang coast, Beiyuhe river, Luotanghe river basin as well as the both sides of major roads and the region that seismic peak acceleration is the largest. Based on this, we take the social environment factors including residential point and so on as the main evaluating indicator into account, put up the risk assessment to secondarily geological hazard. According to the risk assessment, the study area is divided into the high-risk, medium-risk, low-risk and safe area, the proportion was 17%,13%,48% and 22%. The high-risk area are mainly distributed in northwest along Bailongjiang river and Beiyuhe river, Ganju town, Caohe town, Huangping town where the danger of geological hazard is the high level and villages'density is very high. The research results can offer scientific references for the prevention and control of the secondarily geological hazard by earthquake and have also a certein guiding significance for establishing the plan of region hazard's prevention and reduction within the study region.