IMPACT OF INVENTORY FORMS ON RESULT OF REGIONAL ROCKFALL SUSCEPTIBILITY ASSESSMENT

Regional geo-hazard susceptibility assessment is the basis for early warning of geo-hazards. Huairou district is located in the north of Beijing and has favorable geological conditions to rockfall. The widely developed rockfalls threat to the lives and property of local people. Therefore, the region rockfall susceptibility assessment is significantly meaningful. According to investigation, two forms of rockfall inventory maps including point distribution and area distribution for the same 688 rockfalls in Huairou district of Beijing are obtained on site. The rockfall inventory maps provide the necessary background information for building the susceptibility model, which affects the reliability of evaluation. In order to quantitatively assess rockfall susceptibility, frequency ratio(FR)model is applied using GIS.In general, to predict landslides, it is normally assumed that rockfall occurrence is determined by rockfall-related factors, and that future rockfalls will occur under the same conditions as past rockfalls. For the modeling, lithology, terrain, faults and roads construction are considered as significant rockfall-related factors in rockfall occurrences based on site investigation and statistical analysis. After assessing the susceptibility maps, validation is essential to determine the predictive value of susceptibility maps. It also helps to better select the most suitable function and significant variables, thus improving the efficiency of the mapping process. Validation can be performed using a rockfall population independent from the one used to construct the map. Therefore, FR model is run including only 415 rockfalls that randomly selected from the total rockfalls and then validated with respect to the left 273 rockfalls. The prediction-rate curve based on rockfall area inventory shows a better performance in prediction than that based on rockfall point inventory, which reveals that the uncertainty exists in rockfall point inventory. Based on the FR model using rockfall area inventory map, Huairou district is classified into five classes of rockfall susceptibility:very low susceptibility zone(14% of the whole area),low susceptibility zone(20%),medium susceptibility zone(27%),high susceptibility zone(22%), and very high susceptibility zone(17%).This study can provide reference for inventory mapping in regional rockfall susceptibility assessment. The susceptibility map can be a helpful tool for regional land use planning and disaster prevention and mitigation in Huairou district.