Landslide susceptibility zonation using frequency ratio and fuzzy operators (Case study: QalehQafeh basin)

Landslide is one of natural hazards that makes numerous direct and indirect damages cost in year. The purpose of this study was landslide hazard assessment by means of fuzzy logic , Analytical Hierarchy Process and frequency ratio method in QalehQafeh basin, Iran. At first, landslides occurred in QalehQafeh basin were identified using aerial photos and field studies. For landslide susceptibility mapping, effective factors on landslide occurrence such as: slope, aspect, elevation, lithology, precipitation, land cover, distance from fault, distance from road and distance from river were obtained by means different sources and maps. Using this factors and the identified landslide, the fuzzy membership values were calculated by frequency ratio then fuzzy operators were applied to the fuzzy membership values in order to landslide susceptibility zonation then weight of each factor obtained by Analytical Hierarchy Process. Finally, fuzzy map of the each factor is multiplied in the its weight that obtained using AHP method. At the end, the results map was verified base upon comparing with ground landslide, in order to accuracy assessment. Among the fuzzy operators, in the case in which the gamma operator (γ=0.3) showed the best accuracy (Qs=0.74) while the case in which the fuzzy ‘sum’ operator was applied showed the lowest accuracy (Qs =0.001). According to landslide susceptibility map of gamma (0.3), about 17% of the occurred landslide points located in the high and very high susceptibility zones of the landslide susceptibility map, but approximately 63 % of them indeed located in the low and very low susceptibility zones

Keywords:

Landslide susceptibility zonation , Fuzzy Logic , Frequency ratio , Fuzzy Analytical Hierarchy Process , QalehQafeh basin