Investigating factors effective in occurrence of landslides in a region and the zoning of the resulting risks can effectively help reduce the damage caused by this phenomenon. The present research is an attempt in this field, and by analyzing the effective factors of landslide formation, attempts to carry out the zoning of the risk of mass movements of Gharah Chay watershed using analytic hierarchy process (AHP). Gharah Chai Basin is one of the sub-basins of the Atrak River. In this study, first the factors affecting the occurrence of landslides in the area were investigated, and the most important factors were identified to be lithology, slope alignment (structure, topography), slope, slope direction, land use, distance from village, the drainage network density, distance from river, distance from fault, and elevation classes in order, and then the landslide distribution map was prepared. In the hierarchical analysis method, the ten above factors were used. In this method, the factors considered are compared in pairs and the weight of the factors is calculated. For classifying the factors, they were scored with taking the percentage of slip level into account.
At the end, the zoning model was obtained by considering the weights obtained for each factor and the scores obtained. Accordingly, the range was divided into five level of risks. The map was divided into five classes with very high (2.6 km²), high (14.4 km²), medium (14.5 km²), low (4.6 km²) and very low risk (1.8 km²).