A GIS-based comparative study of the analytic hierarchy process, bivariate statistics and frequency ratio methods for landslide susceptibility mapping in part of the Tehran metropolis, Iran

The high hillsides of the Tehran metropolis are prone to landslides due to the climatic conditions and the geological, geomorphological characteristics of the region. Therefore, it is vitally important that a landslide susceptibility map of the region be prepared. For this purpose, thematic layers including landslide inventory, lithology, slope, aspect, curvature, distance to stream, distance to fault, elevation, land use, and precipitation were used. Next, weighted raster thematic maps with assigned values for their classes were multiplied by the corresponding weights and combined to yield a simple map where each cell has a certain landslide susceptibility index (LSI) value. After reclassification, this represents the final susceptibility map of the study area. Finally the three maps were compared to assess the strength of the corresponding methods. In this study area, 74% of landslides occurred in highly or completely shaly units. Lithology, slope, distance to fault and distance to stream data layers were found to be important factors in the study area. The outcome of this comparison was the conclusion that the active landslide zones do not completely fit into the high and very high susceptibility classes. However, 99.6% of these landslide zones fall into the high and very high susceptibility zones of the bivariate statistics (WI) method, or 74.5% in the case of the analytic hierarchy process (AHP) method and 97.2% with the frequency ratio (FR) method. The results showed the WI and FR methods to give a more realistic picture of the actual distribution of landslide susceptibility than the AHP method.