بررسي عوامل موثر در وقوع زمين لغزشها و پهنه بندي خطر زمين لغزش (مطالعه موردي : حوزه آبخيز شيرين رود- سد تجن

An Investigation of Effective Factors On Landslide Occurrence and Landslide Hazard Zonation (Case Study Shirin Rood Drainage Basin - Tajan Dam)

In drainage basins of the northern part of Iran, acombination of natural and human factors have caused numerous landslide-related damages. One of the main strategies for restricting the damage caused by the activity of landslides is to avoid these regions. To accomplish this, landslide hazard zonation map of the area should be prepared. At the beginning, in this research, through field work and review of previous works, the following nine factors were recognized as primary effective factors on landslide occurrence: altitude, slope, aspect, rainfall, land use, geology, distance from road, distance from fault, and distance from hydrographic network. After preparing the map for above-mentioned factors in GIS environment (using Ilwis, Arc/Info, Idrisi and Arc/View softwares), these maps were overlaid with landslide inventory map. Analyses of the results indicated that aspect and distance from hydrographic network have little effect on landslide occurrence in the area. Then, by considering the other seven factors, landslide hazard zonation map of the area was prepared by using the following four methods: Valuing information, Valuing area accumulation, Index overlay, Analytical Hierarchy Process (AHP). The results have shown that in all four methods, the regions in which serious land use changes have occurred, belong to high hazard zones and also the regions of drainage outlet have a high potential for landslide occurrence. After this phase the evaluation of landslide hazard zonation methods and their ranking in separation of hazard classes were done. For doing this, the method of area accumulation ratio in each hazard class was used. It was shown that different hazard zones were better separated through index overlay method.