Application of Paleo-morphology Method in the Evaluation of Engineering Geology Parameters for Scrutinizing and Improving the Landslide Hazard Zoning Methods

There are several methods for regional assessment of landslide. The most popular one is based on the preparation of the zoning map of landslide hazard and risk. In recent years، the application of new technologies has resulted in the increase of the precision of landslide hazard zoning models. In these methods، the effective factors on landslide instability are ranked and based on these ranking and some simple rules the necessary maps will be produced. The review of previous works shows that due to the direct effect of experts'' judgment (human error) the results of these methods/models are not satisfactory consistent with observed landslides. On the other hand، the large scale landslide hazard maps which are expected to have higher accuracy than the small scale ones need more accurate site data that is not usually available in most regions or their provision is not cost effective. It seems that most part of this differences and error arises from inappropriate evaluation of geology and engineering geology factors. In this study the method of “Paleo-morphology” is suggested for preparing landslide zonation maps. This method is based on the study of the source of deposited material. In this method، after a careful study of a selected area the geomorphological map of the present circumstance will be prepared. Then، by considering the basic structural geology of the region، the paleo structure of the region will be reconstructed. Susceptibility of different formations to generate sand، silt or clay-rich layers through mechanical and chemical weathering is the main factors that have to be taken into account. The source of eroded material from different formation can be recognized by comparing these two maps. Then، by simple evaluation of the geotechnical characteristics of the same weathered and eroded material، the ranks of masses can be used for improving the models. The method and its application in Alborz Mountain، northern Iran is introduced in this paper. First، this area was studied and its hazard zonation map was prepared using conventional models such as the Anbalagan method. Then the method of scoring was modified using the “Paleo-morphology” method. Finally، the hazard zonation map was prepared based on the modified method. Comparison of the outputs using the Anbalagan and Paleo-morphology methods showed a meaningful and great improvement in the precision of the results obtained from the Paleo-morphology method.