The Influence of Active Tectonic on the Alluvial Fan Morphology Using Geomorphological Indicators at Structural Boundaries in Southern Alborz

The study measured the forms and landscapes caused by tectonic activity is the subject of tectonic geomorphology. Fans of such forms of tectonic activity along the tectonic that climate change is the most important factor controlling them. The purpose of this study is to investigate the role of tectonic factors in the development and morphology changes of the alluvial fans of Jajroud، Heble Roud and Eyvankei. In this study، the topographic maps، geology، satellite photos and the digital elevation model (DEM) were used as the main data. In addition، the morphology of the alluvial fans of the region was studied closely and through a field study. Then، using the geomorphic indexes which includes the sinuosity of the 28 English Abstracts mountain in-front (SMF) Ratio of valley floor width to valley height (VF)، Drainage Asymmetry factor (AF)، Stream Length-Gradient Index (SL)، Transverse Topographic Symmetry Factor (T)، Fan Comicality Index (FCI)، the region in terms of tectonic activities were assessed. Through combination of these indexes the index of active tectonic (Iat) were obtained. The results show that according to the Iat amounts، the region is active in terms of neotectonic activities. So that Heble Roud alluvial fans are ranked as the geologic activities are high and for Eyvankei and Jajroud alluvial fans are placed at the medium level of geologic activities. The database of Institute of Geophysics، University of Tehran (1937-2012) has recorded the most earthquakes near the fault of Garmsar، especially in the western parts of it; and it seems that it has more activity than its eastern part.