The effect of active tectonics in the evolution of the alluvial fans of Behbahan, Iran

Alluvial fans are geomorphological forms in river systems that are often formed in dry areas and mountain fronts, where rivers meet the plains. They are an erosional and sedimentary system and some factors such as the shape and lithology of the catchment, tectonic activities and climate affect their formation and evolution. In this research, ۷ fans were identified in Behbahan area. Next, using the Digital Elevation Model (DEM), the map of the drainages network extracted and seven geomorphic indices including the sinusoidal index of the mountain front (Smf), the width of the valley to the height (VF), the asymmetry of the drainage basin (Af), and hypsometric integral (Hi) were calculated for each of the alluvial fans and their upstream basins. The obtained results showed that the smf index values have a minimum value of ۱.۰۸, which indicates active tectonic activity and a maximum value of ۱.۳۳ which indicates semi-active tectonic activity. For the VF index, in the north part have high tectonic activity. AF index in watershed number ۳ and ۴ with a small amount of ۱۵ and ۱۶.۵ indicates active tectonic activity and erosion on the right bank. The HC index shows that these basins are in a young stage. The HI index indicates a tectonic active and semi-active state. The values of the Iat index in the region for basins No. ۳ and ۴ are ۱.۱۶ and ۱.۳۳, a state of intense tectonic activity, in basins No. ۱, ۵, and ۶ with values of ۱.۸۳ activity. High tectonics and basins number ۲ and ۷ with values of ۲.۳۳ and ۲.۱۶ show moderate tectonic activity.

کلیدواژه ها:

active tectonics ، alluvial fan ، geomorphic indices ، Behbahan