Geomorphic Signatures of Active Tectonics in the Talaghan Rud, Shah Rud and SefidRud Drainage Basins in Central Alborz, N Iran

Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics.These indices have the advantage of being calculate from ArcGIS and remote sensing packages over large area as a reconnaissance tool to identify geomorphic anomalies possibly related to active tectonics.This is particulary valuable in west-central Alborz where relatively little work on active tectonics based on this method was done,so this method is new and useful. Based upon values of the stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf),we used an overall index(Iat) that is a combination of the other indices that divides the landscape into four classes of relative tectonic activity. The moderat class of Iat is mainly in the south of Manjel dam,while the rest of the study area has high active tectonics (shahrud drainage basin and sefidrud drainage basin),and high to very high(Taleghan and Alamut drainage basin). The stream network asymmetry (T)was also studied using morphometric measures of Tranverse Topographic Symmetry.Analysis of the drainage basins and subbasins in the study area results in a field of T-vectors that defines anomalous zone of the basin asymmetry.Acomparsion of T index clearly coincide with the values and classes of active tectonics indices and the overall Iat index.