Evaluation of active tectonics using geomorphic indices in a mountainous basin of Iran

ABSTRACT This study aims to evaluate the tectonic activities of the Vark basin, located in the great basin of Dez River in northwestern Iran, using geomorphologic indices combined with the geographical information system technique. Some geomorphic indices were used to achieve this aim. In this regard, the indices of stream length (SL), drainage asymmetry (Af), hypsometric integral (Hi), valley floor ratio (Vf), basin shape (Bs), and mountain sinuosity (Smf) were estimated to reach an average index of relative tectonics (Iat), indicating the intensity classes of tectonic activity. The mean SL,Hi,Vf, andBsvalues were estimated as 2273, 0.55, 0.45, and 1.75, respectively, regarding the active class of tectonic activity. Therefore, considering theAfandSmfindices with values of 27 and 1.14, the basin was categorised as having semi-active conditions. The overallIat, with a value of 1.33, represented the very high class (1.0 <Iat< 1.5) of tectonic activity. Hence, by calculating the index of relative active tectonics, the study area is observed as the intensive class concerning tectonic movements. Overall, the mean values of theIatfor all sub-basins were calculated as 1.50, 1.17, and 1.83, revealing the very high and high classes of active tectonics in the basin. The results obtained on tectonic activity were further confirmed during field observations by examining the structurally complex joints, folds, slips, faults, and fractures of the area, which reflect the dynamic nature of the regional tectonics.