Active Tectonics Analysis by usingGeomorphic Signatures in the Gorgan Drainage Basin in North Eastern Alborz

The present study carried out to identify neo tectonic activity of the Gorgan River basin in Golestan province، in North of eastern Alborz range is investigated by four geomorphic indices including the stream– gradient index (SL)، drainage basin asymmetry (Af)، reveres symmetry of topography (T) and mountain front sinuosity (Smf). Result from the analysis is accumulated and expressed as an index of relative active tectonics (Iat)، which divided into four classes from relatively low to highest tectonic activity. The high class values low tectonic activity for Iat mainly occur in the south and southwest of the Gorgan River Drainage Basin، while the rest of the study area has classes of Iat suggesting moderate to low tectonic activity. The results of this study، show that high values of T-vectors are related to Gorgan River are resulted from Caspian، segments of North Alborz and Khosh yeilagh faults activity. In this area increase trend of tilting collimate with faults can be reason the existence of an active tectonics region in the west part of the eastern Alborz. Other results of this study show low Smf and high SL values. The rate of tectonic activity in this area will increase from north to south. This increase can be related to the position of peaks stream length-gradient index along the fault and segment fault. Also value of drainage basin asymmetry is calculated for all of the sub catchments greater or less than 50 that shows tilt for each stream toward West or East. Length of the T- vector in eastern Alborz proportionate with measure of tilting and class of active tectonics. On the other hand، other results of this research are high levels of tilt and drainage basin asymmetry. The results of the review to propose the relative active tectonics index in the region، represent areas with focus on low tectonic activity in the central part of Gorgan Drainage Basin، while other areas have moderate to high categories were tectonic activity which indicates the study area is neo tectonically active.