Tectonic Geomorphology of Atrak River , NE Iran

Atrak River region, northeast Iran is a quaternary tectonically active region. There are many geologic structures that they are formed by the collision of the Arabian and Eurasian plates. This area has extended from north east Iran to the of kope dagh zone. The study area is Atrak river basin and it has been divided to 56 Sub-basin for calculation of 6 geomorphic indices. Finally, this region was classified in 4 relative tectonic activity classes.


Introduction
Neotectonics is a major factor controlling landform development in quaternary tectonically active regions.The effect factors in morphology region are tectonics, lithology, climate and human.If tectonic has been most effective factor in region, it's related to tectonic geomorphology.The study area (Figure 1) of Atrak River basin is at north east of Iran [1] [2].The river is located in the Kope dagh and Atrak basin is divided to 56 sub-basins (Figure 2).
This area belongs to Kope dagh province [3].Dominant structural trend in Kope dagh province (Figure 3) is NW-SE.From tectonics view, it contains the Kope dagh hinterland or Kope dagh fold and thrust belt that formed in passive margin of Eurasian plate until late Triassic and then marine sedimentation on Kope Dagh proforeland basin has continued to Eocene.Kope dagh hinterland has uplifted related to Karakorum foreland basin in northeast along Eshghabad fault.
The western part of studied area has located in South Caspian foreland basin.Dominant structural trend in  South Caspian foreland basin province (Figure 3) is NW-SE.From tectonics view, it contains the northern foreland basin of West-Central Alborz and lesser Caucasus hinterland in the south margin of Eurasian plate since late Eocene.Although median part of South Caspian and Black sea basin has uplifted by collision between Eurasian and Cimmerian plates [3].This area has semi active tectonics regim in compared to Alborz [4]- [11], Central Iran [12]- [18] and Zagros in the southern Iran [19]- [22].

Materials and Methods
This article applies a quantitative geomorphologic method to an area in the Zagros to evaluate rates of active tectonics.Considering the diversity of the morphotectonic features [23] [24].Spatial tools including geographic information systems (GIS) and morphometric analyses may provide useful information on this subject, we have analyzed below geomorphic indices by [25] method (Table 1).Also, results were shown in Figure 4.
To study the indices, there is a formula which we turn to describe each one of indices; It is necessary to have some primary maps to calculate the indices, and the most important of which are: Digital Elevation Model (DEM), the drainage network and the sub-basins map of the Atrak basin that have been extracted from DEM. DEM (SRTM) extracted from a digitized topographic map (1:30,000).

Results and Discussion
We computed a single index (Iat) from the six indices to characterize relative active tectonics.Previous studies in Iran [26]- [42] tend to focus on a particular mountain front or area to discuss relative tectonic activity and     2 shows the result of the classification for each sub-basin.

Figure 1 .
Figure 1.Location of the study area.

Figure 2 .
Figure 2. Fifty six sub-basins of the Atrak River basin.

Figure 4 .
Figure 4. Distribution of six indices and classification of them into three classes.

Table 2 .
Values of Lat.