Evaluating the effects of neotectonic activities on basin shape Indices (Case study: Zanjanrud sub-basins)

Rivers are very sensitive to changes in discharge and sediment load as well as tectonic forces. Many of the changes that occur over time in the morphology of the channel can be related to the mentioned changes. Morphometric analysis is the first step understanding the basin dynamic activity. Combined variables and indicators can be effective in identifying the complications and surface landform of river channels and show their temporal and spatial changes. In addition, in addition, geomorphological indices (Morphotectonic indices) are considered to be very useful methods in evaluating and recognizing tectonic activities and can provide quantitative results and quantitative description of morphometric features in The basin scale can be used to explain the structural controls, geological history and geomorphology and processes of its drainage network. In addition, the morphometric parameters of the basin play an important role in the hydrological processes governing the basin because it largely determines their hydrological response.

Zanjanrud is the main river basin completely limited to the area of ​​Zanjan province. The river originates from the heights of Soltanieh in the east and flows to the northwest and finally in the west of Rajein village it joins Qizil-Uzen. Regard to the objectives of the research, first, using the DEM of the basin (ASTER-DEM: 30m), the extractable sub-basins was identified in the WMS software environment. In this step the number of 107 sub-basins could be separated, of which 52 sub-basins were selected based on the minimum area of approx. 20 Km2 for the evaluation and analysis of shape indices and tectonic. These sub-basins were named according to the outstanding settlement inside them. After determining the shape indices and estimating and comparing the state of neotectonic of the sub-basins, a field survey was conducted to closely examine and validate the findings.

At the first, the shape of the studied sub-basins was quantified using different indices. Then, the morphology of the sub-basins was evaluated using different shape indices and then the different indices were checked in terms of correlation in terms of the results related to tectonic activity. Finally, the neotectonic of the sub-basins has been estimated using the results of the shape indices and the data related to the faults. The results show that the Kazbar sub-basin is most elongated sub-basin, which together with 7 sub-basins with very high elongation rate are located in the western half of the Zanjanrud basin.The frequency of sub-basins with the shape index 2 to 3 is in the SE half of the basin. Out of the 8 sub-basins with shape index less than 2 in the eastern half of Zanjanrud basin, 1 sub-basin is located in the northern part and 7 sub-basins are located in the southern part of the basin, which can be seen in the SE half. The upstream sub-basin is not included in the classification due to the unusual shape that cannot be compared with other sub-basins.

The results of classification of the indices shows that the accumulation of sub-basins with high rate of elongation and as a result with high neotectonic activity is in the NW part of Zanjanrud basin and especially in the northern side of this part.Out of the 51 sub-basins, the concentration of 8 sub-basins with mean index of higher than 5 and a total of 16 sub-basins with an average shape index higher than 3.5, indicates the highest level of neotectonic mobility in this part of the basin. This finding is consistent withthe region's latest map of active faults, in which the frequency of faults (including the Sohrein fault, the Qaracherian fault and the Kenavand fault) is in the NW part of the basin.According to the study results of the shape of the sub-basins, the SW side of the Zanjanrud basin has an average level of neotectonic activity. This finding, along with the results related to the NW part, can strengthen the hypothesis that the western half of the basin is more active than its eastern half. The neotectonic mobility in SE side of the basin is moderate and is higher than NE part of the basin. As previous studies have shown, many faults are involved in the morphology of the region.