1. Hamed Alianpour, Department of Applied Geology, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran.
2. Saeid Asiabar, Azad university
3. Maryam Dehbozorgi, Professor of Geologyy, Faculty of Geology, Kharazmi University, Tehran, Iran
4. Reza Nozaem, Professor of Department of Geology, University of Tehran. Iran
5. Nasim Ramezani, Faculty of Geology, Kharazmi University, Tehran, Iran
1-Introduction
Determining the anomalies resulting from active tectonics in rivers using geomorphological indices is very useful and can be associated with revealing active structures in the region. The evaluation of structures and landforms throughout their history of occurrence is the main subject of tectonic geomorphology (Shum et al., 2002, 276). The study of active tectonics is of great importance in assessing geological hazards, which is doubly important in areas with intense tectonic activities in the Holocene and Pleistocene (Ramazan et al., 1402)
2-Materials and methods
In this study, using Arc GIS software and a digital elevation model of 30 meters using the Strahler method, watersheds were divided and extracted. Then, by using topographic maps on a scale of 1:25000 and geological maps on a scale of 1:100000 and aerial photos on a scale of 1:20000 and through the Arc GIS software, different application layers including waterways, basins, faults, lithology and lines height, was prepared and finally, in order to carry out the present research in the area of Western Alborz and Azerbaijan, the studied area was divided into 50 basins and the value of the normal slope index was calculated for all parts of the main and secondary waterways and divided into 5 categories, then with Drawing the longitudinal profile of the longest river of each basin in MATLAB software, the numerical value of this index and the concavity index were calculated separately for each basin. Also, the Knickpoint extraction of a fault was carried out due to the sudden changes in the slope of the river in collision with the main faults, in order to investigate the tectonic activity of the region. Finally, the geological units and main structures of the region were examined and analyzed with the results of the longitudinal profile of the river and field observations.
3-Results and discussion
The results of quantitative investigation of changes in the longitudinal profile of the river and extraction of river channels in 54 drainage basins indicate high tectonic activity in the central and northern parts of the study area in the Bisotun-Taqebistan, Sahneh and Mianrahan faults. The normal slope index (Ksn) and concavity () calculated using the longitudinal profile and in the MATLAB software; indicate that the high values ​​of these indices show good agreement with the known faults of the study area. Using the values ​​of the normal slope index in the entire study area, the Ksn map of the region was prepared using the IDW interpolation method for the entire region. According to this map, the southern parts of the region, including the areas around the Bisotun-Taqebistan, Menghlat and Peru faults, show almost the highest value of this index. Also, the southern branches of the Mizanrahan and Qeshlaq faults have high values ​​of this index. The areas between the Sahneh and Mizanrahan faults, the areas between the Morvarid and Qeshlaq faults, and the southwestern parts of the region have the lowest values ​​of this index. In this study, the river breaks in the study area were extracted using a new method and then separated from each other according to the factors affecting their formation. In this method, the river breaks located in the longest river of each basin were extracted using the longitudinal profile obtained from the digital elevation model of each basin in the MATLAB software (Kirby et al., 2007). The data are processed and modified by the software and then the river breaks are extracted using the longitudinal profile of the river. Also, unlike the old methods, the river breaks of rivers with a length of less than 10 km can be extracted. A high percentage of the extracted river breaks are related to faults in the study area, which can indicate the possible effect of faults on changing the slope of the riverbed and their recent activity. In the southernmost part of the study area, several river breaks have been created by the action of the Kooh-e-Safid, Shirazi, and Sarab faults. The presence of numerous river breaks in the basin of the Bisotun-Sahneh thrust at the intersection of the fault with the river indicates the possible recent activity of these faults. Numerous river breaks in the central parts of the Bisotun-Sahneh thrust, near the village of Chalabeh, as well as the increase in the normal slope index of the river in contact with the fault in this area indicate the greater activity of this part of the fault .
4- Conclusion, Keywords
- Current very high and high tectonic activity in the Bisotun-Taghbostan thrust zone and the Sahneh-Morvarid fault zone as part of the Zagros Main Fault (MRF) and moderate and relatively high activity in the Mianrahan fault and the Kooh-Safid fault zone as a branch of the Zagros Thrust Fault (ZTF) in the study area based on the results of quantitative analysis of the longitudinal profile of the river and the extraction of the river break.
- Acceptable correspondence of the occurrence of earthquakes with the level of tectonic activity based on changes in the longitudinal profile of the river as initial studies to identify seismically active areas and long-term earthquake forecasting in areas with high tectonic activity.
The visited Raba and finally the tectonic activity of the area were analyzed and evaluated.
Keywords: Active tectonics,longitudinal profile of the river,Rudshekan,Sanandaj-Sirjan,Active tectonics