نوع مقاله : مقاله پژوهشی
استادیار دانشگاه پیام نور، دانشکده علوم، گروه زمین شناسی، تهران، ایران.
عنوان مقاله [English]
Tectonic geomorphology is the knowledge that can quantify the impact of active tectonics using geomorphic indices as quantitative measurements and descriptions of landforms and landscapes on rivers; thus, quantitative conditions measurements Provides them with the opportunity to identify the status of areas with active tectonic structure. Extraction of geomorphic indices using Digital Elevation Models (DEM) in GIS software environment in recent decades has been accurate and reliable method in drainage basin analysis, as one of these indices for rapid evaluation of activity. In order to study the active tectonics in the study area, the morphotectonic parameters of the rivers have been used. With the study of topographic landforms and the model of drainage systems by using geomorphic indices and the geological structure of each area, it is possible to evaluate the active tectonic performance and to determine the absence of active tectonic movements. The quantitative measurements provide conditions that allow them to identify the status of active tectonics areas. Along with the advancement of tectonic science of geomorphology, scientists have found that active tectonic processes can affect the shape and function of rivers being one of the most important observations that occur rapidly. And consistently respond to deformation caused by active tectonics at the surface reflecting minor changes in topography, thus examining drainage pattern and river diversion provides important information on structural expansion and evolution of the area. the Alborz orogenic belt is a part of the named area, and the placement of the studied area in the central Alborz has caused the area to be affected by this tectonic movements. This mountain range is the result of two orogenic movements, one of them is Precambrian ores (Acinitic), the course of which is essentially a metamorphism that leads to the interconnection and hardening of the paving stones in the Precambrian, The second one is the Alpine orogeny movements that it happens in Mesozoic and Cenozoic periods. This mountain range is approximately 600 kilometers long and 100 kilometers wide along the south side of the Caspian Sea. The northern margin of the Alborz line is usually sloping. General trend of study area is NE-SW. Firstly, Rivers and basins of the area were extracted using STRAHLER method using 30 m accuracy digital elevation model in Arc GIS software. Then the necessary modifications to the wells and extraction basins were carried out using topographic maps and satellite images and finally the study area was divided into 18 sub-basins. Finally, for the extracted basins, geomorphic indices including hierarchical anomaly indices (Δa), longitudinal river gradient (SL), basin shape (Ff), drainage density (Dd) and relative prominence (Bh) in 18 drainage basins were calculated and finally the relative active tectonic index (IAT) was measured. A tectonic activity zoning map was prepared for each indicator in the study area and the results of the indices were analyzed. Based on the calculations obtained from the hierarchical anomaly index, the index shows very high and high values in sub-basins 2, 6, 9, 10 and 13 along the Khazar, North Alborz and Azarak faults. The values obtained from the basin shape coefficient index calculations are also very high and high along the mentioned faults and in the aforementioned basins. In basins 12, 13 and 15 that lie along the Hassan Gile fault, the values obtained from the relative prominence indices and drainage basin density are very high and high. The extension of these faults in basins 12, 13 and 15 increases the longitudinal gradient index and thus indicates a high rate of morphotectonic anomalies in the area. Finally, by calculations with relative active tectonic person and comparing it with other calculated indices, it was found that sub-basins 12, 13 and 15 affected by Hassan Gil fault activity Very high and sub-basin 6, which is affected by the Azarak fault activity, shows high index. It should be noted that other minor faults formed due to high tectonic activity in the area have a significant impact on the increase of morphotectonic indices and have caused some sub-basins. High levels of indicators and sometimes very high. Studies in this part of central Alborz show that recent relative tectonic activity is high and very high due to the active faults in the region such as Azarak, Caspian and northern Alborz. About 66.5 percent of the area is dominated by these faults, as well as other minor faults formed by recent tectonic movements, suggesting moderate to high tectonic activity. So it can be understand that this area of Alborz totally having the high active tectonic based on morphometric indices.