نوع مقاله : مقاله پژوهشی
نویسندگان
1 کارشناس ارشد تکتونیک، دانشگاه خوارزمی تهران.
2 استادیار دانشکده علوم پایه، دانشگاه آزاد واحد لاهیجان.
3 استادیار دانشکده علوم زمین، دانشگاه خوارزمی تهران.
4 استادیار دانشکده زمین شناسی، دانشکدگان علوم، دانشگاه تهران.
چکیده
کلیدواژه‌ها
عنوان مقاله [English]
نویسندگان [English]
Introduction
one of the methods for studying active tectonic movements is the use of Morpho tectonic information .in the study of active tectonic , tectonic geomorphology is very valuable which can determine the effect of active tectonic on the river. Iran is one of the active regions of the earth due to its location in the Alpine-Himalaya mountain belt. The Alborz orogenic belt is also a part of this region, and the location of the studied area in Western Alborz and Azerbaijan has caused this region to be affected by tectonic processes resulting from this collision. In this study, in order to evaluate the amount of recent tectonic activity, the number of 50 watersheds along with the longest possible route of their rivers were extracted in the ArcGIS 10.1 environment, and then the geomorphic indices of hierarchical anomaly (∆a), Branches (R), longitudinal gradient of the river (SL), shape of the drainage basin (Bs), were calculated in 50 drainage basins and finally, by combining the mentioned indices, using the relative active tectonic index (Iat), the extent of the case The study is classified into four categories of very high, high, medium and low tectonic activity. The Sangavard fault (Firouzabad-Mujdar), which is the main fault of the studied area, affects the studied area from the north to the south and causes very high tectonic activity, as well as the Andalibi and Niki faults in the east and the Sheikh fault. Janlu and Niakhrem near the south-western part and the Kalin-Qiya fault in the west have very high tectonic activity. Landslide evidence from field observations proves the results of four geomorphological indicators in the studied area.
Methodology
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 morphometric indicators including hierarchical anomaly (∆a), branches (R), longitudinal gradient of the river (SL) ) and the shape of the drainage basin (Bs) have been evaluated in order to investigate the tectonic activity of the region. And in the last stage, the geological units and the main structures of the region were investigated and analyzed with the results of measuring geomorphological indicators and field observations.
Results and Discussion
In order to determine the level of relative recent earth-building activity in the target area, 4 geomorphological indices were calculated in 50 sub-basins. In order to measure the hydrometric indices, waterways and drainage basins of the region were extracted using a digital height model with an accuracy of 30 meters. Then the hierarchical indices, branches, shape of the drainage basin and longitudinal gradient index of the river were calculated. A zoning map was prepared separately for each index in the study area. Hierarchical anomaly index (∆a) was classified into three categories (high activity, medium activity and low activity) in terms of tectonic activity and in total 30 basins out of 50 basins of the studied area had high and medium activity. 21 basins showed high activity. The branching index (R) was divided into 3 categories (high tectonic activity, medium tectonic activity and low tectonic activity) according to the calculations, and out of 50 basins of the studied area, 38 basins have high activity and It showed average. According to the obtained values and results, the drainage basin shape index (Bs) was classified into 3 classes (high tectonic activity, medium tectonic activity and low tectonic activity). Out of 50 sub-basins of the entire sub-basin area, 32 showed high and medium amount of geo-structural activity according to drainage basin shape index (Bs). Like other indicators, the longitudinal gradient index (SL) was classified into 3 classes, according to which the activity level of the faults was checked. From the total of 50 sub-basins of the studied area, according to the values obtained from the river longitudinal gradient index (SL), 29 sub-basins have high and medium activity. Finally, in order to classify the region based on relative geo-structural activity index (Iat), geomorphological indices of hierarchical anomaly (∆a), branching index (R), drainage basin shape index (Bs) and river longitudinal gradient index (SL) were classified into three categories in terms of geological activity based on the values they had, and for each basin, the values of geomorphological indices (S/n) were measured and divided into 4 categories of relative tectoniv activity. (Iat) were divided. Of the 50 sub-basins in the studied area, 31 have very high and high tectonic activity.
Conclusion
By examining and evaluating the values obtained from the morphometric indices and putting together all the results for each of the faults separately and matching the sub-basins located on the important faults of the studied range in all the indices. It was shown that in the results of all morphometric indices, the sub-basins where the active bergsels of the region were located had a high activity category. The tectonic evidences obtained from field observations also prove the recent tectonic activity of structures and faults in the region. tectonic evidences such as faulting and folding in Neogene and Quaternary units, displacement of Neogene units due to the activity of the aforementioned faults, thrusting of old units on young units are a strong evidence of the high activity of the structures related to the faults. The scope of the study is The existence of travertine mines along the Sheikh-Janlu fault and the existence of landforms such as alluvial barracks, the creation of triangular surfaces, the tilting of layers, the creation of gorges and the existence of V-shaped valleys are among the results. The results of the morphometric indicators confirm the recent topographical activity of the area.
کلیدواژه‌ها [English]
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