عنوان مقاله [English]
Tectonic activity at the point of collision and subduction, at the boundaries of subcontinents and orogenic belts, is often very dynamic and rapidly changes the characteristics of the earth's surface. The study of the structure of roughness and their morphology in areas with active tectonics using spatial data is often discussed as morphotectonics.The Darrehshahr catchment area is located in folded Zagros in Ilam province and has a slippery structure such as fault folds, turned and dormant. Due to the geology of the region and the special morphology of the slopes and the placement of hard layers on the loose layers that have the property of kneading, there is a good ground for tectonic activity in this region, especially landslides. This indicates active tectonics in the area.
To study and accurately estimate the geomorphic indicators of The Darrehshahr region, the region was cut from a digital elevation model (DEM map with an accuracy of 10 meters) received from ASTER satellite using Global Mapper 18 software. Using digital elevation model, the hydrological map of the region was drawn according to the Australian classification. Using ArcGIS 10.5 and Portable Basemap Server V3.1 software, topographic maps of 1/50000, hydrological maps and layers created were matched with Google Earth satellite imagery, and a new composite map was created. On the combined map, the main ridges and the bottom ridges of the region were carefully drawn. Mathematical relations specific to tectonic indices were implemented on the generated maps and the data required for tectonic analysis in the region were extracted. SPSS software has also been used to draw some diagrams. To study and measure active tectonics in the region, geomorphological indicators including hypsometric curve, hypsometric integral have been used. After calculating the desired geomorphic indices, evaluation and classification of relative tectonic activity in the study area has been done.
The number obtained from the hypsometric study shows that the study area is in class 3 in terms of tectonic activity and the shape of the hypsometric curve of the area indicates the maturity stage of the area. At this stage, geomorphic processes occur almost in a balanced way. Due to the shape of this curve, there are semi-active tectonic activities in the region. The hypsometric integral of the region is equal to 0.25, which indicates the intersection of the drainage network at a smoother surface. The value of the asymmetry index of the drainage basin is such that in terms of tectonic activity, the right side of the area is in class 1 and the left side of the area is in class 3. In the mentioned region, where the river flows to the southeast, the tectonic rotation is to the north. In the northern part this value is less than 50 and the main river is tilted to the north. The tributaries on the south bank are longer on the right than the tributaries on the north bank on the left and have to travel a longer distance to flow into the main waterway (Seymarreh River) because of the asymmetry index. The drainage basin is larger than 50. In this region, the value of transverse topographic symmetry index is equal to 0.29, which indicates the semi-symmetry of the study area. This basin is in class 3 in terms of tectonic activities. Also, the tendency of drainage network to the northern half of the region and semi-active tectonics in the southern half of the region is due to the low slope and protrusion of the synovial valley, Seymarreh synchronous. The relatively high values of the Mountain Front sinusoidal index for the Kabirkuh and Melleh Kuh anticlines indicate that tectonic activity in these two anticlines is in Class 2. There are also semi-active tectonic activities within these anticlines. In the mentioned area, the value of the basin shape ratio index is equal to 2.45, which is in class 3 in terms of tectonic activities. This figure shows that the area is elongated and tectonic activity is almost active in this area. The ratio of the ratio of the width of the valley floor to its height for the whole region is equal to 4.31. According to the value of this index in terms of tectonic activity of this region is in class 3. The value of this index varies from 0.27 to 10.51 in the study area, small values are related to the northwest valley where tectonic activity is more active. The final value of the river canal sinusitis index in the study area is 1.47. According to the obtained value, this basin is in class 3 in terms of tectonic activity. We also conclude that the Seymarreh River flowing in this basin has reached equilibrium and there is very little tectonic activity in the Seymarreh River area.
In general, in the plain unit of the Darrehshahr region, there is semi-active tectonics with very little tectonic motion and the plain level has reached relative stability. However, in the geomorphic unit of the mountain and its foothills, there are still relatively strong tectonic activities and it has caused changes in this geomorphic unit. In general, according to the results of Table 8, most of the tectonic activities that have affected the Darrehshahr area are in Class 2 and 3, and this area is in the maturity stage. Tectonic activities in this region are semi-active and inactive, and this range is almost equilibrium and the rate of change as a result of these activities is low. However, due to the geology of the region and the specific morphology of the slopes and the placement of hard layers on the loose layers that have the property of kneading, there is a good ground for tectonic activity in this region, especially landslides.
Keywords: Tectonic activity, Geomorphic features, DarrehShahr, Equilibrium.