The Evaluation of the Active Tectonics of the Sirvan River Basin Using Geomorphic Indices

Rivers are sensitive to tectonic movements and there is a close relationship between river formations and tectonic movements. The term morphotectonic states the relationship between geomorphology and tectonics, and in many cases morphotectonic, is considered to be geometric tectonics. In recent years, geomorphic tectonics has been a significant tool for identifying active tectonic forms and providing seismic hazard maps and understanding the history of current land surveys. There are several methods to study the tectonic condition of a region or basin. In the meantime, geomorphic indicators in the evaluation of the tectonic activities are useful and reliable tools because they can be used for areas that have experienced a tectonic activity. They are easily identified. These indicators allow geomorphologists to quantitatively measure and reasonably compare different landforms and compute morphological indices. The studied area is considered to be an active area in terms of its location (folded Zagros) and the tectonic is considered as an active region. Accordingly, the evaluation and the study of tectonic activity and its effects in regional planning and land use planning and environmental management are of great importance. In this study, the morphotectonic status of the Sirvan basin was evaluated.  

In this research, in order to investigate the effect of tectonics on the studied sub-basins, the sources and findings of the research in the field of research were collected through library studies. In addition, to evaluate the studied sub-basins, geomorphologic indices and evidence were used. The research data included 30m DEM, STRM, the topographic map of 1: 50000 and the geological map of 1: 100000of the studied basin. The ARCGIS software was used to evaluate the indicators and final output mapping. According to the objectives, in order to investigate the effect of tectonics on the studied sub-basins, eight indicators including mountain front (SF) index, drainage basin asymmetry index (AF), longitudinal gradient of the river (SL), reverse topographic symmetry index (T), surface congestion index (P), hypersonic integral index (Hi), sinusoidal river index (S), and basin shape index (BS) were used. After assessing the basin based on the existing indicators, the studied sub-basins for each of the indicators and the final results were obtained.

In this study, to evaluate the tectonic condition of the studied sub-basins, each of the indicators was considered. The results of the SL (Sudden Slope) evaluation indicated that the Sirvan sub-basin with SL of 3133 was the most active sub-basin for this indicator. The evaluation of the T index (inverse topographic symmetry index) indicated that the Shevishe River basin with a coefficient of 4 had the highest degree of asymmetry. The P (Surface Water Condensation) evaluation indicated that the highest density was achieved by 397. It was related to the Gheshagh sub-basin, and according to this indicator, the sub-basin was considered to be the most active sub-basin. Based on the HI index (hipsometric integral) Shoeisheh sub basin with a coefficient of / 420 was considered to be the most active sub-basin. In terms of S (sinusoidal river), the sub-basin of Gheshlagh with a coefficient of 1.31 had the lowest coefficient and, therefore, the most active sub-basin for this index. It was also considered as the longest and most active sub-   basin for BS (basin shape) of Gheshlagh basin with a coefficient of 2.14.

In this research, the geomorphic indices were used to study the tectonic conditions of the studied sub-basins. The results of the assessments were different in different sub-basins. Consequently, according to the Smf index (indicating the extent of tectonic congestion and erosion in the region), of the studied sub-basins, Shevishe basin with a Smf level of 11.1 was the most active sub basin. In terms of the AF index (detection of tilt in the drainage basins due to tectonic activity), of the studied sub-basins, the Gheshlagh basin with a factor of 4.70 had the highest stroke. After assessing the basins based on the existing indicators, in order to classify the basins in terms of tectonic activity, the tectonic activity (Lat) partial evaluation index was used. The results of this indicator indicated that, of studied Sub-basins, Shevisheh sub basin with Class 2 average, had a more active status than the other sub-basins. Accordingly, it is necessary to pay attention to the status of tectonic activity of the sub-area in carrying out any planning, land use planning and management, avoid any risky actions, optimize the use of natural resources, and reduce the harmful effects of any planning.