عنوان مقاله [English]
The faults of the northern section of Qom-Zafreh faulting system with right-lateral right-angled movements, along with reversed components configure the northern parts of the central Iran zone. In this research, seismic potential and tectonic stresses of this fault system are investigated based on geomorphometric and morphotectonic methods. Field data and morphotectonic evidence in the area have been used to analyze the data. To this end, were measured some geomorphic indices and their adaptation to the location of the main faults. These indicators, as the most widely used in the tectonics and neotectonic evaluation studies, are considered as the first category. The second category is the indices related to the catchment basin dynamics. On the one hand, the characteristics of the mentioned indices are sensitivity to the movements of sliding and steady-state faults and, on the other hand, the reason for the predominance of deformed phenomena in relation to the erosion in the region. To calculate geomorphic indices in 18 sub-basins in the study area, the TecDEM extension program was also used. The initial results indicate the high tectonic activity near the main faults of the northern part of the Qom-Zafare zone such as Bidadeh fault, Qom fault, Kashan fault, and other faults. These findings are consistent with landforms and tectonic activities existing in the region.
Materials and methods
In this research, the seismic potential and tectonic activity of the northern section of the Qom-Zafare fault system have been evaluated using geomorphometric and morphotectonic methods in the sub-basins of the study area. In order to investigate the tectonic activity, the study area was divided into 18 sub-basins. Then, to measure and evaluate the tectonic activities of the study area, we measured geomorphic indices and their adaptation to the location of the main faults.
In order to calculate the geomorphic indices of the study area, they were classified into two general categories: 1) Dynamic indicators of the surface including longitudinal gradient (SL), sine wave of the mountain front (Smf) and ratio of valley width to valley height (Vf). 2) Dynamic catchment indicators of the catchment area including drainage basin asymmetry (AF), hypsometric integral (Hi) and drainage basin shape (Bs). To improve the quality of measuring the tectonic and neotectonic indices, the computational capability of the TecDEM software, as an add-on, has been employed in the Matlab software environment. After extraction, the results of the geomorphic indices were separated into ArcGIS environment by separating study basins of each study area and to obtain the tectonic activity index (Iat). Based on the obtained values from the active land development index (IAT), the five study areas were very active, active, moderate, and low activity and very low activity.
Results and discussion
The study area includes the northern section of Qom-Zefreh fault zone, which includes a large part of the Qom province. This zone extends from the east and south-east to the Central Iran and from the north to the Alborz zone and from the west and southwest to Sanandaj Zone of Garrison.
In general, there are active tectonic processes and seismic faults in the northwest-southeastern region. Measurements and investigation of the evidence of the activity of faults in quaternary sediments indicate the change in the process of these faults and cause the alteration of these faults to be generally right-angled, although the left-handed movements in some of the secondary or non-essential faults are due to their orientation in relation to the main stress.
In order to conclude and evaluate the seismic potential and tectonic activity in this part of the Qom-Zefref fault zone, these indicators are divided into two general categories: dynamic indicators of catchment basins, then by the relative activity index Iat. They were classified into three categories. Finally, by integrating the Iat index layer and other information layers, including the deformation of the main faults and the intensity of seismic centers in the ArcMap10.3 software environment, based on seismicity and tectonic activity, we determined five classes of very low, low, moderate, high and very high. By the way, we extracted the seismic potential zonation map and tectonic activities of the study area. In this research, for the first time, geomorphic indices are used for zonation of seismicity and tectonic activities in terms of the relative tectonic activity index of Iat, in contrast to other studies only used geological parameters (lithology).