عنوان مقاله [English]
The identification and analysis of the active tectonic or denudation processes through the analysis of the deformation and landform changes consist one of the fundamental objectives of the tectonic geomorphological studies. Rivers are among the groups of geomorphologic elements that flow on a wide range of different landforms and can reveal the critical relationships among uplift, lithology, and denudation of heights. With regard to the evolution of landforms, this group of information and the relations between them are preserved by the bedrock properties. River Incision is the primary mechanism by which landscapes adapt to climate change and tectonic forces. Among the many factors that affect the Incision rate, the distribution of slope and steepness of water channels can be systematically effective. The main purpose of this study is to investigate the sequence of mountainous and foothills landforms in Damghan region using slope changes and erosion-incision reaction of rivers on the surface of these landforms as one of the key factors in landscape evolution.
There are many models for calculating the river incision rate, but the most widely used is the SPIM model, which is presented in the form of the following equation:
The SPIM model is based on simple geometric parameters, such as the slope and area of the drainage basin extracted from the DEM elevation map. Some parameters are related to energy considerations, such as the rate of energy consumption in the channel bed and ridges, in which case; m: 0.5 and n: 1 are used as experimental constants in the formula.
In order to calculate the values of this index and prepare a river incision map, first the whole study area was divided into 64 sub-basins so that the resulting section values are suitable for surface interpolation. In the next step, the values of effective indicators in the SPIM formula including river slope, drainage surface area and erosion efficiency were calculated for each of the sub-basins. To calculate the erosion efficiency index, first the steepness values of the rivers of each basin were calculated from the formula of stream power incision, based on power regression, in the form of the following equation.
In the above formula Ɵ is the amount of concavity and KSN is the amount of steepness.
After obtaining the steepness values of rivers in each of the 64 catchments, the erosion efficiency relationship was used as follows:
U is actually the rate of elevation or change in altitude of the area relative to the base level, which was calculated using the radar interfrometry method to determine the amount of vertical displacements in the area.
In order to prepare and analyze the slope and incision rate of rivers in Damghan region, and to convert point values into raster levels containing value, the inverse distance weighted interpolation method or IDW was used.
Results and Discussion
Comparison of longitudinal profiles taken from the slope map and incision rate of Damghan region shows the close relationship between these two parameters; Both of these parameters together play an important role in analyzing the tectonic status of the areas. In such a way that in examining the condition of the longitudinal profiles of the region from north to south, there are prominent features such as mountain belts or foreberg shapes; The slope rate and incision rate of the river increase and in front of where there are depression constructions such aspull apart basins or the end parts of longitudinal profiles that are based on alluvial plains, the slope rate and the following incision rate of the river decreases.
Therefore, the analysis of longitudinal profiles taken from the slope map and incision rate of rivers in Damghan region can be effective in identifying and analyzing the effect of active fault mechanisms on the sequence of landforms in the region. the areas that have mainly high slope and incision rate of the river and are shown prominently in the longitudinal profile, represent the performance of faults in the form of transpressional, which leads to the formation of elevated landforms. In contrast, the concave areas in the longitudinal profile of the slope and incision of the rivers in the region are mainly representative of the areas where the gentle slope has led to a reduction in the slope of river systems and thus reduced river incision capacity.these areas are either mainly based on flat lands which are in the southern part of mountain structure in form of alluvial sediments or they are collapsed structures due to transtentional motion of faults such as Astaneh pull-apart basin.
The activity of faults with different mechanisms causes the uplift or subsidence of landforms to form a series of successive landforms in an active tectonic environment. The rise and fall of these structures have led to an increase or decrease in their slope which will effect on the waterway systems that flow on these landforms. Wherever the fault mechanism leads to an increase in the height and elevation of the landforms, the slope of the river increases and as a result the incision power of the river increases. From the analysis of longitudinal profiles taken from the slope map and the incision of the river, it can be concluded that this method is very useful in identifying the sequence of landforms affected by tectonic processes. In a way, by examining the process of changing these longitudinal profiles, we can understand how active faults function in shaping landforms in compressive or tensile form. Wherever the slope of the waterway is high and the incision rate of the river is high, it indicates the existence of a elevated axis. This landform can be a mountain ridge or even elevated forms among alluvial sediments.wherever the slope and incision rate of channel show low values, it can indicate the existence of a concave tectonic basin.