Evaluating the influence of recent tectonic activity on the river evolution using the identification of knickpoints in the south of Central Alborz Belt

Authors: MASOOMEH ALAEI, ALIREZA NADIMI, HOMAYON SAFAEI, MARYAM DEHBOZORGI

Abstract: Change in the steepness of river profiles caused by tectonic forces (uplift and material weakening in fault zones) causes the formation of the tectonically formed knickpoints (TFKs), which is an important geomorphic feature in bedrock river morphology. In this research, knickpoints in a wide area of the south of Central Alborz using the stream gradient (Gd) and the normalized steepness index (k$_{sn}$) were identified. According to the location of the knickpoints in relation to the faults in the area, the TFKs were identified. Analysis of the extracted TFKs with the longitudinal profile, logarithm slope-area plots, and natural logarithm gradient-distance plots confirmed their correspondence with the active segments of faults. Investigating the characteristics of TFKs such as length, height and gradient indicated that TFKs related to Mosha and North Tehran faults are high-altitude and the TFKs related to Taleghan and Eshtehard faults are long-distance. The identification of numerous TFKs on the active fault segments of the area and their confirmation based on field observations indicate a high rate of uplift and recent tectonic activity in the southern side of Central Alborz, which shows the importance of seismic studies due to the possibility of destructive earthquakes in the future.

Keywords: Bedrock rivers, stream gradients, tectonically formed knickpoints, active tectonics, Central Alborz

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