Zoning Tectonic Activities of Banarovan Using Morphotectonic Indices

1. There is almost no region in the world that has not undergone tectonic changes during the recent millennia (Keller & Pinter, 2001). For this reason, evaluation and investigation of active tectonic processes and their effects, for example earthquakes, are of vital importance for many human activities including the design and construction of cities,
power plants, and dams as it helps minimize their risks and damages (Soleymani, 1999).
The Benaravan fault, located on the east of a mountain, is part of the Mianeh-Ardebil
fault. The 20 km long Benarvan fault is one of the most significant ones in the region. It
is located on the southern skirt of Azerbaijan’s Mount Bozgush and extends in the
southwest-northeastern direction. Its route features special attributes concerning domain
instabilities and geomorphological phenomena (Monroe & Wicander, 2001). Tectonic
and geomorphic activities, relatively low-resistance lithology (Miocene era degenerative
sediments), intense faulting of the region and being located in the very high risk region
of earthquake (Benarvan fault and adjacent faults), and the high level of subterranean
waters result in the possibility of natural risks such as earthquake and other types of mass
movement. The significance of such a research is due to the location of numerous
residential areas across the Benavran fault. So far, there have been many studies on the
behavior of faults based on morphotectonic indicators in Iran and the world, the of which indicate the potential of these indicators in analyzing the behavior of faults.
2. Material and In this research, the basin was divided into sub-basins initially in order to ease calculations
and outcome comparisons. Then, using quantitative indicators, the researchers investigated the effects of tectonic activities on the valleys and riverbeds. The bulk of the
data needed for indicators was acquired from 1:25000 scale topographic maps, especially
digital and aerial maps (Keller & Pinter, 2002). The morphological indicators used for
the region are the following: hypsometric curves and integrals, asymmetry index of the
drainage area (asymmetry factor), symmetry factor of the transverse topography, stream
length gradient index (SL), valley width to height ratio (VF), the V ratio, and drainage
basin shape ratio (BS). After calculating the geomorphic indicators of the studied area,
the researchers estimated the tectonic activities using the IAT index. The IAT index is
obtained from the mean value of different geomorphic indicator classes.
3. In this research, the waterways and the basin border were marked using a 1:25000 and
1:100000 scale geologic maps, respectively.
3.1. The hypsometric curve and integral
Eight hypsometric curves were produced for the studied basin. According to the curves
for sub-basins, sub-basins 1 and 2 had an under-curve area of above 50%, being relatively
convex. This indicated the young age of the basin. Moreover, the convex form of the
dimensionless curve indicated the prevailing of neo-tectonic activities over eroding ones.
3.2. Calculating the asymmetry index of the basin.
The asymmetry index was higher in basins 2, 5 and 6, and lower than 50 in 1, 3, 4, 7 and
8, which points out their deviation. The T index indicated the semi-asymmetric form of
the majority of sub-basins that fall into class 2 regarding their tectonic activities. The river
gradient index was one of the significant indicators for differentiating between active and
non-active tectonic areas. The mean stream length gradient index or SL for the basins
varied from 482 for basin 2 to 71 for basin 6. The VF index showed that the bulk of the
basin is within the active area; indicating that tectonic activities have not given the stream
sufficient opportunity for erosion. The basin shape index for each case indicated that
basins 2 and 7 are active and elongated, while the rest are inactive and fall into class 3.
3.3. Relative evaluation of regional tectonic activates according to geomorphic
indicators (IAT)
In this study, eight morphotectonic indicators were calculated for each of the 8 basins,
dividing them into 3 geomorphic levels. Then, the values for geomorphic index (S/n) were
measured discretely for each basin; being classified into 4 levels, i.e. the index of relative
active tectonics (IAT) of the study’s expanse. The classification for geomorphic
indicators proposed by Hamdoni, Irigaray, Fernandez, Chancon & Keller (2008)
classified these indicators based on the quantitative value into 4 classes. The class
quantities of all indicators were combined, and their mean values were presented as the
IAT index, indicating the tectonic activity. According to the results obtained from the
IAT index, there is very strong tectonic activity in basin 2, with strong, moderate and
weak tectonic activation witnessed in the remaining basins. The results of evaluation
showed that the basins’ tectonic activities range from very strong to strong, moderate and weak.
4. Quantitative measurement allows geomorphologists to compare different landforms in a
factual, rational manner, subsequently calculating morphologic indices. Regarding the
hypsometric curve and integral for sub-basins 1 and 2, the under-curve area was above
50%, indicating its young age. Also, the convexity of dimensionless curves indicated the
prevalance of neo-tectonic activities over eroding ones. For sub-basins 3 to 8, the undercurve area was below 50%, resulting in a more concave hypsometric curve that indicated eroding activities in these sub-basins. Concavity in the dimensionless curve indicated the dominance of eroding activities over neo-tectonic ones.
4.1. The asymmetry index of the drainage basin
In basins 2, 5 and 6, this index was above 50, while for basins 1, 3, 4, 7 and 8, it was
below 50. This indicated the deviation of basins. The topographic symmetry index
indicated that the majority of basins are semi-symmetric, falling into class 2 regarding
their tectonic activities. In the studied region, the SL index for the main waterways of 8
sub-basins was measured. The mean value of the gradient index or SL for the basins
varied from 482 for basin 2 to 71 for basin 6. According to the valley width to height
index, the bulk of the basin is within the active region. This indicated that tectonic
activities have not given the regional stream sufficient opportunity for erosion. The V
ration index, called the valley morphology index, was obtained via comparing the
transverse area of the actual valley to the area of a hypothetical semicircle with a radius
equal to the valley depth. In sub-basin 7, it indicated the existence of a valley with larger
width and less depth, the type which incurs higher erosion.
The basin shape index indicated that basins 2 and 8 are active and elongated, while the
rest are inactive and fall into class 3. The IAT index classified the tectonic activities of
the region in the three classes of very strong, strong and moderate. According to this
index, there is no basin with weak activities in the region. According to the segmentation
map, the highest activity occurred in sub-basin 2, and the least in sub-basins 3, 4 and 7.
The study and evaluation of different geomorphic indicators of the region show that it is
young and active regarding neo-tectonic activities, yet this activity is not equal in all
sectors. In sub-basin 2, young activities were the highest. This could be attributed to the
stronger activity of the major and minor faults, resulting in the rise of the area.