Active Tectonics of Kangavar Area , West Iran

Kangavar area is located in the Sanandaj-Sirjan belt in the west Iran. Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics. These indices have the advantage of being calculated from Arc GIS and remote sensing packages over large area as a reconnaissance tool to identify geomorphic anomalies possibly related to active tectonics. This is particularly valuable that relatively little work on active tectonics based on this method is done, so this method is new and useful. Six geomorphic indices are calculated in the study area. Then, based on index of active tectonics values that calculated by average of six geomorphic indices, two relative tectonic activities levels are revealed. The low class of Iat is mainly in the sub-basins of 3, 4, 15, 16, 17, 19 & 22 while the rest of the study area has moderate active tectonics in the other sub-basins. Our results show that the moderate value is located on faulted area, which shows 3 class of relative tectonic activity.


Introduction
The study area is around of Kangavar city in the Sanandaj-Sirjan belt in the west Iran (Figure 1).Sanandaj-Sirjan overthrust belts have formed by metamorphic rocks of the northeastern part of Arabian plate.This province has continued to the north part of Dead Sea fault in the south Turkey.Late Cretaceous-Paleogene sequences in this belt have piled up on a wedge top part of Zagros proforeland basin, before regional metamorphism.Recently, pre-Cretaceous deformed and metamorphic rocks have exposed in this province by upthrusting of basement wedges.
Kabodarahang depression on the north margin of this area with Urmieh-Dokhtar is an index cases from Supra-Arc troughs.This basin is significant in marking loss of the fore-arc basin beneath back-thrusts antithetic to the subduction direction and can explain the presence of younger molasses in a setting referred to as a suture zone [1]- [3].
In this research, area is divided into 24 sub-basins and the following indices are calculated: stream-gradient index (Sl), valley floor width-valley height ratio (Vƒ), and mountain-front sinuosity (Smf), drainage basin asymmetry (Aƒ), hypsometric integral (Hi) and drainage basin shape (Bs).We use geomorphic indices of active tectonics, known to be useful for assessment of relative tectonic activities.Methodology for active tectonic studies [4]- [7] has been previously tested as a valuable tool in different tectonically active areas, namely SW USA [8] the Pacific coast of Costa Rica [9], central Zagros, Iran [10].

Materials and Methods
The calculated geomorphic indices are suitable for assessment of tectonic activity of the study area.The geomorphic indices such as: stream-gradient index (Sl), valley floor width-valley height ratio (Vƒ), mountain-front sinuosity (Smf), drainage basin asymmetry (Aƒ), hypsometric integral (Hi) and drainage basin shape (Bs) are calculated in Kangavararea by using of topographic data and DEM (Figure 2 and Figure 3).On the other hand, the area was divided into 24 sub-basins, and for each one, above indices were calculated, then all of the indices were combined to obtain index of active tectonics (Iat) by new method [11].Therefore, sub-basins can be compared  together.The study area is located between longitudes 47˚30'E -48˚30'E and latitudes 34˚N -35˚N in the Kermanshah province, west Iran.Based on previous work on the salt and mud diapirism [12]- [22] and neotectonics regime in Iran [23]- [28], Zagros in south Iran is the most active zone [29]- [41].Then, Alborz [42]- [75] and Central Iran [76]- [88] have been situated in the next orders.

Results and Discussion
To study the indices, there is a formula which we turn to describe each one of indices; It is necessary to have some primary maps to calculate the indices, and the most important of which are: Digital Elevation Model (DEM), the drainage network and the sub-basins map of the Kangavar area that have been extracted from DEM (Figure 4).DEM extracted from a digitized topographic map (with 10 m intervals).

The Stream-Gradient Index (SL)
The rivers flowing over rocks and soils of various strengths tend to reach equilibrium with specific longitudinal profiles and hydraulic geometrics [89]- [91] defined the stream-gradient index (SL) to discuss influences of environmental variables on longitudinal stream profiles, and to test whether streams has reached equilibrium.The calculation formula is in this manner: ( ) where (∆H/∆L) is local slope of the channel segment that is located between two contours and L is the channel length from the division to the midpoint of the channel reaches for which the index is calculated.This index is calculated along the master streams of 13 measurable sub-basins (Table 1, Figure 5).The SL index can be used to evaluate relative tectonic activity.An area on soft rocks with high SL values can be indicated for active tectonics.Based on our results, there are two classes (Figure 6).
Valley floor width-valley height ratio (Vƒ): Another index sensitive to tectonic uplift is the valley floor width to valley height ratio (Vƒ).This index can separate v-shaped valleys with small amounts from u-shaped valleys with greater amounts.The calculation formula is in this manner: ( ) where Vƒw is the width of the valley floor, and Eld, Erd and Esc are the altitudes of the left and right divisions (looking downstream) and the stream channel, respectively [90].[4] found significant differences in Vƒ between tectonically active and inactive mountain fronts.Also, they found significant differences in Vƒ between tectonically active and inactive mountain fronts, because a valley floor is narrowed due to rapid stream down cutting.Vƒw value is obtained by measuring the length of a line which cuts the river and limits to two sides of a contour through which the river crosses (Table 2).Based on [11], Vƒ values are divided into 3 classes: 1 (Vƒ < 0.3), 2 (0.3 < Vƒ < 1), and 3 (Vƒ > 1).Therefore, all of the valleys are in 1 class and show V-shape valleys (Figure 7).
Mountain-front sinuosity index (Smf): This index represents a balance between stream erosion processes tending to cut some parts of a mountain front and active vertical tectonics that tend to produce straight mountain fronts.Index of mountain front sinuosity [3] is defined by: where Lj is the planimetric length of the mountain along the mountain-piedmont junction, and Ls is the straight-    line length of the front.The Mountain fronts sinuosity classification map of the study area has been drawn in Figure 8. Smf is commonly less than 3, and approaches 1 where steep mountains rise rapidly along a fault or fold [90].Therefore, this index can play an important role in tectonic activity.Considering that mountain fronts sites are independent from basins places, chances are some of them have various fronts (Table 3).Values of Smf are readily calculated from topographic maps for sub-basins.Based on [11], Smf values are divided into 3 classes: 1 (Smf < 1.1), 2 (1.1 < Smf < 1.5), and 3 (Smf > 1.5) and in the study area most of the obtained values are in 3 classes.
Asymmetry factor (Aƒ): This index is related to two tectonics and none tectonic factors.None tectonic factors may relate to lithology and rock fabrics.It is a way to evaluate the existence of tectonic tilting at the scale of a drainage basin.The index is defined as follows:

Af Ar At =
where Ar is the right side area of the master stream basin (looking downstream) and At is the total area of the basin that can be measured by GIS software.To calculate this index in the area At and Ar are obtained using the sub-basins and the master river maps.Aƒ is close to 50 if there is no or little tilting perpendicular to the direction of the master stream.Aƒ is significantly greater or smaller than 50 under the effects of active tectonics or strong lithologic control.The values of this index are divided into three categories.1: (Aƒ < 35 or Aƒ > 63) 2: (57 < Aƒ < 65) or (35 < Aƒ < 43) and 3: (43 < Aƒ < 57), based on [11].
Among the obtained values (Table 4), a map has prepared that it shows Asymmetry factor of study area (Figure 9).
Basin shape index (Bs): Relatively young drainage basins in active tectonic areas tend to be more elongated than their normal shape to the topographic slope of a mountain.The elongated shape tends to evolve into a more circular shape [4].The horizontal projection of the basin shape may be described by the basin shape index or the elongation ratio, Bs [7].The calculation formula is:

Bs Bl Bw =
where Bl is the length of the basin measured from the headwater to the mount, and Bw is basin width in the widest point of the basin.
To calculate this index in the area, Bl and Bw are obtained using the sub-basins (Table 5) and the master river maps then the values are divided into 3 classes.1: (Bs > 4) 2: (3 < Bs < 4) 3: (Bs < 3), based on [11].According to Figure 10 the maximum value belongs to sub-basin No. 4 (Class 3).
Hypsometric integral index (Hi): The hypsometric integral (Hi) describes the relative distribution of elevation in a given area of a landscape particularly a drainage basin.The index is defined as the relative area below the hypsometric curve and it is an important indicator for topographic maturity.H max , H min and H ave are calculated on DEM.This index is calculated to all sub-basins in the area.The hypsometric integral reveals the maturity stages of topography that can, indirectly, be an indicator of active tectonics.
In general, high values of the hypsometric integral are convex, and these values are generally >0.5.Intermediate values tend to be more concave-convex or straight, and generally have values between 0.4 and 0.5.Finally, lower values (<0.4) tend to have concave shapes [11].We can consider class 1 for Hi > 0.5, class 2 for Hi between 0.4 and 0.5 and class 3 for Hi < 0.4 and so, sub-basin No.18 shows younger topography (Table 6, Figure 11).

Results and Discussion
The average of the six measured geomorphic indices (Vƒ, Smf, SL, Af, Bs and Hi) was used to evaluate the dis-   tribution of relative tectonic activity.Through averaging these six indices (Table 7), we obtain one index that is known index of active tectonics (Iat).The values of the index were divided into four classes to define the degree of active tectonics: 1-very high (1 < Iat < 1.5), 2-high (1.5 < Iat < 2), 3-moderate (2 < Iat < 2.5), 4-low (2.5 < Iat) [11].Thus, there are low relative tectonic activities in sub-basin No. 3, 4, 15, 16, 17, 19 & 22 and moderate relative tectonic activities in the other sub-basins (Figure 12).Also, based on [25], this area is a moderate seismic risk zone with following seismicity parameter: b = 0.82, Mmax = 7.1.Focal mechanisms of several earthquakes are reversed and thrusted such as Changureh (Ms = 6.4, 2002) This area is struck by low to moderate earthquakes with low frequency, medium repeat time and down to 10 Km focal depth.Intensity of earthquakes is in high levels in which there are cold igneous rocks.Sometimes, focal depths exceed to 70 Km that it is indicator for initial stages of thick-skinned tectonics.The most serious seismic hazards in Kangavar area, are settlement in Qorveh plainand surface faulting.

Conclusions
The calculated geomorphic indices are suitable for assessment of tectonic activity of the study area.The six geomorphic indices; stream-gradient index (Sl), valley floor width-valley height ratio (Vƒ) and mountain-front  sinuosity (Smf), drainage basin asymmetry (Aƒ), hypsometric integral (Hi) and drainage basin shape (Bs) have calculated in Kangavararea.
Therefore, firstly the area was divided into 24 sub-basins and for each one, indices were calculated, then all of the indices were divided into relative tectonic activity classes.Afterwards, the six measured indices for each sub-basin were compounded and a unit index obtained as index of active tectonics (Iat).According to this index, there were low and moderate relative tectonic activities levels.
Low relative tectonic activities level has been found in sub-basin No.

Figure 1 .
Figure 1.Physiographic-tectonic zoning map of Iran's sedimentary basins Iran modified from [1].The study area is shown in the black rectangle.

Figure 2 .
Figure 2. Digital Elevation model of the Kangavar area.

Figure 3 .
Figure 3. Shaded Relief of the Kangavar area for identification of drainage pattern based on digital elevation model.

Figure 4 .
Figure 4. Determination of sub-basins in the Kangavar area based on Digital Elevation model (DEM).

Figure 5 .
Figure 5. Stream length-gradient values along the master streams.

Figure 6 .
Figure 6.Classification of sub-basins based on stream length-gradient index.

Figure 7 .
Figure 7. Classification map for the valley floor width to valley height ratio.

Figure 8 .
Figure 8. Classification map for Mountain-front sinuosity index.

Figure 9 .
Figure 9. Classification map for Asymmetry factor index.

Figure 11 .
Figure 11.The hypsometric integral classification map for study area.

Figure 12 .
Figure 12.Relative tectonic activity classification and fault map of study area.

Table 1 .
Values of stream length-gradient index.

Table 2 .
Values of Vf index.

Table 3 .
Values of Smf index.

Table 4 .
Values of Af index.

Table 5 .
Values of Bs index.

Table 6 .
Values of Hi index.