Change the dip of the river channel that is a factor in the change of the dip of water level is under the effect of rocks type and active tectonics [2] . Stream- Length gradient index (SL) is an indication of compromise between erosive processes such as river streams and tectonics activities [13] [14] and [15] . This index is defined as follows [14] :

where, l is the length of the river channel form the upstream to the point that the SL index (Stream-Length gradient) is calculated and is the dip of that section of the river channel. This index is under the influence of uplifting in the area. Therefore, motional components with horizontal displacements like strike- slip faults don’t have a strong effect on this index.

The calculated values of this index in the studied area were estimated by digital elevation model and GIS system that their values are shown in Figure 3. The thresholds of this index shows that the effected channels by tectonics movements have calculated values more than 500 meters; and values less than 300 meters represents those basins that are more affected by erosive processes of river streams. In order to find the SL index (Stream-Length gradient) anomaly that depends on the rock strength, at first a simple map of lithological units was

prepared from geology map of northwest of the Iran, then various levels of relative rock strength based on the rock type and field observations was defined and suggested as a map of lithological units with different relative strength (Figure 4). Different levels of rocks strength are defined as follows:

1. Very low strength: Marl, silt, Quaternary sediments and young alluvial terraces

2. Low strength: gypsum marl, sandy Marland siltstone

3. Moderate strength: conglomerate, sandstone and molasse deposits

4. High strength: pyroclastic rocks and volcanic ash

5. Very high strength: ignimbrites, basalts, andesites, tracky andesite and volcanic rocks

After preparing the map of relative rocks strength, SL values plotted on this map (Figure 4) and their relationship with rock strength was analyzed. SL index was analyzed based on relative rock strength in different basins and its anomalies were found as follows.

1) In Western AjiChay River, the maximum value of SL index is in the northeast of the Tabriz city and located in Marl sediments. With the regard to soft bed of this river, high valued of SL index can be associated with the activities of the North Tabriz Fault; the graph of SL values along the river longitudinal profile shows that the highest SL index value pertain to the location of Tabriz fault (Figure 6).

2) OujanChay River with a length of 76 kilometers originates from the Sahand mountain, has anomaly in two points; the range of SL index value of this river is between 127 and 629. Tabriz fault nearly intersect this river in Bostanabad city perpendicularly (Figure 5), from this point towards southeast, river bed is composed of the pyroclastic and volcanic ash and SL index value is increased when the river passes the dacite and andesite domes, in which, this value of SL index is explained by high value of river bedrock strength in this area.

3) The values of SL index along the AjiChay River are mainly low and less than 300. The riverbed of Eastern AjiChay is composed of soft marl and siltstone sediments that their low SL index values reflect low tectonic activity of this basin. But in upstream of the river and in northeastern of the Bozghush mountain range, values of SL index suggested a high anomaly (Figure 5 & Figure 6). With the regard to the field observation of riverbed composition that is young alluvial terraces, the high value of index in this area could be in association to uplifting these alluvial sediments as a result of reverse faults activities in the north of Bozghush mountain.

4) SL index value along ShahrChay River differs from 25 to 1024. Roughly, the northern half section of the river has SL index value less than 300 that with the regard to the high relative bedrock strength of this section, unlike what is expected the index value of this area is less than 300. The low value of this index

necessarily is not a result of domination of erosive forces over tectonics ones, because in this area ShahrChay River is parallel to Tabriz fault and in somewhere riverbed located on the strike of the Tabriz fault (Figure 5).

In lower half of the ShahrChay River, the high value of SL index to some extend could be a result of very high strength of riverbed rocks and to somewhat a result of tectonics uplift, because in spite of the fact that bedrock of the end section of the river composed of very low strength sediments, SL index value is greater than 500 that reflects the active tectonics of this area (Figure 5).

5) SL index value of the GharanghuChay River differs in its two halves like the SharhChay. From the mid-river towards its upstream, SL index value is low and in the downstream of it SL value is high (Figure 5 & Figure 6). In the downstream

of the river SL values reach 2965 which is associated with riverbed lithology of this section of the river that passes the relative high strength rocks (including ignimbrites, basalt, andesite and trackyandesite), however, in the end section of the river in spite of sediments with very low strength, SL index is greater than 500 that reflects high active tectonics in this section of the river, consequently, both factors of tectonics and high strength of the lithology caused the index value approaches up to nearly 3000 (Figure 6).

6) In Aydougmush river, SL index value differs from 86 at the upstream to 8041 in the downstream section of the river. A severe anomaly of SL index is seen along the river in two points (Figure 6). The first anomaly is seen where the SL value reached 1947 and bedrock of the river is formed by conglomerate and molasse sediments with moderate strength, therefore, high value of index in this area could be explained by high active tectonics. In this part of basin, old folds of marl sediments and Miocene sandstone are refolded by recent tectonics and created fantastic forms. The second anomaly is seen in the end section of the river where SL value reached 8041 that bedrock is composed of ignimbrites and acidic tuffs and due to very high strength of these sediments, this value of SL index is not unexpected.

Hypsometric integral (Hi) shows height distribution in a specific area. Hypsometric curve involves drawing height ratio versus area ratio and calculating the area under the curve. Hypsometric integral is independent of the size and height of the basin [16] . The beneficial use of hypsometric curve is that the drainage basins with different sizes can be compared with each other [2] [17] [18] . High values of this index suggest the active and young areas and low values show the old areas that the erosive processes are dominant and less affected by the active tectonics of the region [12] . In the studied region, this index was obtained by plotting the curve by digital elevation model and calculating the area under the curve which represents the value of hypsometric integral index. The values of Hypsometric integral (Hi) are classified into three categories: Hi < 0.4, 0.4 < Hi < 0.5 and Hi > 0.5. With the exception of Aydogmush basin, all other basins have a hypsometric integral index less than 0.4 that could be due to the effects of sediments compaction with low strength and their faster erosion against erosive agents in the mentioned region (Figure 7).

The asymmetric factor (Af) is a way to evaluate the existence of tectonic tilting at

the scale of a drainage basin. The method may be applied over a relatively large area [2] [19] . This index is defined as follows:

where, Ar is the area of basin in right-hand of the main channel (facing downstream) and At is the total area of the drainage basin. Numerical values of Asymmetry factor (Af) near 50, indicates the symmetry of basin, and thus the lack of tilting as a result of uplift, but numerical values more or less than 50 indicates a tilted basin that can be a result of active tectonics or lithologic structural control.

The values of this index are measured for basins of the region that their results are shown in Table 1. Index values are classified into three categories: Af-50 > 15, 15 > Af-50 > 7 and Af-50 < 7. Obtained values reflect that most of the basins are tilted towards the west that can be attributed to tectonics structures. In some sections of AjiChay basin, immigration of river bed can be observed due to basin tilting in silts and marl bedrocks (Figure 8).

Relatively young drainage basins tend to be elongated in shape. With continued evolution or less active tectonic processes, the elongated shape tends to evolve to

a circular shape [20] . Horizontal projection of basin shape may be described by the elongation ratio. The Index of drainage basin shape (Bs) [21] [22] , expressed by the equation:

where, Bl as the basin length is the distance between the lowest basin height and farthest point of it and Bw as a basin width is measured in the widest section of basin. High value of this index represents elongated basins that are more seen in younger area of basin and more associated with frontal mountain fronts due to fast uplifting of relevant structures [23] . The values of index divided into three classifications: Bs > 4, 4 > Bs > 3; and <3. Values of the Bs index over the study area, are calculated (Table 2).

This ratio represents the relation between tectonic activity and valley formation that is defined as follows:

Vfw is the width of the valley floor; Eld is the elevation of the left side of the valley; Erd is the elevation on the right side; and Esc is the average elevation of the valley floor. V shape and narrow valleys are associated with active mountain front and represent fast uplift and riverbed erosion occurred along the valley path. With the decrease of tectonics activities, erosive agents leading to the more increase of valley floor width and U shaped valleys are formed [2] . Silva et al. [4] believed that this index should be measured in a specific distance of mountain front (1 - 1/5 km). In the studied region, index values for main valleys that intersect faults front are calculated. Low value of Vf (Ratio of valley floor width to valley height) shows more basin uplift [2] . The Vf index values are classified into three categories: Vf ≤ 0.5; 1 > Vf > 0.5; and Vf > 1.

The lowest value of Vf in the region is found in western AjiChay basin at F point (Figure 9). According to the bedrock lithology of this point that are composed of sandstones and Miocene red marls, low value of this index reflects high tectonic activity that is associated with active Tabriz fault.

Calculation of this index is a method for evaluating a river inside a basin and intensity of asymmetry change in different part of the valley.

where Da is the distance basin midline to active meander belt (main active stream) and Dd is the distance from the basin midline to the basin divider [23] . When there is no change in the basin asymmetry, transverse topographic symmetry factor (T) is close to zero; as the asymmetry increases, T values approach 1. In perfectly symmetric basin T index is equal to. The index values are classified into three classes: class 1 (T ≥ 0.4), class 2 (0.4 < T < 0.2) and class 3 (T ≤ 0.2). Calculated values for this index are in good consistency with values of AF index, in other words, it represent tilting and symmetry of transverse topography of the rivers in most basins of the region. Obtained values of symmetry of transverse topography are shown in Table 3.

The sinuosity of mountain front index (Smf) is defined as below [16] [19] :

where, Lmf is the length of the mountain front along foot of the mountain where

a change in slope from the mountain to the piedmont occurs; and Ls is the straight line length of mountain front. The sinuosity index of the mountain front reflects the balance between the tendency of river to create an irregular mountain front and vertical active tectonics that tends to create direct and prominent front [20] . Therefore, tectonics activities tend to create a smooth and direct mountain front that is coincided with boundary of an active fault, whereas erosive processes make the mountain front indirect. Sinuosity of mountain front index (Smf) is divided into the three classes [12] : class 1 (Smf ≤ 1.1), class 2 (1.1 ≤ Smf < 1.5) and class 3 (1.5 ≤ Smf). In the studied area, calculation of the sinuosity of mountain front index was evaluated by topographic map with the scale of 1:50000 in GIS system. Mountain front segments that has been measured shown in Figure 10 and also obtained results are shown in Table 4.

In present study, relative tectonic activity of a region has been evaluated by use of geomorphic variables. Relative tectonic activity index (Iat) is obtained by average of the different classes of geomorphic indices, which is used for evaluation of relative active tectonics in a desired region that has four different classes [12] .

Where, class 1 is a region with very high activity that 1 < Iat ≤ 1.5, class 2 has high activity with 1.5 < Iat ≤ 2, class 3 has a moderate activity with range of 2 < Iat ≤ 2.5, and finally class 4 is a region with low tectonic with values of the Iat index greater than or equal to 2.5 (2.5 ≤ Iat). Relative active tectonics classes (Iat) are acquired by collecting all seven geomorphologic indexes of the studied area. Based on the obtained values of each class of Geomorphic indices for each basin and taking the average of them (S/n), the studied area is divided into three tectonic zones. The first group shows an area with high active tectonics with values of 1.5 < S/n ≤ 2, the second group with a moderate active tectonics with values of 2 < S/n ≤ 2.5 and the third group an area with low active tectonics with values of 2.5 ≤ S/n (Table 5).

AHP that stands for Analytical Hierarchy Process is one of most known multipurpose decision making techniques, which is based on binary comparisons and decision maker makes the decision by providing hierarchical tree, and then conducts a series of binary comparisons. These comparisons determine the weight of each factor versus other competing alternatives in decision making. Finally, the logic of analytical hierarchy process emerges resulting matrixes of binary comparisons with each other in such a manner that optimum decision could be made [24] . It seem that one could determine weight and priority of each abovementioned indexes by examining affluent factors on each index and by using data and results of indexes’ estimation, in order to, instead of relying

merely on average of each index in Iat method, weight and significance of each index compared to other indexes be the basis of active tectonics of studied region. In the determination of Iat index, index weighting have not been performed and all indexes have an equal significance, therefore, regarding to the fact that some indexes are directly and some other indirectly associated with active tectonics of the region, it seems reasonable that some indexes has more weight than the other indexes. Consequently, with the purpose of analysis this sort of system, the resulted maps of classified indexes were prepared in the form of valued and raster layers in GIS. Then, with the aim of identifying priorities and integrating resulted maps, Geomorphic indices were prioritized using decision-making rules, so that by maintaining the rank of these indexes, all of them could be integrated and finally impact factors were applied by the use of Expert Choice and ArcGIS software’s and output raster was obtained. Applied coefficients for the indexes were determined as follows: Hi = 1, SL = 1.5, BS = 0.9, Smf = 1.4, Vf = 1.3, Af = 1.1 and T = 1.2. The overlapped final layer of relative active tectonics has been prepared by applying mentioned coefficients that according to which only Oujan Chay and Aydoghmush basins lie in the class 1 with high relative active tectonics (Figure 11 & Table 1). With regard to earthquake epicenter maps of recent year and 110 past years, the most stress focus is along the Tabriz fault and studied region lie in the pre-seismic stage (Figure 11).

Based on previous work on the salt and muddiapirism [25] - [41] and neotectonicregimein Iran [42] - [51] , Zagros in south Iran is the most active zone [52] - [93] . Then, Alborz [94] - [151] and Central Iran [152] - [169] have been situated in the next orders. Thus, the study areas have not been affected by strong regional shortening. It means that, there is disperse seismicity along major faults such as the Tabriz, Daman Jan and Benaravan faults (Figure 11).