Geomorphic indices are useful tools for studying relative active tectonics of a specific area. In this study, the relative active tectonics of Bozgoush region (NW of Iran) has been investigated based on Geomorphic indices. The studied indexes include: the stream length-gradient (SL), hypsometric integral (Hi), the ratio of valley floor width to valley height (Vf), the shape of the drainage basin (Bs), the sinuosity of mountain front (Smf), asymmetric factor of drainage basin (Af) and transverse topographic symmetry factor (T). In the present study, gathered data from various morphometric indexes of six basins are aggregated, and their obtained result is provided as relative active tectonics of the region or Iat index that shows a proper illustration of the relative active tectonics of the mentioned region. In order to develop a correct analysis of the mentioned area, the AHP (analytic hierarchy process) model with a studied weight, the final overlapped layer of relative tectonics is prepared with applying coefficients. With the comprehensive field studies, evidences like deep valleys, river bed immigration, landslides, sudden change in river cycles and surfaces of faults were found that are in good consistence with obtained data of relative active tectonics of the region. After measuring these indexes, it was found that Aydoghmush and OujanChay basins have a high relative active tectonics. With regard to the obtained results of present study, it seems that Tabriz fault has the most seismic and motional potential in northern basins of the region. In addition, in Aydoghmush basin, in southern part of the region, Qeynarjehchartagh fault has a high active tectonics that according to the estimated values has been identified as an active young structure in the region.
The studied region is located in the north western of Iran and as a mountain range with east-west direction with an approximate length of 90 km and width of 30 km. According to the global model of plate tectonics, active tectonics of Iran is due to convergence of Eurasia and Arabia continental crusts. This convergence makes the movement of the Arabian shield to the north side of Eurasia shield, and as a result, leads to compression of the Iran plateau between the two crusts. Studied region is divided into 6 basins that are interrupted by extended branches of Tabriz fault; thereby their structural position and tectonics regime will be determined in Quaternary period. Southeast part of Tabriz fault passes from the northern and southern slopes of Bozghoush Mountain. In this region the trend of faults is east-west and northwest-southeast that their most important faults are northern and southern faults of this mountain which lead to subsidence of both sides of Bozghoush mountain from Sarab plain in north and Myaneh plain in south and uplifting of its central part. The mechanism of these faults has determined strike-slip with reverse dip-slip component [
Geomorphologic indexes are useful to identify the specific characteristics of an area, for example, to determine the level of active tectonics. These indexes are useful for identification of areas that undergo rapid tectonics deformation. Each of these indexes provides a relative classification of the intensity of active tectonics. For a specific area, using the several indexes rather than an index provides more meaningful results [
In this study, many morphometric parameters have been evaluated and by determination of I at index and conducting analytic hierarchy process, relative tectonics of the region has been examined. To achieve this goal, the indexes were measured and finally by averaging all of them relative active tectonics (Iat) of each basin has been determined. According to the field studies in the region, impact factor of each index was calculated with Expert Choice software based on its effect on the active tectonics of the region; and final result of the integrated AHP model with raster data has been provided for determining the relative active tectonics of each basin in the mentioned region.
The studied area is located in northwest of Iran and south of the Sabalan volcanic rocks at coordinates of 45˚37' - 48˚00' east longitude and 36˚30' - 38˚30' north latitude (
In western Alborz, oldest rocks are metamorphic rocks around Zanjan which belongs to Precambrian that are covered by Kahar formation with a little metamorphic rocks of late Precambrian. During the Eocene under-marine volcanic
activities in Azerbaijan (Western Alborz) had been dominated so that the intensity of these activities are increased to the West. During the Pyrenees orogeny and alongside extensive magmatic activity that mainly are made of granite and syenite, the produced magma had been injected into the green tuffite [
According to [
Geomorphology is a powerful tool for examining relative tectonics. Description of different forms and topography of the earth surfaces is defined with relations of size, height (maximum, minimum and average) and their dips. In this study, all related indexes with the change of the river channel and watershed basins have been studied and relative tectonics of the region has been evaluated by the use of a single index, i.e. Iat index, which is the result of estimating 7 geomorphic features [
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 [
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
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
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 (
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 (
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 (
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 (
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 (
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 (
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 (
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 (
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 (
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 (
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 [
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 [
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
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
Basin | Ar(sq km) | At(sq km) | |Af-50| | Class |
---|---|---|---|---|
Western Ajichay | 2332.3 | 4632.8 | 0.34 | 3 |
Ojanchay | 717.19 | 1047.3 | 18.48 | 1 |
Eastern Ajichay | 2571.2 | 3915.5 | 15.67 | 1 |
Shahrchay | 527.05 | 2204.7 | 26.09 | 1 |
Gharanghuchay | 2372.5 | 3605.3 | 15.81 | 1 |
Aydoghmush | 646.04 | 1826.2 | 14.62 | 2 |
a circular shape [
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 [
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 [
The lowest value of Vf in the region is found in western AjiChay basin at F point (
Basin | Bl(m) | Bw(m) | Bs | Tectonic class |
---|---|---|---|---|
Ojanchay | 57844 | 31989 | 1.81 | 3 |
Western Ajichay | 130160 | 80932 | 1.61 | 3 |
Eastern Ajichay | 90689 | 63602 | 1.43 | 3 |
Shahrchay | 80660 | 49562 | 1.63 | 3 |
Gharanghochay | 115150 | 69822 | 1.65 | 3 |
Aydoghmosh | 95445 | 34828 | 2.74 | 3 |
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 [
The sinuosity of mountain front index (Smf) is defined as below [
where, Lmf is the length of the mountain front along foot of the mountain where
Basin | Da(m) | Dd(m) | T(m) | Tave(m) | Tectonic class |
---|---|---|---|---|---|
Western Ajichay | 14761 | 22575 | 0.65 | 0.5 | 1 (High Activity) |
13720 | 27662 | 0.5 | |||
11195 | 28897 | 0.39 | |||
4668 | 10099 | 0.46 | |||
Ojanchay | 986 | 2746 | 0.36 | 0.19 | 3 (Low Activity) |
712 | 6680 | 0.11 | |||
1088 | 10515 | 0.1 | |||
1729 | 8510 | 0.2 | |||
Eastern Ajichay | 5673 | 9745 | 0.58 | 0.29 | 2 (Moderate Activity) |
5064 | 11826 | 0.43 | |||
1673 | 20402 | 0.08 | |||
1768 | 28894 | 0.06 | |||
Shahrchay | 13220 | 16567 | 0.8 | 0.65 | 1 (High Activity) |
12875 | 17906 | 0.72 | |||
9658 | 16424 | 0.59 | |||
3782 | 7621 | 0.5 | |||
Gharanghuchay | 1937 | 15656 | 0.12 | 0.47 | 1 (High Activity) |
13242 | 33491 | 0.4 | |||
13642 | 19591 | 0.7 | |||
7468 | 11051 | 0.68 | |||
Aydoghmush | 5722 | 8069 | 0.71 | 0.65 | 1 (High Activity) |
5278 | 10061 | 0.52 | |||
4654 | 10361 | 0.45 | |||
9993 | 10877 | 0.92 |
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 [
Basin | Segment | Lmf(m) | Ls(m) | Smf(m) | Tectonic class |
---|---|---|---|---|---|
Western Ajichay | A | 2263 | 1797 | 1.26 | 3 (Low Activity) |
B | 2862 | 1048 | 2.73 | ||
C | 8955 | 6794 | 1.32 | ||
D | 4208 | 3028 | 1.39 | ||
Ojanchay | E | 1714 | 1632 | 1.05 | 2 (Moderate Activity) |
F | 3152 | 2855 | 1.1 | ||
G | 9581 | 6425 | 1.49 | ||
Shahrchay | H | 3461 | 1713 | 2.02 | 3 (Low Activity) |
I | 4003 | 3486 | 1.15 | ||
Eastern Ajichay | J | 2936 | 2406 | 1.22 | 3 (Low Activity) |
K | 4548 | 2633 | 1.73 | ||
L | 9845 | 3980 | 2.47 | ||
M | 944 | 791 | 1.19 | ||
N | 29440 | 13533 | 2.18 | ||
O | 10410 | 5553 | 1.87 | ||
P | 5179 | 2817 | 1.84 | ||
Gharanghochay | Q | 8814 | 6182 | 1.43 | 3 (Low Activity) |
R | 3494 | 2104 | 1.66 |
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 [
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 (
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 [
Basin | Class of: | S/n | Iat class | Assessment | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Bs | AF | T | VF | Hi | SL | Smf | ||||
Ojanchay | 3 | 1 | 3 | - | 3 | 2 | 2 | 2.33 | 2 | Moderate |
Western Ajichay | 3 | 3 | 1 | 3 | 3 | 2 | 3 | 2.57 | 3 | Low |
Eastern Ajichay | 3 | 1 | 2 | - | 3 | 3 | 3 | 2.5 | 3 | Low |
Shahrchay | 3 | 1 | 1 | 3 | 3 | 2 | 3 | 2.29 | 2 | Moderate |
Gharanghochay | 3 | 1 | 1 | 3 | 3 | 1 | 3 | 2.14 | 2 | Moderate |
Aydoghmush | 3 | 2 | 1 | - | 2 | 1 | - | 1.8 | 1 | High |
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 (
Based on previous work on the salt and muddiapirism [
Geomorphic indices provide useful tools for studying intensity of tectonic activity. Geomorphologic topography, indexes calculation and classes of the relative tectonic activity have a good consistency with the significant structures of the region. After studying the geomorphologic indexes and their calculation in the region, it was found that a district with the area of 2895.7 km2 has been identified as high active tectonics (class 1), an area of 5808.4 km2 as moderate (class 2) and finally an area of 9385.6 km2 (class 3) as low active tectonics. A comparison of field observations of active tectonics like deep valleys, river bed immigration, landslides, sudden change in river cycles and surfaces of faults clearly coincide with the values and classes of relative tectonic activity.
By estimating this index, it was found that low active tectonics (class 3) mainly occurs in the upper part of the region’s basins, while moderate and high active tectonics (classes 1, 2) occur in the middle and lower parts of the basins.
Channels displacing is the best way to detect subsurface structures and is also one of the most important morphological evidences. In the case of OujanChay and Aydoghmush River, one could observe the effect of tectonics on river displacement in the end section of the river. In this section, the existence of various faults like Tabriz caused deep valleys and meandering of the river path. River path displacement is observed in several parts of the basin that the most path deviation is more evident at the end section of the river.
Alluvial terraces of studied region are tectonics terraces that have a multilevel and one could found tilting and fault-derived deformation in them like OujanChay basin that as a result of Tabriz fault with NW-SE direction leads to river terraces with high active tectonics in this basin. Areas with relative high active tectonics mainly located in locations that rocky sediments have many deep fractures and create significant folding in these areas. The existence of narrow valleys was confirmed by field observations of faults and tectonics features that is an evidence of active tectonics and uplifting in this region. Active structures were identified by estimating SL anomaly index such as Qeynarjeh Chartagh reverse fault in the south part of Aydogmush basin that based on available evidences shows a high active tectonics.
This work has funded by department of geology, Islamic Azad University, Science and Research branch, Tehran, Iran. Also, Special thanks to vice-president for research in Science and Research branch, Tehran.
Eynoddin, E.H., Solgi, A., Pourkermani, M., Matkan, A. and Arian, M. (2017) Assessment of Relative Active Tectonics in the Bozgoush Basin (SW of Caspian Sea). Open Journal of Marine Science, 7, 211-237. https://doi.org/10.4236/ojms.2017.72016