جستجوی مقالات مرتبط با کلیدواژه « حوضه زهکشی » در نشریات گروه « زمین شناسی »

The studied area is located in edge of southern Central Alborz between important faults of the north Tehran, Mosha, Taleghan, Ipak and Eshtehard and includes significant earthquakes. In this research, the tectonic activity rate of the region has been evaluated using geomorphological indicators.

In order to assess the relative tectonic activity through the study area, sub-basins and stream network were extracted by using Arc Hydro Tools software (an extension of Arc GIS software, ESRI) based on the DEM and in turn, 23 sub-basins have been resulted. The active tectonic 5 geomorphologic indices were used as follow: Stream length–gradient index (SL), Asymmetric factor (Af), hierarchical anomaly index (Δa), concavity index and normalized steepness index.Stream Length–Gradient Index (SL): The SL index indicates an equation between erosive processing as streams and rivers flow and active tectonics. The SL is defined by Eq. (1) SL= (∆H/∆Lr) Lsc.    (1)Where ΔH is change in altitude, ΔLr is the length of a reach, and Lsc is the horizontal length from the watershed divide to midpoint of the reach. The SL index can be used to evaluate relative tectonic activity.  The quantities of the SL index were computed along the streamsfor all sub-basins. Asymmetric Factor (Af): 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. Af is defined by Equation (2).Af= 100(Ar/At) (2) Where Ar is the area of the basin to the right (facing downstream) of the trunk stream and at is the total area of the drainage basin. If the value of this factor is close to 50, the basin has a stable condition with little or tilting; while values above or below 50 may result from basin tilting, resulting from tectonic activity or other geological conditions such as lithological structure.Hierarchical anomaly index (Δa): The hierarchical anomalies index is calculated based on the number of hierarchical anomalies expressed by Equation (3). Hai→j= 2(j-2)−2(i-2)(3) Where i is the primary stream, j is end stream and Hai → j the number of hierarchical anomalies of each stream. The number of hierarchical anomalies has been calculated in Equation (4).Hat= Σ (Hai →j × Nsi →j)  (4) Where (Ns_i → j) is the total number of streams entering the high-level streams. The index Δa is expressed by the following relationship.Δa=Hat/ N1 (5)Where Hat is the number of the hierarchical anomaly and N1 is the number of first-order segments of the streams. Normalized steepness index and Concavity index: Flint’s empirical power-law defines the river profile in a steady-state: S=KSA-θ  (6)Where S, Ks, A, and θ indicate the slope, the steepness index, the drainage area, and stream concavity, respectively. In addition, Ks and θ are directly computed by the regression analysis of the slope-area data. Further, a steady-state landscape demonstrates that erosion, incision, and uplift rates are equal and stable over time. Different empirical studies indicated a direct relationship between the values of the steepness index (Ksn) and the bedrock erosion rate or rock uplift rate in the steady-state of river systems.KS= (E/K)( 1/n)   (7) Where E denotes the uplift of the bedrock and K indicates the erosion coefficient which relies on the climatic and morphotectonics conditions of the area. Finally, n represents a positive exponent which is associated with the predominant erosion process of the area.  In the present study, Ksn was normalized to a reference concavity θref = 0.45 these parameters were implemented to fit a steady-state stream power solution to individual river longitudinal profiles in Matlab (Topotoolbox). The best profile was obtained from the matching of the uplift rate (U = E) or erosion (K) and the predicted rate. Furthermore, normalized steepness and concavity indices were determined using the longitudinal profile of the river.

In this research, 5 morphological indicators related to the river channel and drainage basin were calculated for each basin, and for each of the 23 sub-basins, the rate of tectonic activity was defined for each of the indicators. The indices represent a quantitative approach to differential geomorphic analysis related to erosion and depositional processes which include the river channel and valley morphology as well as tectonically derived features, such as fault scarps. We also evaluated the outputs of the morphometric analyses based on field-based geomorphological observations. Thus, these results are proved to be extremely beneficial to evaluate relative rates of active tectonics of this region. The values of morphological indicators show that the basins with high tectonic activity have a good match with the main faults of the region, such as North Tehran, Mosha, Taleghan and Ipak faults and show high correlation with observed landforms during the field investigations such as the fault gorges, Strath terraces, multiple elevated alluvial terraces and knickpoints.

 In this study, geomorphic indicators were used to investigate the tectonic activity of the region and it was found that the studied region has high tectonic activity along the North Tehran, Mosha, Taleghan, Emamzadeh Davoud and Ipak fault zones.

Geomorphic indices of active tectonics are useful tools to analyze of the active tectonics in a large area. These indices have the advantage of being calculate from the software and remote sensing packages over large area as a reconnaissance tool to identify geomorphic anomalies possibly related to active tectonics. This is particulary valuable in Ajichai basins where relatively little work on active tectonics based on this method was done, so this method is new and useful. Based upon valuable of the stream length-gradient index(SL), drainage basins asymmetry(Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), drainage basins index shape (Bs), and index of mauntain front sinuosity (Smf), we used an overall index (Iat), that is a combination of the other indices that divides the landscape into four classes of relative tectonic activity. The moderate class of Iat is mainly in the class 2 (high), with 1045.46 Km2 ,11.26 percent, class 3 (moderate), with 2940.67 Km2 ,31.67 percent and with 5297.30 Km2 ,57.06 percent occupying of all zone. The stream network asymmetry (T) was also studied using morphometric measures of Transverse Topographic Symmetry. Analysis of the drainage basins and sub-basins in the study area results in a field of T-vectors that defines anomalous zone of the basins asymmetry. A comparison of T index clearly consist with the values and classes of active tectonics indices and the overall Iat index.

Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics in an area. These indices have the advantage of being calculated using ArcGIS and RS (Remote Sensing) packages over large areas as a reconnaissance tool to identify geomorphic anomalies possibly related to active tectonics. This is particularly valuable in Great Karoun River Basin of Zagros, relatively little work on active tectonics based on this method was done. The study area in central Zagros fold- thrust-belt of the southwestern Iran is an area with NW–SE oriented structures provides an ideal location for testing the concept of an index to predict relative tectonic activity on a basis of river system or mountain front. Based upon values of the stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf), overall index as index of relative active tectonic (Iat) was resulted that is a combination of the other indices. This indices are used to divide the landscape into four classes of relative tectonic activity. After measuring indices it is concluded that this part of the Zagros zone has variable rates of active tectonics. Based on corrected Iat values, the study area was divided into three parts: class 1 (very high relative tectonic activity, %24 in area; such as some parts of the east and central zone Main Zagros Reverse Fault and Dezful embayment fault have the most influence); class 2 (high relative tectonic activity, 63% in area; such as most parts of the area in east, west, north and center action of faults are lower than the previous class); class 3(moderate, 10% in area; such as most parts of the area in north and south action of faults are the lowest). Therefore, we dont have class 4 in this area, and 1% of basin is not measured for the indices because it is located in coastal plain of Khuzestan.

Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics. These indices have the advantage of being calculated ArcGIS and Remote Sensing software packages over large areas as a reconnaissance tool to identify possible geomorphic anomalies related to active tectonics. This method is particularly new and useful in areas relatively little work has been carried out on active tectonics based on this method. Based upon the values of stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf), we used an integrated index (Iat) that is a combination of the other indices. This index divides the landscape into four classes of relative tectonic activity. According to the Iat results, sub-basins 4 and 6 show zones of low tectonics activity (Class 4), sub-basins 1, 2, 7, 9, 10, 11, 12, 14, 15 and 19 fit to areas of moderate tectonic activity (Class 3), and high tectonic activity is represented by sub-basins 3, 5, 8, 13, 16, 17 and 18 (Class 2). The Tranverse Topographic Symmetry (T) was also studied using morphometric measurements, which finally gave a plot of T-vectors defining anomalous zones of basin asymmetry. A comparison between T index and map of relative tectonic activity showed a consistent coincidence between areas of higher Iat classes with zones of greater asymmetry.

Structural development, caused by active tectonics leads to deformation of morphologyfeatures. The Mosha-North Tehran fault zone, located in south edge of the Central Alborz consists of significant tectonic structures. Hence, study on morphotectonic signs is a proper method for evaluation of relative tectonic activities in the area. In this research, six main morphometric indices such as stream length-gradient (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height(Vf), drainage basin shape (Bs), and mountain front sinuosity(Smf)were considered. The computations and probes of these indices indicate three classes of relative tectonic activity in the study area from low to high level. Consequently, the drainage basins with high class of tectonic activity mostly coincide with the main faults in south edge of the Central Alborz.

Water causes erosion of different forms in nature and creates diverse landforms on the earth’s surface depending on the manner it appears in nature. Although water is itself a former factor, it flows under the morphological effect of earth’s surface (Ramasht, 2005). The difference of earth’s surface topography and its consequent of water movement on it, cause the formation of sub-basins. In order to recognition of morphology and morphometry of Damavand cone, the region drainage basins must be distinguished. Therefore, in this study 5 drainage basins were identified based on the main criteria including topographic contours with 10 m intervals, drainage system (main and subsidiary rivers, main and subsidiary streams), DEM map of the region, slope map, aspect map and satellite images. Area, perimeter, height classification for classifying the morphological landforms in different levels, hypsometric, drainage density, etc. were then calculated by using the ArcGIS software. The Damavand cone, with a height more than 5,000 m above the sea level, has a very hard-pass slopes. Our purpose in this paper is to identify the effect of drainage basins conditions on the erosion and formation of geomorphological landforms by using of SPOT and ASTER satellite images as well as data analysis o in GIS environment.

The paper presents a method for evaluating relative active tectonics based on geomorphic indices useful in evaluating morphology and topography. Indices used include: stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf). Results from the analysis are accumulated and expressed as an index of relative active tectonics (Iat), which divided into four classes from relatively low to highest tectonic activity. The study area along the south flank of the central Alborz mountain range in north Iran is an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than a single valley or mountain front. The recent investigations show that neotectonism has played a key role in the geomorphic evolution of this part of the Alborz mountain range. Geomorphic indices indicate the presence of differential uplifting in the geological past. The high class values (low tectonic activity) for Iat mainly occur in the south and southeast of the Karaj drainage basin, while the rest of the study area has classes of Iat suggesting moderate to high tectonic activity. Around the Amirkabir Lake, Iat has the highest value. The distribution of the indices defines areas associated with different mountain fronts and estimates of relative rates of tectonic activity. More than half of the study area is classified into classes 2 or 1 of high to very high tectonic activity in terms of the apparent geomorphic response. In different tectonic environments with greater rates of active tectonics, the values of indices would differ as well as their range in value. The stream network asymmetry (T) was also studied using morphometric measures of Transverse Topographic Symmetry. Analysis of the drainage basin and a number of sub-basins in the study area results in a field of T-vectors that defines anomalous zones of the basin asymmetry. We test the hypothesis that areas with great stream migration are associated with indicatives values of Iat.