عنوان مقاله [English]
Earth is a dynamic system that changes and evolutions are among its adherent characteristics (Ramesht & et al., 2002: 30). Almost during of a few recent thousand years, any regions on the earth’s surface are affected byneo-tectonic activities. In fact, today neo-tectonic is changing the earth's surface (Wallace, 1977). Neo-tectonic activity deals with studying the active processes and effective dynamic that are building the earth and landscapes (Keller and Pinnter, 2002: 80). Therefore, using geomorphologic indices of neotectonic activities, studying tectonic activities will be accomplish within a short time and
also are usable for more accurate researches in the future. Geomorphologic indicesareuseful tools for assessment of neo-tectonic activities, because of using these indices, identify the areas, with fast or slow neo-tectonic activities in the past (Ramirez and Herrera, 1998: 317). These indicators are used for studying the active tectonics particularly.Geomorphologic indicators in the study of neo-tectonic activities was used by Bull and McFadden (1977) for first time and followed by other researchers such as Rockwell et al (1985); Wells et al.(1988); Silva et al ( 2003); Guarnieri& Pirrotta (2008). In Iran , Khayam and Mokhtari (2003); Madady & et al(2003); Vahdati Daneshmand & et al (2005); Gorabi and Nohegar (2006); Yamani et al (2007); Maghsodi and Kamrani (2007); Karami (2008); Bayati Khatibi (2008); Rameshat et al (2008); Roustaei et al (2008); Seif and Khosravi (2009) used these indices for determining the neo-tectonic activities. Major or minor active fault systems, several alluvial terraces in the margin of Jajroud River and its sub- branches, waterfalls, widening or narrowing bed channels, changing in flood channel and longitude and width of river profiles indicate that neo-tectonic is active in these regions. Thus, due to the importance of fully evaluating the tectonic activities, especially the young and contemporary tectonic movements and their hazards such as non equilibrium slopes, the present study was designed to determine the neo-tectonic activities in Jajroud Basin in the NE Tehran province (Iran). Further, has been tried for innovating in the methodology, judge about the neotectonic activities in their case study area based on results of calculating and measuring these indices and geodynamic data.
In order to achieve the goals of this research, documentary information, 1:50000 topographic maps (5 sheets) and 1:100000 geological map of Tehran province (in order to drawing the region's fault layers), Palsar radar images (for producing of DEM) and geodynamics data of permanent stations of Jajroud basin have been the important research tools. For the analysis of neo-tectonic activities in the case study area, have been used such geomorphologic indices as Drainage Basin Asymmetry Factor, the Ratio of Valley-Floor width to Valley Height, Basin Shape Factor, Transverse Topographic Symmetric, Hypsometric Integral, River Sinuosity IndexandStream Length-Gradient index. Arc GIS software was used to digitize the topographic mapsand drawing of river networks for calculating these indices, also in order to measure the Stream Length- Gradient Index, have been draw the longitudinal Jajroud river profile using DEM (derived from the Pulsar radar satellite images). GPS observations of the permanent station of Jajroud basin in distinctive time span (from 2006 until 2010) were analyzed by the GAMIT- GLOBK software on daily basis. Then the analyzed times series for the E, N, H elements were drawn. The Basis method of this research is the analysis subsequent of geomorphologic indices and confirmation of them by the analysis of time series obtained from the GPS observations data of the permanent station in the case study catchment.
Results of the calculation of geomorphologic indices Drainage basin asymmetry factor: Based on the results of drainage basin measurements, in the equation; Af=100(212.73/696.830=29.11, we can say that the drainage basin is of active neotectonic movements and the east side of the basin is more active than its west side. Lengths of the runoffs in the east side are longer than of in the west side, which is the result of the tilting towards the west of the basin (western bank of the river).
Ratio of valley–floor width to the valley height: 15 longitudinal cross-sections and calculated the VF indices using 1:50000 topographic maps for each cross-section have been draw. Regarding the mean values obtained in the upper, middle and lower sections of river, was concluded that tectonic activities with more than activity in the apex of the basin compare in lower parts and outlet .Uplifts are more in the upper parts and the valleys are narrower, showing that Mosha-Fasham Fault is active in these parts of the basin.
Basin shape factor: the extended shape and high value of the basin shape factor that is about 1/22 show that this basin is very active in terms of neo-tectonic activities.
Transverse topographic symmetric: 8 cross-sections on the basin have been determined and were calculated their values, as 0.33 on average. This value shows the activation of neo- tectonic in the basin and river is eroding.
Hypsometric integral: Hypsometric integral of the basin shows that it is in its young stage. The curves in non-dimensional curving show the domination of neotectonic activities over erosion activities in the study catchment basin, meanwhile the concave in non-dimensional curving shows that erosion activities are active in the basin.
River sinuosity index: The value of this index is S= 6.4/3.4 = 1.35.
Stream length- gradient index: For evaluation of this index in the basin area, have been used a 100 m DEM and were calculated its value in 100 m distances. The obtained value was 0.16 to 48.63. The maximum values were for the 1600 and 1800 m, and the lowest value was for the 3400 m high. By referring the geologic map of the basin, were found that the longitudinal gradient of the river has a close relation to the lithologic situations of the basin and its faults activities.
Behavioral analysis of the permanent station of Garmabdar's GPS records: In this research, were considered and analyzed the GPS records of Garmabdar geodynamic station in Jajroud basin based on 5 years records (2006 to 2010) in order to determine earth crust deformations, and the main faults of the region movements and also to evaluate the results obtained from the indices calculations. All of the recorded data of the GPS station were processed based on the daily records and the time series were calculated for the three trajectories of E (east-west), N (north – south) and H (for height). The calculations showed that the speed of changes in relation to the Eurasia plate in Garmabdar station for the N-S trajectory is 10.86 mm/ year and0.61 mm /year for the E-W trajectory.
According to these changes, it was concluded that the direction of changes in the basin is towards the NE, which can be related to the seduction of oceanic crust of the Caspian sea beneath the north of Iran (Elbruz), which have a considerable role in the crustal movements of the earth and motivation of the main faults of the region .These activities probe tectonic active movements of the study area, correspondingly.
The geomorphologic indicators are very important in the assessment of neo-tectonic activities, since using these indicators, were easily identified the areas that have experienced fast or slow tectonic activities. The Jajroud basin with two major fault systems, including Masha-Fasham and North of Tehran faults, is one of these active regions. All of the major or minor active fault systems, several alluvial terraces in the margins of Jajroud River and its sub- branches, waterfalls, widening or narrowing of the bed channel, changing in flood channel and in the longitude and widthwise river profiles show that the region is active one. The results of shape analysis in this research also showed that the region is an active area for neotectonic movements, but values of activities are not the same in all parts of it; the upper parts are more active than the other parts (table 1). On the other hand, sinuous changes in the height direction, and linear changes in both the E-W and N-S directions in the time series resulted from the GPS station data in Garmabdar show the northward changes in the study area, and approve faults activities and active tectonic movements in the region, too.
Table 1: Results of the assessment of geomorphic indices of active tectonic in Jajoud catchment basin (Source: Authors)
Drainage basin asymmetry factor
Ratio of valley – floor width to valley height
Basin shape factor
Transverse topographic symmetric
River sinuosity index
Stream length- gradient index