@2024 Afarand., IRAN

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ISSN: 2538-4384    Geographical Researches 2021;36(2):149-160

Background
The explanation of historical seismic features of a region is dependent on the study of landscapes and landforms as well as the study of vibration detections records.
Previous Studies
Geomorphic indicators were recently used in Iran in western aspects of Sahand Mountain [Samander et al., 2017], Tehran's watershed basins [Najafi et al., 2015], and northern basins of Shahrchai [Karami et al., 2013]. There was a hypothesis in the past that the upper reaches of the Zayanderood were joined to the Karoon river and they flowed into the Persian gulf [Oberlander, 1965]. This hypothesis has been rejected recently and it is shown that mentioned streams were not connected to Karoon and they made a close lake themselves [Ramesht et al., 1999]. There is no significant new-tectonic study in Murghab River which is one of the northern west upper reaches of Zayanderood. Some experts just mentioned that Shazand, Khansar, and Dalan faults cross this region [Nadimi et al., 2012; Safaei et al., 2011]. Nadimi et al. (2007) found some evidence of the neo-tectonic activities of the Shazand fault.
Aim(s)
This study aimed to analyze the neo-tectonic situation of the Murghab basin using the evidence and geomorphological indicators and their analysis.
Research type
Research type is not mentioned.
Research society, place and time
The current research is carried out in that part of the Murghab basin which is located in Shazand fault from 2018-2020.
Sampling method and number
The sampling method and the number of samples are not mentioned.
Used devices&materials
Arc Map, Arc View, and Global Mapper were used to calculate the relative indicator of active tectonics.
Findings by Text
Faults system of the region Three faults with the direction of northern west-southern east are the main faults in this region that have moved and crushed the rocks in the same direction as Zagros (Figure 3). Their structure analysis shows a reverse sliding movement to the right side. The evidence of these slides can be detected from rocks movements and the fault surface (Figure 4). Some smaller faults with angles of 34 to 42 degrees from the linear faults. These faults have a common function and they sometimes have sliding movements to the left side. These faults are made through pulling cracks in the same direction as the pushing forces from the Arabic plate. Calculation and evaluation of neo-tectonic indicators Hypsometry Integral index (Hi) varies from the minimum of 0.34 in the sub-basin number 11 to the maximum of 0.54 in the sub-basin number3. According to this index, sub-basins number 3, 15, and 16 are active, sub-basins number 1, 2, 4, 5, 12, 14, and 17 are semi active and the remainders are inactive (Graph 1) Basin's shape index (Bs) varies from the minimum of 1.1 in the sub-basin number 16 to the maximum of 4.2 in the sub-basin number 12. According to this index, sub-basins number 5, 12, and 17 are active, sub-basins number 8, 9, 14, 15, and 18 are semi-active, and the remainders are inactive. Asymmetry factor index (Af-50) varies from 3 in the sub-basin number 12 to 17 in the sub-basin number 10. According to this index, sub-basins 10, 11, 13, 14, and 16 are active, sub basins 1, 2, 4, 5, 6, 7, 9, and 15 are semi-active and the remainders are inactive. According to the SL index and considering the geological formations and the effect of the faults, sub-basin 3 is active, sub-basins 2, 4, 5, 6, 12, 14, 15, and 16 are semi-active and the remainders are inactive. The analysis of the river profile in sub-basin 3 shows that this river crosses the Shazand fault and in that region, there is a steep slope and a decrease in the amount of SL up to 432. This sudden change represents the effect of the reverse vertical activity of the Shazand fault on this part of the river (Graph 2). Sinuosity index (S) varies from 1.03 in sub-basin 12 to 1.28 in sub-basin 18. Accordingly, sub-basins 5 and 12 are active, sub-basins 9, 10, 11, and 18 are inactive and the remainders are semi-active. Facet % index varies from 65% in sub-basin 18 to 92% in sub-basin 2 that are inactive and active sub-basins, respectively. Valley area index (V) varies from 0.48 in sub-basin 3 to the maximum of 0.91 in sub-basin 18. Accordingly, sub-basins 2, 3, 4, 5, 6, 12, 12, 14, 15, and 16 are semi-active and others are inactive (Graph 3). Finally, the relative index of active tectonic (Iat) was calculated using all other indices amounts. Sub-basins 2, 3, 4, 5, 14, 15, 16, and 17 are active, sub-basins 1, 6, 7, 8, and 17 are semi active and the remainders are inactive (Figure 5, Table 1). Most of the sub-basins along the Murghab River are unsustainable in terms of tectonic. Hence, the hypothesis that Shazand fault is active is approved. Neo-tectonic effects on the rivers' route There are some pieces of evidence that the route of some of the streams in the Murghab River net has changed. It seems that the streams used to be in the same direction as the region's mountain i.e. from northern west toward southern east. Shazand fault activities create a vulnerable, erodible surface and its base level fell down. In conclusion, the regressive erosion and streams degradation have been accelerated. Those streams in higher altitudes are deviated from their route and have rotated up to 90 degrees toward northeast and joined the lower reaches of the river. It can be clearly seen in Khamiran village (Figure 6). There is a dam on the Khamiran river which is built in 1992 (Figure 7). This is a heterogeneous soil dam that was constructed to divide 9 billion square meters of water between 5000 ha farms. The effects of neo-tectonic on Koron lake Gullies are abundant between Varposht and Tundaran villages. The majority of these gullies are more on the left side of the Murghab river with detached sediments and less on the right side with shale and lime sheets (Figure 8)
Main comparison to the similar studies
The results of the current study are consistent with the results of Nadimi et al. (2007) that approve the movements along the Shazand fault and in southern parts of Golpaygan city. Hence, Shazand fault activities are similar to sliding movements of Abadeh, Dehshir, Shahre Babak, and Baft faults [Safari, 2014].
Suggestions
There is no suggestion reported.
Limitations
There is no limitation reported.
Conclusions
The neo-tectonic situation of a part of Murghab basin which is located in the Sanandaj-Sirjan zone and along Shazand fault was studied in this article. The results show that Shazand falul.t is divided into some branches and has a horsetail structure. Its reversed clock-wise movements are clear. According to Iat index, most of the sub-basins in this region are active and semi-active. Streams network of Murghab basin shows a rotation in the streams' route which is related to the region's neo-tectonic activities. This evidence is consistent with other recent studies in the Sanandaj-Sirjan zone. Then, it can be concluded that this region is prone to the earthquake.
Acknowledgments
None.
Conflict of interest
None.
Ethical Permissions
None.
Funding Sources
None.

TABLES and CHARTS

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