ارزیابی تکتونیک فعال حوضه‌ دینور (غرب ایران) با استفاده از تحلیل پارامترهای مورفومتریک

شبکه ‏های زهکشی به ‏شدت تحت تاثیر فعالیت‏های تکتونیکی قرار می ‏گیرد و ارزیابی پارامترهای مورفومتریک به درک بهتر وضعیت تکتونیک فعال در حوضه ‏ها منجر می‏ شود. شرایط زمین‏ شناسی و وقوع زلزله‏ های متعدد بیانگر وضعیت ناآرام تکتونیکی حوضه‌ دینور بوده و تحلیل پارامترهای مورفومتریک شبکه‌ زهکشی می‏ تواند به درک بهترِ وضعیت تکتونیک فعال این حوضه منجر شود. هدف اصلی از اجرای این مطالعه ارزیابی و شناخت وضعیت تکتونیک فعال حوضه‌ دینور و زیرحوضه‏ های آن است. در این پژوهش از پانزده شاخص‏ مورفومتریک برای ارزیابی وضعیت تکتونیک فعال استفاده می‏‏ شود. با استفاده از آنالیز مولفه‏ های اصلی پارامترهای مورفومتریک با بیشترین همبستگی انتخاب شد و بر اساس آن‏ها relative active tectonic index برای حوضه‌ دینور و زیرحوضه‏ های آن محاسبه شد. نتایج نشان می‏ دهد زیرحوضه‏ هایی با فعالیت تکتونیکی خیلی زیاد و زیاد 91درصد مساحت حوضه‌ دینور را دربر گرفته ‏اند. پراکنش فضایی زیرحوضه‏ ها از نظر میزان فعالیت تکتونیکی نظم خاصی را در دو زون زمین ‏شناسی سنندج سیرجان و زاگرس نشان نداده و این امر بیانگر فعالیت تکتونیکی در کل محدوده‌ حوضه‌ دینور بر اثر کوتاه‏ شدگی فلات ایران و زون زاگرس تحت فشارش صفحه‌ عربی است. شواهد ژئومورفولوژیکی و وقوع زلزله‏ های دستگاهی از دیگر شاهدهای فعال‏ بودن تکتونیک منطقه در عصر حاضر است.

Active tectonics evaluation from morphometric indices for the Dinevar Basin in northern Zagros, western Iran

Active tectonics evaluation from morphometric indices for the Dinevar Basin in northern Zagros, western IranIntroductionActive tectonic assessment has significant applications in environmental planning, natural hazard assessment, and landuse management (Pedrera et al., 2009). Active tectonic zones are constantly at risk of devastating earthquakes that seriously threaten human life and properties. Quantitative evaluation of tectonic activities can provide more accurate information about the state of tectonic activity. In this regard, the analysis of morphometric parameters of drainage networks—as the quantitative description of drainage networks (Strahler, 1964)—has shown particular usefulness in identifying tectonic activities (Gao et al., 2016). The morphometric analysis involves the calculation of linear, shape, relief, and slope parameters of the drainage networks (Nag and Chakraborty, 2003). Quantitative assessments of drainage networks identify tectonic and/or erosional transformations responsible for the evolution of landscapes (Segura et al., 2007). In tectonically active regions, drainage networks exhibit the relationship between surface processes and structural deformations (Burbank and Anderson, 2001), and thus their morphometric parameters assist in identifying active tectonic zones (Chen et al., 2003). Study area The Dinevar basin with an area of 2214 km2 is extended from 47 03 E to 47 50 E and 34 25 N to 34 50 N in the west of Kermanshah Province, western Iran (Fig. 1). The basin is a sevenorder basin with a dendritic pattern and involves 13 subbasins with areas ranging from 17 to 571 km2. Geomorphologically, the Dinevar basin constitutes of three units, fluvial plains, hills, and highlands. The highlands of Dalakhani, Bisotun, and Hajar are mainly composed of carbonate formations and characterized by steep slopes and high relief. Materials and methodsGeomorphological characteristics of the Dinevar basin were investigated during a field study in 2020. The boundaries of the Dinevar basin and its subbasins were extracted from the DEM in GIS environment. Stream ordering was determined using the Strahler ordering system (Strahler, 1964), and then geometric features of the basin (area, environment and length of the basin), characteristics of the drainage network (number and length of streams) and topographic features (minimum, medium and maximum elevations) of the Dinevar basin and its subbasins were calculated. Subsequently, values of the morphometric parameters including six linear, six areal, and three relief parameters were calculated (Table 2). The main parameters were determined using the Principal Component Analysis (PCA) method. Based on the values of these parameters and the Relative Active Tectonic Index (RATI) method, the active tectonics of the Dinevar basin and its subbasins were calculated and classified. Finally, by taking the geological, lithological and geomorphological conditions of the basin into account, the active tectonic and its spatial differences in the Denver basin and its subbasins were determined.Results and discussionThe circularity ratio (Rc) is expressed as the ratio of the area of the basin to the area of a circle having the same perimeter as that of the basin (Strahler, 1964). Rc is mainly controlled by geology and structure, relief, slope, climate, stream frequency and length within the basin area (Rai et al., 2018). High Rc values, approaching 1, indicate that the basin shape is circular. The Rc values of (0.4> Rc), (0.4 Rc) represent high, medium and low tectonic activity, respectively (Shukla et al., 2014). The Rc value for the Dinevar basin is 0.17 and fluctuates between 0.06 and 0.33 for the subbasins. Based on the Rc values, the Dinevar basin and all its subbasins indicate high tectonic activity. This is mainly due to the tectonic uplift of the Dinevar basin which reinforces the erosion processes and thereby prevents the formation of circular basins.The relief ratio (Rr) determines the overall slope and the degree of erosion of the basin (Sanaullah et al., 2018) and reflects the lithological conditions. Based on the Rr values, drainage basins are divided into three classes with high tectonic activity (Rh <0.1), medium tectonic activity (Rh> 0.1 <0.05) and low tectonic activity (Rh <0.05) (Shukla et al., 2014). The Rh value in the Dinevar basin and subbasins 1, 2, 5, 6 and 8 is less than 0.05 and indicates low technical activity. The Rh value for subzones 7, 9 and 12 are more than 0.1 indicating high tectonic activity in these basins. The elongated shape of the basins is one of the important factors responsible for the low values of Rh parameter in the Dinevar basin and most subbasins. The Ruggedness number (Rn) for the Dinevar basin 4.48 and varies between 2.97 and 5.32 for its subbasins (Table 3). The ordering of the subbasins follows a reverse trend, where subbasins with the lower values for each parameter have an order of 5. The RATI value for the Dinevar basin is 2.35 and varies between 2.05 and 4.35 for its subbasins (Table 6). Based on the RATI values, the subcategories are classified into 5 categories: class 1 with very high tectonic activity (2.05 2.51), class 2 with high tectonic activity (2.51 – 2.97), class 3 with medium tectonic activity (2.97 3.43), class 4 with low tectonic activity (3.43 – 3.89) and class 5 with very low tectonic activity (3.894.35). Accordingly, subbasins 2, 5, 7 and 8 fall into class one with highest tectonic activity, while subbasin 3 and 4 place in class five with lowest tectonic activity. ConclusionIn this study, we used linear, areal, and relief morphometric parameters to evaluate the active tectonics of the Dinevar basin and its 13 subbasins located in the NW Zagros Mountains. Based on the results of the RATI method, the Dinevar basin places in a class with very high tectonic activity. The tectonic activity of the subbasins located close to Sahneh and Mianrahan faults, as well as the subbasins developed in the Bisotun massif, is higher than the other subbasins. Subbasins with very high, high and moderate tectonic activity cover about 96% of the area of the Dinevar basin, indicating an increase in tectonic activity in the entire basin. In general, the active tectonic of the Dinevar basin can be inspected in two aspects. First, the active tectonic and tectonic uplift of the Dinevar basin result from the shortening of the high Zagros zone due to the pressure from the Arabian plate. Evidence such as subbasins being at the young stage of the erosion cycle, young drainage networks, high relief of the subbasins, high drainage density, narrow and deep stream beds and the lack of hierarchical order in the drainage network all are associated with the tectonic activity and tectonic uplift of the entire Dinevar basin due to shortening of the high Zagros zone. Second, the existing faults in the basin are active and cause changes in the flow path of the streams, displacement and disconnection of the streams, and drainage network anomalies. Therefore, as revealed by our results, the NW Zagros is tectonically very active and the occurrence of devastating earthquakes in this region is very likely, it is thus necessary to pay more attention to this issue in the urban and regional planning.Keywords: Active tectonic, drainage network, morphometric indices, RATI, Zagros.