تحلیل وضعیت تکتونیکی زیرحوضه های لواسان با استفاده از شاخص های ژئومورفیک و تصاویر راداری (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
موقعیت زمین ساختی ایران سبب شده است تا این فلات ناآرامی های زیادی داشته باشد. از جمله منطقه های ناآرام آن فلات واحد البرز است. بر این اساس، در پژوهش حاضر کوشش شده است تا وضعیت مورفوتکتونیکی زیرحوضه های لواسان در دامنه های جنوبی البرز بررسی شود. در این پژوهش متناسب با هدف های مدنظر از مدل رقومی ارتفاعی ۳۰ متر، نقشه توپوگرافی ۱:۵۰۰۰۰، نقشه ۱:۱۰۰۰۰۰ زمین شناسی و تصاویر راداری سنتینل Sentinel به عنوان داده های پژوهش استفاده شده است. ابزارهای مهم این مطالعه نرم افزارهای GMT، ARCGIS، SPSS و شاخص های استفاده شده برای ارزیابی وضعیت تکتونیکی منطقه مطالعه شده است. پژوهش حاضر در دو مرحله انجام شده است. در مرحله اول با استفاده از شاخص های مورفوتکتونیکی، وضعیت تکتونیکی زیرحوضه ها ارزیابی و در مرحله دوم با استفاده از تصاویر راداری و روش سری زمانی SBAS میزان جابه جایی عمودی منطقه ارزیابی و سپس این جابه جایی با وضعیت تکتونیکی زیرحوضه ها تحلیل شده است. نتایج به دست آمده از شاخص IAT نشان داده است که حوضه های مطالعه شده فعالیت تکتونیکی فعّالی دارند. درواقع، حوضه های برگ و کند میانگین امتیاز ۸۸/۱ و حوضه های لواسان و افجه میانگین امتیاز ۲ را دارند؛ بنابراین حوضه های برگ و کند از نظر شاخص IAT وضعیت تکتونیکی فعّال تری دارند. همچنین، بر اساس نتایج به دست آمده از روش سری زمانی SBAS منطقه مطالعه شده در طی دوره زمانی ۳ ساله (از تاریخ 6/1/2016 تا 21/12/2018) 79 میلی متر بالاآمدگی و 14 میلی متر پایین رفتگی دارد که به دلیل داشتن بالاآمدگی زیاد می توان آن را به فعالیت های تکتونیکی نسبت داد. سرانجام، در نتایج تصویر راداری فعّال بودن منطقه از نظر تکتونیکی تأیید شده است.Analysis of Tectonic Status of Lavasan Sub-Basins Using Geomorphic Indicators and Radar Images
The tectonic positioning of Iran has led to significant seismic activity in the region, particularly in the Alborz Unit. This study focused on investigating the morphotectonic status of Lavasan Sub-basins located on the southern slopes of the Alborz. To achieve this, a digital elevation model with 30-meter resolution, a 1:50,000 topographic map, a 1:100,000 geological map, and Sentinel-1 radar images were utilized as research data. The analysis employed GMT, ArcGIS, and SPSS software, along with specific indicators to assess the tectonic condition of the region. The research was conducted in two stages. Firstly, the tectonic conditions of the sub-basins were evaluated using morphotectonic indicators and secondly, the vertical displacement of the region was assessed using radar images and the SBAS time-series method. The results of the study indicated that Lavasan Sub-basins exhibited high tectonic activities with Barg and Kond basins averaging a score of 1.88 and Lavasan and Afjeh basins averaging a score of 2. Consequently, the latter basins demonstrated a more active tectonic status based on the IAT index. Additionally, the results obtained from the SBAS time-series method over a 3-year period (from 01/06/2016 to 12/21/2018) revealed a 79-mm elevation and a 14-mm depression, which could be attributed to tectonic activity, thus corroborating the accuracy of the results obtained from morphotectonic indicators.Keywords: Morphotectonics, Morphotectonic Indices, SBAS, Lavasan IntroductionIran, situated within the Alpine-Himalayan tectonic active zone, has been significantly impacted by tectonic activities throughout its history. The formation of the Indian Ocean is a direct result of this tectonic convergence. The Iranian plateau, due to its tectonic positioning, has experienced various seismic events, including those within the Alborz Unit. The presence of newborn landforms in Alborz Region, such as cliffs, anticline morphology, and seismic activity, serves as evidence of the high frequency of recent tectonic activities, a concept explored in geomorphological tectonics. Geomorphological tectonics focuses on the study of landforms shaped and transformed by tectonic activity. Landforms in regions with active tectonics are the product of a complex interplay between vertical and horizontal movements of crustal blocks and erosion or sedimentation by surface processes. Therefore, assessing and studying tectonic activities and their impacts is crucial in regional development planning, land management, and environmental conservation. Catchments are one of the key areas used to investigate the tectonic status of a region. River systems, in general, serve as valuable tools for studying tectonic interactions as rivers, drainage networks, and alluvial fans are highly sensitive to tectonic changes. Accordingly, this study focused on examining the morphotectonic status of Lavasan Sub-basins located on the southern slopes of the Alborz. Materials and MethodsThis study utilized a digital elevation model with a 30-meter resolution, a 1:50,000 topographic map, a 1:100,000 geological map, and Sentinel-1 radar images as primary research data. Key research tools included GMT, ARCGIS, and SPSS software, along with specific indicators used to assess the tectonic condition of the region. The research was conducted in two stages. Firstly, the morphotectonic status of the studied basins was evaluated using 8 indicators, namely branching ratio (Br), basin drainage density (Dd), drainage basin asymmetry (AF), longitudinal river gradient (SL), basin shape (Bs), inverse topographic symmetry (T), hypsometric integral (Hi), and river sine index (S). In the second stage, 27 radar images of Sentinel 1 (SLC type with VV polarization) were employed to assess the vertical displacement of the region as detailed in Table 3. Following the preparation of the images and necessary preprocessing, a specific pair of images was selected based on the timeline for radar interference (refer to Figure 3). Subsequently, interferograms were generated using radar interferometry and ultimately, the vertical displacement of the region was determined using the SBAS time-series method. Research FindingsThe evaluation of the branching ratio (Br) in the studied basins revealed that Kond Basin with a coefficient of 4.64 exhibited the highest branching coefficient, indicating greater tectonic activity compared to other sub-basins. Similarly, calculation of the drainage density index (Dd) demonstrated that Kond Basin, with a coefficient of 3.57 had the highest drainage density (Figure 3), signifying elevated tectonic activity compared to other sub-basins. Furthermore, the drainage basin asymmetry (AF) index indicated that Kond Basin with a coefficient of 61.2 displayed the highest asymmetry, suggesting a more active tectonic state. The longitudinal river gradient index (SL) revealed that Kond Basin with a coefficient of 2698 had the highest gradient, positioning it as the most active basin. Additionally, the basin shape index (Bs) highlighted that Afjeh Basin with a coefficient of 2.87 exhibited the highest coefficient, indicating it as the most active basin. The inverse topographic symmetry index (T) and the hypsometric integral index (Hi) also identified Afjeh Basin as the most active basin with a coefficient of 2.87. Moreover, the river sinusoidal index (S) indicated that Kond Basin with a coefficient of 1.19 had the lowest coefficient, designating it as the most active basin based on this index. Finally, the results from the SBAS time-series method revealed a 79-mm increase and a 14-mm decrease in the region over a 3-year period (from 01/06/2016 to 12/21/2018). Discussion of Results & ConclusionAssessment of the tectonic status of the studied sub-basins using morphometric indices indicated that all sub-basins exhibited significant tectonic activities. Specifically, the results obtained from the IAT index categorized the study basins as having high tectonic activities. Barg and Kond basins had an average score of 1.88, while Lavasan and Afjeh basins had an average score of 2, signifying a higher level of tectonic activity in Barg and Kond basins based on the IAT index. Comparative analysis of the results revealed that Kond Basin demonstrated a more active tectonic status across various indices, including Br, Dd, AF, SL, T, and S, positioning it as the most active basin among the study basins. Furthermore, the findings from the radar images corroborated the tectonic activity in the study area. The results obtained from the SBAS time-series method over a 3-year period (from 01/06/2016 to 12/21/2018) indicated a significant elevation of 79 mm and a depression of 14 mm, which could be attributed to tectonic activity, thus validating the accuracy of the results obtained from the morphotectonic indices.
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