ارزیابی تکتونیک فعال نسبی حوضه خرم رود با استفاده از شاخص‌های مورفومتری و تحلیل الگوی فرکتالی (لرستان، شمال غرب کمربند زاگرس)

شبکه های آبراهه‏ای به تغییرات نامحسوس ناشی از فعالیت تکتونیکی گسل‏های سطحی و زیر سطحی بسیار حساس هستند و می‏توانند در مطالعات پهنه بندی مناطق با میزان فعالیت های تکتونیکی متفاوت، در سطح زمین راهگشا باشند. هدف از این پژوهش بررسی پویایی تکتونیکی حوضه رودخانه خرم آباد با تلفیق نتایج حاصل از تحلیل شاخص‏های کمیژئومورفیکیو تحلیل ابعاد فرکتالی خطواره‏های گسلی می باشد. حوضه خرم آباد در کمربند چین خورده رانده زاگرس و در زیر پهنه لرستان واقع شده است. با توجه به اینکه هندسه و تحول جنبشی ساختارها در زیر پهنه لرستان غالبا به وسیله گسل‏های راندگی کور کنترل می‏شوند، بررسی شبکه‏های آبراهه‏ای، تغییرات در رخساره‏های رسوبی و ضخامت لایه‏ها و الگوی چین خوردگی‏ها در سطح زمین می توانند در شناسایی مناطق با فعالیت تکتونیکی نسبی مفید واقع شوند. به همین منظور،7 شاخص کمی ژئومورفیک در 47 زیرحوضه مورد مطالعه قرار گرفته‏اند. شاخص‏های sl، af، vf، bs، hi،smf   و s با استفاده از تکنیک gis در حوضه خرم آباد محاسبه شده‏اند. با توجه به رده‏بندی شاخصiat ، نقشه پهنه‏بندی در 4 رده خیلی فعال، فعال، متوسط و فعالیت کم تهیه گردید. با استفاده از تکنیک‏های سنجش از دور، خطواره‏های گسلی با ترکیبی از روش های اتوماتیک و دستی، از تصاویر ماهواره‏ای لندست و مدل‏های سایه روشن استخراج شدند. در نهایت با استفاده از تحلیل فرکتالی به روش مربع شمار، ابعاد فرکتالی این خطواره‏ها در 6 پهنه محاسبه شد. بر این اساس، پهنه های n2 و n5 فعالیت تکتونیکی بالا نشان می‏دهند. نتایج حاصل از بررسی شاخص‏های مورفومتری، مشاهدات میدانی و ابعاد فرکتالی، در نواحی شمالشمال شرق و جنوبجنوب غرب حوضه، تکتونیک خیلی فعال و فعال و در برخی زیر حوضه‏ها فعالیت متوسط را تائید می‏کنند و از نظر لرزه خیزی مناطق پرخطر محسوب می‏شوند.

Assessment of relative active tectonic of the Khorramabad Basin using morphometric indices and fractal model analysis (Lorestan, northwest Zagros belt)

IntroductionTectonic geomorphology is defined as the study of landforms produced by tectonic processes, or the application of geomorphic principles to the solution of tectonic problems. (zovoili,2004). These indices have been developed as basic reconnaissance tools to identify areas experiencing rapid tectonic deformation (keller & Pinter, 1996). Geomorphological analyses allow the study of modifications that affect river basins, particularly modifications due to active tectonics, and investigate the morphotectonic evidence of the area. Attempts to quantify tectonic deformation from landscape analyses have been performed for decades (e.g., Bull and McFadden, 1977; Wells, et al., 1988; PérezPeña et al., 2010; Sarp and Duzgun, 2015; Gao et al., 2013; Demoulin et al., 2015; Luirei et al., 2015; Topal et al., 2016; Cheng et al., 2016; Mathew et al., 2016; Topal, 2019; Obaid and Allen 2019). The aim of this paper is to extract information on active tectonic, situation of the fault lineaments and landscape evolution of the study area.MethodologyIn this paper we used Aerial image, topographical map, geological map, Digital Elevation model (DEM), Radar Topography Mission (SRTM) data and applied software such as ArcGIS, Google Earth, ENVI and Global mapper. The first step for calculating morphometric analysis in the region is to digitize topographical maps with the scale 1:25000 by ArcGIS software to extract required data and then morphometrical data is formulized and calculated exactly and the results is interpreted. The DEM data of 30 m have been used to generate the drainage basin. For study of morphotectonic of region, we must receive the geomorphic indices. These indices are particularly used to study active tectonics. The indices: streamgradient index (SL), drainage basin asymmetry (Af), drainage basin shape (Bs), hypsometric integral (Hi), valley floor widthvalley height ratio (Vf), Transverse River Sinuosity Index(S) and mountainfront sinuosity (Smf) were calculated using GIS technique in Khrramroud Basin. From these indices the relative active tectonics index value (Iat) was determined. The acquired values and classes are according to ElHamdouni et al. (2008) and enclosed references. In this study, by means of remote sensing methods and ETM images and based on surface deformation like curved, truncated and offset structures the lineament which are related to the activity of subsurface or conceal faults are mapped. Ultimately, the results of these quantitative indices were compared to analyzing of the fractal dimension of the study area.Results and discussionThe rivers are highly sensitive to subtle landscape fluctuations induced by tectonic activity and can assist in differentiating active segments of geologic structures. Because drainage basins represent dynamic systems that may retain records of formation and progression since most tectonogeomorphic processes occur within its confines. Therefore, morphometric analyses of river networks, drainage basins and relief using geomorphic indices, as well as geostatistical analyses of topographical data have become useful tools for investigating landform evolution. As part of the Alpine–Himalayan orogenic system, the Zagros Orogen represents a mountainous region along ∼1500 km with an extensive active crustal deformation and intense seismic activity in a northwest–southeast direction (Gürbüz and Saein, 2018).Zagros foldthrust belt is a foreland portion of Zagros orogeny in SW Iran. Khorramroud basin is in the Zagros foldthrust belt at Lorestan subzone. In this paper we are undertaking a tectonic geomorphology of Khorramroud River catchment. The aim of this paper is to determine the most geomorphic indices and the analysis of the fractal dimension using the Box Counting method. Results of the calculation of geomorphologic indices: The value of the SL index varies from 9.25 to 574 in the region with low and high tectonic activity, respectively. Af index, 15 subbasins are classified in class 1 (high activity), 24 subbasins in class 2 (moderate activity) and 8 basins in class 3 (low activity). The presence of active fault system in these regions can be attributed to this asymmetry and tilting. The values calculated from the Bs index are classified in the classes 1, 2 and 3 which indicate the asymmetry of subbasins. In 3 basins, the values of this index are classified in class 1, in 12 subbasins in class 2 and 32 subbasins in class 3. Vf index, 5 subbasins are classified in class 1, 13 subbasins in class 2 and 29 basins in class 3. S index, 5 subbasins are classified in class 1 and 41 subbasins in class 2. Hi index, 16 subbasins are classified in class 1, 22 subbasins in class 2 and 9 subbasins in class 3. The mountain front of the study area is divided into 20 sections along the study area, in order to assessment of the Smf index. Then, this index is calculated for different sections. Measured values of the Smf index for most part of the study area show high relative activity. The classification used in this paper for each geomorphic index is calculated from El Hamdouni’s method. By using relative tectonic activity Index (Iat) the area was investigated into 4 classes of tectonic activities as very high, high, medium and low. Based on this classification, the north, northeast and south, southwest regions have very high to high tectonics activities.In this study, by means of remote sensing methods and ETM images and based on surface deformation like curved, truncated and offset structures the lineament which are related to the activity of subsurface or conceal faults are mapped. Next, regarding to the study area, is created 6 squares with dimensions of 23.9 km, in order to applying the Box Counting method. In the fractal analysis, the fault lineaments of each square are evaluated separately. The fractal dimension is quantified for each square. Finally, they are drowned on the loglog graphs. N2 and N5 zones indicate the maximum fractal dimensions. These values are 1.7806 and 1.8264, respectively. ConclusionAccording to the values of the calculated indices, to determine the total tectonic activity, the relative active tectonics index (Iat) was evaluated. Based on the results of this study, the north, northeast and south, southwest regions of the basin have very high to high tectonics activities which are confirmed by the fractal analysis.