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

Introduction Tectonic 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; Perez-Pena 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. Methodology In 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: stream-gradient index (SL), drainage basin asymmetry (Af), drainage basin shape (Bs), hypsometric integral (Hi), valley floor width-valley height ratio (Vf), Transverse River Sinuosity Index(S) and mountain-front 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 El-Hamdouni 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 discussion The 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 tectono-geomorphic 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 (Gurbuz and Saein, 2018).Zagros fold-thrust belt is a foreland portion of Zagros orogeny in SW Iran. Khorramroud basin is in the Zagros fold-thrust 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 sub-basins are classified in class 1 (high activity), 24 sub-basins 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 sub-basins. In 3 basins, the values of this index are classified in class 1, in 12 sub-basins in class 2 and 32 sub-basins in class 3. Vf index, 5 sub-basins are classified in class 1, 13 sub-basins in class 2 and 29 basins in class 3. S index, 5 sub-basins are classified in class 1 and 41 sub-basins in class 2. Hi index, 16 sub-basins are classified in class 1, 22 sub-basins in class 2 and 9 sub-basins 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, north-east and south, south-west 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 log-log graphs. N2 and N5 zones indicate the maximum fractal dimensions. These values are 1.7806 and 1.8264, respectively. Conclusion According 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, north-east and south, south-west regions of the basin have very high to high tectonics activities which are confirmed by the fractal analysis.