Based on visual interpretation with the color combination of R G and B bands 5, 4, and 7, we identified three lithological divisions, which are Quaternary deposits (Qt), Bakhtyari (Bk), and Asmari Formation (As). Each lithological unit has a distinct texture, color, and relief. The Qt mainly comprises gravel, sand, silt, and clay along the river (coarse and fine grain). The Qt is characterized by blue, light red, and dark red colors (Figure 9). Blue represents the built-up areas, and light to dark red represents the agricultural areas and other vegetation covers. The Qt unit covers the majority area of the study area. It extends from the middle part near the Alvand River to the south area. This area extends approximately 45.62% of the study area.
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The Bk is classified as a conglomerate, sandstone, and shale. Bk was found in the research region. According to the Landsat satellite image, Bk is dark and pale blue with a few dark red spots. The heavy red indicates the land is densely vegetated, whereas the light blue patch denotes open areas. Bk is also known for its small-height hills. This lithological unit accounts for approximately 3.45% of the studied area. It consists of limestone and is the oldest rock formation in the study area. It was formed between the Oligocene and the Miocene. The Landsat 8 image indicates it by the light green color with a few light blue spots (Figure 9). The light green color refers to the marks on the frontal outcrop, which has a rough texture. It is mainly distributed in the middle part of the study site. It is located in the core of the anticline. The total area is about 39.67% of the study area. Because both units have comparable visual morphology, color, texture, and relief, Qt and Bk are difficult to distinguish from Landsat 8. However, the Bk deposits can be located using the association notion. Qt primarily accumulates on the foot slope of denudation hills, where the denudation processes form it. As a result, the narrow flat zones that lie on the border between mountainous and flat lands are frequently referred to as Qt. Moreover, because of the alluvial processes close to the denudation hills, it has poor material sorting and a high clay concentration.
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The lineament maps were created with the help of automated lineament extraction. All linear shapes that did not match the geological or structural lineaments were removed from the maps, and the previous processing was retained. This method was applied to the four directional filters of PCA1, the panchromatic band (B8), and the four SRTM shadings of the digital terrain module. Alongside these maps, we will find data representing the number, length, and frequency of lineaments as a function of length in the survey space and directional roses formed by the proportion of cumulative lineament lengths. The first principal component (PCA1) results show a map with 1195 line segments (Figure 10-a), with an average length of 13332.54 m, a minimum length of 349 m, and a maximum length of about 2533 m. The proportions between 80% and 100% dominate the overall distribution of lineaments (Figure 10-c). According to the directional roses of the lineaments for PCA1 (Figure 10-d), the NW-SE direction is the most pronounced.
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The panchromatic band yielded 14172 line segments with a minimum length of 450 m, a maximum length of 12822.88 m, and an average length of 19902180.13 (Figure 11-a). The panchromatic lineament typically follows the same direction as the PC1, with a minority approaching the NE-SW and N-S directions ( Figure 11-d). For the class between 500 and 1000 m, the distribution frequency reached 100%.
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The lineaments derived from SRTM around 1115 (Figure 12-a) range from 530 m to 5657 km, with an average length of 3364417 m. The class with lengths between 981 m and 1.5 km (60-80%) dominates the lineament population (Figure 12-c). The directional diagram (Figure 12-d) shows two main routes, NW-SE and approximately E-W.
All directional roses of PCA1, the panchromatic band, and STRM have similar patches showing NW-SE dominance. This orientation corresponds to the major faults shown in the geologic maps of the research area (Figure 3).
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The density maps show the places where the lineaments are most pronounced. The northwest-southeast and southern parts of the area All directional roses of PCA1, the panchromatic band, and STRM have similar patches showing NW-SE dominance. This orientation corresponds to the major faults indicated in the geologic maps of the study area. Figure (13) shows the highest densities. As this is one of the areas that has undergone numerous orogenic cycles, the topography in this area is highly fractured. The density maps produced from PCA1, STEM, and the panchromatic band (Figures 13, b,c, and d, respectively) closely correspond to the main fault map (Figure 13-a).
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According to (Alavi 2008), three families dominate the distribution of lineaments in this area. The direction of an essential family varies between NW-SE, NE-SW to E-W, and N-S, which is consistent with the general direction of the major faults. The structure of the first directional group is associated with the latest Neoproterozoic and earliest Cambrian (550–540 Ma). These faults have displaced pan-African structures within the Arabian Shield to the northeast. The Recent Main Fault (MRF) and other blind faults extending northwest to Southeast are part of the Zagros Orogen (NW-SE). The second group that trended from NE-SW to E-W formed during the Permian and Triassic openings of the Neo-Tethys Ocean. This group follows the general trend of transformation faults (NE-SW). The third group comprises structures formed during the Pan-African orogen (670–570 Ma). Examples of these faults are ZFTBs that run in an N-S direction.
Based on the correlation of our remote sensing results, we can see that all data sets provide similar or identical results. We used geologic maps of major faults in the target region to confirm our results. In addition, we rely on two other aspects that play a role in validating these conclusions. The first is the lithologic map, and the second is the comparison of the lineaments with the slope map.
When the lineaments are superimposed on the lithologic map of the study region, we can see that most of the lineaments are concentrated in the areas composed of competent rocks. In contrast, the lineaments become weaker in the less complicated and brittle formations. In the NW-SE trending surface anticlines, which form “whaleback” limestones that are mostly resistant, there is a conspicuous concentration of lineaments in this area. In the north, the Oligocene and Miocene sandstones and conglomerates of Agha Jari and Bakhtyari contain a high concentration of geological lineaments. At the same time, the friable Cretaceous to Quaternary formations (sandstones, marls, and boulders) have barely perceptible geological lineaments (see Figure 14).
The morphology and geomorphology of the land are most likely caused by tectonic processes leading to the dips and depressions created by the movement of faults. It becomes clear by comparing the lineaments with the slope maps, one of the validations of lineaments.
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The slope maps were created from the digital terrain module (Figure 15) with the lineaments from the PCA1, the panchromatic band, and the STRM. The overlay shows that most lineaments are concentrated in areas with steep slopes and substantial variations in topographic profile, especially in the southwest (Sarpol Zahab) and the northeastern part. In contrast, the areas with low slopes (the central area) show a decrease in lineaments. The reversal faults resulting in significant frontal escarpments in the Zagros SFB are called the Mountain Front Fault (Berberian 1995; Figure 15).
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The Sarpol Zahab (2017) earthquake offered significant insights and mapped new limits on the dynamics in the area. It refers to the fault associated with the Sarpol Zahab earthquake as the “Sarpol Zahab fault”. It differs significantly from the Mountain Front Fault and the other faults in the other Zagros parts. The Mountain Front Fault has steeper fault planes (∼20-60◦) compared to the Sarpol Zahab fault (∼11◦), which is the first difference (Ali et al. 2022). Second, most earthquakes on the Mountain Front Fault had reverse processes, but the Sarpol Zahab earthquake had a SW-directed slip that was highly oblique to the local roughly N-S range front topography. Finally, the Mountain Front Fault uplifts from the basement into the lower to middle sedimentary cover, where shallow centroid depths are observed (Nissenetal., 2011), where it affects the evolution of major surface anticlines ( Berberian, 1995; Blanc et al., 2003).
Consequently, the Mountain Front Fault in the Sarpol Zahab region had previously been mapped as a set of short, NW-striking segments that paralleled the regional direction of fold axes (Figures 16). As shown in Figure 16 b, the N-S Sarpol Zahab fault angles sharply with overlying folds, from which the fault must be detached. Following the Sarpol Zahab earthquake, Barnhart et al. (2018) observed an afterslip near the up-dip limit of co-seismic slip on a sub-horizontal structure located at ∼10 to 14 km depth, which supports this interpretation.
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