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The structural map of the research area and locations of collected paleostress data. F1 to F24 are faults number 1 to faults number 24.
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This research assessed stress regimes and fields in eastern Iran using fault-slip data and the tectonic events associated with these changes. Our stress analysis of the brittle structures in the Shekarab Mountains revealed significant changes in stress regimes from the late Cretaceous to the Quaternary. Reconstructing stress fields using the age an...
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Context 1
... this study, the fault kinematic data, including the orientation of the main fault planes and associated strike, were measured at 37 sites ranging in age from the late Cretaceous to the Quaternary ( Figure 4). In order to obtain stress tensor inversion in the study area, the majority of brittle structures, such as the orientation of fault planes, slicken lines, and indicators of the sense of motion, were collected (Table 1). ...
Context 2
... Cretaceous units were scattered throughout the entire parts of area (site numbers 13, 17, 32, and 33) (Figures 2 and 4). There were two outcrops of the Cretaceous period in the ophiolites and peridotite units (site numbers 13 and 17) (Figure 4). The faults observed in site numbers 13 and 17 were reverse, and the stress regime was compressional. ...
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As a part of the Kermanshah ophiolite in western Iran, the Cretaceous Nourabad-Dinavar ophiolitic complex is a remnant of the Neo-Tethys oceanic lithosphere and represents transitional mantle-crust and upper crust units in the Nourabad and Dinavar regions, respectively. All the units were affected by the two metamorphic regimes of static metamorphi...
Citations
... Furthermore, all maps pertinent to this research were created using GMT software, as illustrated in Figure 1. In this research, to estimate seismic strain rates, we employed two different zoning approaches: 1) For a general investigation based on tectonic zones, we considered occurred earthquakes, information about the tectonics of the study area, mechanisms of the faults, focal mechanisms of the earthquakes, seismic states, fault trends, and geological evidence presented in various studies, e.g., Zagros (Navabpour and Barrier, 2012), Kopeh Dagh (Hollingsworth et al., 2006); Alborz (Rashidi, 2021), Sistan (Ezati et al., 2022b(Ezati et al., , 2023, resulting in fourteen defined tectonic zones. 2) For detailed investigation, we segmented the study area into 336, 1°× ...
... Further investigations reveal the presence of extraterrestrial blocks, such as Shotory and Tabas, along with Posht-Badam, Dasht Bayyaz-Bardsir, and Yazd blocks (Ezati et al., 2022a;2022b;Rashidi et al., 2023b). These blocks demonstrate an east-west stretching pattern influenced by diagonal stresses in the south-north direction ( Figure 1). ...
Rhombic structures have been observed in the Qom-Zefreh-Nayin-Dehsheir-Baft region, specifically along the direction of the dextral faults, which have caused significant changes in strike length. This study investigates the geological features and fault interactions in the region through the examination of aerial images, fault-lithology correlations, petrology, crustal thickness, and seismic studies. The analysis of aerial photos and geological correlations revealed the presence of ophiolites and pluto-volcanics associated with faults and rhombic structures. By conducting field geology and combining various geological studies, a pull-apart basin was identified in the area, contributing to the formation of three rhombic structures. This basin played a crucial role in the genesis of the region’s ophiolites and pluto-volcanics. The research suggests that the initial tensional stress leading to the pull-apart basin was caused by the right step of a dextral fault within the Urumieh-Dokhtar magmatic arc. This fault formation occurred due to the oblique Arabian subduction towards the Iranian plateau. During the Zagros orogeny, the stretched area persisted, leading to the formation of oceanic crust in this location. The subduction angle changes from subduction to super-subduction, resulting in the classification of the region into two types: C and E genes. Different types of magma, including alkaline, subalkaline, shoshonite, calcalkaline, and adakitic, were identified in this region. The study highlights the significance of tholeiitic arcs, abyssal features, crust thickness, and seismicity in understanding oblique diagonal subduction models and tensional pull-apart basins, which are crucial in the transition from subduction to super-subduction. This research offers valuable insights into the geological complexities of the region and opens up opportunities for further exploration of similar models.
... Tectonic activity in the western and eastern domains of the Lut Block (as a rigid block) with a thin crustal structure have been observed along the basement faults (Ezati et al., 2022a(Ezati et al., , 2022bMehrabi et al., 2021;. The eastern limit of the Lut block, Nehbandan fault system (Rashidi et al., 2023b), overprints the Sistan suture zone (SSZ). ...
Kerman province in SE Iran has always experienced devastating earthquakes. Therefore, it is necessary to carry out an up-to-date probabilistic seismic hazard analysis (PSHA) in order to the risk reduce and increase the resilience of the infrastructures. This study provides PSHA with emphasis on uncertainties in different steps of analysis. To create an integrated seismic catalog with moment magnitude, a magnitude conversion algorithm was proposed which can be applied with the reference to IRSC main catalog. To achieve the best results, active seismic zones of Kerman province and its around areas, have been carefully identified. Seismic source zones were modeled by four criteria: seismicity, faults, geological conditions, and focal mechanisms. Seismicity parameters (Gutenberg-Richter recurrence law coefficients, Mmax and Mmin, as well as activity rate) were determined for all the seismic source zones. Ground-motion models have been applied in accordance with the region and the existing uncertainties have been identified and reduced as much as possible. The results of this study are presented in form of bedrock seismic hazard maps for PGA and spectral acceleration in 0.2 s and 1.0 s periods with a probability of 2% and 10% in 50 years, to meet all structural design needs in the region. Our results indicate the maximum and minimum PGA with the 475-year return period (0.58 g and 0.05g) are related to the Faryab city, and the Lut plain, respectively. Also, our results of the 2475- return period show Faryab city and Lut plain have highest and lowest PGA (0.92 g and 0.1 g), respectively.
... In certain regions of the Earth, significant seismic activity has been observed, including past occurrences of large earthquakes, as documented by [18][19][20][21]. Understanding historical seismic events and their locations is crucial for conducting seismic hazard analysis, as emphasized by [22]. ...
The Alborz mountain range in northern Iran is part of the active and seismic Alpide belt, where assessing seismic hazards is crucial due to the region’s history of large instrumental earthquakes and destructive seismic background. Moment rate estimation, which quantifies tectonic activity, offers a novel approach to understanding the energy potential of active tectonic regions. In this study, a regional perspective is employed to investigate the maximum horizontal acceleration for Tehran, the major city in Alborz, resulting from the Sorkh-e Hesar and Ghasr-e-Firuzeh faults located approximately 7.5 km southeast of Tehran. These faults have a seismic potential of Mw 6.5 and a gravity of ~0.5723. While previous studies have identified faults in northern Tehran as the greatest seismic risk, our findings suggest otherwise. The calculated geological moment was 5.18218 × 1017 Nm/y, with a seismic moment rate of 1.83375 × 1014 Nm/y, providing valuable insights into fault activity and seismic potential in the study area.
... For a comprehensive tectonic analysis of the study area, a combination of structural and current/paleo-stress is required (Rashidi and Derakhshani, 2022). Therefore, we used stress data from recently published articles by some authors (Jentzer et al., 2017;Ezati et al., 2022b). The Tensor software (Delvaux et al., 1997;Delvaux et al., 2012;Delvaux and Sperner, 2003) was applied to illustrate the structural data, especially for the faults with slickenlines. ...
... In orogenic belts with long deformation history (e.g., East Iran orogen), the general patterns of the deformations (e.g., folds) are related to buckling phases of orogenic belts during various geological times. Here, we used the drastic temporal changes in the stress regimes of East Iran orogenic during the post-late Cretaceous, which have been published by some researchers (Jentzer et al., 2017;Ezati et al., 2022b) (Figure 17). Directions of the maximum stress (σ1) in the late-Cretaceous-late Paleocene, Eocene-Oligocene, Miocene, late Miocene-late Pliocene, and Quaternary have been obtained as N290° ( Ezati et al., 2022b), N035° (Ezati et al., 2022b), N090° (Jentzer et al., 2017), N060° (Jentzer et al., 2017), and N045° (Ezati et al., 2022b), respectively ( Figure 17). ...
... Here, we used the drastic temporal changes in the stress regimes of East Iran orogenic during the post-late Cretaceous, which have been published by some researchers (Jentzer et al., 2017;Ezati et al., 2022b) (Figure 17). Directions of the maximum stress (σ1) in the late-Cretaceous-late Paleocene, Eocene-Oligocene, Miocene, late Miocene-late Pliocene, and Quaternary have been obtained as N290° ( Ezati et al., 2022b), N035° (Ezati et al., 2022b), N090° (Jentzer et al., 2017), N060° (Jentzer et al., 2017), and N045° (Ezati et al., 2022b), respectively ( Figure 17). Therefore, by changing the stress regime, the characteristics of folds and faults related to the splays (e.g., geometry, mechanism, and strain rates) could have changed several times. ...
Introduction: The East Iran orogen has experienced multiple buckling phases resulting in the formation of strike-slip fault splays. The geometric and kinematic characteristics of these splays are influenced by folding mechanisms. This study focuses on investigating the structural characteristics and tectonic evolution model of the Khousf splay, located in the northern terminus of the Nehbandan right-lateral strike-slip fault system.
Methods: Field visits and geometrical properties from map views were used to analyze the structural features of the Khousf splay. The splay was found to consist of a multi-plunging anticline and syncline, referred to as the Khousf anticline and Khousf syncline, respectively. Flexural slip was identified as a significant mechanism for the formation of these structures. Structural evidence, including parasitic folds, active folds, and strike-slip duplexes, suggested that flexural slip occurred on discrete movement horizons among the rock units.
Results: Analysis of the parasitic folds in the cores and limbs of the Khousf anticline and syncline revealed M, W, Z, and S shapes, with complex slicken-line patterns observed on faults parallel to the beds at the limbs. The analysis results indicated strain partitioning and inclined left- and right-lateral transpressional zones. Shortening estimates obtained from profiles in the Shekarab inclined transpressional zone were approximately 33%, 65%, and 68% for NE-SW, N-S, and NW-SE profiles, respectively. In the Arc area, which is the core of the anticline, shortening estimates from NE-SW and N-S profiles ranged from 14% to 10%. Structural analysis of the folds in this area revealed broad, close, semi-elliptical, and parabolic shapes, suggesting that secondary folds with NW-SE axis directions have been superimposed on the first-generation folds with E-W axis directions in the Khousf refolded splay.
Discussion: The findings of this study highlight the structural characteristics and tectonic evolution model of the Khousf splay in the northern terminus of the Nehbandan right-lateral strike-slip fault system. The results suggest that flexural slip played a crucial role in the formation of the multi-plunging anticline and syncline in the Khousf splay. The presence of parasitic folds and complex slicken-line patterns on faults indicate the complexity of deformation processes. The observed strain partitioning and inclined transpressional zones suggest a complex tectonic history in the study area. The superimposition of secondary folds with different axis directions on first-generation folds adds further complexity to the structural evolution of the Khousf refolded splay. Overall, this study provides new insights into the structural characteristics and tectonic evolution of the Khousf splay in the East Iran orogen.
The Sistan suture zone comprises the boundary between Lut and Afghan blocks. The north-south shear between Iran and Afghanistan is accommodated by several right-lateral strike-slip fault systems. The study area (northern Birjand Mountain range) is a part of Khousf splay; the most important faults in the Khousf splay are sinistral with reverse component and thrust with sinistral component faults; the Khousf splay is a sinistral transpressional zone including shear folds, pop-ups, positive flower structures, and duplexes. In this research, we used field data including geometric and kinematic characteristics of the faults to determine the structural deformation model of the northern Birjand Mountain range. In the northern Birjand Mountain range, several ~E-W striking faults cut through geological units; geometric and kinematic analyses of these faults indicate that almost faults have reverse components which reveal existing of compressional stress in the study area. The northern Birjand Mountain range has been characterized by main reverse faults with ~E-W striking faults. Moreover, most of the faults in the Khousf splay are thrust with left-lateral components, which were activated as a result of the NE-SW direction stress regime. The Khousf splay is a sinistral shear zone, and the beginning of deformation in this splay is from east to west. Structural analysis in the study area indicates that the F1 and F2 reverse faults have southward dips and F3 and F4 reverse faults have northward dips. Investigating the faults in the northern Birjand Mountain range implies that these reverse faults join the Nehbandan fault system. The Nehbandan fault system has splays in the Northern and Southern terminals, and the northern terminals of the Nehbandan fault are reverse faults with nearly E-W striking. The main reverse faults of the study area include F1 to F4 faults which are continuations of the Nehbandan fault system. Therefore, the kinematics and geometry of these faults in the northern Birjand Mountain range suggest pop-up and positive flower structures in a sinistral transpressional zone.
Afghanistan is in a seismically active area and is historically hit by destructive earthquakes. It is located on the edge of the Eurasian tectonic plate, bordered by the northern boundary of the Indian plate, and with the collisional Arabian plate into the South. The Hindukush and Pamir Mountains within Afghanistan are the western extension of the Himalayan orogeny uplifted and sheared by Indian and Eurasian plate convergence. These tectonic activities have created several active deep faults across the country and in the Hindukush-Himalayan region, where high-magnitude earthquakes have historically occurred. Earthquakes in Afghanistan are primarily driven by the relative northward movements of the Arabian plate past western Afghanistan and the Indian plate past eastern Afghanistan as both plates subduct under the Eurasian plate. These tectonic movements caused ground shaking from high to moderate and low from the northeast through the southwest of the country. On June 22, 2022, southeastern part of Afghanistan was hit by a destructive Mw6.2 earthquake. The purpose of this study is to develop an ArcGIS Pro database of compiled geologic faults and regions of heightened seismicity for spatial analyses of earthquake disaster severity across Afghanistan. These spatial analyses place better constraints on the placement of active and historic seismicity along mapped and known active faults for progress in earthquake disaster management. Furthermore, we define current hazards associated with building and infrastructural design and competency given the recurrent and eminent seismicity within Afghanistan and describe possible directions and solutions to mitigate the threat to life and property.
The Shotori mountain range is located along the northern terminus of the Nayband fault on the eastern and western domains of the Tabas and Lut blocks, respectively. This range with NNW-SSE trending and approximately 120 km long includes a series of thrust faults approaching the right-lateral strike-slip Nayband fault. Since the Shotori range has experienced various geological events since the Triassic, our investigations suggest that the basement of the Central Iranian subcontinent of the Shotori range contains the early Triassic deep sedimentary with normal faults which confirms Triassic tensional tectonic stress regime in the region. After the middle Triassic, the mountain range has experienced thrust and strike-slip regimes. Therefore, in this study, we reconstruct the stress regimes for different geological periods using fault-slip data. The inversion of fault-slip data reveals drastic temporal changes in the maximum stress regime (σ1) over the Triassic, Jurassic, Cretaceous, Paleogene, Neogen, and Quaternary. The reconstruction of the stress field based on the age and direction of fault movement reveals that the direction of the maximum horizontal stress axis (σ1) under a tensional stress regime was approximately N129° in the Early Triassic. This stress regime is the cause of thinning and subsidence of the Shotori sedimentary basin. During the middle Triassic, the σ1 direction was about N81° and the upper Triassic, the σ1 direction was almost N115°. The middle Triassic and upper Triassic stress states exhibited two distinct strike-slip and compressive stress regimes. This stress regime led to the uplift of the Shotori sedimentary basin. During the Jurassic, the direction of the maximum horizontal stress axis (σ1) was ∼NW-SE under a compressive stress regime. During the Triassic, the σ1 direction was ∼N-S. This stress regime led to the formation of the high topography of the Shotori Mountain Range. In the Late Cretaceous, the direction of the maximum horizontal stress axis (σ1) under the extensional stress regime was ∼NE-SW. This stress regime led to the uplift of the Paleogen Dacite in eastern Iran. During the Neogene, the σ1 direction was ∼N6o°. The Quaternary tectonic regime is strike-slip and the σ1 direction is ∼N50°, consistent with the current convergence direction of the Arabia–Eurasia plates. Our paleostress analysis reveals four recognized stress in this area, which includes compressional, transtensional, transpressional, and strike-slip regimes. Our findings indicated that the crustal diversity of the tectonic regimes was responsible for the formation of various geological structures, such as folds, faults by different mechanisms, and the present-day configuration of the Shotori sedimentary basin.
