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Mr Mohamad Khalaj,
Volume 6, Issue 3 (9-2019)
Volume 6, Issue 3 (9-2019)
Abstract
Abstract
Seismic potential investigation of Tehran as the capital of Iran is an essential issue because their accumulation around a fault may indicate its seismic potential. Stress trajectories for this estimate are useful. In this research, fault slip data is used for paleo stress analysis. Base on that, the study area divided into 6 stable stress regions and the mean stress tensor related to each region determined. Then the mean stress tensor rotated based on Anderson’s theory representing a compressional tectonic regime. The Stress trajectory map drew based on rotated mean stress tensor acting on the regions during geological time. The resulted map showed the arrangement of sigma1 trajectories in the area obeyed the overall tectonic regime in Iran and limited converge through the junction ignoring addition in stress magnitude and seismic hazard in the junction of major faults.
Given the importance of Tehran as the political-economic capital of the country, and its location in Alborz Basin with high faults density. and due to the seismic background of the area, the necessity of seismic risk assessment in this area becomes more evident. In this research, we have attempted to produce and present a map of faults in the Tehran wide area, focusing on faults in the eastern part of Tehran, Mamlouk, Ghasre Firozeh and the margins, with accurate structural elements and drawing of the stress trajectories, convergence of the trajectories, and stress accumulation at convergence sites, assess seismic hazard at this location based on longitudinal stress data (Katsushi Sato, 2011; Yamada and Yamaji, 2002; Yamaji, 2000; Sippel et al., 2009).
Based on field observations and data collected, scratch faults were selected for collecting and analysis of longitudinal paleo stresses as they record all deformation stages. After collecting the fault data, we stabilized them using the Multiple Inverse Method (MIM) and zone boundaries, and by drawing a Mohr's circle (without scale) for each range, seismic potential analysis was performed (Katsushi Sato, 2011; Yamada and Yamaji, 2002; Yamaji, 2000; Sippel et al., 2009).
To separate the stress phases, obtain the reduced stress tensor, obtain different stress and stress parameters, and plot the stress trajectories, the study area had to be divided into smaller ranges. It is not possible to determine the size of the stress components and the principal stresses by longitudinal stress methods and it is not possible to draw a scaled circle. Therefore, it is possible to draw a circle without scales for fault data only. This circle enables the overall analysis of the field shape, the arrangement of the data in the graph, and the comparison of the relative components of the fault data stress. By the Mohr's circle (without scale) method, the principal minimum stress and the maximum stress difference (s1 - s3) are considered as base (0) and unit (1), respectively, and assume the same size with respect to the relation (F = (s2 - s3) / (s1 - s3)) between the calculation of the middle stress field shape and the field shape factor. Studies show that tensile tectonic structures are not dominant structures in the region. For the kinetic analysis of fault data, precise rock mechanics such as the internal friction angle and the Amonton-Columbus criterion cannot be used precisely. But given the arrangement of the fault data, a large degree of comparison can be made between the kinetic features and especially the fault dynamics of each range. Therefore, the main maximum stress must be horizontal. Assuming that all the faults are coherent and based on Anderson's theory of faulting that the main minimum stress is vertical in the compressive stress regime, the position of the principal stress axes of each range is returned to the conditions of the fault formation (vertical minimum stress). In all ranges, the principal minimum stress is near vertical. After rotation of the data and the vertical axis of the minimum stress was set, the trajectory maps were drawn for horizontal stresses (main and maximum stresses).
A study based on longitudinal stress studies and Andersen's theory introduces the main maximum stress trend N017E, which is in good agreement with the general crustal shortening trend of the Central Alborz (Vernant et al., 2004). Therefore, the major faults of the region do not have a significant impact on the disturbance of the stress field within the region and, in fact, the convergence of these faults does not lead to the convergence of stress trajectories. The positioning of the poles of the fault plates on the main stress plates indicates that along with the crustal deformation in this part of Alborz, the regional structures have been rotated and decomposed. In fact, the reason for the polarization of fault plates on the main stress sheets with zero shear stress is that the rotation and positioning of faults coincide with the rotation and deformation of other geological structures and phenomena such as folds and joints. The arrangement of the poles of the fault plates in the Mohr's circle indicates that the faults in zone 3 have less dynamic potential than elsewhere.
Keywords: Stress Trajectory, Multiple Inverse Method, Convergent Faults, Seismic Hazard, Mamlouk, Ghasre Firouzeh.
Dr. Shahrokh Pourbeyranvand,
Volume 8, Issue 2 (9-2021)
Volume 8, Issue 2 (9-2021)
Abstract
Seismic risk investigation by Strain rate variation study in central
Alborz by using GPS data
Abestract
The Alborz Mountains, South of Caspian Basin and separates Central Iran from Eurasia. Talesh and Kopeh Dagh bound the Alborz as major thrust belts in the west and east respectively. The tectonic evolution of this important region is still unsolved and there are many questions to answer, such as the origin of the Alborz Mountains as well as its crustal structure. The Alborz is of great important in natural and most particular, seismic hazard investigations, because of the existence of Tehran megacity. This importance resulted in development of a relatively dense network of GPS stations in this regions and adjacent areas. The Alborz Mountains formed successively during the collision of Central Iran with Eurasia in the Late Triassic (Cimmerian Orogeny) and the collision of Arabia with Eurasia. Tectonic activity in this belt is currently thought to be controlled by two motions with different velocities, the 5 mm/yr northward convergence of central Iran to Eurasia causing a compression from 7 Ma and the 4 mm/yr left‐lateral shear northwestward motion of the South Caspian Basin resulting in a left lateral transpressive tectonic environment in the Alborz . Since middle Pleistocene transtensional motion is also observed in the region because of acceleration of SCB motion toward North West.
GPS studies in the Zagros started in 2000 and are continuing by gradual expansion of the permanent GPS network and several GPS campaigns and temporary stations. These studies have significantly improved our understanding of the surface deformation in the Alborz. In this study the interpolation of GPS velocity vectors in a rectangular grid and calculation of the strain at the center of each grid cell, were used for the study of the strain rate variations in the central Alborz. We used velocity vectors from Djamur et al. (2010) to estimate the strain rate field in the Alborz. To avoid edge-effects in the strain calculation, we only showed the results for the central part of the dataset. The GPS velocities are interpolated onto a rectangular north-south grid of 0.2 by 0.2 degrees and strains are calculated at the center of each grid cell, following the methodology of Haines et al. (1998) and Beavan & Haines (2001). The study of the strain rate variations can help in understanding the tectonic settings of the region and the obtained results, combined with other geodetic, geological and seismological studies, already performed in the region, can provide a comprehensive insight into the geodynamic evolution of the range.
The results showed spatial variations in principle strain rate axes directions and areal strain rate or dilation, which in combination with seismicity data, reveals important information about the fault movement mechanisms in the area. Observed anomalies in dilation, showed important correlations with seismicity, subsidence and uplift, dip slip and strike slip movements on the faults in the region and confirmed deformation partitioning which takes place due to tectonic forces, acting on pre-existing faults and weak fracture planes. The partitioning of the deformation causes dominant strike slip motion in some parts of the Central Alborz, while shortening occurs dominantly on other parts of the mountain range. These different parts are spatially separated in the region and correlate with the seismicity with regard to the faulting mechanisms expected from the orientation of the major faults and the directions of strain rate axes.
Key words: areal strain rate Central Alborz, deformation partitioning, dilation, faulting mechanisms, GPS, seismic ris
Alborz by using GPS data
Abestract
The Alborz Mountains, South of Caspian Basin and separates Central Iran from Eurasia. Talesh and Kopeh Dagh bound the Alborz as major thrust belts in the west and east respectively. The tectonic evolution of this important region is still unsolved and there are many questions to answer, such as the origin of the Alborz Mountains as well as its crustal structure. The Alborz is of great important in natural and most particular, seismic hazard investigations, because of the existence of Tehran megacity. This importance resulted in development of a relatively dense network of GPS stations in this regions and adjacent areas. The Alborz Mountains formed successively during the collision of Central Iran with Eurasia in the Late Triassic (Cimmerian Orogeny) and the collision of Arabia with Eurasia. Tectonic activity in this belt is currently thought to be controlled by two motions with different velocities, the 5 mm/yr northward convergence of central Iran to Eurasia causing a compression from 7 Ma and the 4 mm/yr left‐lateral shear northwestward motion of the South Caspian Basin resulting in a left lateral transpressive tectonic environment in the Alborz . Since middle Pleistocene transtensional motion is also observed in the region because of acceleration of SCB motion toward North West.
GPS studies in the Zagros started in 2000 and are continuing by gradual expansion of the permanent GPS network and several GPS campaigns and temporary stations. These studies have significantly improved our understanding of the surface deformation in the Alborz. In this study the interpolation of GPS velocity vectors in a rectangular grid and calculation of the strain at the center of each grid cell, were used for the study of the strain rate variations in the central Alborz. We used velocity vectors from Djamur et al. (2010) to estimate the strain rate field in the Alborz. To avoid edge-effects in the strain calculation, we only showed the results for the central part of the dataset. The GPS velocities are interpolated onto a rectangular north-south grid of 0.2 by 0.2 degrees and strains are calculated at the center of each grid cell, following the methodology of Haines et al. (1998) and Beavan & Haines (2001). The study of the strain rate variations can help in understanding the tectonic settings of the region and the obtained results, combined with other geodetic, geological and seismological studies, already performed in the region, can provide a comprehensive insight into the geodynamic evolution of the range.
The results showed spatial variations in principle strain rate axes directions and areal strain rate or dilation, which in combination with seismicity data, reveals important information about the fault movement mechanisms in the area. Observed anomalies in dilation, showed important correlations with seismicity, subsidence and uplift, dip slip and strike slip movements on the faults in the region and confirmed deformation partitioning which takes place due to tectonic forces, acting on pre-existing faults and weak fracture planes. The partitioning of the deformation causes dominant strike slip motion in some parts of the Central Alborz, while shortening occurs dominantly on other parts of the mountain range. These different parts are spatially separated in the region and correlate with the seismicity with regard to the faulting mechanisms expected from the orientation of the major faults and the directions of strain rate axes.
Key words: areal strain rate Central Alborz, deformation partitioning, dilation, faulting mechanisms, GPS, seismic ris
Abolghasem Goorabi, Seyed Mohammad Zamanzadeh, Mojtaba Yamani, Parisa Pirani,
Volume 8, Issue 3 (12-2021)
Volume 8, Issue 3 (12-2021)
Abstract
Evaluation and comparison of the accuracy of fault and seismic data in fractal analysis of northwest Zagros tectonic
Introduction
Complexity of natural processes especially tectonic processes that shape landscapes cannot be evaluated by classic geometry. In comparison with integer dimension of Euclidean space, fractal geometry can analyze features with non-integer dimension (Turcotte, 1977:121). Fractal behavior in such features shows self-similarity that this component is independent of the accuracy of investigation (Baas, 2002, 311). In fact, fractal dimension, is scale-invariant (Phillips, 2002, 144). Spatial variations of fractal parameters are an important factor in studying the tectonic state of regions. By determining the fractal dimension of Linear structures such as faults, it is possible to compare their geometry disorder (Suk moon et al, 1996:5). This parameter affects seismic behavior of fault because earthquake is an event related to faulting (Bachmanov, et al, 2012: 221) and Their concentration in an area indicates tectonic activity. In this research we performed fractal analysis using box counting method on fault and seismic data of northwest of Zagros about different scales of fault and different time periods of earthquake epicenters of two organizations with various detail to find and examine their fractal behavior by fractal dimension.
Methods
Data in this research can be divided to three clusters: 1. Fault lines of two scales of geology maps (1:100000 and 1:250000), 2. Earthquake epicenters of two periods of times prepared by two organizations (20 century data of Institute of Geophysics and 1900-2020 data of International Institute of Earthquake Engineering and Seismology) and 3. The second cluster with exert of Magnitude of completeness of earthquakes that show the minimum magnitude above which the data in the earthquake catalog is complete. Fractal analysis applied on these data by box counting method. To achieve this goal firstly, under study area divided to 6 boxes that contain main fault trends horizontally and vertically (A: folded Zagros in west of Kermanshah, B: faulted Zagros around Kermansha and east of kermansha, C: folded Zagros near mountain front fault, D: An area between faulted and folded Zagros near Khoramabad, E: Area around Balarud fault and F: An area between Balarud and mountain front fault to faulted Zagros). To calculate fractal dimension of fault lines and distribution of earthquake epicenters, box counting method suggested by Turcotte (1997) were applied by using Hausdorff dimension, which in two quantity of size (side length of grids) and number (number of grid boxes containing earthquake epicenter or fault) are used to calculate FD (total fractal dimension) value (Schuller et al, 2001: 3). Relation between reciprocal of side length (quantity of size) and number of boxes containing point and linear features (quantity of Number) was drawn Logarithmically as a linear regression in Excel that shows fractal dimension.
Result and discussion
Larger values of fractal dimension indicate greater geometric disorder (Sukmono et al., 1996: 5). Analysis of faults of two scales represent that faults geometry is fractal and the amount of FD for scale of 1:100000 compared with scale of 1:250,000 is larger but their result approximately is same. The FD values for both scales are locate between 1 and 2 that expresses development of the fractal community of faults has a linear trend. On the other hand, for earthquakes, increase in FD values shows that earthquakes are not clustered and are distributed homogeneously (Oncel & Wilson, 2002: 339) along a line in understudy area. Calculated number-size values for faults and earthquakes represent both partial and popular FD changes. Based on partial FD, two populations can be classified: (a) Background with FD larger than popular FD; (b) Threshold with FD lower than popular FD.
Conclusion
Fractal analysis of faults of two scales of geology maps reveals that the order of active areas with high FD values in both scales are same but due to different details of faults in geology maps of geology survey and oil company, in scale of 1:100000 area labeled B and in scales of 1:250000 area labeled A is the most tectonically active region, however, area labeled E in both scales has lowest value. The order of active areas based on FD values for earthquake epicenters of 1900-2021 data of geophysics institute do not support other results because area labeled C with low density of faults and earthquake epicenters is in the first order and area labeled A is on the contrary of it. However, FD results of 20 century earthquake epicenters with exert of magnitude of completeness are reliable and higher magnitude of earthquakes spatially recent Ezgeleh earthquake in area labeled A is its evidence.
Keywords: Fractal, Tectonic, Northwest Zagros, Fault, Earthquake
Bibi Zahra Hosseini Giv, Sara Kiani, Syed Morovat Eftekhari, Mahdi Saghafi, Siros Esmaeili,
Volume 10, Issue 2 (9-2023)
Volume 10, Issue 2 (9-2023)
Abstract
Introduction
Today, in addition to exploiting environmental resources, humans must be able to recognize environmental hazards and try to reduce their damages. The location of Iran in the Alpine-Himalaya mountain belt has made Iran one of the high-risk seismic areas, and the east of Iran is no exception to this rule. The fault activities of eastern Iran, especially east and west of Lut, are a serious threat to the residents of eastern Iran. The activity of old and young faults and the emergence of new faults have provided the basis for the occurrence of destructive earthquakes in these areas. And it still continues and has been able to provide problems for the population living in the east of Iran.
The purpose of this research is to investigate the role of the Giv fault system in the occurrence of morphotectonic evidence and active tectonic analysis in the studied area, which has achieved favorable results according to the model used and the studied sources. The model used in this research, which is derived from similar examples in foreign sources, mostly deals with the destructive aspect of tectonics and has achieved the desired goals. Based on this, it should be seen if the morphotectonic evidence of the Giv fault system can be a sign of more activity and more threat in this part of the range (southern domain of Baghran mountains) or not? After studying various sources, the sources that answer the research questions were selected and further analyzed, and the conceptual model derived from these sources, which has a qualitative-analytical aspect, was used. Therefore, according to the main objectives of this research, which follows the destructive and instantaneous tectonic aspect, sources were selected that provided the most information to answer the research question, the sum of the information expressing the active tectonics in the studied area.
Research Methodology
The Giv fault system is a part of the Nehbandan-Kash fault in the east of the Lut block, and in the Giv plain, north-east of the Lut, with an almost west-east direction, it passes through the south of the Giv village and continues to Deh Mir and Karijgan in the west of the Giv plain. Giv village is located in Khosf County in South Khorasan province and in the center of Giv plain, south of Baghran Birjand Mountains and north of Shah Mountain.
The current research is of applied and developmental research type, and according to the history of seismicity of the region and historical data, it can be a step in the direction of knowing the seismic risk areas and also reminds the local residents to be more prepared. The conceptual model used in this research, which is derived from similar foreign examples, examines mostly the destructive aspect of tectonics.
In this research, the library work started by collecting and receiving a series of domestic and foreign sources, followed by the translation of foreign sources over a long period of time. Also, statistics and information were received from Geological Organization and Geophysics Institute, Birjand University, Birjand Seismological Center. Field studies, interviews, surveys and field measurements, using geological and topographic maps and satellite images, and using Google Earth and Arc GIS software, analysis and synthesis of information were carried out. Most of the data were used as qualitative data and to some extent quantitative data in the analysis.
Result and Discuction
The morphotectonic evidence in the studied area indicates a high risk of seismicity in the Giv fault pack, which is more dangerous than other parts of the Giv fault system.All the evidences such as uplift and cliffs in the south of Giv, significant change of the bridge river near the mouth and bed digging in this section show the uplift and activity of the South Giv fault and the travertine formation associated with the earthquake in the south of Giv, as well as the evidence of the growth of the Young Giv fold in 5 km. North of Giv village, such as the deviation of Pol and Minakhan rivers and excavation of the Minakhan river bed (Antecedence phenomenon), the presence of three generations of alluvial fans in the vicinity of the Young Giv fold, all indicate active tectonics and the rise of the Giv fold and the occurrence of destructive earthquakes. All the above-mentioned evidences are a serious alarm for the residents of Giv fault, especially Giv village, and require more study work, strengthening of villages, and proper planning for construction works so that the past tragic events of Giv village do not repeat in the future and this issue is taken into consideration in the discussion of land development.
Today, in addition to exploiting environmental resources, humans must be able to recognize environmental hazards and try to reduce their damages. The location of Iran in the Alpine-Himalaya mountain belt has made Iran one of the high-risk seismic areas, and the east of Iran is no exception to this rule. The fault activities of eastern Iran, especially east and west of Lut, are a serious threat to the residents of eastern Iran. The activity of old and young faults and the emergence of new faults have provided the basis for the occurrence of destructive earthquakes in these areas. And it still continues and has been able to provide problems for the population living in the east of Iran.
The purpose of this research is to investigate the role of the Giv fault system in the occurrence of morphotectonic evidence and active tectonic analysis in the studied area, which has achieved favorable results according to the model used and the studied sources. The model used in this research, which is derived from similar examples in foreign sources, mostly deals with the destructive aspect of tectonics and has achieved the desired goals. Based on this, it should be seen if the morphotectonic evidence of the Giv fault system can be a sign of more activity and more threat in this part of the range (southern domain of Baghran mountains) or not? After studying various sources, the sources that answer the research questions were selected and further analyzed, and the conceptual model derived from these sources, which has a qualitative-analytical aspect, was used. Therefore, according to the main objectives of this research, which follows the destructive and instantaneous tectonic aspect, sources were selected that provided the most information to answer the research question, the sum of the information expressing the active tectonics in the studied area.
Research Methodology
The Giv fault system is a part of the Nehbandan-Kash fault in the east of the Lut block, and in the Giv plain, north-east of the Lut, with an almost west-east direction, it passes through the south of the Giv village and continues to Deh Mir and Karijgan in the west of the Giv plain. Giv village is located in Khosf County in South Khorasan province and in the center of Giv plain, south of Baghran Birjand Mountains and north of Shah Mountain.
The current research is of applied and developmental research type, and according to the history of seismicity of the region and historical data, it can be a step in the direction of knowing the seismic risk areas and also reminds the local residents to be more prepared. The conceptual model used in this research, which is derived from similar foreign examples, examines mostly the destructive aspect of tectonics.
In this research, the library work started by collecting and receiving a series of domestic and foreign sources, followed by the translation of foreign sources over a long period of time. Also, statistics and information were received from Geological Organization and Geophysics Institute, Birjand University, Birjand Seismological Center. Field studies, interviews, surveys and field measurements, using geological and topographic maps and satellite images, and using Google Earth and Arc GIS software, analysis and synthesis of information were carried out. Most of the data were used as qualitative data and to some extent quantitative data in the analysis.
Result and Discuction
The morphotectonic evidence in the studied area indicates a high risk of seismicity in the Giv fault pack, which is more dangerous than other parts of the Giv fault system.All the evidences such as uplift and cliffs in the south of Giv, significant change of the bridge river near the mouth and bed digging in this section show the uplift and activity of the South Giv fault and the travertine formation associated with the earthquake in the south of Giv, as well as the evidence of the growth of the Young Giv fold in 5 km. North of Giv village, such as the deviation of Pol and Minakhan rivers and excavation of the Minakhan river bed (Antecedence phenomenon), the presence of three generations of alluvial fans in the vicinity of the Young Giv fold, all indicate active tectonics and the rise of the Giv fold and the occurrence of destructive earthquakes. All the above-mentioned evidences are a serious alarm for the residents of Giv fault, especially Giv village, and require more study work, strengthening of villages, and proper planning for construction works so that the past tragic events of Giv village do not repeat in the future and this issue is taken into consideration in the discussion of land development.
Gholam Hassan Jafari, Zeinab Karimi,
Volume 10, Issue 4 (12-2023)
Volume 10, Issue 4 (12-2023)
Abstract
Abstract
In geosciences, morphotectonic indicators are used to investigate the effectiveness of land surfaces from neotectonic activities. In this article, the results of morphotectonic indices by tectonic zones of Iran, according to the energy released from the earthquake of 1900-2009 and the position of the basins relative to the types of faults (young seismic faults), Quaternary and pre-Quaternary) were analyzed. For this purpose, 110 years old Iran seismic data was extracted from the geodatabase, and during the programming process in MATLAB, it was converted from point-vector to surface-raster. In addition the results of the evaluation of morphotectonic indices of 142 basins of different zones were used; 8 inactive basins, 40 semi- active basins, and 94 active basins. Inactive basins are located in Alborz, Zagros, and Central Iran. . The results indicate that the amount of energy released can't examine a significant role in evaluating the morphotectonic indices of the basins. Basin’s location in the area of Quaternary faults and young seismic is of great value in the tectonically active basin. The lie of semi-active basins adjacent to active basins, or the lie of inactive basins adjacent to semi-active and active basins; and it should be borne in mind that the thresholds used to estimate the tectonic activity status of basins cannot be used as a definite and mathematical criterion in estimating the tectonic status of basins.
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