Stress

Open Access Article

1 - Determination of stress state and tectonic regime changes in the brittle structures of Chah Yusuf Mountain (East of Gonabad)
فرهاد زارعی Ghaemi Ghaemi

In this study, structural elements, such as faults and fractures and their formation mechanisms and relationships with tectonic regime of Chah Yusuf Mountain in East of Gonabad city have been recognized and discussed. Their relation with regional fractures, based on dat More

In this study, structural elements, such as faults and fractures and their formation mechanisms and relationships with tectonic regime of Chah Yusuf Mountain in East of Gonabad city have been recognized and discussed. Their relation with regional fractures, based on data’s from satellite image process and field data, is also shown. Major faults in this area were identified by using fault plain features such as striations, stretching vein and cumulative steps of minerals that helped us to determine fault mechanisms. In general, faults were oriented in three main directions: 1) Reversed faulting along N90-120˚, 2) Right lateral strike –slip faults along N140-160˚ and 3) Normal faults along N0-15˚. Based on the obtained data and using the inversion method, the orientation of the principal stress axes (σ1، σ2 and σ3) and the ratio of the principal stress differences R in the studied area were analyzed. The results showed two different tectonic regimes in the formation of regional structures: 1) Compressive tectonic regime, major stress along NNE-SSW, which generated structures of folds and reversed faults. 2) Shear tectonic regime, compressive stress along NE_SW and tensile stress line NW-SE, which generated structures such as strike-slip faults, normal faults, vein and tensile fracture. So, the major stress direction in this region is NNE-SSW, which shows its relation to the Late Cenozoic Arabia –Eurasia oblique continental collision. Manuscript profile

Open Access Article

2 - Paleostress analysis of Mansour-Abad area (southeast Rafsanjan - Kerman Province) using Multiple Inversion Method
لیلا عبادی Alavi Ghassemi

This study uses multiple inversion method to analyze slip data on shear planes and faults containing slickenlines in different rock units, and evaluates paleostress field in Mansour-Abad area. It was gathered the required kinematic data in 18 stations according to the s More

This study uses multiple inversion method to analyze slip data on shear planes and faults containing slickenlines in different rock units, and evaluates paleostress field in Mansour-Abad area. It was gathered the required kinematic data in 18 stations according to the stratigraphic age of the rock units. It was used the most important shear sense indicators, including mineral steps, Riedel shears and tension fractures. According to the multiple inversion method, which calculates stress tensor from the inhomogeneous fault data (data without any knowledge of stress field orientation or fault classification), four parameters of stress ellipsoid shape and axes were analyzed. It was found 3 different phases of compression, extension-shear and shear- compression using the phase separation in this method. The maximum principal stress orientation in different locations changes from N24˚ to N162˚ between Cretaceous and Neogene, while the minimum principal stress orientation changes from N79˚ to N116˚. The NW-SE strike of the reverse faults indicates that these faults developed during the activity of compressional phase. During the extensional-shear phase of the activity, local sedimentation occurred in the area. Late shear deformation of area, and change in stress field orientation, resulted in a block rotation between the fractures. Further increase in the rotation caused the fractures to increase in size, and provide space for intrusion of the magma. Manuscript profile

Open Access Article

3 - Paleostress analysis in Bozqush Mountains, northwest Iran
احد نوری Parisa Amini Sharifi Moayyed

Knowledge of the local stress field in a region is important in the structural and affecting factors on structural kinematics studies. Therefore, in this paper after describing the basic theoretical principles of stress inversion method from slickensides, it was used More

Knowledge of the local stress field in a region is important in the structural and affecting factors on structural kinematics studies. Therefore, in this paper after describing the basic theoretical principles of stress inversion method from slickensides, it was used field measured heterogeneous fault –slips as raw data to determine the average state of the principal stress axes in order to analyze the regional geodynamic situation of this area. The results of the reduced stress tensor from fault-slip measured data, show 21/156، 64/012 and 14/251 states for σ1، σ2 and σ3 axes respectively. The results of analysis of these data show substantial agreement between the determined principal stress axes and recent tectonic research in this region. Manuscript profile

Open Access Article

4 - Seismotectonics of the west of Golestan province, the east of south Caspian region
Maryam Agh-Atabai Marjan Tourani

Golestan province is located in one of the seismically active zones of Iran. The seismicity maps of Golestan province show that density of earthquakes in the west is more than the east. In this research, the parameters including b-value, recurrence time and seismic mome More

Golestan province is located in one of the seismically active zones of Iran. The seismicity maps of Golestan province show that density of earthquakes in the west is more than the east. In this research, the parameters including b-value, recurrence time and seismic moment were studied to investigate the seismicity of the west of Golestan province. The focal mechanism of earthuqakes and field data were used to determine the stress orientations in the study area. The estimated b-value is obtained as 1.24±0.2 which is comparable with the Alborz. Since the northern and southern parts of the study area have different geomorphological and structural characteristics, some of these parameters were calculated for two subdivisions; Dasht-e-Gorgan in the north and foothill in the south. Results of this study show that the earthquakes in the Dasht-e-Gorgan compared to the foothill are smaller with shorter recurrence times. For the foothills, the calculated P-axes using the stress tensor inversion method is found to be subhorizontal with trend N-NNE. For this region, at least two trends, N and NW, is calculated using field data. This result show the change of stress directions during the structural evolution of this area. The calculated p-axes trend for the Dasht-e-Gorgan is NE. In both studied areas, the focal mechanisms of greater earthquakes are consistent with the E-W to NE-SW trend of main faults especially the Khazar fault. But, the smaller events in the Gorgan Plain show a different trend and mechanism. Comparison of these two subdivisions shows that the northern Alborz foothill is more dangerous than the plain. Manuscript profile

Open Access Article

5 - Cenozoic superposed deformation in the south of Central Iran: Implication for folding and tectonic stress field in Rafsanjan structural belt
لیلا عبادی Seyd Ahmad Alavi Mohamad Reaz Ghasemi

The South Central Iran Block has experienced polyphase intensive deformation in the Cenozoic time. Large-scale superposed folds in South Rafsanjan document the Cenozoic tectonic events within the South Central Iran Block. In this study, a case study of this deformation More

The South Central Iran Block has experienced polyphase intensive deformation in the Cenozoic time. Large-scale superposed folds in South Rafsanjan document the Cenozoic tectonic events within the South Central Iran Block. In this study, a case study of this deformation inferred from regional-scale Rafsanjan superposed folds in the south of Central Iran is presented to reconstruct the deformation sequence and tectonic regime during crustal shortening. These data indicate that the superposed folds, dominated by a two-stage tectonic transpression regime which experienced two phases of superposed folding, leading to the orthogonal superposition of WNW–ESE-trending folds onto NE–SW trending folds. Structural analyses and fault kinematic analyses in the Rafsanjan Structural Belt indicate a two-stage syn-folding paleo-stress field during the Cenozoic. The early phase of tectonism is characterized by late Miocene NW-SE transpression, which led to the development of NE-trending fold structures and causing the occurrence of an orogeny perpendicular shortening. This tectonic event was most likely associated with progressive anticlockwise rotation of the Central Iran Block. Subsequent tectonic event from Late Miocene until Quaternary contributed to a phase of contraction that overprinted the early NNE–SSW shortening in the interior parts of the studied area and generated a large-scale NE-convex fold belt and the typical large-scale superposed folds within the South of Central Iran Block. In terms of geodynamics, the later tectonism is likely to have been related to the NE-directed convergence between the Arabian and the Eurasian Plates. Manuscript profile

Open Access Article

6 - Reconstruction of present-day local stress field affecting the North Tabriz Fault and surrounding areas based on earthquakes focal mechanism by using inversion method
Ahad Noori Behnam Rahimi

In this research, present-day tectonic stress field affecting North Tabriz Fault and surrounding areas was reconstructed by using 37 compiled earthquakes focal mechanism from various sources. Triangle diagrams were used to determine the sense of the earthquakes focal me More

In this research, present-day tectonic stress field affecting North Tabriz Fault and surrounding areas was reconstructed by using 37 compiled earthquakes focal mechanism from various sources. Triangle diagrams were used to determine the sense of the earthquakes focal mechanism. The sense of these data varies from strike-slip to thrust regime. Stress separation process was applied on data set for separation of the various tectonics regimes from a poly-phase system to obtain reduced stress tensors. This was done because most of the data participated in them and reconstructed stress fields completely cover the stresses affecting the region. The results of inversion analysis and internal separation of the data set show three stress regimes acting in this region. Considerably, all three stress regimes have a horizontal pressure stress with NW-SE to NNW-SSE trend. The direction of maximum pressure in each first, second and third regimes is 09/329, 28/310 and 03/138, respectively. In this research, present-day tectonic stress field affecting North Tabriz Fault and surrounding areas was reconstructed by using 37 compiled earthquakes focal mechanism from various sources. Triangle diagrams were used to determine the sense of the earthquakes focal mechanism. The sense of these data varies from strike-slip to thrust regime. Stress separation process was applied on data set for separation of the various tectonics regimes from a poly-phase system to obtain reduced stress tensors. This was done because most of the data participated in them and reconstructed stress fields completely cover the stresses affecting the region. The results of inversion analysis and internal separation of the data set show three stress regimes acting in this region. Considerably, all three stress regimes have a horizontal pressure stress with NW-SE to NNW-SSE trend. The direction of maximum pressure in each first, second and third regimes is 09/329, 28/310 and 03/138, respectively. Manuscript profile

Open Access Article

7 - Difference of in situ stress regime dependent on Structural position and geomechanical characteristics, Case study- Gachsaran and Asmari formations, SW Iran
Hossein Talebi Seyd Ahmad Alavi Mohamad Reaz Ghasemi Shahram Sherkati

Estimation of in-situ stress tensor in sedimentary basins using information obtained from exploration and development oil and gas wells during the drilling and logging process may be used for estimation of in-situ stress tensor in sedimentary basins. The in-situ stress More

Estimation of in-situ stress tensor in sedimentary basins using information obtained from exploration and development oil and gas wells during the drilling and logging process may be used for estimation of in-situ stress tensor in sedimentary basins. The in-situ stress magnitude and orientation and the resulting stress regime around the studied wells have been several application in secondary recovery programs from hydrocarbon reservoirs as well as wellbore stability analysis. In this paper, the magnitude of in-situ stress is estimated by using abovementioned data in some oil wells located in the south west of Iran. Increasing the oil production by hydraulic fracturing design and sand control in the multi-layer reservoirs such as the Marun giant oil field with loose sand horizons and also improving drilling performance in the Gachsaran formation¬ requires knowledge about the prevailing stress conditions. This research, tries to analyze the stress regime of the Asmari and Gachsaran Formations around the selected wells in the Marun and Lali fields using constructed Mechanical Earth Models (MEM) and their differences are discussed. The calculated stress magnitudes in studied wells indicate a significant drop in magnitude of horizontal stresses from the Gachsaran to Asmari reservoirs in the Marun oil field. The magnitudes of the three principal stresses resulted that SHmax is the maximum principal stress and the Shmin is the minimum principal stress, thus a strike-slip stress regime (SHmax>Sv>Shmin) dominates in the Gachsaran sequence and the Asmari formation of the Lali oil field. however, in the Gachsaran formation of Marun giant oil field, stress regime is reverse-strike slip but normal stress regime is dominated in it's Asmari reservoir. The In-situ stress condition indicates that the structural condition and the depth difference of these structures plays an important role in the tectonic stress regime changes. Manuscript profile

Open Access Article

8 - Analysis of stress regime in Shah Deniz oilfields and wellbore stability, in south Caspian Sea basin
Parvaneh Alizadeh Saeid Mohammad Hassanpour sedghi Ali Kadkhodaie Malek Mohammad Gity

20.1001.1.17357128.1398.13.50.3.7

Wellbore instability is one of the main problems during drilling of oil and gas wells. Analyzing and wellbore instability prediction is important. In-situ stress measurement and stress regime are important for stability studies. This study was carried out in one of the More

Wellbore instability is one of the main problems during drilling of oil and gas wells. Analyzing and wellbore instability prediction is important. In-situ stress measurement and stress regime are important for stability studies. This study was carried out in one of the oilfields in the south Caspian basin in Iran. The compressional stress regime in the studied field was determined based on regional stress indicators and larg scale tectonic observations. . This study presented the effect of borehole inclination and azimuth on borehole stability under reverse fault regimes. The magnitude of stresses was determined from measured sonic velocities, density log and predicted pore pressure utilizing the Eaton method. In this study, the modified Lade model have been utilized to perform stability calculation for different inclinations and azimuths. In this study, to perform stability calculation with the use of STABview software is presented. It is shown that drilling wells parallel to maximum in-situ horizontal stress (NE-SW) causes less stability problems. The results of this study could help in the mitigation and/ or prevention of wellbore stability issues in this oilfield. Manuscript profile

Open Access Article

9 - Determining paleo-stress based on the study of discontinuities and folds in Zagros Collision Zone; Case Study: Kermanshah Region
سپیده رضابیک عبدالله سعیدی Mehran Aryan علی سربی

20.1001.1.17357128.1400.15.57.5.7

The studied zone is in the Northern part of Zagros Suture Zone (Kermanshah). The presence of deep sea sediments, oceanic crust remnants, platform carbonates, igneous and metamorphosed rocks of active margin and carbonate sequence of passive margin that are assembled in More

The studied zone is in the Northern part of Zagros Suture Zone (Kermanshah). The presence of deep sea sediments, oceanic crust remnants, platform carbonates, igneous and metamorphosed rocks of active margin and carbonate sequence of passive margin that are assembled in the studied area show a compressional tectonic regime from the late Cretaceous up to the present. As a result of convergent regime, a very complicated structural zone is developed. The main purpose of this study is stress characteristic analysis in Zagros Suture Zone (Kermanshah).To recognize and study the arrangement of stress axes a great amount of data were gathered from the folds axial surface and the faults which are appeared within the rocks specially the radiolaritic rocks. The data includes characteristics of fault surface geometry, fault slip and lineation slip. The stress recording patterns for data in this study is Multiple Inverse Method and comparison with stress position by using folds axial surface. By studying folds it was obtained the situation of main stress σ1, σ2 and σ3 respectively as 029, 127, 234 and by using the method Multiple Inverse Method, the situation of main stress is obtained as 059, 304, 194. Based on the investigations in the study area and measurements on Cretaceous rocks, the results show that the main stress direction since Cretaceous up to the present is northeastern with minor changes. The estimations of stress direction were the same in both folds and faults. As a result, the shortening direction has been constant, so the shortening faults all show one direction of stress. Manuscript profile

Open Access Article

10 - A new look at the rotation of Central Iran: A case study of the Anar fault, east block of the Yazd
Hamidreza AfkhamiArdakani farzin ghaemi Fariba Kargaran Bafghi Ahad Nouri

The Anar fault in the east of Yazd city, with a north-northwest-south-southeast strike, is a basement fault that separates the Yazd block from the Posht Badam block, and its current activity is a dextral strike-slip with a reverse component. The paleostress analysis was More

The Anar fault in the east of Yazd city, with a north-northwest-south-southeast strike, is a basement fault that separates the Yazd block from the Posht Badam block, and its current activity is a dextral strike-slip with a reverse component. The paleostress analysis was done on this fault in order to obtain the tectonic history of central Iran in the period from Devonian to Cretaceous. After analyzing 110 fault data in 13 stations of 2 tectonic phases, it was determined that the maximum stress obtained is between the azimuths of 90 to 110 and 190 to 220 and the angle of stress direction changes in the period from Devonian to Cretaceous is 130 degrees. Based on the studies on the barite veins and the dextral displacements that were seen on them, the separation of the stress phases was done, which indicates that the NNE stress direction is older. Further, according to the previous studies of sedimentology and tectonics in central Iran, it was concluded that the cause of this change in tension was the movement towards the northeast along with the 130 degree counter-clockwise rotation of central Iran. Manuscript profile

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