Tectonics
Mohammad Hossein Tahriri; Hamid Saffari
Abstract
The Doruneh fault system with more than 700 km length, after the main Zagros fault, is known as the largest fault in Iran. In this research, this fault system is divided into 3 main parts because the mechanisms of its different parts are different. The western part is reported to have a left lateral ...
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The Doruneh fault system with more than 700 km length, after the main Zagros fault, is known as the largest fault in Iran. In this research, this fault system is divided into 3 main parts because the mechanisms of its different parts are different. The western part is reported to have a left lateral strike-slip mechanism with a reverse component, the middle part is a left lateral strike-slip mechanism, and the eastern part is reported to have a reverse mechanism. In this study, seismicity parameters and their temporal and spatial changes along this fault system are analyzed using seismic data collected from 1980 to 2023 and based on the maximum likelihood method. In this regard, the temporal changes of b-value shows two significant drops, which indicate two relatively strong Torbat-e Heydarieh earthquakes in 2010 and the Fariman earthquake in 2017. Despite the fact that the scientific community is not yet able to accurately predict earthquakes, according to the studied method and with the continuous monitoring and analysis of various earthquake parameters, especially b-value, it is not far from expected to predict the occurrence of possible earthquakes in the future.
Tectonics
Amir Shafiei bafti
Abstract
Radon is a radioactive noble gas . The best places for accumulation of radon in groundwater would be geodynamic active areas,deep basement faults and fractures. This paper aims to investigate the relationship between the radon gas concentrations with the behaviors of active tectonic faults. Jorjafk fault ...
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Radon is a radioactive noble gas . The best places for accumulation of radon in groundwater would be geodynamic active areas,deep basement faults and fractures. This paper aims to investigate the relationship between the radon gas concentrations with the behaviors of active tectonic faults. Jorjafk fault with a length of nearly 160 km from North-West to South-East in southern central Iran. This fault shows active tectonics aspects, The distribution of Davaran Mountain seismic centers shows low Seismicity for the region. In addition, the few focus of the events in the south of the mountain and unequal distribution and lack of clear trend is among its seismic properties. For the measurement of radon concentration in water resources leading to the Jorjafk fault,, 35 sampling stations were identified as suitable, and on two occasions the samplings were performed. The highest and lowest concentrations measured in the first stage were 53, 183, and 138 Becquerel's respectively for the stations of 13, 3 and 8, and in the second stage, the highest and lowest concentration were measured with values of 56, 233, and 169 Becquerel's respectively for the stations of 29 and 25. By comparing the obtained concentrations for each station and its compliance with seismic activity in the region, it was observed that in places where seismic activity is higher, the concentration of radon gas is also higher. Therefore, it can be said that the areas with high concentrations of radon gas, have more potential and are more likely to earthquake events
Geophysics
Mohammadreza Jamalreyhani; Abdolreza Ghods; Seyyed Khalil Mottaghi; Esmail Shabanian; Morteza Talebian; Beijing Chen
Abstract
One of the main issues in Zagros is the extent that basement and the thick sedimentary layer participate in the observed seismicity. During Nov. 2013, five magnitude ~5 Mw events hit a region in the western end of Lurestan arc of Simply Folded Belt (SFB) of Zagros. We used the Iran-China temporary network ...
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One of the main issues in Zagros is the extent that basement and the thick sedimentary layer participate in the observed seismicity. During Nov. 2013, five magnitude ~5 Mw events hit a region in the western end of Lurestan arc of Simply Folded Belt (SFB) of Zagros. We used the Iran-China temporary network and data from regional permanent networks to relocate the events using a multiple event relocation method, calculate regional moment tensor and centeriod depths for the five moderate events and estimate a velocity model for the two nearby seismic stations using joint inversion of the receiver functions and dispersion curves. Our results show a seismic cluster of about 30 km long and 15 km width. The moment tensor solutions of the five moderate events indicate an almost pure thrust mechanism. The aftershock cloud indicate a low angle east dipping fault plane (i.e., , dip in the range of 23 o -39 o ) as the causative fault plane. The calculated centeroid of the five moderate events are about 14 km and the focal depth of all events calculated by multiple event relocation are about 10-16 km. The results indicate that the thickness of sedimentary column is less than 8 km and thus showing the whole seismic cluster happened within the basement. This observation proves wrong the hypothesis of vertical separation of mainshock and aftershocks in Ssimply folded belt FB of Zagros (Nissen et al. 2011) and implies that in the Lurestan arc the sedimentary layers are deformed aseismically.
Tectonics
Amir Shafiei bafti
Abstract
. Kouhbanan fault system in south of central Iran is one of the most active and seismic faults, has length of nearly 200km and seismic history from B.C to the present. Epicenter of seismic activities for this fault situated often near fault zone or on the Kouhbanan fault zone branches and other attached ...
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. Kouhbanan fault system in south of central Iran is one of the most active and seismic faults, has length of nearly 200km and seismic history from B.C to the present. Epicenter of seismic activities for this fault situated often near fault zone or on the Kouhbanan fault zone branches and other attached faults. Identify of ruptured and non-ruptured segments can clear the way to finding the areas that have the potential for creating earthquake. Field observation and library data were used for this purpose. According to the spatiotemporal distribution of historical and instrumental earthquakes, may be concluded, the most earthquakes are located where the fault branches or in its bend locations. Earthquake occurred in studied region, often known with absence of high magnitude earthquakes (M≥ 6.5). Interesting point is that in the period of about 160 years ago (Earthquake record time span) along of active faults, especially Kouhbanan fault zone, an area that is less a re-ruptured or be consecutive or earthquake epicenters are few. For earthquake risk assessment, we use Kijko& Sllevoll (1992) method, which show that the earthquake risk and seismicity rate is higher from other regions and earthquake have higher magnitude and less recurrence time. According to the obtained results, for earthquakes (M≥ 7) results should be used with caution.
M.A Alimi
Abstract
The sequence of seismicity including three earthquakes in the Mohammadabad region, eastern Iran, within a period of 30 years has made it one of the most outstanding seismically active regions in the country. The Mohammadabad fault system is described using earthquake and satellite imagery data to support ...
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The sequence of seismicity including three earthquakes in the Mohammadabad region, eastern Iran, within a period of 30 years has made it one of the most outstanding seismically active regions in the country. The Mohammadabad fault system is described using earthquake and satellite imagery data to support a simple tectonic model. The interaction between the Mohammadabad strike-slip fault system and basement structures and also the en-echelon array of fault segments have resulted in formation of the Mohammadabad pull-apart basin and Tajkuh contractional zone. The Daqq-e-Mohammadabad basin is a topographic depression formed in a right-step releasing step-over related to the Mohammadabad-Taleb dextral strike-slip fault system. Geomorphologic evaluation of the Mohammadabad deformation zone at surface indicates both normal and reverse faulting. Normal faulting is obvious in the margin of the basin and reverse faulting is seen in the zone of contraction at the Taleb-Tajkuh left-step restraining step-over. The model presented for the formation of adjacent extensional and contractional structures based on traces of the Mohammadabad strike-slip fault system, basin, and uplifts to the south of the area is a double step-over (releasing and restraining) model. Fault segments associated with this step-over may be capable of earthquake ruptures. The linkage of main strike-slip zones (Mohammadabad-Taleb and Taleb-Tajkuh) by transverse faults could increase potential generation of large earthquakes and activity of sympathetic faults.
Sh Eghtesadi; M Shokati Amghani
Abstract
Modelingof bouguer gravity anomaly and tsunami warning due to Makran subduction zone (case study: Beris region)
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Modelingof bouguer gravity anomaly and tsunami warning due to Makran subduction zone (case study: Beris region)
S Eslami Farsani; M Talebian; A Saidi; M Pourkermani
Abstract
The purpose of this research is to study active faulting in western part of the Middle East, between Caspian Sea to the east and Mediterranean Sea to the west. This region covers several countries and thus geological maps have different scale and errors in locations. The mismatch between fault traces ...
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The purpose of this research is to study active faulting in western part of the Middle East, between Caspian Sea to the east and Mediterranean Sea to the west. This region covers several countries and thus geological maps have different scale and errors in locations. The mismatch between fault traces in geological maps with their actual position on the ground is sometimes up to several hundred meters. The main goal of this study was to prepare continues map of active faults together with seismicity for the entire region of interest. This map also shows the slip rate of the active faults, estimated based on available geodetic measurements (GPS) or other published data. All available information including geological maps, satellite images, topographic data, GPS measurements, and earthquake data were imported into Arc GIS system. The Landsat 7 satellite images were used to correct location of active faults and measuring young offsets along the faults. Most of active faults bound the mountains implying that they control current topography of the region. The earthquakes are more frequent in the Zagros, especially in western part, around junction of the North and East Anatolian faults. This is in contrast with the Dead Sea region where lower seismic activity observed. However larger earthquakes are distributed over entire region, though we have more record of historical earthquakes in NW Iran, Eastern Turkey and the Dead Sea region probably related to documentation of historical data rather than occurence of earthquakes. In the eastern Zagros (NW of Iran) total shortening is partitioned into pure strike-slip and thrusting. In the middle part (eastern Turkey) the Zagros trends east-west and most of shortening is taken up by pure thrusting. The Central and Eastern Turkey is dominated by strike-slip faults and rotation of blocks. Shortening across left-lateral and right-lateral systems in eastern Turkey cause the Turkish block to move to the west and subduct in Hellenic trench. Comparing rate of shortening with moment released by earthquakes in Zagros and Caucuses suggest that part of shortening is taking up by creep.
H Safari; M.R Ghassemi; M Bahrami
Abstract
This opinion exist that basement of the Sanandaj-Sirjan Zone was cratonized during Cimmerian and Laramide Orogenic phases and so, therefore it is considered as an aseismic (or low-sesimicity) zone. The Shahreza area in the central part of the zone is selected as a case study area for investigation on ...
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This opinion exist that basement of the Sanandaj-Sirjan Zone was cratonized during Cimmerian and Laramide Orogenic phases and so, therefore it is considered as an aseismic (or low-sesimicity) zone. The Shahreza area in the central part of the zone is selected as a case study area for investigation on seismicity and recent movements and verifying of this hypothesis. We used Geoinformatic techniques (including: Remote Sensing, GIS and field surveying methods) in this research to detect the structures of the area and their kinematics, to locate earthquake foci, to find neotectonic evidences of active faults, and proofs for high seismicity of the area. Our results shows that the Shahreza fault (and Dehaghan fault located in southwest of study area) having a dextral strike-slip mechanism is the main structural trend in the area. This fault zone is truncated and offset by the Nosratabad fault (with strike N50-70E and sinistral strike-slip mechanism). In the intersection area of these main trends, many earthquake foci (with strike-slip focal mechanism) are located. Other than several earthquakes, neotectonic evidences for fault activity are are observed in the Shahreza area.
M Tatar; S.M Momeni; F Yaminifard
Abstract
The V shape kink of the AlborzMountains at its southern end reaches to the Garmsar city located 100 km southeast of Tehran metropolis. We investigated seismicity and seismotectonic features of the Garmsar area by precisely locating of microearthquakes recorded by our local dense seismological network ...
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The V shape kink of the AlborzMountains at its southern end reaches to the Garmsar city located 100 km southeast of Tehran metropolis. We investigated seismicity and seismotectonic features of the Garmsar area by precisely locating of microearthquakes recorded by our local dense seismological network and by the Iranian Seismological Center (IRSC). Our results indicate high seismic activity at the central and western parts of the Garmsar fault. Three computed focal mechanisms revealed compressional movements of the central part of this fault. Very little seismic activity is observed on the Eyvanekey and the Pishva faults. The only computed focal mechanism for the northern hills of the Garmsar fault shows tensional movements in this area, which refers to strain release among the Garmsar and Sorkheh reverse faults. Most of the calculated focal mechanisms in the Garmsar area indicate compressional and strike slip motions with overall P axis direction of 10° to 35°. The calculated P axis with NW-SE trend, close to the Sorkheh fault, is different from the other calculated P axes that show NNE-SSW direction. This is probably due to rotating of structures in this area, as revealed by recent GPS measurements in this region.
A. Sistanipour; M. Pourkermani; M. Arian
Abstract
Bafq-Baghin fault system has formed by 8 fault segments. On this fault system has not recorded any historical seismic data. Instrumentally earthquakes are located in low depth and their magnitude is from small to medium. Morphometric parameters and the presence of fault scarp along the fault segments ...
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Bafq-Baghin fault system has formed by 8 fault segments. On this fault system has not recorded any historical seismic data. Instrumentally earthquakes are located in low depth and their magnitude is from small to medium. Morphometric parameters and the presence of fault scarp along the fault segments indicate their activeness. Recent earthquake epicenters of the region (2005-2009) have northeast-southwest trend are located at the intersection of southeast of the Bafq-Baghin fault system. Field investigations and satellite images of region show that the concentration trend of recent earthquake epicenters is located on the cross fault trend that introduced as Rafsanjan-Zarand fault. This fault is one of the X faults in the region that has formed by movement of shear zone.
M. R. Ebrahimi; Mohammad Tatar
Abstract
Masjed Soleyman reservoir is located in Zagros Mountain of western Iran, which is one of the most seismically active zones of the Alpe-Hymalaya belt. So, it seems to be necessary to carry out widespread studies, especially on the impact of this reservoir with 177 m height and 261 million m3 capacity ...
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Masjed Soleyman reservoir is located in Zagros Mountain of western Iran, which is one of the most seismically active zones of the Alpe-Hymalaya belt. So, it seems to be necessary to carry out widespread studies, especially on the impact of this reservoir with 177 m height and 261 million m3 capacity on occurrence of induced seismicity in the surrounding region. The Gutenberg-Richter relation is one of the well-fitted empirical relations in seismology: it represents the frequency of occurrence of earthquakes as a function of magnitude: , where N is the cumulative number of earthquakes with magnitude larger than M and A and b are constants. In this paper we used b-value to study the heterogeneities in the crust beneath and around the Masjed Soleyman reservoir. In order to better understanding of the impact of this reservoir on seismic activity, a local seismic network of 5 seismological stations was installed in the area on June 2006. About 1924 Seismic events recorded during a period of 15 month were used in this study. We maped both surface and cross-section view of b-value in the region using the computer program ZMAP. The study area was divided into grids with spacing of 0.01o in latitude and longitude. A circle was drawn around each grid point and its radius was increased until it included N=50 earthquakes. The b-value was calculated by using a maximum likelihood method for the selected 50 earthquakes and the grid point was colored corresponding to the b-value. The results show high value of b-value due to reservoir induced earthquakes beneath the Masjed Soleyan lake. The most important factors known responsible for increased heterogeneity in this area, are reservoir loading and increased pore fluid pressure that cause occurrence of swarms and heterogeneous stresses in the area.
Mohammad Tatar; M. R. Ebrahimi; F. Yamini Fard
Abstract
Masjed Soleyman reservoir is located in Zagros Mountain of western Iran, which is one of the most seismically active zones of the Alpe-Himalaya belt. So, it seems to be necessary to carry out widespread studies, especially on the impact of this reservoir with 177 m height and 261 million m3 capacity ...
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Masjed Soleyman reservoir is located in Zagros Mountain of western Iran, which is one of the most seismically active zones of the Alpe-Himalaya belt. So, it seems to be necessary to carry out widespread studies, especially on the impact of this reservoir with 177 m height and 261 million m3 capacity on occurrence of induced seismicity in the surrounding region. During impounding of the reservoir regards to national and international catalogues such as International Institute of Earthquake Engineering and Seismology (IIEES) and EHB catalog, an incensement in seismic rate is observed in the Masjed Soleyman region, and 90 days after completing the impounding, an earthquake with magnitude Mw=5.6 is occurred in the close vicinity of the Masjed Soleyman reservoir. In order to better understanding of the impact of this reservoir on seismic activity, a local seismic network of 5 seismological stations was installed in the area on June 2006. Seismic events recorded during a period of 15 month were used in this study. The largest recorded earthquakes during the monitoring of Masjed Soleyman reservoir have magnitudes of ML=3.9 and ML=3.6. Statistical methods such as correlation of the water level changes with variation of the regional seismicity, the foreshocks and aftershocks pattern and decay rate of aftershocks reveal the existing of induced seismicity in the Masjed Soleyman region. In absence of a local network before 2002 September, 25 earthquake (Mw=5.6), our observations indicate this earthquake is truly the first and largest induced earthquake that have been occurred and recognized in Iran.
Ahmad Zamani; S. Farahi Ghasre Aboonasr
Abstract
The Iranian plateau is one of the active tectonic regions on the earth. Non-uniformly distribution of deformation and repetitive activity of faults have cause a complex pattern of tectonic and seismotectonic activity of Iran. Therefore, in order to study the seismic and geological behaviors of different ...
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The Iranian plateau is one of the active tectonic regions on the earth. Non-uniformly distribution of deformation and repetitive activity of faults have cause a complex pattern of tectonic and seismotectonic activity of Iran. Therefore, in order to study the seismic and geological behaviors of different parts of the country one has to perform tectonic and seismotectonic zoning. Tectonic and seismotectonic zoning of Iran began by conventional methods in the past and developed by numerical zoning in recent years. Conventional methods aren't capable for producing detailed zoning maps. Recently numerical data and statistical and mathematical models have used for produce modern numerical maps. The advantage of numerical pattern recognition is that this method is a powerful tool for objective interpretation of massive of data. Multivariate statistical methods not only apply for tectonic zoning, but also this is useful to reveal the degree of significance and relationship between effective variables on tectonic zoning. In this paper, a large numbers of up-to-date geophysical, seismological, geological and geomorphological data have analyzed by using multivariate statistical methods to produced self-organized numerical tectonic and seismotectonic zoning of Iran. Based on this techniques a seven zoning tectonic and seismotectonic map has constructed for Iran. The role and significance of various parameters have also investigated using ANOVA method. The results indicate that some of the parameters play more important role in self-organized zoning. Based on relationships between parameters, they are been classified into 12 groups. Variables in each group present maximum correlation with each other. It is interesting to note that despite the frequent application of a- and b- values of the Gutenberg Richter magnitude frequency formula, these values show poor correlation with others and do not play a significant role in zoning.
F. Yamini-Fard; A. S-Moradi; M. Hosseini; R. Norouzi
Abstract
From June 2004 to December 2008 low seismic activity was recorded near North-Tehran, Taleghan and Kahrizak faults and inside of Tehran city. In contrast, seismic activity along Mosha, Garmsar and North-Alborz faults is considerable. Generally seismic activity decreases from 51 degrees longitude to west. ...
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From June 2004 to December 2008 low seismic activity was recorded near North-Tehran, Taleghan and Kahrizak faults and inside of Tehran city. In contrast, seismic activity along Mosha, Garmsar and North-Alborz faults is considerable. Generally seismic activity decreases from 51 degrees longitude to west. Two earthquakes with 15 and 17 km depth were located in the west of Tehran city. The calculated focal mechanism for one of them is pure strike-slip. High seismic activity is observed along Mosha fault close to Damavand, Boumehen cities and Lavasant-e-Bozorg region. Calculated focal mechanisms along this fault includes both strike-slip, and reverse mechanisms that implies transpression motion, dominantly left-lateral slip along this fault that continued to Lavasanat region in south of the eastern end of the North Tehran fault. Precise location of some events shows depth range of 4-32 km. Generally, calculated focal mechanisms in studied region include both strike-slip and reverse mechanisms and seems that in southern part, approaching Central Iran, reverse mechanisms are dominant. It implies slip partitioning in southern margin of Central Alborz.
A. Zamani; M. Agh-Atabai
Abstract
The 31 March, 2006 earthquake with Mw=6.1 destroyed villages in the Darb-e-Astaneh (Silakhor) region of the Lurestan province. The epicenteral area of this earthquake lies near the Main Recent Fault (MRF) and its right lateral mechanism indicates that it belongs to this fault zone. The main shock was ...
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The 31 March, 2006 earthquake with Mw=6.1 destroyed villages in the Darb-e-Astaneh (Silakhor) region of the Lurestan province. The epicenteral area of this earthquake lies near the Main Recent Fault (MRF) and its right lateral mechanism indicates that it belongs to this fault zone. The main shock was followed by relatively large number of aftershocks. In this research, the aftershock sequence of this earthquake has been studied by measuring quantitative indices of coefficient of variations (CV), the exponent of the power spectral density function, and the generalized multifractal dimensions. The results reveal the presence of fractal structure in the temporal and spatial distribution of aftershock sequence. The multifractal behavior of the aftershock sequence indicates the clustering of the earthquake activity and the degree of the heterogeneity in the seismotectonic and geodynamic processes in the focal region. The results show that the multifractal dimensions of the aftershock sequence decreases and the multifractal dimensions of aftershock epicenters increases with time. It seems that these changes in the multifractal dimensions are related to the activity of secondary and sympathetic faults and changes in the tectonic stress regime of the region. The results also indicate that the multifractal method rather than monofractal approaches is a powerful tool for quantitative analysis of aftershock process's clustering behavior.
