جستجوی مقالات مرتبط با کلیدواژه « northeast of iran » در نشریات گروه « علوم پایه »

The Fariman complex is located in the northeast of Iran and southeast of Mashhad, contains a variety of rocks from the Permian to the present era that have undergone several stages of deformation. In this paper, the structural geometry of faults and folds of the region is analyzed and based on it, the deformation stages of Fariman complex are identified, which indicates its evolution during 3 stages of deformation. In the first stage of deformation, tectonic forces along with the thermal stage have caused the transformation of sediments and the formation of first generation foliation and folds in the region. First-generation thrusts also formed during this phase, thrusting Palaeotethys remnants. The second stage of deformation has led to the formation of the second generation of thrusts and folds in the region. Kinematic analysis of second generation thrusts indicates two reverse motion phases with leftlateral strike-slip component and right–lateral strike–slip with reverse component.Its reverse motions, which result in the formation of misplaced massive carbonate associated with the second stage of deformation, and its dextral motion, which cut and displace previous structures and affect all rock units in the region, the third stage of deformation is analyzed.

the events of extremum rainfall in northeastern Iran during the last 20 years (2021-2000) have been studied using rainfall indexes. For this purpose, data from synoptic meteorological stations of Mashhad, Sabzevar, Quchan, Neishabour, Bojnourd and Gonbad Kavous were used and Atmospheric patterns leading to these extremum events and the trend of extreme indexes were investigated using linear regression. The results showed that in all stations studied, highest standard deviation for all extreme indices was related to Gonbad Kavous station, which indicates the higher probability of unconventional rainfall for this station. The highest frequency distribution index of number of very heavy precipitation days (R20mm) in the statistical period and in the seasonal period with 37.4% frequency belongs to winter and in the monthly period with 19.3% frequency belongs to March. Synoptic analysis of heavy rainfall in the northeastern region of the country, mean sea level pressure maps, geopotential elevation and wind field maps at 850 hPa, omega pattern at 700 hPa and specific moisture distribution pattern at 850 and 700 hPa were used. The results showed that the most important feature of large-scale patterns leading to extreme rainfall is their high persistence in the eastern part of the Mediterranean. These blocking patterns are accompanied by the deployment of a low pressure system on the ground and the middle and upper levels of troposphere, which includes rising speeds in the lower levels of troposphere and adequate moisture supply from sources from the Sea of Oman, the Red Sea and the Persian Gulf.

In recent years, dust storm has become a serious environmental concern and has attracted a lot of attention among atmospheric scientists. Northeast of Iran is a large and strategic population area. Due to its proximity to large arid regions in Central Asia, this region has a high risk of experiensing dust events. In recent years, it has faced many problems regarding dust phenomena. This study is conducted to investigate seasonal dust events in northeastern Iran. To achieve this goal, a combination of station data, reanalysis, satellite and output of the WRF-Chem numerical model have been used simultaneously to improve our understanding of the dust seasonal cycle in northeast of Iran. Accordingly, this research was organized in two parts: monitoring and modeling of dust phenomenon. The results of this study may be useful for forecasting dust storms as well as spatial planning. To investigate the dust events seasonal variabilities, the dust surface mass concentration of MERRA-2 dataset, aerosol optical depth (AOD) of the combined Dark Target (DT) and Deep Blue (DB) algorithms of MODIS sensor of Terra and Aqua satellites were examined during the long-term period (2004-2018). Since the emission of dust is highly dependent on biophysical components, it is necessary to use numerical models. The WRF-Chem numerical model was used for this purpose. The study area includes northeastern Iran and parts of Central Asia. The horizontal resolution of the child domin of 30 km model was performed with 32 vertical levels. The NCEP / FNL is used as boundary conditions with 3-hourly time step and 1-degree horizontal resolution for the model configuration. Four extreme dust events were selected to investigate the transport of dust to northeastern Iran. The selected dust events occurred on November 13, 2007, May 29, 2008, June 8, 2015, and October 17, 2017 in northeastern Iran. Therefore, case events were simulated with a time step of 180 seconds and output every three hours using GOCART, AFWA, UoC_S01 and UoC_S11 schemes. The results showed that the maximum dust activity occurred in spring with AOD value equal to 0.59 and dust surface mass concentration is 645.2 µg m -3. The summer is in the next place. Seasonal analysis of AOD and dust using satellite and reanalysis data, showed that Aralkum, Kyzylkum, Karakum and Kara-Bogaz-Gol are the main dust sources in Central Asia that are active in all seasons. Comparison of dust simulation results for PM2.5 and PM10 variable with observational data of air quality control stations in Mashhad showed that GOCART scheme can well depict dust events and provide a low bias towards station data. Also, the study of correlation coefficient between simulation and observation showed that the GOCART scheme explains nearly 90% of the variance of data. The root mean square error (RMSE) for the GOCART scheme is less than 20 micrograms per cubic meter for PM2.5. Accordingly, the GOCART scheme is a suitable scheme for dust study in Northeast of Iran and the WRF-Chem model can be used to operationally forecast dust storms. The dust detection algorithm (DDA) of the AIRS sensor and the aerosol optical depth (AOD) of the MODIS sensor confirm the contribution of the mentioned sources of dust in transferring dust to the northeast of Iran. The results showed that three of the case studies occurred as a result of the passage of an extratropical Rossby wave and the deepening of the trough on the territory of Turkmenistan. In contrast, the summer case study is the result of the establishment of a summer circulation pattern that has occurred with the simultaneous establishment of an anticyclonic circulation in the southern part of Turkmenistan and the northeastern parts of Iran and a cyclonic circulation in the Sistan plain and southeastern parts of the country.

In order to study the biostratigraphy of the Upper Cretaceous deposits in north of Lut block, one stratigraphic section in Bahabad south-west Bajestan area was selected and sampled. The thickness of the Upper Cretaceous deposits in this section is 152.48 meters and based on lithological changes it is divided into five rock units: clastics rocks, gypsiferous marl, lower limestone, marl and upper limestone. The lower boundary due to lack of outcrop is not recognizable and the upper boundary underlies the recent erosional deposits. In biostratigraphic studies with the exception of two basal rock units that have no fossils in the other three rock units: lower limestone, marl and upper limestone 53 genera and 47 species of benthic foraminifera were recognized and two biozones identified as follows:Biozone 2: Rotorbinella campaniola- Pararotalia tuberculifera- Pseudocyclammina massiliensis assemblage zone Biozone 1: Rotorbinella mesogeensis- Pararotalia boixae- Dicyclina sampoi assemblage zone. According to the determined biozones and fossils associations the age of four basal rock units are Cenomanian and upper limestone unit is Santonian- Early Campanian. A sedimentary gap is visible during Turonian- Coniacian between marl and upper limestone rock units in this section.

Summary: Crustal velocity structure beneath four broadband seismic stations located in northeast of Iran, including Shahrood (SHRO) and Maraveh Tappeh (MRVT) stations set up by Iran National Seismic Network (INSN) and Sabzevar (SZBV) and Jarkhoshk (JRKH) stations set up by Iranian Seismology Center (IRSC), have been investigated by joint inversion of P receiver function and Rayleigh wave phase and group velocity dispersion curves. A three-year teleseismic data (2012 -2014) with epicentral distance of 25o-90o and magnitude more than 5.5 have been used to determine the receiver functions by iterative deconvolution in time domain proposed by Ligorria and Ammon (1999). Iterative deconvolution in time domain to determine the receiver functions are more stable with noisy data in comparison to frequency domain. The fundamental mode of Rayleigh wave group and phase velocity dispersion curves have been provided by the study on the structure of crust and upper mantle of the Iranian Plateau for the period interval of 10-100 seconds made by Rahimi (2010). A combined inversion of body wave receiver functions and Rayleigh wave velocities increases the uniqueness of the solution over the separate inversions, and also, facilitates explicit parameterization of the layer thickness in the model space. Moho discontinuity depth is one of the most important parameters for investigation of crustal structure. The results of this study indicate an average crustal thickness varying from 38 km beneath Maraveh Tappeh (MRVT) station in north of the study region up to 44 km beneath Shahrood (SHRO) station in west of the region. Moreover, the results of this study suggest that the average crust thickness beneath Sabzevar (SZBV) and Jarkhoshk (JRKH) stations located in center and east of the study region is 40 km. In general, northeastern Iran region has a thin crust compared to the crusts in the other areas investigated in this research work. It has also been shown that the joint inversion method can cause ±2 kilometers of error.
Introduction: Iran is situated in one of the world's seismic regions and the possibility of destructive earthquakes in most regions of the country has given great significance to recognition of Iranian seismic nature from a seismic and seismotectonic standpoint. The seismicity within Iran suggests that much of the deformation is concentrated in the Zagros, Alborz and Koppeh Dagh mountains, and in east of Iran, surrounding Central Iran and the Lut desert. The aim of this research is to study the crustal structure and Moho discontinuity of northeastern Iran region, Binalood mountains and Koppeh Dagh by the analysis of receiver function and surface waves dispersion.

Methodology and Approaches: Receivers functions are time series obtained from three-component seismometers, and are created by deconvolving the vertical component from the radial and transverse components of the seismogram to isolate the receiver site effects from the other information contained in a teleseismic P and S wave. The depth-velocity trade-off in receiver function causes nonuniqueness in the inverse problem. However, by incorporating information of absolute shear wave from dispersion estimates and joint inversion of these two datasets, this shortcoming can be compromised. To determine the receiver functions, we have used iterative deconvolution in time domain, proposed by Ligorria and Ammon (1999) that is more stable with noisy data in comparison to frequency domain. We have processed teleseismic events with epicentral distance of 25o-90o and magnitudes more than 5.5 that are recorded at a three-year time interval of 2012 to 2014. We have set the parameter a of the Gaussian filter to 1.00, which gives an effective high frequency limit of about 0.5 in the P wave. In order to eliminate the source, path and instrument effects, deconvolution of the vertical component from the horizontal components of the seismograms has been used. All receiver functions have been grouped by azimuth (<10◦) and distance (<15◦), and in order to improve the signal-to-noise ratio, the individual receiver functions within each group have been stacked. The fundamental mode of the Rayleigh wave group and phase velocities dispersion curves have been provided from the study carried out by Rahimi et al., (2014) on the structure of crust and upper mantle of the Iranian Plateau for the period interval of 10-100 seconds. Joint inversion of two independent data sets has been performed by considering appropriate weighting parameter obtained from Herrmann and Ammon program (2003). Minimizing standard error between real and predicted data is the criteria for getting the desired final and close to the earth real model. The inversion package requires that the real velocity structure is represented by a set of flat-lying, homogeneous, isotropic velocity layers. The starting model comprises of the layers having 1-km thick as the top 6 km of the model space, 2-km thick between the depths of 6 and 66 km, and 4 km thick between the depths of 66 and 78 km. The starting velocity for each layer in the model has been Vp=8.0 km/s, which equates to upper mantle velocity.

Results and Conclusions: The results of this study suggest that the average crust thickness beneath Shahrood (SHRO) station, located in west of the study region is 44 km and the average crust thickness beneath Sabzevar (SZBV) and Jarkhoshk (JRKH) stations located in center and east of the study region is 40 km. Furthermore, the crust thickness beneath Maraveh Tappeh (MRVT) station located in north of Koppeh Dagh region in is 38 km. In general, northeastern Iran region has a thin crust compared to the crust in other areas of northeast of Iran.

The genus Thymus is investigated to find the best morphologically differentiating characters in Northeast of Iran. In this study، we examined more than 480 herbarium and field-collected specimens from different populations and measured 34 quantitative and qualitative (vegetative and generative) characters. The results of the multivariate analysis (principal component analysis) and nonparametric Test (K independent samples) indicated that the morphological characters such as number of pair lateral vein and aristati and ciliate of upper lobe calyx differentiate the species under study. For the first time، the taxa Thymus fedtschenkoi، T. linearis subsp. linearis، T. kotschyanus var. eriophorus، T. carmanicus and T. kotschyanus var. glabrescens and T. eriocalyx، are reported for the flora of Khorassan provinces. In Flora of Turkey، T. kotschyanus var. glabrescens is a valid taxon، but in Flora iranica this variety is synonymed under T. eriocalyx.

Metaschistura cristata is a small nemacheilid loach species found only in Turkmenistan and Iran. The present study reports data on its feed habits and preferences, based on 1029 specimens collected in the northeast of Iran. Maximum age, based on opercula readings, was 6+ years for both sexes. Specimens ranged in size from 24 to 98 mm total length and weighted from 0.08 to 7.32 g. Length-weight relationships implied positive allometric growth for both sexes and sex ratio was 1:1. Small relative gut length (<1) confirmed that M. cristata is a carnivorous species. The values of relative gut length (13.2-86.4%) and gastrointestinal index (53.6-94.4%) increased significantly (P<0.05) with an increase in the age class from 0+ to 6+. The highest value of gastrointestinal index was observed in May. Based on the Ivlev index, the preferential feed ingredients were blood worm (chironomidae) and ephemeroptera. Overall, the present study provides evidence that the population of Metaschistura cristata in the northeast of Iran is in the unique condition; however, more experimentation is necessary to determine biological effects of this species on the ecosystems.

The genus Matthiola R. BR. (Brassicaceae) consists of 48 species in the Iranian plateau، of which only seven species are distributed in northeast of Iran. Six species erre collected from the region under study including M. afghanica، M. alyssifolia، M. chenopodiifolia، M. chorassanica، M. dumulosa and M. farinose. Two species، M. flavida and M. revoluta were recorded for the first time in this study. Some specimens of an unknown taxon entitled Matthiola sp. are also collected in the region and included in the present study. In this study، we tried to use a set of morphologically informative characters which could determine species boundaries and also provide appropriate identification key to the genus in the northeast of Iran. 71 morphological features including quantitative and qualitative were examined on 68 herbarium and field-collected accessions followed by statistical analyses. The results of the univariate analysis indicated that «presence/absence of trichome on the stem and leaf» and «presence/absence of glandular trichomes on the sepal and pedicel» did not significantly differentiate the species and they were excluded from the subsequent analysis. The results of multivariate analysis showed that the species under study were grouped within three groups. First group included specimens of the species M. alyssifolia، the species M. afghanica، M. chenopodiifolia، M. dumulosa، M. farinosa، M. flavida and Matthiola sp. were placed in second group and third group included specimens of the two species M. chorassanica and M. revoluta.

The genus Salvia is morphlogically investigated to provide an identification key based on morphological characters in the Northeast of Iran. In this study, we examined more than 350 herbarium and collected specimens of different populations and measured 79 quantitative and qualitative (vegetative and generative) characters. The results of the multivariate analysis (principal component analysis) and Nonparametric Test (K independent samples) indicate that the morphological characters such as blossom shape, ring of trichome inside of corolla and protrusion style differentiated the Salvia species. For the first time, the species Salvia shariffi is reported in the Jonoubi and Shomali Khorassans