P Gholami Zadeh; M.H Adabi; M Hosseini-Barzi; A Sadeghi; M.R Ghassemi
Abstract
The Miocene sediments in Neyriz region crop out in Zagros Crushed Zone, between Zagros Main Fault and Zagros Ophiolite Zone. For paleoenvironmental studies of these sediments, two stratigraphic sections (Kuh-e Asaki and Horgan sections) have been measured and sampled. The thicknesses of these two ...
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The Miocene sediments in Neyriz region crop out in Zagros Crushed Zone, between Zagros Main Fault and Zagros Ophiolite Zone. For paleoenvironmental studies of these sediments, two stratigraphic sections (Kuh-e Asaki and Horgan sections) have been measured and sampled. The thicknesses of these two sections are 424 and 440 m respectively and contain red and green sandstone, conglomerate and marl which are bounded unconformably between the Jahrum Formation and Bakhtiari conglomerate. Based on the field and petrographic studies, 14 sedimentary facies related to proximal, mid fan-delta; transition zone, delta slope and prodelta have been recognized for the Miocene succession. Due to the slope facies formed by the turbidity currents, grain fall and debris flows, the coarse grained clasts and poorly sorted texture, a fan-delta model is suggested for the succession. Also, the development of the slope facies indicates a paleo-slope and slope-type, deep-water fan-delta. The frequent intra-formational disconformities, irregular changes in grain size and present of gravity flows indicate an active tectonic sedimentary basin and reflux of coarse grained sediments (catastrophic events) to the proximal parts of Zagros Basin.
A. S Khalifeh Soltani; S. A Alavi; M. R Ghassemi
Abstract
Fractal analysis of drainages and fractures is a useful tool to determine the maturity structure of a region. With the help of fractal geometry, this study investigates the fractal dimension of drainages and fractures in the southwestern part of Lenjan, and examines the role of geological structures ...
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Fractal analysis of drainages and fractures is a useful tool to determine the maturity structure of a region. With the help of fractal geometry, this study investigates the fractal dimension of drainages and fractures in the southwestern part of Lenjan, and examines the role of geological structures after determining the most active part of region. In order for fractal analysis of fractures and drainages, box-counting method has been used. To achieve this, four parts A, B, C and D of high structural density were first detected in the region, and the fractal dimensions of drainages and fractures were then calculated and compared. Results of fractal analysis of fractures suggest that sector B is the most active part of the region, while fractal analysis of drainages indicates greater tectonic activity in sector A. The larger number of earthquakes and higher density of fractures in sector B, however, could indicate it as the most active part of the study area. Therefore, contradicts in different results obtained from the fractal dimension analysis of fractures and drainages can be explained by the varieties in lithology. The structural studies indicate the existence of a dextral transpression zone in the study area. The dextral transpression zone resulted in uplift of sector B by development of positive flower structures in this part of the region. Therefore, increased tectonic activity in part B is due to formation of positive flower structures and consequent tectonic uplift.
A Malaekeh; M.R Ghasemi; S Hakimi; A Bahroudi
Abstract
The Vijehnan anticline is located to the south of the Gilan-e-Gharb, in the simply folded belt of the Zagros. For analyzing the geometry and kinematics of the anticline, we first produced a geological map using a variety of satellite imagery, published geological maps and field studies. Four structural ...
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The Vijehnan anticline is located to the south of the Gilan-e-Gharb, in the simply folded belt of the Zagros. For analyzing the geometry and kinematics of the anticline, we first produced a geological map using a variety of satellite imagery, published geological maps and field studies. Four structural cross sections (A1-A2, B1-B2, C1-C2, D1-D2) perpendicular to the fold axes are produced in AutoCAD software. To analyze the geometry and kinematics of this fold, the horizontal shortening has been calculated for two cross sections. The average shortening of these cross sections is 11 percent. Kinematics analysis of the Vijehnan anticline based on the Publet & McClay model (1996) indicated that the geometry of the anticline is of detachment fold type. This result is also confirmed by the scheme which was introduced by Jameson (1987). To ensure the accuracy of the results, aspect ratio of the fold have been used which is presented by Sattarzadeh et al. (2000). The calculation of this factor indicates that the Vijenan anticline classified as detachment fold.
N Afsari; F Taghizadeh-Farahmand; M.R Ghassemi
Abstract
The AlborzMountains are part of the Alpine-Himalayan orogenic belt, situated to the south of the Caspian Sea and north of the Central Iran. . The region is undergoing extensive crustal deformation and shortening between the north-central Iran and the rigid SouthCaspianBasin crust. In this study, we used ...
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The AlborzMountains are part of the Alpine-Himalayan orogenic belt, situated to the south of the Caspian Sea and north of the Central Iran. . The region is undergoing extensive crustal deformation and shortening between the north-central Iran and the rigid SouthCaspianBasin crust. In this study, we used the P-wave receiver function modeling to investigate the crustal structure beneath the eastern part of the AlborzMountains from data recorded between 2004-2010 in Sari and Semnan seismic networks of short-period seismographs, permanently deployed across the area. We observed clear conversions (Ps) from the Moho boundary, and we used them to define a model for the crust of the eastern Alborz. Our analysis indicates a thickening of the crust from ~51±2 km beneath the northern part of the eastern Alborz to ~62±2 km beneath the central part of the region, then a thinning of the crust to ~52±2 km towards south of the eastern Alborz Mountains.
N Saboor; M.R Ghassemi; M Eskandari; A Nazari.F; M Ghorashi; F Seenaian
Abstract
Depending on their structural maturity, seismogenic faults, , may rupture in one segment or as multiple segments; they also may show different slips on their segments. Mature faults break in long ruptures with small slip, while immature faults rupture as short segments but are more energetic. On the ...
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Depending on their structural maturity, seismogenic faults, , may rupture in one segment or as multiple segments; they also may show different slips on their segments. Mature faults break in long ruptures with small slip, while immature faults rupture as short segments but are more energetic. On the other hand, the mature faults demonstrate clustering pattern in their earthquake recurrence pattern. Also, the ground motions produced by earthquakes on immature faults are larger than those generated by earthquakes on mature faults. In this paper, we defined maturity of major faults in EasternIranseismotectonicProvince, considering their segmentation, rupture length, displacement vector on the rupture and the history of clustered earthquake sequence on the fault. Then, the response spectrum of ground motions caused by large earthquakes occurred on these faults were calculated. To reduce the effect of unknown wave paths, we used ground motions recorded in the near field. Earthquakes of different mechanisms were selected in magnitude range from Mw=5.7 to 7.1. We compared the obtained response spectrum with those resulted from the experimental model presented by Boore et al. (1997). Study of this parameter can help to recognized ground motion potenial of the faults, and considering it in extracting attenuation equations increases the accuracy of the results for seismic hazard assessment. Using our evaluation for structural maturity of the faults, we try to present a model for evolution of seismic activity in Eastern Iran.
M Nazemi; M Qurashi; M.R Ghassemi; M Arian
Abstract
Geomorphic characteristics of alluvial fans on the sides of the ShotoriMountains in east of Tabas represent two different groups . The first group is older and is more dominant with their heads near the ShotoriMountains' hillside and their toe spreading to the central parts of the plain. These alluvial ...
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Geomorphic characteristics of alluvial fans on the sides of the ShotoriMountains in east of Tabas represent two different groups . The first group is older and is more dominant with their heads near the ShotoriMountains' hillside and their toe spreading to the central parts of the plain. These alluvial fans on which no main recent channel sedimentation is occurring, are often consisted of old alluvial sediments with a thin cover of newer ones. The second group includes younger and active alluvial fans consisted of more recent sediments of stream bed, which are located at the termination of the first group or at the southern foothills of the ShotoriMountains. It can be said that in the first group, recent active sedimentation process by the main channel has been transferred to the lower parts and toe of the alluvial fan, but in the latter group sedimentation has been done on top of the alluvial fan and on older sediments. In other words, the first group consists of two obvious old and active (recent) parts, while the second group only includes recent and active alluvial fans. Our investigations indictaes that geomorphic pattern of these two alluvial fan groups has a clear relation with location and mechanism of active faults and geomorphic surfaces in the plain of Tabas and eastern slopes of the Shotori Mountains; in other words, it is related to the mechanism of structural evolution of this mountain. According to this pattern, wherever there is the active fault of the catastrophic 1978 earthquake at the front of mountain along which the ShotoriMountains are being uplifted, the second type of alluvial fans is formed. Where the fault is located in central parts of the plain as a result of deformational front propagation, and the old part of the alluvial fan and mountain are being uplifted along it, the first type of alluvial fans (with two separate parts) is formed. This uplift is accommodated by active faulting and folding associated with bedding plane faulting. Migration of deformational front during geologic evolution of the ShotoriMountains has caused four different geomorphic levels along with three generations of alluvial fans. It is concluded that investigating on geomorphic pattern of alluvial fans will provide valuable data about the location of active Quaternary faults in alluvial plains. This pattern shows an active fault near Boshruyeh (east of the ShotoriMountains). Although no major earthquake has been reported from the fault, all morphotectonic evidences show its activity and thus the occurrence of large earthquakes in the future is expected.
J Hassanpour; S.A Alavi; S Jahani; M.R Ghassemi
Abstract
Located in the Fars region of Simply Folded Belt of the Zagros orogen, the Dadenjan salt diapir is exposed in the core, with a tendency toward the southwestern flank of the salt-cored Dadenjan anticline. The diapir is also currently situated within a transtension zone between overlapping segments of ...
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Located in the Fars region of Simply Folded Belt of the Zagros orogen, the Dadenjan salt diapir is exposed in the core, with a tendency toward the southwestern flank of the salt-cored Dadenjan anticline. The diapir is also currently situated within a transtension zone between overlapping segments of the dextral Karehbas fault zone. This diapir is sourced from the latest Precambrian-Early Cambrian Hormuz evaporitic series. The geometry of strata flanking the diapir suggests pre-orogenic, long-term salt activity by “downbuilding”, in which syn-depositional, shallow drape folding resulted in thinned and progressively rotated strata adjacent to the rising diapir. Geometrically, halokinetic sequences adjacent to this diapir are completely different on either sides of the diapir, implying different salt rise-sediment accumulation interactions. The diapir and its related anticline are bound, on both sides, by wide synclines, each with a thicker sedimentary pile than the neighboring anticlines. These synclines have acted as depocenters for the continuously rising Dadenjan diapir, accumulated significant volumes of supplied sediments, thereby facilitated the rise of salt by downbuilding mechanism. The thick sedimentary pile within these synclines has subsequently been strong enough to resist against folding and locally disturbed, to some degree, the normal stress transfer during the Zagros folding. They have therefore prevented neighboring anticlines from normal propagation and regular shape development either along or across their strikes. The Neogene Zagros folding squeezed up the salt diapir, intensified its activity and resulted in partial extrusion of the salt.
M Nemati; A.R Ghods; M.R Ghassemi
Abstract
Due to absence of an appropriate scale for estimation of ML for the earthquakes in eastern Alborz Range, we calculated 1113 synthetic Wood-Anderson peak amplitudes from waveforms of 215 earthquakes recorded by 23 stations at local hypocentral distances. The events were recorded by two local temporary ...
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Due to absence of an appropriate scale for estimation of ML for the earthquakes in eastern Alborz Range, we calculated 1113 synthetic Wood-Anderson peak amplitudes from waveforms of 215 earthquakes recorded by 23 stations at local hypocentral distances. The events were recorded by two local temporary seismological networks installed during 2007 and 2008 by the Geological Survey of Iran (GSI) and the stations of the permanent network of the Institute of Geophysics of University of Tehran (IGUT). Both temporary networks were installed for two discontinuous periods of nine months in the eastern- middle Alborz. In order to estimate an empirical attenuation curve for ML amplitudes, A, read from the stations at very short hypocentral distances, we fit a parametric relationship to the peak amplitude readings while considering geometrical spreading, intrinsic attenuation and stations corrections. We obtained the following empirical attenuation relationship:
Log Aij=-1.986log (Rij/100)-0.00452(Rij-100)-3+Sj
Where Rij is hypocentral distance in km between the jth station pair and ith earthquake and Sj is value of station correction for the jth stationThe realtionship clearly indicates a larger attenuation for shear waves in short hypocentral distances below 20 km. Our new ML relationship implies that using ML relationship derived for hypocentral distances larger than 50 km would overestimate ML magnitude of events recorded by our local networks by about half of unit magnitude. Thus we suggest that for local networks in other regions lacking any local ML relationship, ML relationship derived in this study to be used.
R Razavi Pash; M.R Ghassemi; H Safari
Abstract
The study area is located in western Alborz range, and is part of the Lahijan sinistral strike-slip fault system. This area is observed as a depressed basin on the digital elevation model. This research uses field studies, remote sensing techniques and statistical methods to investigate and analyze geometry ...
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The study area is located in western Alborz range, and is part of the Lahijan sinistral strike-slip fault system. This area is observed as a depressed basin on the digital elevation model. This research uses field studies, remote sensing techniques and statistical methods to investigate and analyze geometry and kinematics of the faults in the Rostam-Abad area, and benefits structural and geomorphic evidences to introduce a pull-apart basin in the area. Our analysis indicates that the Rostam-Abad area is located in the overlap zone of two sinistral strike-slip fault segments of the Lahijan fault zone with a left-step array. Presence of frequent normal faults, extensional fractures, rhombic pattern of the depression, extensive alluvial deposits, and intrusion of igneous dykes in young sandstones within the Rostam-Abad depression also verify a local extensional tectonic regime in this region.
Z Hamidi Beheshti; H Alimohammadian; M Talebian; A Shahidi; M.R Ghassemi
Abstract
Geomagnetism is one of the most applied techniques of geophysics in geology. Today, this method is applied in different disciplines such as Magnetic fabric of rocks, palaeomagnetism and environmental magnetism. Each of these magnetic methods is suitable for a particular lithology. Therefore, the potential ...
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Geomagnetism is one of the most applied techniques of geophysics in geology. Today, this method is applied in different disciplines such as Magnetic fabric of rocks, palaeomagnetism and environmental magnetism. Each of these magnetic methods is suitable for a particular lithology. Therefore, the potential of sandstones of Shemshak Group, in central AlborzMountain range were examined to record their response to the application of some conventional magnetic methods. This rock unit is formed during two major tectonic events of early and middle Cimmerian and has great coverage not only in the study area but also in a vast majority of Iran. The total number of 135 oriented core samples was taken from 18 stations. In this study combination of magnetic and petrographic data are examined. The result of magnetic mineralogy analysis of all samples (except samples from stations 10 and 15) show irreversibility i.e. minerals such as hematite and magnetite, have formed during the heating stage. The results of thermal demagnetization analysis showed that ferromagnetic minerals present in the samples (except samples from stations 10, 14 and 15) have demagnetized below 400 °C and by proceeding heating, samples show zigzag pattern or show abnormal increase in susceptibility. This indicates that, the magnetic minerals are formed during heating in one stage and due to unstability lose its susceptibility in other stage. The magnetic susceptibility (Km) vary from 200-400×10-6 SI for more stations of study area, indicating abundance of paramagnetic mineral in this rock unit. From petrography point of view all the sandstone samples are classified as arenites and ratio of quartz to lithic fragment and feldspar is relatively low, which may indicate low mineral maturity. Comparison of magnetic mineralogy and thermal demagnetization data for two stations S10 and S15 show that there is an inverse potential relationship between amount of stable ferromagnetic mineral in a sample and amount of its alteration during heating stage. The results of this study reveal the poor nature of Shemshak Group sandstones for palaeomagnetic studies due to their low mineral maturity and water percolation which increase the possibility of acquisition of chemical remanent magnetization (CRM). The high sedimentation rate of sandstones cause magnetic inclination and declination error, and low ferromagnetic mineral fraction in samples, make them unsuitable to record magnetic directionsduring formation of rocks. However, abundance of paramagnetic minerals such as biotite in these rocks, proves their applicability for magnetic fabric studies.
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.
