M. Maghsoudi; F. Rafia; M. Ghorashi
Abstract
Classification of discontinuities and fractures in rock plays an important role in study and problem solving in geosciences fields, especially in Engineering Geology and Rock Mechanics. Nowadays, joints are classified on the basis of two geometrical parameters of dip and dip direction, presented on stereonets. ...
Read More
Classification of discontinuities and fractures in rock plays an important role in study and problem solving in geosciences fields, especially in Engineering Geology and Rock Mechanics. Nowadays, joints are classified on the basis of two geometrical parameters of dip and dip direction, presented on stereonets. It is clear that the behavior of discontinuities cannot be thoroughly presented by these parameters in solving such related problems, as stability of geotechnical structures like rock slopes and tunnels. The present paper deals with the results of a research within which a new method of joint classification by 3 parameters has developed. This is done in 3D environment software, utilizing Matlab and SPSS softwares as supporting programs. Two employed parameters are conventional dip and dip direction, while the third parameter can be one of other joint characteristics such as infilling, length, aperture and so on. In order to check the validity of the method, it was applied in one of the Neyriz Marble quarries, where rock mass contains well defined and clear joints. In this research, the type of infilling of joints has been taken into account as the third parameter, and the results were compared to the traditional 2-parameters classification. This revealed that one joint system defined on stereonets, in new 3-parameter classification, is distinguished as two separate joint systems regarding their type of infilling, namely, iron oxides and non-filling. Field investigation shows the joint system with no infilling is contributing in instability of rock walls and also occurrence of spalling phenomenon in toes of some benches. Utilizing SPSS software, a regression analysis has been performed for each set of joint data, and it is shown that a better correlation factor exists between the values in the new 3D classification. It also shows that the more non-filling joints extend northward, their dips tends to 90°, and this can be a key in slope stability studies, as well as in mining design and planning.
Z. Hosseinmardi; M. Ghorashi; M. R. Ghassemi; M. Talebian
Abstract
The outcrop of northern part of North Eshtehard Thrust has been selected for study of structural evolution and geological processes. The study area includes folding structures with different scales from regional to outcrop which belong to fault related folding category. Analysis of joints in the region ...
Read More
The outcrop of northern part of North Eshtehard Thrust has been selected for study of structural evolution and geological processes. The study area includes folding structures with different scales from regional to outcrop which belong to fault related folding category. Analysis of joints in the region among upper red formation strata shows two main sets which are usually tensional (j1 & j2). These joints are visible in sandstone units of upper red formation and most of them are filled with gypsum. It is obvious that the j1 joints are younger than j2. j1 and j2 joints are related to folding processes. The local stress field which could be measured from the joint study is σ1=337/75, σ2=189/13 and σ3=077/03 and corresponds with the given paleostress direction for southern part of central Alborz.
Z. Mardani; M. Ghorashi; M. Arian; Kh. Khosrotehrani
Abstract
Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics.These indices have the advantage of being calculate from ArcGIS and remote sensing packages over large area as a reconnaissance tool to identify geomorphic anomalies possibly related to active tectonics.This ...
Read More
Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics.These indices have the advantage of being calculate from ArcGIS and remote sensing packages over large area as a reconnaissance tool to identify geomorphic anomalies possibly related to active tectonics.This is particulary valuable in west-central Alborz where relatively little work on active tectonics based on this method was done,so this method is new and useful. Based upon values of the stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf),we used an overall index(Iat) that is a combination of the other indices that divides the landscape into four classes of relative tectonic activity. The moderat class of Iat is mainly in the south of Manjel dam,while the rest of the study area has high active tectonics (shahrud drainage basin and sefidrud drainage basin),and high to very high(Taleghan and Alamut drainage basin). The stream network asymmetry (T)was also studied using morphometric measures of Tranverse Topographic Symmetry.Analysis of the drainage basins and subbasins in the study area results in a field of T-vectors that defines anomalous zone of the basin asymmetry.Acomparsion of T index clearly coincide with the values and classes of active tectonics indices and the overall Iat index.
T. Majidi Niri; H. Nazari; M. Ghorashi; M. Talebian; A. Kaveh Firooz
Abstract
Pishva fault with about 35km length is located between Alborz and Central Iran structural zones in southeast of Varamin. General trend of the fault is NW-SE (N38W, 33NE) which has reverse mechanism accompanied by sinistral component. Achieved Morphotectonic studies along the Pishva fault reveal its activity. ...
Read More
Pishva fault with about 35km length is located between Alborz and Central Iran structural zones in southeast of Varamin. General trend of the fault is NW-SE (N38W, 33NE) which has reverse mechanism accompanied by sinistral component. Achieved Morphotectonic studies along the Pishva fault reveal its activity. 3-5 seismic events with recurrence time of 3265 years are identified by studying on two Paleoseismic trenchs T1 and T2, The youngest and oldest events are 0.87 Ka and 29 Ka respectively. According to Wells and Coppersmith equations (1994), the biggest and smallest computed earthquake magnitudes are respectively 7.08 and 5.9. It would be possible to assign Shahr-e-Rey 1384 AD earthquake to this fault, since Event 1 is 870 years old.
M Foroutan; H. Nazari; B. Meyer; M. Sébrier; M. Fattahi; K. Le Dortz; M. Ghorashi; Kh. Hessami; M. R. Ghassemi; M. Talebian
Abstract
The evaluation of seismic potential along the Dehshir fault with 550-km length (by count of northern and southern splays) is critical considering that more than 3.5 million people live in cities and towns located at vicinity of the fault. The Dehshir fault is considered as westernmost limit ...
Read More
The evaluation of seismic potential along the Dehshir fault with 550-km length (by count of northern and southern splays) is critical considering that more than 3.5 million people live in cities and towns located at vicinity of the fault. The Dehshir fault is considered as westernmost limit of N-striking dextral strike-slip faults set that slice Central and eastern Iran. Due to the lack of large recorded earthquakes (instrumental and historical) in Central Iran, access to seismic potential of active faults by studying the earthquake catalogs seems to be impossible. No instrumental earthquake has been recorded greater than mb 4.7 around the Dehshir fault and also historical data shows no evidence for occurrence of large earthquake around the fault. No sign of destruction in Marvast historical castle (at a less than 10 km far from the Dehshir fault) built in Islamic period (~700-1250), shows any remarkable seismic activity until 750-1300 years ago. However, several evidence of geomorphologic markers such as drainages, gullies, streams and alluvial fans offsets, represent activity of the Dehshir fault in Late Quaternary. Of Geomorphic evidence at Marvast and Harabarjan sites record dextral - slip on the Dehshir fault during the Late Pleistocene-Holocene as major movement with minor dip - slip component. Rake of the fault movement has been considered for assessing to amount of horizontal and vertical slip rate on the Dehshir fault. This value in the North Marvast site has been calculated ~10 degrees and according to right bank offset on the Marvast river is ~7 degrees with horizontal and vertical displacements of 13 m and 1.5 m, respectively. Combining cumulative offset markers with OSL dating implies the Dehshir fault in Late Pleistocene-Holocene time period slips at horizontal and vertical components about 1±0.3 and 0.1 mm yr-1, respectively. We observed a minimum dextral offset along the Marvast fault segment in west of Harabarjan about 2 m that allow us assuming the related magnitude and date of last large paleoearthquake on the Dehshir fault is about Mw 7 and 2000 years ago, respectively.
M. Abdideh; M. Qorashi; K. Rangzan; M. Aryan
Abstract
This paper present a new method for evaluating relative active tectonics based on morphometric indices useful in evaluating morphology and topography. Indices used include: Bifurcation ratio (BR), Basin Relief (Bh), Drainage Density (DD), Ruggedness number (Rn), Stream frequency (Fu), Form Factor (FF), ...
Read More
This paper present a new method for evaluating relative active tectonics based on morphometric indices useful in evaluating morphology and topography. Indices used include: Bifurcation ratio (BR), Basin Relief (Bh), Drainage Density (DD), Ruggedness number (Rn), Stream frequency (Fu), Form Factor (FF), Shape Factor (Ll), Sinuosity (Sl) and Elongation ratio (Re) of drainage basin. Results from the analysis are accumulated and expressed as an index of relative active tectonics, which we divide to from relatively low to highest tectonic activity. The study area in the central Zagros fold – thrust belt of the south western Iran is an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than river system or mountain front. The study area has variable rates of active tectonics resulting from the collision between the continental Arabian plate and the so – called Iranian block belonging to Eurasia that has produced linear NW – SE anticline forms and thrusts. We test the hypothesis that areas of known, relatively high rates of active tectonics are associated with indicative value index of relative active tectonics.
M. Talebian; S. H. Tabatabaei; M. Fattahi; M. Ghorashi; A. Beitollahi; A. Ghalandarzadeh; M.A. Riahi
Abstract
The Iranian plateau lies between the Arabian and Eurasian plates and accommodates approximately 22 mm/yr of N-S shortening. About 9 mm/y of this shortening is taken up by folding and thrusting in the Zagros while the remaining 13 mm/yr is taken up in the Alborz and Kopeh-Dagh. The Central Iran ...
Read More
The Iranian plateau lies between the Arabian and Eurasian plates and accommodates approximately 22 mm/yr of N-S shortening. About 9 mm/y of this shortening is taken up by folding and thrusting in the Zagros while the remaining 13 mm/yr is taken up in the Alborz and Kopeh-Dagh. The Central Iran block is relatively stable and thus moves to the north with an average velocity of about 13 mm/y. As the stable Afghanistan block lies to the east, the northward motion of Central Iran produces a right-lateral shear in eastern Iran, which is distributed mainly over a few major faults to the west (~5 mm/yr) and east (~ 8 mm/yr) of the Lut desert. Limited information is available about the slip rates of individual faults in eastern Iran; therefore in this study we try to combine all geological, geodetic and available Quaternary dating results to estimate the fault slip rates and distribution of active deformation in eastern Iran. Finally, we report the results from OSL dating of samples taken from uplifted plain deposits near the south end of the Bam-Baravat fault. These results show that this fault is growing in the vertical direction with at a rate of ~ 0.5 mmy-1. Considering geometric relation between the Bam-Baravat and the south Bam earthquake fault, we estimate a slip rate of about 2 mm/y for the south Bam earthquake fault.
M. Asadi sarshar; A. Bahroudi; M. Qorashi; M. R. Ghassemi
Abstract
Estimate of moment rate is comparatively reckoned as a new method for dealing with tectonic activities rate in different regions and it prepares the way for putting together different methods. In fact, moment rate states rate of energy which exists in deformation system. There are three different approaches ...
Read More
Estimate of moment rate is comparatively reckoned as a new method for dealing with tectonic activities rate in different regions and it prepares the way for putting together different methods. In fact, moment rate states rate of energy which exists in deformation system. There are three different approaches to state moment rate that each one express tectonic motion and movement of a region from a particular view. These three approaches consist of: geodetic (surveying), seismic and geology methods. Geodetic method which is determined on the basis of gained strain rate tensor from geodetic data, shows deformation rate (including seismic and aseismic) that is happening in the region at this moment in time. Moment rate which has gained on the basis of historical and instrumental catalogues, shows the total released seismic energy during quake events which are available in earthquake of region and geologic moment rate which gained with geometric parameters of faults, reveals potential of the faults in releasing stored elastic energy in. Geodetic moment rate, seismic moment rate (on the basis of historical and instrumental earthquake data) and geologic moment rate are estimated for Central Alborz region. The most moment rate in the study area belongs to geodetic approach (8.83×1019 Nm/yr) and then geologic moment rate (0.12×1019 Nm/yr) and finally the least quantity belongs to seismic moment rate (0.022×1019- 0.046×1019 Nm/yr). Considering, distribution of earthquake epicenters, the most seismic energy is released in the south parts of Central Alborz and considering high geodetic and geologic moment rates in north parts, it seems, north parts of Central Alborz have higher seismic potential.
R. Khavari; M. Ghorashi; M. Arian; Kh. Khosrotehrani
Abstract
The paper presents a method for evaluating relative active tectonics based on geomorphic indices useful in evaluating morphology and topography. Indices used include: stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height ...
Read More
The paper presents a method for evaluating relative active tectonics based on geomorphic indices useful in evaluating morphology and topography. Indices used include: stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf). Results from the analysis are accumulated and expressed as an index of relative active tectonics (Iat), which divided into four classes from relatively low to highest tectonic activity. The study area along the south flank of the central Alborz mountain range in north Iran is an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than a single valley or mountain front. The recent investigations show that neotectonism has played a key role in the geomorphic evolution of this part of the Alborz mountain range. Geomorphic indices indicate the presence of differential uplifting in the geological past. The high class values (low tectonic activity) for Iat mainly occur in the south and southeast of the Karaj drainage basin, while the rest of the study area has classes of Iat suggesting moderate to high tectonic activity. Around the Amirkabir Lake, Iat has the highest value. The distribution of the indices defines areas associated with different mountain fronts and estimates of relative rates of tectonic activity. More than half of the study area is classified into classes 2 or 1 of high to very high tectonic activity in terms of the apparent geomorphic response. In different tectonic environments with greater rates of active tectonics, the values of indices would differ as well as their range in value. The stream network asymmetry (T) was also studied using morphometric measures of Transverse Topographic Symmetry. Analysis of the drainage basin and a number of sub-basins in the study area results in a field of T-vectors that defines anomalous zones of the basin asymmetry. We test the hypothesis that areas with great stream migration are associated with indicatives values of Iat.
M. Shokri; M. Ghorashi; H. Nazari; R. Salamati; M. Talebian; J.-F. Ritz; H. Mohammad khani; M. Shahpasand zadeh
Abstract
The Astaneh fault with a length of more than 75 km is located in NW of Damghan. Morphotectonic investigation along the Astaneh fault and left - lateral displacement in quaternary deposits shows that, Astaneh is an active fault. It is necessary to recognize paleoseismicity of Astaneh fault because, this ...
Read More
The Astaneh fault with a length of more than 75 km is located in NW of Damghan. Morphotectonic investigation along the Astaneh fault and left - lateral displacement in quaternary deposits shows that, Astaneh is an active fault. It is necessary to recognize paleoseismicity of Astaneh fault because, this fault is located in seismic zone of Komes historical earthquake with Ms=7.9 (Ambraseys & Melville, 1982). Many people (more than 45000) were killed in Damghan city in Komes historical earthquake. In this paper, 4-5 paleo events along the Astaneh fault are presented through paleoseismological investigation.
A. Lashkari; M. R. Ghassemi; M. Qorashi
Abstract
The Caspian (Khazar) fault is the boundary between the Caspian plain and AlborzMountain. As a major tectonic feature, this fault may be considered as the northern mountain front fault of the AlborzRange. Subsidence of the Caspian Sea in north, uplift of the Alborz Mountain, and its over thrusting on ...
Read More
The Caspian (Khazar) fault is the boundary between the Caspian plain and AlborzMountain. As a major tectonic feature, this fault may be considered as the northern mountain front fault of the AlborzRange. Subsidence of the Caspian Sea in north, uplift of the Alborz Mountain, and its over thrusting on southern part of South Caspian basin has occurred along the Caspian fault. In this paper, a segment at the fault which is located between longitudes 52° 30׳ and 53° 00׳ - in the northern part of geological map of Qaemshahr - is considered as a segment that does not outcrop. This paper introduces the general structural and morphotectonic characteristics of this zone and describes the characteristics of the active anticlines (growing folds) and morphotectonic effects in this zone such as effects on rivers.
H. Nazari; J-F. Ritz; R. Salamati; M. Ghorashi; A. Ghasemi; H. Habibi; F. Jamali; Sh. Javadipur
Abstract
Tehran and its surrounding region are within affecting zone of some active faults of North Tehran and Mosha in north-north east and Parchin and Pishva in south. In addition, there are some other shorter faults and linear markers within the urban area of Tehran such as Niavaran, Mahmoudieh and Davoudieh ...
Read More
Tehran and its surrounding region are within affecting zone of some active faults of North Tehran and Mosha in north-north east and Parchin and Pishva in south. In addition, there are some other shorter faults and linear markers within the urban area of Tehran such as Niavaran, Mahmoudieh and Davoudieh faults in the northern part of city, and Rey and Kahrizak scarps in the south.
Previously, according to occurrence of several historical earthquakes in Rey area and also some geomorphologic evidences, most of these markers with the linear scarps in south Tehran alluviums were mentioned as active faults.
From seismotectonic and urban geology point of view whether these faults exist or not are an important issue. Recent seismotectonic studies including paleoseismology and geophysics investigations have failed to prove existence of such faults beneath the observed surface scarps. So in this paper according to delivered data from our paleoseismology, geophysical and seismotectonic investigations and also some geological evidences of foreland basin deposits (late Quaternary) in the Central Alborz (ex: shoreline evidences in Parchin area-south east of Tehran) and in some other place such Kordan fan (west of Karadj), we suggest that these scarps may be a kind of shoreline in front of the Tehran piedmont or the actual faults may be in different place than that suggested by observation of surface escarps.
In this research we use satellite imagery (Land Sat, Spot, Quick birds), aerial photos and GPS kinematics to do Digital Elevation Model (DEM) through the Kahrizak scarp with paleoseismology trenching and geophysical (Geoelectric and Georadar) investigations on different parts of Rey and Kahrizak scarps.
F. Jamali; K. Hessami Azar; M. Ghorashi
Abstract
The N-NW trending Qom-Zefreh fault system has long been recognized as one of the major faults in Central Iran. We have used observations of faulting, recognized on satellite images and aerial photos, in conjunction with field investigations, to infer fault activity along this structure ...
Read More
The N-NW trending Qom-Zefreh fault system has long been recognized as one of the major faults in Central Iran. We have used observations of faulting, recognized on satellite images and aerial photos, in conjunction with field investigations, to infer fault activity along this structure in an area between Zefreh and the north of Kashan. Right-lateral strike-slip motion along this fault can be inferred from the associated lateral offset of stream beds and alluvial fan observed on aerial photographs and on the field. Morphological features and observations of fault exposure in several places also indicate that the western block is up-thrown relative to the eastern block across reverse component of the Qom-Zefreh fault system. Using changes in fault geomorphology and fault trace orientation we have defined two segment boundaries and structurally divided the Qom-Zefreh fault system into three segments in the region, namely Zefreh, Kashan and Ravand segments. The recognition of these segments is important because it may have implication in assessment of seismic hazard for the Kashan region.
B. Vahdati Daneshmand; M.R. Ghassemi; M. Ghorashi; N. Haghipour
Abstract
According to historical maps of Iran, changing the course of Sepidrud from Dastak to Kiyashahr has occurred in a very recent time. Although migration of meandering streams over the delta plain is a natural phenomenon and oscillations of Caspian Sea might have affected the course ...
Read More
According to historical maps of Iran, changing the course of Sepidrud from Dastak to Kiyashahr has occurred in a very recent time. Although migration of meandering streams over the delta plain is a natural phenomenon and oscillations of Caspian Sea might have affected the course of SepidrudRiver, the deflection of Sepidrud between Astaneh and Koochesfahan is probably related to activity of concealed structures wit
hin the delta deposits. This research uses calculation of morphotectonic indexes to study effects of active range boundary within range faults in study area on drainage pattern and river streams.
