GEOSCIENCES
Year:2015 | Volume:24 | Issue:95 (TECTONIC)|Papers Count:39

Structural data from the Kuh-Banan oblique-slip fault system show that this active fault controls the structural architecture of the Tikdar- Goorchoieh area, north of Kerman. The Kuh Banan fault system is consisted of three fault branches with mean trend of N70E in the north of the Tikdar - Goorchoieh village. These fault branches with a dip of 50-70 toward the northwest and slip rake of 50-80 N indicate the prevalent reverse with right-lateral strike-slip motion of the fault. The main strand of Kuh-Banan fault system with a northwest-southeast strike is reported between the Dehsu rock series and Shemshak Formation whereas the fault branches with a northeast-southwest trend are situated between the Hojedk Formation and Neogene alluviual deposits and Quatrnery sediments. In this area, the Dehsu rock series (Late Neo-Proterozoic-Lower Cambrian) is composed of dolostone and evaporitic rocks which thrusted over the sandstones, shales and limestones of the Hojdak Formation (Jurassic). According to the structural evolution of the Kuh-Banan fault system in the study area, the first fault branch (F3) with three fault slip motion in the northeast-southwest direction has developed between the Shemshak Formation and Dehsu rock series in north of Tikdar. The later fault branches of F1, F2, and F4 with the same trend have propagated from the main fault and developed between the Dehsu rock series with the Hodjek, Shemshak and Dahu (equivalent of Lalun) Formations.

Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics in an area. These indices have the advantage of being calculated using ArcGIS and RS (Remote Sensing) packages over large areas as a reconnaissance tool to identify geomorphic anomalies possibly related to active tectonics. This is particularly valuable in Great Karoun River Basin of Zagros, where relatively little work on active tectonics based on this method was done. The study area in central Zagros fold- thrust-belt of the southwestern Iran is an area with NW–SE oriented structures provides an ideal location for testing the concept of an index to predict relative tectonic activity on a basis of river system or mountain front. 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), overall index as index of relative active tectonic (Iat) was resulted that is a combination of the other indices. This indices are used to divide the landscape into four classes of relative tectonic activity. After measuring indices it is concluded that this part of the Zagros zone has variable rates of active tectonics. Based on corrected Iat values, the study area was divided into three parts: class 1 (very high relative tectonic activity, %24 in area; such as some parts of the east and central zone where Main Zagros Reverse Fault and Dezful embayment fault have the most influence); class 2 (high relative tectonic activity, 63% in area; such as most parts of the area in east, west, north and center where action of faults are lower than the previous class); class 3(moderate, 10% in area; such as most parts of the area in north and south where action of faults are the lowest). Therefore, we don’t have class 4 in this area, and 1% of basin is not measured for the indices because it is located in coastal plain of Khuzestan.

The E-W trending North Qazvin Fault is situated in north & northeast of Qazvin city in south-central Alborz. Across the fault, Karaj formation (Eocene) is thrusted over Hezardarreh Formation (A) and the alluvial B Formation. It could be the source for the 1119 AD earthquake with an estimated magnitude of Ms: 6.5. The North Qazvin Fault is a seismically active fault, therefore it is one of the most important earthquake threats for the Qazvin as an industrial city of Iran. Morphotectonicand detailed field studies along a part of the North Qazvin Fault allows us to measure horizontal and vertical offsets caused by recent movements on this fault. One of the measured horizontal and vertical displacements due to the recent movements on the fault is 4 and 3.5 meters, respectively. The geometry (strike, dip and rake) of the North Qazvin Fault in this part is 090o, 45o, 51o respectively. Our investigations show that the North Qazvin Fault is a north-dipping compressional fault. The North Qazvin Fault and its surrounding faults such as Najm-abad fault appear as a propagating fault system which has left-lateral compressional kinematics in southern part of the west-central Alborz.

In order to survey the extensional forces dominated in central Alborz since Late Triassic (Norian) to Middle Jurassic (Early-Bajocian), synsedimentary normal and strike-slip fault systems in Balladeh valley which contains significant distribution of Shemshak Group have been studied. Analysis of σ orientation for 404 fault planes in 35 normal fault systems, show two major extension directions at NNE (020o) and NE (070o) trends during sedimentation of Shemshak Group. Also, the presence of a minor extension direction trending WNW (300o) which is coincident with extension direction of synsedimentary strike-slip fault systems implies the existence of transtentional basins in the Shemshak basin at that time. The southward movement of southern edge of Eurasia (from latitude of 30° to 15o) and its clockwise rotation for some 40o-50o during Triassic-Jurassic periods led to domination of N-S extension in early times of Shemshak Group sedimentation, and as soon as the Eurasian plate rotated, the extension direction was changed into a NE-SW trend. These separated records of paleostress axis trends are also due to the high sedimentation rates and subsidence in Norian-Rhaetian and Toarcian-Aalenian during Shemshak Group sedimentation. The minor extension trending WNW-ESE (278o-307o) is due to σ2/σ3 permutation between N-S σ2 direction of stress tensor and its σ2 axis. Low values of Φ (less than 0.4) generally correspond to situation characterized by σ2/σ3 permutation; therefor it causes multidirectional extension in extensional stress regimes. About 80 percent of sites which show WNW-ESE paleostress extension trend have low Φ values. This issue explains σ2/σ3 permutation of N-S major extension trend. The areas of mentioned stations and also those ones with strike-slip fault systems σ3 directions of which are directed WNW-ESE had high basin crustal anisotropy.

The Alborz Mountains 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 South Caspian Basin crust. In this study, we used the P-wave receiver function modeling to investigate the crustal structure beneath the eastern part of the Alborz Mountains 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.

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 Eastern Iran seismotectonic Province, 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.

Understanding paleoseismic characteristics and seismic capability of faults is very important for evaluation of seismic risk in any area. Using geomorphic markers as indirect method in paleoseismic studies is an appropriate and practical method in understanding the tectonic activity the mountainous areas. Gigantic landslides are among the markers for this purpose. Usually these landslides are related to tectonics and it is generally interpreted as landslides triggered by earthquakes. Major landslides in the Noor valley (Central Alborz) are used in this study as geomorphic markers for seismic capability of faults. No major historical earthquake is reported from the Noor valley arae, however gigantic landslides in the valley indicate that multiple major seismic events have occurred in earlier periods which are not recorded in historical records. According to geomorphic characteristics of these landslides, we determined 3 different age classes (Late Holocene, Early Holocene, and Late Pleistocene) for them. These ages provides possibility for identifying of multiple earthquake events in the area. According to the relationship between the earthquake magnitude and the maximal volume of the related landslides, we estimated magnitudes of the earthquakes to be 7.7±0.49 to 7.9±0.49. Based on the distribution of the landslides the eastern segment of the Baladeh fault seems to be responsible for the earthquakes.

The long-lived Fars paleo-high, located in SE Zagros Mountains is a prolific hydrocarbon province as it contains 15% of the world’s proven gas reserves. Subsurface data sets acquired during the recent hydrocarbon exploration in the region indicated fold style variation and structural complexity deep in the sedimentary cover, understanding of which is essential for petroleum system modelling and selection of new targets for gas at depth. In order to analyse the fold style in Fars paleo-high, this study presents a new regional balanced cross-section with a length of~130 km and a depth of 12 km, across the Fars paleo-high. The section was constructed using seismic profiles, exploration wells and field data. The results show that variation of fold style happens in accordance to variation in mechanical properties of rock units across the Fars paleo- high, as well as from surface down to the depth of sedimentary cover. Detachment folding, followed by limb thrusting, which happens above 8-12 km below sea level, is the main deformation mechanism of sedimentary cover. In the middle of sedimentary cover, however, tectonically over-thickened Triassic evaporitic rocks efficiently decouple the geometry of post Triassic succession with respect to the underlying Permo- Triassic reservoir carbonates. Restoration and balancing of the regional cross-section indicated 20% of shortening across the Fars Paleo-high, accommodated by folding and thrusting. Abrupt change in the level of synclines accompanied with trends of seismicity and linear exposure of old geological units, proposes involvement of at least two main basement reverse faults in the deformation of cover sequence.

Geomorphic characteristics of alluvial fans on the sides of the Shotori Mountains in east of Tabas represent two different groups . The first group is older and is more dominant with their heads near the Shotori Mountains’ 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 Shotori Mountains. 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 Shotori Mountains 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 Shotori Mountains 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 Shotori Mountains). 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.

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.

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 ML 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 =1.986 log [rij/100]-0.00452 (Rij-100) -3+SjWhere R  is hypocentral distance in km between the jth station pair and ith earthquake and Sj is value of station correction for the jth station The realtionship clearly indicates a larger attenuation for shear waves in short hypocentral distances below 20 km. Our new ML relationship implies ML 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.

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.

The existence of lateral propagation of folds above blind reverse faults is an important hypothesis and is generally accepted. In this research, the growth pattern of active folds (e.g., Herang and Kuh-e-Namaki anticlines) in the Fars Arc located in the Zagros Fold-Thrust Belt is investigated from tectonic geomorphology point of view. The main goal of this research is to use geomorphometric indices such as drainage pattern, drainage density, drainage basin asymmetry factor and stream length-gradient to determine direction of lateral fold growth with a special focus on the process of linkage of several different fold segments. Geomorphological studies show that some folds in the Zagros did not develop from a single embryonic fold but by lateral linkage of several different fold segments. The linkage type (linear or en-echelon linkage) of different fold segments depends on the alignment of the initial embryonic folds. Investigation of geomorphometric indices in the study area shows that the Herang anticline resulted from lateral growth and en-echelon linkage of three embryonic folds while the Kuh-e-Namaki anticline resulted from linear growth of a single embryonic fold and cannot be considered as a result of linkage of several different segments.

In this study, attenuation behavior of moderate to large earthquake aftershock sequences occurred in Iranian plateau as been investigated according to the empirical Omori Law. Due to proper recordings of instrumental earthquakes from 1990 to 2012, important earthquakes of this period were selected. After determination of aftershock sequences using temporal-spatial window defined by Gardner & Knopoff (1974), 14 sequences having enough recordings and appropriately distributed over the Iranian plateau were investigated in terms of attenuation behavior curve. Therefore, the Omori curve and parameters (p, c and k) were plotted and calculated for each sequence. Results show that for the Iranian plateau earthquakes, p-values range between 0.39 and 2.7, parameter c values vary from 0.01 to 5, and paremeter k shows values in the range of 10 to 1427.4. This high variability is taken to indicate not only a variety of aftershock occurrence patterns in the Iranian plateau, but also an incomplete and inhomogeneous earthquake catalog. By using the present database, therefore, it is not easily possible to have a zonation based on temporal attenuation behavior of aftershock activities over the Iranian plateau. However, the estimations of aftershock attenuation rate for each locality can be used to analyze seismic hazard. Present study showed that the p-values and hence the aftershock attenuation rates in the Alborz and Zagros regions are greater than those in the eastern and central parts of Iran. The higher the rate, the greaterthe energy release, which means a shorter time to gain background seismicity. This result is comparable and consistent with the amount of energy released in theseismotectonic zones of the Iranian Plateau. Moreover, 7 out of 14 earthquake sequences have secondary aftershocks, which give two values for each Omori parameters. Results demonstrated that with a higher earthquake magnitude, the occurrence of the next big event as well as secondary aftershocks is more likely. Furthermore, for the 7 sequences with secondary aftershocks, a trend of P2 variations is observable. P2 is more than 2.5 for 3 of these sequences that have magnitudes above 7 and occurred along the Iranian plate boundaries. For the other 4 intraplate events, which have magnitudes less than 7, P2 is less than 2. This might be due to a magnitude change or tectonic setting and distance of hypocenter to the main fault nodes. Resultsalso showed that the c and k parameters are highly affected by number of recordings in the catalog. A more complete and homogeneouscatalog would produce well-constrained values for these parameters, which in turnmakes the analysis of the seismicity and physics of the fault zone more accurate.

Seismic values are the main parameters in evaluating the neotectonic activity of a region. In August 11, 2011, two Mb=6.4 and Mb=6.3 earthquakes occurred in Ahar-Varzaghan region within 11 minutes. Seismotectonic investigations imply that the faults generating the events are the young faults of the regions. Also, distribution of the epicenters represent a pattern consistent with the fault trends in the area. Temporal and spatial distribution of the earthquakes (fractal analysis) as earthquake pre-indicators together with a-b values were used to assess the neotectonic activity and explore the seismic model of the Ahar area. Results show a sharp decrease in b-value, indicating that the main shock was associated with a zone of high strain rate. The seismic model presented for the Ahar area illustrates three periods after the main shock including: 1) an early quiescence Q1, 2) an aftershock period B, and 3) a late quiescence Q2. The rather increase in b-value during the Q2 period is interpreted to indicate stress decrease in the region.

Extensive mylonitic fabrics are observed in the north Golpayegan metamorphic rocks in the Sanandaj-Sirjan zone. Earlier researchers did not present any evidence for the relative timing of mylonitic fabrics development. In this paper, the relation between folding and metamorphism events and formation of shear zones in the north Golpayegan are documented. The evidence is systematically presented at the microscopic, outcrop (mesoscopic) and map scales in order to study the relative timing of mylonitization event. The evidence at the microscopic scale indicates that the mylonitization occurred after the first stage amphibolite facies high-grade metamorphism, synchronous with the second stage greenschist facies retrograde metamorphism. The evidence at the microscopic and outcrop scales are compatible with each other and show the mylonitization event during the second stage (D2) folding, coeval with the greenschist facies metamorphism. Transposition of mylonitic foliations on the limbs of the second-generation microscopic and mesoscopic folds is documented. At the map scale, concordance of stretching lineations with second-generation fold axes, and folding of mylonitic foliations during the third stage of deformation also indicate mylonitization event during second stage (D2) deformation. Through a correlation of the isotopic ages, an Early Paleocene age is proposed for the mylonitization during D2 event in the north Golpayegan.

There is a close relationship between resistance to slip along decollement surfaces and presence of deep and shallow decollement levels in thin- skinned fold and thrust wedges. Decollement units in lower (Upper Red Formation) stratigraphic levels in Mianeh-Mahneshan fold belt have an effective role onthe geometry and kinematics of deformation of the area. In order to understand the fold geometry and folding mechanisms, and to exploredepth-to-the-decollement surface, we carried out data collection and field study in an area between Mianeh and Mahneshan cities. Folded structures in the study area are different from other structures within the area, as well as from the structures in the neighboring Alborz Mountains. The rise of salt domes along with the plasticity of marls in the Upper Red Formation have resulted in extreme complexities in folding pattern. In order to analyze syn-sedimentary structural features and interpret the geological evolution of the area, we used detailed structural measurements, sedimentological and sedimentary environment features, sedimentary rock studies, and paleogeography. One of the results of this study was the interpretation of syn-sedimentary growth structures in the Mianeh-Mahneshan area, which helped us to construct six structural cross-sections (AA′, BB′, CC′, DD′, EE′ and FF′) across the folded structures. Measured shortening along two Sections AA’ and DD’ is 46.65% and 38.05%, respectively, with an average of 42.3%. These values are different from those estimated forthe neighboring Alborz and Zagros Orogens, where shortening ranges between 16-30%. We attribute this difference to local intense shortening in the study area caused by several factors such as basin slope, deep faults and weak beds along decollement surfaces. This study indicates that dominant folding mechanisms in the study area are detachment folding, and fault-propagation or fault-bend folding. The presence of evaporitic material (gypsum and salt) within the succession has played a major role in the kinematics of folding.

Zagros fold-thrust belt has been crossed by different transverse faults with NNW-SSE trend and dextral mechanism. These faults often show en-echelon geometries on the surface because of presence of detachment layers at base and within the cover sequence. The Karehbas fault is one these faults located in Fars province about 65 km to the east of the Kazerun Fault zone. Presence of the Hormoz salt as a basal detachment and ductile horizons within the sedimentary cover have caused the fault to appear on the surface as several north-northwest-trending en echelon segments. At least six segemnts have been recognized in northern and southern parts of the Karehbas fault. In this study two southern segments, the Mengharak and Kalagh segments of the Karehbas fault zone to the south of Firuzabad are introduced and their mechanism are analyzed. Riddle and anti-riddle faults and drag folds and terminations are used to analyze the dextral kinematic for both segments. These strike-slip fault segments terminate in thrusts that are sub-parallel to the regional the Surmeh and Kalagh thrusts in the south. These fault terminations are in the hanging-wall of the Surmeh and Kalagh thrusts, and expose formations that are older than those in the hanging-wall of the latter thrusts. Therefore, the Mengharak and Kalagh segments introduced in this study have strike-slip mechanism, and according to this mechanism, their geometry and their structural position in continuation of the northern and central segments of the Karehbas fault, they are introduced as the southern segments of the Karehbas fault. Based on the thrusting of the Asmari Formation over the Bakhtiari Formation in the positive flower structure along the Mengharak segment, the minimum amount of displacement on these fault segments are evaluated equal to the thickness of the Mishan Formation.

Situated 15 km NW of the Izeh city, Tukak and Kamarun anticlines are located in northwest of the Izeh zone in the Zagros fold-and-thrust belt. The Tukak anticline measures about 17 km length by 3.3 km width on the Asmari formation outcrop, while the Kamarun anticline shows a maximum length and width of about 15 km and 3.5 km, respectively, on the same formation. The SE termination of the Kamarun anticline and the NW termination of the Tukak anticline form together an en-echelon array. Both anticlines represent nearly symmetrical box-fold geometry, in which the Pabdeh formation is the oldest outcrop in each anticlinal core and the Asmari formation constitutes most of their surface outcrop. Based on surface geology, 4 cross-sections across the Tukak anticline and 3 cross-sections across the Kamarun anticline (D-D' is a common section crossing the en-echelon plunges), and one longitudinal section through both structures were constructed. Since the Bangestan horizon is taken to indicate a position upper than sea level, the cross-sections were used to construct the UGC map on the Upper Khami horizon. In Tukak anticline, which is bigger than the Kamarun anticline, the UGC map of the Upper Khami horizon illustrates vertical and horizontal closures of 250 m and about 4.3 km2, respectively.

The aspect ratio of folds is among the most important parameters indicating geometrical features of folds. Based on the aspect ratio, folds are categorized into two groups of buckle and forced folds. The NW-SE trending Qitoleh anticline, which is located in NW of the Lurestan structural subzone and in the vicinity of the High Zagros Fault, has unique structural characteristics that make it different from other folds in the Zagros Folded Belt. In rock units older than Cretaceous, the anticline consists of four en-echelon buckle folds whereas shows high aspect ratio and forced fold geometry in Tertiary units. Such a variation in the fold style from the surface down to the depth is interpreted as the imposed influence of the High Zagros Fault on intermediate detachment horizons. Such a fold style, which is also observed in other anticlines neighboring the SE part of High Zagros Fault, can be used as a model to interpret similar folds adjacent to the major reverse basement faults in other parts of the Zagros belt.

This paper aims at evaluating relative active tectonics in the Jarahi-Hendijan drainage basin based on geomorphic indices. 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 analyses were combined to achieve an index of relative active tectonics (Iat), which is divided into four classes implying relatively low to very high tectonic activity. The study area is located across the Zagros Mountains belt (high Zagros, folded belt, and frontal lowlands) in southwest Iran, and comprises 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. Recent investigations show that neotectonism has played a key role in the geomorphic evolution of this part of the Zagros ranges. Geomorphic indices indicate the presence of differential uplifting in the geological past. Higher values of Iat (low tectonic activity) mainly occur in the southwest of the Jarahi- Hendijan drainage basin, while the rest of the study area falls into classes of Iat that indicate moderate to high tectonic activity. Baghmalek and Takhtderaz sub-basins show the highest values of relative tectonic activity. The distribution of this index defines areas associated with different faults and relative rates of tectonic activity. Nearly 40% of the study area is classified into Classes 1 and 2 implying very high to high tectonic activity, and 37% is grouped as Class 4, which is taken to indicate low tectonic activity. Areas of higher relative tectonic activity represent lower Iat values.

In this research, the stress state in the Zagros fold and thrust belt is studied using inversion method analysis of focal mechanisms of earthquakes related to active faults of this region. Geological, structural and seismic differences throughout the Zagros fold and thrust belt led us to divide it into five structural zones to make the analysis of a homogenous stress state in each zone possible. Stress analysis in the Zagros belt was done using a large body of available earthquake dataset. For this purpose to be achieved, focal mechanism data of the Zagros earthquakes was first collected from different sources, then were integrated in the analysis after doing a process of corrections and controls. The present research uses Dyngli Software to analyze stress separation in the defined structural zones. Results show that different parts of the Zagros fold and thrust belt are characterized by at least three, and in some cases four, separate stress regimes. It is evidently shown that the orientations of the first and third stress regimes in Zones 1 and 2, third and fourth regimes in Zone 3, third regime in Zone 4, and first, second and fourth regimes in Zone 5 are in a good agreement with previous studies particularly GPS geodesy results. Crustal displacement directions already determined by GPS geodesy show that, on the one hand, shortening is not uniform across the whole length of the Zagros ranges, and on the other hand strain field orientations and fault slips are also different. This could be related to multiple stress regimes in the Zagros belt. Furthermore, considering a thin-skinned tectonic model in the Zagros, those stress regimes that are compatible with GPS results seem to occur within the sedimentary cover, causing a relatively continuous seismic response in the form of earthquakes of small magnitude. Therefore, the first, second and fourth stress regimes in Zone 1, second regime in Zone 2, first and second regimes in Zones 3 and 4, and third regime in Zone 5 are suggested to be linked to basement, in which stress concentration causes large magnitude earthquakes in Zagros. Also, results showed that compressional stress orientations are normal to the structural trends in all zones; the second compressional regime in Zones 1, 2, 3 and 5, and first regime in zone 4 are normal to the folded and thrusted structures.

Anjireh-Vejin Mines of Tiran are located 60 km west of Isfahan. Exposed rocks in these mines are Early Cretaceous (Early Baremian-Albian) in age. These rock units are exposed in NW-SE trending anticlines plunging shallowly to SE in three Vejin Paein, Vejin Bala and Anjireh- Chekab Mines. Folding in all three mines exhibits same style, indicating that the mines are closely structurally related. At the SW side of all the mines, anticlines formed above the hangingwall of a major reverse fault are breached and expose older Cretaceous units. In the trenches of Anjireh-Chekab mines, which cut the steeply-dipping and overturned limb of the anticlines, older rock units are observed. In the trench cutting the Vejin Bala mine, layers in the SW limb are of steeply-dipping to locally overturned attitudes. Structural evidence from these mines clearly indicated that all the three mines are situated in a unique anticline with overturned SW limb and a folding style that consistently characterize “break-thrust fold” model. This anticline plunges gently by 15o to N150o. In btreak-thrust model, as folding progressively advances, a major reverse fault is being generated along the overturned limb of the anticline, which is well observed along the SW part of the mines in the study area. The mines are separated by E-W trending faults producing the present geometry. In addition to presenting a fold style model, we explored the relation between faults and fractures in all the mines using field observations and satellite images. Fractures are dominantly oriented along NW-SE direction sub-parallel with the strike of the axial plane of the anticlines. Structural analysis revealed three types of ore concentrations:1) parallel to the original stratigraphic layering, 2) along the reverse fault in the overturned limb of the anticline, and 3) in the fracture systems.

Different characteristics of the rock units and their stratigraphic relationships, as well as magmatic and metamorphic activities in the southern part of the Sanandaj-Sirjan Zone resulted in identification of different tectono-stratigraphic units based on their tectonic environments reflecting the opening and closure of the Neotethys Ocean in southern Iran. The major tectono-stratigraphic units identified in this study are as follows: sediments deposited in the aulacogen setting in southern part of the Central Iranian platform of Paleozoic to Middle Triassic age; Triassic volcanic rocks and turbiditic sediments; low-grade flysch-type sediments of Jurassic-Early Cretaceous age deposited in a forearc basin; Lower Cretaceous carbonate platform sediments; suture zone-related rocks containing ophiolite, radilolarite and glaucophane schists; Tertiary flysch- type sediments containing exotic blocks of Lower Cretaceous carbonate, ophiolite and of the Zagros Formations formed over the edge of High Zagros zone; retro-arc foreland sediments of Central Iran which unconformably overlie the deformed rocks of northeastern part of the area; and finally post-orogenic molasse-type sediments resulted from post uplift erosion of the Zagros orogeny, deposited in the internal and marginal parts of the southern Sanandaj-Sirjan zone.

An array of en-echelon strike-slip faults in eastern Iran results in the formation of releasing and restraining bends or stepovers, within which some faults are hidden in the extensional and contractional parts of the structures. This is investigated in the East Neh-Esmaeilabad left- stepping restraining stepover. Transpressional deformation in the transverse structure associated with the stepover is expressed as folding and uplifting in the Late Neogene, Quaternary and recent deposits, revealing the Shusf fault as a hidden and blind thrust. Processing of magnetic anomaly maps shows the existence of the Shusf magnetic lineament, which consistently well correlates with the Shusf fault and its hidden segments. Also the hidden part of the fault was investigated by the differential GPS profiles constructed perpendicular to the trend of the Shusf fault scarp. In this study, we used surface morphology surveys, fan median method and satellite images to calculate the cumulative horizontal and vertical offsets related to the Late Quaternary active tectonics along the Shusf fault, measuring mean values of 92 and 4.25 m, respectively. Analysis of the velocity vector recorded in the Nehbandan geodynamic station across the Shusf fault indicates the present-day evolution of the stepover expressed as uplift and left-lateral displacement.

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.

Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics. These indices have the advantage of being calculated from ArcGIS and Remote Sensing software packages over large areas as a reconnaissance tool to identify possible geomorphic anomalies related to active tectonics. This method is particularly new and useful in areas where relatively little work has been carried out on active tectonics based on this method. Based upon the values of 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 integrated index (Iat) that is a combination of the other indices. This index divides the landscape into four classes of relative tectonic activity. According to the Iat results, sub-basins 4 and 6 show zones of low tectonics activity (Class 4), sub-basins 1, 2, 7, 9, 10, 11, 12, 14, 15 and 19 fit to areas of moderate tectonic activity (Class 3), and high tectonic activity is represented by sub-basins 3, 5, 8, 13, 16, 17 and 18 (Class 2). The Tranverse Topographic Symmetry (T) was also studied using morphometric measurements, which finally gave a plot of T-vectors defining anomalous zones of basin asymmetry. A comparison between T index and map of relative tectonic activity showed a consistent coincidence between areas of higher Iat classes with zones of greater asymmetry.

The Touchahi earthquake of Aug 27, 2010 (MN 5.9; IRSC- Mw 5.7; USGS) occurred at 19:23:49 UTC (23:53:49 local time on 5 Shahrivar 1389) in south of Damghan city. No foreshock were reported before this earthquake whereas 85 aftershocks (MN 1-5) were registered by IRSC  until 1 month after the mainshock. According to our field study after the event, surface rupture of causative fault was not observed but we measured some fractures related to this event with dominant strike of N120o-140o. According to our observations of 32 towns and villages that were damaged in this seismic event, maximum intensity (I0) of VIII+ in MMI scale occurred near the Touchahi village in ~85 km south of Damghan city. Unfortunately in this earthquake 4 people were killed. Focal mechanisms of the Touchahi seismic event and its greatest aftershock is solved using the first P motion method. The fault plane solution show near vertical plane for the causative fault of the earthquake and suggests a left- lateral mechnism. The mechanisms associated with the fault show mainly left-lateral strike-slip motion, on a NE -SW striking fault plane. Based on location of the earthquake epicenter, its aftershocks location, the fault plane solution (left-lateral strike-slip with N039o strike and dip direction toward NW) and field observations, the causative fault of Touchahi earthquake is one of the active fault branches that is situated in north of Darestan mountain and south of  Touchahi, Koohzar and Kooshahi villages. This fault with left-lateral strike-slip mechanism by general strike of NE-SW and dip direction toward NW is indicated as Touchahi fault.

The Karbasi anticline is located to the west-northwest of the Jahrom town, and 40 km to the northwest of Aghar gas anticline in interior Fars region. The anticline has an asymmetric structure, and some faults with large strike separations are observed in it. Because of the importance of comparison between the folds, and understanding folding patterns in different systems, analysis and description of basic elements of fold style is considered as a major components in structural studies. The aim of this study is to analyze the elements of fold style in the Karbasi anticline located in the interior Fars, in order to contribute to the exploration goals of hydrocarbon. The software used in this study include Tectonics FP, Global Mapper, and software related to Geo Modelling. Analysis of fold style elements in the different parts of the Karbasi anticline indicates changes in the pattern of folding. The changes in the western part of the Karbasi anticline is different from other parts of the anticline. Based on prepared stereoplots, fold axis and axial plane show major changes in the western part of the anticline. In the study area Dashtak Formation as a middle detachment unit plays a major role in development of the geometry of folds. Based on our results, it seems the western part of the anticline is affected by more deformation. It is probable that in this part, the Nezam-Abad fault has caused rotation of the western plunge of the fold towards north, and has affected the Karbasi anticline. Based on the modeling done for the study area, a secondary fault is indicated related to the Nezamabad fault.

In the east of Tabriz city, south of Eskandar village, Upper Cretaceous rock units are exposed. The structures in these rock units include meso-scale folds inclined towards NNE, and a thrust system which has transported Upper Cretaceous units in three thrust sheets towards NW. This thrust system has cut the NNE-verging folds in Upper Cretaceous units. These deformed rock units are unconformably overlain by the Miocene beds. The vergence of folds in the Miocene units is toward SSW. There are SW-verging thrust faults and right-lateral strike-slip faults parallel to the North Tabriz fault in the study area. We conclude that the N-verging structures in Upper Cretaceous rock units has been formed in the time interval between Upper Cretaceous and Miocene and were cut by the North Tabriz fault. The structural characteristics of the Upper Cretaceous rocks as the remnants of the Upper Cretaceous oceanic crust in the Neotethyan marginal basin indicate that the probable subduction direction of this basin was towards south.

Tabriz Fault is one of the major faults of Iran that is situated in the northwest of Iran and central part of the Iranian Azerbaijan. The fault has a well-known paleoseismological history, and being situated adjacent to the Tabriz city with two millions of inhabitants makes it a big seismic hazard. In this research, a study of instrumental seismic data, remote sensing and field observations along the Tabriz Fault Zone from north of Miyaneh to the west of Marand cities helped us to define three main segments along the fault. Fault Movement Potential (FMP) has a close relationship with tectonic stress in and around a given fault zone. Therefore, the stress state was analyzed using direct inversion method to estimate potential movement of each segment of the Tabriz Fault. Results showed that the middle and southern segments of the Tabriz Fault have a FMP of 0.67-0.73, implying their high potential of reactivation and generating large and destructive earthquakes, assupported by the richseismic history of these segments. Therefore the results of this research estimate a 70% movement probability for the North Tabriz Fault. In contrast, the northern segment of the Tabriz Fault (western part of the fault close to the Marand city) shows a FMF of 0.3-0.37, indicatingits lower potential of reactivation compared to the middle and southern segments. This is also in agreement with the poor seismic history of the northern segment.

Cheshmeh Khouri is an area which mainly comprises a zone of parallel, en-echelon faults along which metallic and non-metallic mineralization is observed. Structural controllers are important factors in the formation of the structural elements of the area such as dykes, faults, joints, folds, and particularly mineral veins. Three types of dykes are observed: E-W trending wedge-shaped dikes, NW-SE trending folded dikes, and ring dikes, which are all kinematically controlled by structural movements of the area. A regional sinistral shear-compression (transpression) regime across the fault sets of the area has given rise to a large-scale counterclockwise rotation of andesitic blocks, developing a bookshelf structure over the area. Rotation of these blocks has provided open spaces for injection of ore-bearing hydrothermal solutions, which caused widespread alterations. Block rotation has also caused formation of dextral shear zones along the faults, which eventually controlled mineralization through the joint and minor fracture networks associated with these shear zones. Formation of mineral veins affected by the dextral shear zones of the bookshelf structure in the area, and defining the structural complexities and sequential elements as well as mineralization phase led to present a laboratory model which showed a good consistency with the results derived from others studies.

Earthquake is an undeniable phenomenon that can cause financial and social damage if occur in populated areas. Vulnerability of buildings is not just function of magnitude and distance from the epicenter but also depends on physical properties of soil. In this study we evaluate physical properties of alluvium in an area of approximately 100 square kilometers in west of Tehran between longitudes 51º 15’ to 51o 23’ and latitudes 35o 40’ to 35o 50’. As a first step we collected field data regarding the alluvium deposits as well as location of Quaternary faults. We then combined this information with data from 440 boreholes which were aquired from more than hundred urban development projects. We use sedimentological diagrams of the boreholes to define three zones of coarse-, intermediate- and fine-grained material in the region. We considered physical and mechanical properties of the sediments to produce seismic amplification map of the area which shows three zones of high, moderate and no amplification. Finally, we investigated liquefaction potential of sediments, considering ground water level and structure of the basin and we have concluded that there is no potential of liquefaction in the area of study.

An earthquake with the magnitude of 5.9 M shocked the Qeshm island located in the Persian Gulf on 27 November, 2005 at 13:53:22 local time. The earthquake occurred due to the reactivation of a NE-SW fault with a major reverse mechanism accompanied by a minor strike-slip component. Another earthquake of 5.5 MW occurred on the same day at ca. 20:00 local time. The interesting feature of this earthquake is that the calculated mechanism for its strongest aftershock, which occurred ca. 6 hours after the main-shock, was a strike-slip mechanism that is completely different from the pure reverse mechanism for the main-shock. This study uses inversion of InSAR observation of earth surface displacement field boundary values to solve parameters of these 2 earthquakes. The results show activation of southern part of the Qeshm fault caused by the first earthquake along 7 km of its length. This event induced the second earthquake by activation of another strike-slip fault which is parallel to the Gavarzin anticline. Estimated slip was 96 cm for the first earthquake and 9 cm for the second one. Based on the estimated parameters of the these 2 earthquakes, the maximum displacement induced by the first earthquake was 6.7 cm in west, 4.6 cm in south and 16.4 cm in vertical directions on the earth surface. The maximum displacement of the second earthquake in west, south and vertical directions were 1.3, 1.6 and 1.4 cm respectively.

This study has focused on identifying fault systems in the Hormuz Strait area using compilation of seismic attributes and artificial neural networks. Faults and fractures play an important role in creating areas of high porosity and permeability. In addition, they cut off the cap and reservoir rocks along fluid migration pathways. Intense tectonic activities and salt tectonics have resulted in complex structures in the Strait of Hormuz area. Therefore, precise identification of faults and fracture zones and their extensions has special importance in increasing petroleum production from traps. In order to identify the geometry and kinematics of faults in the Mishan and Aghajari Formations and in the units under the base-Guri unconformity in the Hormuz Strait area (eastern part of the Persian Gulf), we have used structural imaging and visualization techniques of seismic interpretation. The structural imaging of the fault zones was obtained by this technique based on the integration of input attributes in an artificial neural network system and creating new attributes. First, a set of advanced attributes were introduced as input for the artificial neural network system to train and compile the calculated attributes on fault and non- fault interpreted points. As a powerful exploration tool, finally, the fault cube was obtained to precisely identify fault systems and better detect faults and fractures in quantitative modeling of the area. As a result of integrated attributes, the high correlation between the faults within the fault cube provides more accurate and reliable tracking of fault extensions. Therefore, three types of fault systems were identified in study area, which are thought to be results of the extensional and compressional tectonics of the Oman Orogeny, vertical tectonic movements of the Zagros Orogeny, and syn-sedimentary salt movements.

In this study, 23 focal mechanisms were calculated by moment tensor inversion of small regionalـlocal earthquakes in the Western Alborz and surrounding areas using wave-form inversion method. Calculated reverse-fault focal mechanisms around the Khazar and Alborz Faults in the Central Alborz, considering southward-dipping nodal plane as the fault plane, are consistent with relatively low-angle thrusts. It also implies dominant compressionsl regime in the north of the Central Alborz. Focal mechanisms in 1990 Rudbar-Tarom Earthquake region show a combination of strike-slip mechanisms and a complex fault system in the middle of the Western Alborz. A major region of dominant strike-slip mechanisms is observed in the Talesh area, located in the west of the South Caspian Basin, and around the Masuleh, Sangavar and Bozqush faults. The only calculated focal mechanism close to the southern margin of the Western Alborz, considering the western part of the North Tehran fault as the fault nodal plane, implies leftـlateral motion in this area. In the south of the western Alborz Mountains approaching the Central Iran, two calculated mechanisms indicate dominant reverse movement, similar to the 2002 Changoreh-Avaj Earthquake. Five focal solutions close to the Kushk-e Nosrat and Soltanieh Faults, considering these faults as the fault nodal planes, are consistent with right-lateral motion along them. Depth of the earthquakes in the studied region is in the range of 2 and 20 km, indicating the brittle upper crust in the region.