North Tabriz Fault Research Articles

Evaluating interseismic deformation patterns in the North Tabriz Fault (Iran) using enhanced fitting of velocity field and analysis of surface deformation

Understanding the mechanisms and locations of interseismic strain accumulation along faults is essential for assessing earthquake hazards. However, the mechanical response during the transition from deep fault locking to creep behavior remains uncertain. Estimating the slip deficit within these transition zones is challenging. This study challenges the assumption of a constant depth distribution of interseismic slip rate along the fault over time and proposes variable locking depths as an alternative model. By rejecting the constant locking depth assumption, singularity issues during stress theorem resolution are resolved. To address this, we employ a methodology considering creep propagation within a fully elastic medium. This approach incorporates long-term deformation resulting from viscoelastic flow in the upper mantle and lower crust. Including viscoelastic effects improves the fit to interseismic deformation rates, yielding lower locking depths compared to fully elastic models. To conduct the investigation, the GPS velocity field is recovered using the forward problem and the boundary element method. Subsequently, a physics-based inversion approach, deep interseismic creep, is employed to determine interseismic deformation patterns on a strike-slip fault. Furthermore, this study examined the correlation between the dislocation parameters and their relationship, as well as established the probability distributions associated with each faulting parameter. This research highlights the importance of considering variable locking depths in understanding interseismic strain accumulation and the transition to creep behavior along faults. The findings contribute to improved earthquake hazard assessment and mitigation strategies by providing valuable insights into fault behavior mechanics along the North Tabriz Fault.

Unveiling crustal deformation patterns along the north Tabriz fault from 2015 to 2022 using multi-temporal InSAR analysis

This paper presents a comprehensive study on the recognition of crustal deformation patterns surrounding the North Tabriz Fault in Northwestern Iran, utilizing Multi-Temporal InSAR analysis. The fault, despite its seismic inactivity for over two centuries, has a long history of ancient seismicity, with earthquake recurrence intervals exceeding two centuries. This makes it highly susceptible to future activity and the generation of significant and devastating earthquakes. However, limited research has been conducted on extracting and modeling deformation patterns of the North Tabriz Fault to identify its active segments. The primary objective of this study is to derive a general trend for fault displacement and investigate regions under pressure in terms of abnormal crustal movements. The results indicate that the Earth's crust in the surrounding regions of the central and northwest segments of the fault exhibits an upward movement ranging from approximately 2 to 10 millimeters per year from 2015 to 2022. In contrast, neighboring areas of the northwestern fault, as well as the northwestern, western, and southwestern parts of Tabriz County, experience ground subsidence with rates ranging from approximately 5 to 40 millimeters per year. These findings are consistent with GNSS-derived line-of-sight measurements obtained from some IPGN stations around the fault with an RMSE of 1.72 mm/yr. Furthermore, the study identifies critical points near the fault that exhibit varying and diverse displacement patterns over time, suggesting significant strain and notable stress within the subsurface environment. According to the analysis of time series data on crustal movements at the identified critical points, it has been found that the prevailing motion pattern of the Earth's crust within the fault zone largely conforms to a sinusoidal descending pattern. Additionally, recent earthquakes in the northwest vicinity of the fault have been observed to occur close to these critical points. Using line-of-sight (LOS) data acquired at these critical points, the study estimates a slip rate of 7.71 ± 0.01 mm/year and a locking depth of 11.27 ± 0.01 km, contributing to a better understanding of the fault's seismogenic behavior. These findings provide valuable insights into the crustal deformation patterns around the North Tabriz Fault, highlighting active segments and regions under pressure.

Mechanism of Ivughli salt dome exhumation, northwestern Iran

ABSTRACT The Ivughli salt dome, located in the West Azerbaijan province of Iran, is sourced in the Miocene Upper Red Formation, which includes salt and gypsum layers, red marl, and sandstone. The salt diapirs of West Azerbaijan are located along the North Tabriz Fault. Faults related to fractures around the Ivughli salt dome have displaced the folded layers and have caused subsidence in some parts of the salt dome. Based on the results of interferometry data, there are smaller and bigger elevation/subsidency rates with a total average of 4 mm for the whole body of the dome. The east of the dome shows high elevation and this may be due to the effect of a hidden fault that branches off the North Tabriz Fault. As well as the role of normal faults in the lower elevation of the western parts of the dome, there may have been subsidence related to surface washing and driven by erosion and agriculture in the region. Regarding the emplacement and shape of the Ivughli salt dome, it is young diapirism and currently acctive. In general, tectonic activity is still causing the rise of the Ivughli salt dome at a rate of movement that is not uniform across its structure.

Estimating the slip rate in the North Tabriz Fault using focal mechanism data and GPS velocity field

Abstract This study delves into slip distribution on the North Tabriz Fault (NTF), a critical aspect of seismic hazard analysis due to its proximity to the Tabriz metropolis. The study operates within a uniform elastic half-space, maintaining constant values for fault geometry and regional rheological parameters throughout the research. To calculate strain boundary conditions, permanent and periodic global positioning system (GPS) data from the northwest region were utilized. The fault was constrained perpendicularly while allowing tangential movement, facilitating the determination of its annual slip rate using the boundary element method, with the Okada analytical model serving as the fundamental solution. The findings underscore the intricate relationship between the fault’s slip rate and boundary conditions, revealing a predominant right-lateral strike-slip motion. The study offers two slip rate assessments, obtained through earthquake focal mechanisms and GPS velocity data, yielding values of 5 and 5.5 mm / year {\rm{mm}}/{\rm{year}} , respectively. Importantly, the alignment of these calculated slip rates with paleo-seismological data underscores the credibility of the results generated via the boundary element method, distinguishing it as a reliable approach when compared to other numerical and analytical techniques. This research provides valuable insights into the behavior and slip dynamics of the NTF, which is pivotal for assessing seismic risks.

Adopting normalized full gradient method for regional‐scale gravity modelling: A case study for Northwestern Iran

AbstractThe normalized full gradient was developed to determine anomalous bodies, such as oil and gas fields or simple geological structures studies. We believe that even in complicated geology, normalized full gradient is practical. We introduce data preprocessing and use step‐by‐step simple‐to‐complicated synthetic tests to develop previous researchers’ ideas for regional‐scale gravity modelling. One of the most important steps of the normalized full gradient is the determination of the N optimum value. We found that prevalent methods such as the standard spectral or maxima method are feasible in simple structures only. So, we have suggested the imaging criteria routine for complicated cases. We trace maximum normalized full gradient responses to detect the normalized full gradient responses at the increasing harmonic numbers as the transition of the extensive part of the anomaly to the sharp part of that. With imaging criteria for the determination of N optimum values, the complicated synthetic test results show the success of the normalized full gradient to understand complicated gravity signals. In the real case, we have studied the Northwestern Iran normalized full gradient model of the Bouguer ground gravity data beneath the seismic profile and prepared a P receiver function depth section to uncover the geometry of the Moho boundary and important interfaces in the crust. We suggest the inferred synthetic model from the Bouguer ground gravity anomaly and P receiver function depth section to normalized full gradient trustworthy test in real cases. According to the synthetic test results, we understand the frame of the normalized full gradient responses in the semi‐real case and truthful responses in the real case. Along with this, we study the second ground gravity profile of Northwestern Iran in a good resolution to uncover the deeper structures. The real case results show the possibility of Moho offset and thinning lithosphere beneath the North Tabriz Fault lithospheric boundary, the possible source of Sahand volcanic centre at the west side of the Moho offset beneath North Tabriz Fault, the deep root of the Sabalan volcanic centre in the lower crust and the lithospheric and asthenospheric wedge with the density contrast beneath Sahand–Sabalan volcanic centres. One of the most important results of our study is the lithosphere–asthenosphere boundary offset and stepped Moho possibility beneath the Talesh Mts next to the South Caspian Basin boundary.

Neotectonics and paleoseismology of the North Tabriz Fault, Azerbaijan Region, Northwest Iran

Structural characteristics and seismic parameters were investigated to reevaluate seismic hazards along the North Tabriz Fault (NTF). Field surveys and paleoseismology on the central segment of the fault, combined with dating of sedimentary units, document multiple surface-rupturing paleoearthquakes during the past 3.5 ka. The calculated moment magnitudes (Mw) for the identified paleoearthquakes range from 6.3 to 7.5, causing surface ruptures of ca. 50 km with a maximum slip per event of 5.7 ± 0.2 m. Kinematic GPS surveys on displaced geomorphic features, combined with the dating results indicate that the central segment of the NTF slips at a rate of 6.4 ± 0.5 mm.yr-1 over the past 7.5 ka. Fault orientations and scattered volcanic vents in Sahand Volcanic Complex (SVC) suggest that its configuration and evolution have been affected by the regional transpression.

Probabilistic fault displacement hazard analysis for the north Tabriz fault

Abstract. The probabilistic fault displacement hazard analysis is one of the newest methods of estimating the amount of probabilistic displacement in fault surface rupture areas. Considering the strike-slip mechanism of the north Tabriz fault, Iran, using the earthquake method and historical earthquakes in 1721 and 1780, the surface displacement of the north Tabriz fault has been investigated, and the probabilistic displacement in different scenarios has been estimated. The north Tabriz fault's 50–60 km long section was selected as the source of possible surface rupture from its historical data. Two scenarios were considered according to probabilistic displacements, return periods, and magnitudes according to paleoseismic studies of the north Tabriz fault. For both scenarios, the probabilistic displacements for the exceedance rate of 5 % in 50, 475, and 2475 years for the probabilistic principle displacements (on the fault) of the north Tabriz fault have been estimated.

A Qslope-based empirical method to stability assessment of mountain rock slopes in multiple faults zone: A case for North of Tabriz

The present article provides an empirical relationship for rock slope stability assessment based on Qslope classification. The relationship is used as a correction procedure for classic Qslope for mountain regions with multiple fractures related to several faults. The relationship is derived from 25 distinct jointed slopes near the North Tabriz Fault (NTF). The NTF triggered numerous micro-faults and fractures in rocky landscapes, resulting in sliding on a variety of scales. The present empirical method is introduced based on a field survey and a stability analysis of the studied slopes based on Qslope principles. The results indicate that the classic formulation of Qslope can be modified to β = 62.6 log10 (Qslope) + 36 for mountain regions with multiple fault zones.• This empirical method can be useful for fast stability assessment on jointed rock slopes.• This relationship can use as a modification for the original formula in multiple faults zones.

Evolution of the stress field at the junction of Talesh – Alborz – Central Iran during the past 5 Ma: Implications for the tectonics of NW Iran

Tectonic stresses governed by the Arabia – Central Iran collision are transferred throughout the Iranian Plateau. The orientation of the maximum horizontal stress (σ1) significantly changes (~90°) in the Persian block of NW Iran. However, the exact spatial extent and boundary conditions for these changes are poorly defined. This study investigates the late Cenozoic stress regime in a key region in NW Iran including the Mahneshan – Mianeh Cenozoic Basin (MMCB), the Garmachay Fault Zone (GFZ), and the southern flank of the Bozqush Mountains (SBM). We mapped folds and fault zones in detail using high-resolution satellite imageries and field surveys. We have measured fault-slip data at 49 localities distributed over the study area. The results of fault-slip inversion analysis indicate significant temporal and spatial changes in both the modern and paleostress fields. In the MMCB and GFZ, the orientation of the horizontal σ1 axis changed from N148°E to N041°E, during the Pliocene and Quaternary times. During the same period of time, it changes from NE-SW to N138°E in the SBM. Our study reveals that the southern boundary of the Persian block corresponds to the deep-seated North Tabriz fault (NTF), which is spread out over several splays at the southern flank of the Bozqush Mountains. The NTF acts as a boundary condition in both the stress and strain fields of the region. The GFZ defines the southeastern border of the Persian block, where the NW-trending maximum compression encounters the remote stress field in the hinterland of the Zagros collision. Our results indicate that independent movements of crustal blocks transfer crustal stresses beyond the collision zone and produce large-scale stress perturbations by discarding compatibility in regional strain/stress fields.

New tectonic configuration in NW Iran: Intracontinental dextral shear between NW Iran and SE Anatolia

The Main Recent Fault (MRF) is a major active strike-slip fault system at the NE border of the Arabian platform and Central Iran. Both geometry and kinematics of the fault system is rather well known along its central part and at its SE termination, while its possible continuation to the northwest is ambiguous. Moreover, less regard has been paid to possible relationships between this major intracontinental fault system and other strike-slip faults in NW Iran – SE Anatolia. This paper investigates both the structural pattern and kinematics of deformation in the region to the north of latitude 37°N, between the North Tabriz Fault and the MRF. We followed this goal through detailed fault mapping, structural field measurements, and fault-slip analyses, complemented by the reconstruction of cumulative geomorphic offsets along the main fault segments. The collected data sets have led us to propose a new tectonic model for the northwest corner of the Arabia – Central Iran collision zone. Our results reveal that the intracontinental dextral shear between Arabia-Central Iran, which is mainly localized along the MRF, continues to the north of latitude 37°N along a branch of the Neotethyan suture penetrating into SE Anatolia. The dextral fault system abruptly dies out at latitude 37.5° N joining two NNW-striking normal fault zones, which accommodate the dextral translation of Central Iran relative to Arabia through ESE-trending extension. The region in NW Iran and SE Anatolia is affected by a heterogeneous active stress field due to different tectonic processes such as tectonic escape, block translation, and localized extension. The dynamics of these processes is either directly governed by the Arabia – Eurasia oblique convergence or indirectly controlled by frontal collision and pure shear deformation in central Anatolia.

Engineering geology and geotechnical characterization of Tabriz Metro Line 2, Iran

The present study was performed in order to determine the engineering geology and geotechnical details of soils and rocks along Tabriz Metro Line 2(TML2) by using the information and raw data which were acquired by borehole drilling and all field and laboratory tests in the study area. The minimum and maximum depths of the boreholes were 15 and 40 m, respectively. The results of their analysis revealed that geologically, the areas of metro route, mainly formed by alternating layers of claystone, siltstone, marl, and conglomerate, covered mainly by the alluvial deposits and in addition to older, dextral, strike-slip North Tabriz Fault (NTF) which is a major and most important geological structure of Tabriz area, there are also many minor and generally young and seismically active faults. The results of investigation on the groundwater depth in boreholes of TML2 also indicated that the groundwater depth varies between 1.5 and 30 m, along the route of metro. Eventually, based on the standard penetration test values (N-SPT), it was revealed that soils of the western parts of TML2 are in the group of dense to very dense, the central parts are in the group of very dense (Bazaar area) and dense (Fahmideh area), and the eastern parts are very dense. And finally the results achieved from determining groundwater sulfate values according to Concrete Code of Iran (CCI) indicated that the amount of soluble sulfate in the soil is mild to extremely high. Accordingly, the amount of sulfate increases from the western to the eastern parts. So that, this value is between 200 and 26,500 ppm. Based on these studies, the average of sulfate in the western, central and eastern parts is, respectively, 1118, 1275 and 4840 ppm. Thus, the groundwater in the east part is highly aggressive, and deterioration of concrete lining of the tunnel is expected in the near future.

Detection of fault segments based on P–T dihedra analysis along the North Tabriz fault, NW Iran

Detection of fault segments is an essential step for tracking main transverse faults. General observations from field studies as well as attitude measurements can give an overall understanding of the lengths of the segments, but these are not always sufficient to accurately identify and characterize them. In this study, we analyze P–T dihedra variations based on their eigenvalues to detect fault segments. The anomalies of local paleostress distribution aid us to detect the segment boundaries. This study focuses on the Northwestern, Central, and Southeastern sectors of the North Tabriz Fault (NTF). Fault azimuth distribution and eigenvalue anomalies as well as the fault attitudes for each interval distance have been used to distinct segment boundaries. The results are verified by checking the presence of the transverse faults at the proposed sites during fieldwork. Results show a new structural arrangement integrated by the already documented NTF segments, combined with 6 related transverse faults. In this way, we confirm the earlier reported segments, and we improve the NFT characterization by introducing new segments bounded by transverse faults.

Short-term seismicity patterns along the most active faults in Iran

In this study, six seismically active fault systems located in different tectonic regimes have been surveyed. The data were from three Persian seismotectonic provinces (Alborz-Azarbaijan, Zagros and East-Central Iran) with different seismic properties, covering a time span of 8 years. The earthquake (Eq.) data have been recorded by the seismological network of the Institute of Geophysics of the University of Tehran, Iran (IGUT), the International Institute of Earthquake Engineering and Seismology of Iran (IIEES), and also include the early large instrumental earthquakes in the Engdahl catalog. During this period, few months of seismic quiescence occurred on the entire length of both Dasht-e Bayaz (DB) and Abiz faults, while most of the moderate and large earthquakes occurred after few months of lack of seismicity on the Main Recent fault, DB, Golbaf and Kazeroun faults. Moreover, single and triple migration patterns of seismicity were regularly seen along Golbaf fault and North Tabriz fault (NTF), respectively. Some large earthquakes (the 2011, MN 5.2 Eq. of Golbaf F. and the 2008, MN 5.2 Eq. of NTF) occurred at the end of these seismicity migration patterns. Along NTF, a diffuse seismicity with no specific seismic pattern has been distinguished. In all the case studies and during the investigated time period the entire lengths of the fault systems were not active at the same time. Finally, there is not a clear relationship between the duration of the seismic gaps and the magnitude of large earthquakes with different co-seismic rupture lengths in depth.

Assessment and mapping of the seismic vulnerability of Tabriz city using the Fuzzy logic

The present study aimed to investigate and zonate Tabriz city, Iran in terms of vulnerability to earthquake hazard using the GIS software. Due to the geographical location of Tabriz over the North Tabriz Fault as an active and seismic fault from the north of the city, the necessity of this issue is highlighted. Based on the 10 most important influential factors in the vulnerability of cities to earthquake (geological and environmental factors), the seismic vulnerability zoning maps were developed by the ARC GIS software using the Fuzzy logic. By the integration of the layers using the Fuzzy method, the final map of the vulnerability of Tabriz city in equilibrium earthquakes was prepared in five zones with very high, high, moderate, low, and very low vulnerability. According to the zoning maps, Tabriz is not well positioned in terms of the occurrence of earthquakes, and most of the populated areas (especially the northern and central parts of the city) have higher vulnerability.

Estimating the slip rate on the north Tabriz fault (Iran) from InSAR measurements with tropospheric correction using 3D ray tracing technique

In this paper, interseismic deformation across the north Tabriz fault (NTF) using 17 ASAR/ENVISAT acquisitions on a single track for the period 2003–2010 have been investigated. One of the main limiting factors on the accuracy of interferometric synthetic aperture radar (InSAR) measurements comes from phase propagation delays through the troposphere. In order to retrieve millimeter velocities of interseismic deformations, it is necessary to improve the tropospheric corrections and correct interferograms. For this purpose, the 3D ray tracing technique based on eikonal equations has been used to estimate the tropospheric corrections. The corrected InSAR measurements are used to derive the interseismic displacement velocity field of the study area. The obtained velocity field has enabled us to accurately estimate the slip rate and locking depth for the NTF, using a simple elastic dislocation model. The numerical achievements show a slip rate of 5.6 ± 0.15 mm/yr below a locking depth of 14.5 ± 0.67 km for the NTF. Generally, the results of this paper are confirmed by the previous studies of the NTF parameters and some differences are due to this paper applied method for tropospheric corrections.

Structural Evolution and Halokinesis of Khaje Salt Diapir, North‒West of Iran

The northeastern part of the Tabriz, Khaje area has been studied to determine the relationship between the orientation of local structures and regional tectonics, and the influence of both on salt deformation. All the pre-Pliocene sedimentary rocks in the area belong to the Miocene Upper Red Formation. Sandstones form most of the outcrops because the other main components of the formation, marl and gypsum, are easily eroded and therefore recessive. The small thickness of sedimentary rock overlying the salt layer indicates that buoyancy of the salt was not the main factor causing diapirism. Folds related to the main faults of the region have been formed as result of the compressive tectonic forces. Two compressive stress systems have operated in the study area. In the first one, the direction of principal stress was NE‒SW and the resulting geological structures have an approximate E‒W trend. This stress system also controlled the salt tectonics in the region. The principal stress in the second system was oriented NW‒SE and is responsible for the most recent structures. The stress systems also caused rapid salt movement. The Khaje diapir is characterized by a series of salt walls trending NW‒SE that has been caused by the first stress system. This diapirism was principally the result of compressive tectonic stresses and faulting, particularly related to the North Tabriz Fault.

Kinematics of the 2012 Ahar–Varzaghan complex earthquake doublet (Mw6.5 and Mw6.3)

On 2012 August 11, an earthquake doublet (Mw6.5 and Mw6.3), separated in time by 11 min, occur in the northwest of Iran. The hypocentres of these earthquakes are close (∼6 km) and located near the cities of Ahar and Varzaghan. The rupture process of both main shocks is retrieved by inverting the near-field strong motions data and using the elliptical subfault approximation method. Our calculations show that the two earthquakes are occurring on two distinct fault planes: the first main shock (M1) has nucleated at a depth of ∼8.5 km, and is located ∼4 km east of the eastern termination of the E-W trending surface rupture. The slip reaches the ground surface west of the hypocentre on an E-W striking fault (N88°E) that dips almost vertically (80°S). This earthquake exhibits a right-lateral strike-slip mechanism. The entire slip is imaged on a single patch that ruptures with an average speed of 2.4 km s−1. The rupture duration is ∼5.6 s and the earthquake releases a seismic moment of ∼8.41E + 18 N·m. The slip reaches the surface with a right-lateral dislocation value of ∼1 m, which is consistent with the observed surface rupture. About 11 min later, the second main shock (M2) nucleates ∼5 km to the west and 4 km to the north with respect to the hypocentre of the M1, and at a depth of ∼16.5 km. The M2 rupture evolves toward shallower depths and to the west on an ENE-WSW oriented fault plane (strike ∼256°) with a dip of ∼60° northward. The slip is essentially distributed on two distinct patches with strike-slip and reverse mechanisms, respectively. The first patch has a pure right-lateral strike-slip mechanism, and ruptures at a relatively fast speed of over 2.8 km s−1, and last for about 2.6 s until it reaches the second patch. The latter has a reverse mechanism (rake∼112°) and extends the rupture toward shallow depths, and to the west at a speed of ∼2.5 km s−1, and its rupture lasts for ∼2.5 s. The top of the slip distribution of M2 stops at a depth of ∼8 km. We observe that aftershocks surround the M1 and most of the M2 slip models. They are not distributed in the region of high slip (∼3.1 m) of M1. We show that the rupture of M2 is controlled by the static Coulomb stress changes caused by M1, with the maximum slip of M2 located in the positive Coulomb stress caused by M1. The M2 rupture stops where it reaches the area of high negative Coulomb stress change (over −10 bars). The cumulative Coulomb stress fields of both main shocks show a transfer of positive static Coulomb stress change of >0.1 bars on the eastern segment of the North Tabriz Fault. This segment did not rupture since the 1721 M∼7.6–7.7 event that has destroyed the city of Tabriz, and that currently hosts 2 million people. The occurrence of this earthquake doublet with different mechanisms reveals the slip partitioning of the oblique convergence regime of NW Iran on the Ahar–Varzaghan complex fault system.

Multi-Criteria Decision Making (MCDM) Model for Seismic Vulnerability Assessment (SVA) of Urban Residential Buildings

Earthquakes are among the most catastrophic natural geo-hazards worldwide and endanger numerous lives annually. Therefore, it is vital to evaluate seismic vulnerability beforehand to decrease future fatalities. The aim of this research is to assess the seismic vulnerability of residential houses in an urban region on the basis of the Multi-Criteria Decision Making (MCDM) model, including the analytic hierarchy process (AHP) and geographical information system (GIS). Tabriz city located adjacent to the North Tabriz Fault (NTF) in North-West Iran was selected as a case study. The NTF is one of the major seismogenic faults in the north-western part of Iran. First, several parameters such as distance to fault, percent of slope, and geology layers were used to develop a geotechnical map. In addition, the structural construction materials, building materials, size of building blocks, quality of buildings and buildings-floors were used as key factors impacting on the building’s structural vulnerability in residential areas. Subsequently, the AHP technique was adopted to measure the priority ranking, criteria weight (layers), and alternatives (classes) of every criterion through pair-wise comparison at all levels. Lastly, the layers of geotechnical and spatial structures were superimposed to design the seismic vulnerability map of buildings in the residential area of Tabriz city. The results showed that South and Southeast areas of Tabriz city exhibit low to moderate vulnerability, while some regions of the north-eastern area are under severe vulnerability conditions. In conclusion, the suggested approach offers a practical and effective evaluation of Seismic Vulnerability Assessment (SVA) and provides valuable information that could assist urban planners during mitigation and preparatory phases of less examined areas in many other regions around the world.

Probabilistic View of Occurrence of Large Earthquakes in Iran

In this research seismicity parameters, repeat times and occurrence probability of large earthquakes are estimated for 35 seismic lineaments in Persian plateau and the surrounding area. 628 earthquakes of historical time and present century with MW>5.5 were used for further data analysis. A probabilistic model is used for forecasting future large earthquake occurrences in each chosen lineament. Based on the processing, it reveals that high risk (P>66%) regions in Iran for MW≥7.0 earthquake occurrence in the next 20 years are Apsheron, Main Recent Fault, Dasht-e Bayaz, Golbaf, Minab, Makran and Bandar-e Abbas areas. North Tabriz fault and Ipac, Toroud and Neyshabour fault systems, which are form the southern border between the north and central Iran, have the largest repeat times (>40 years) for 5.5≤MW<7.0 within the seismic regions in Iran. They are mainly associated with very low probabilities. Furthermore, the results show that central Iran is the calmest area for earthquake occurrence, especially in the next 20 years. The important areas for earthquake occurrence with 5.5≤MW<7.0 in the next 10 years are Talesh, Apsheron, north of Kopeh Dagh, Dorouneh and Golbaf areas. Probability of occurrence of an earthquake in the next 10 years in Alborz including capital and important industrial cities with combined population of 15,000,000 is up to 66%.

Evidence for distributed active strike-slip faulting in NW Iran: The Maragheh and Salmas fault zones

The study area is located in the northwestern Iranian plateau and exhibits ongoing convergence between the Arabian and Eurasian plates not absorbed by the Zagros orogenic belt. In this paper, we provide our geological observations made along the Maragheh and Salmas strike-slip fault zones that affect the southern portion of northwest Iran to the south of the North Tabriz Fault. We use a combined methodology to characterize active faulting along these fault zones that included remote-sensing analysis of high-resolution satellite imagery and aerial photographs, digital elevation models (DEMs), tectonic geomorphology investigations and geological field surveys. Active transtension is a common feature along the Maragheh and Salmas faults, and our observations suggested that the onset of active transtension and related local extension along the faults in Pleistocene occurred no earlier than ~2 Ma. The Maragheh and Salmas fault zones contribute to the accommodation of dextral strike-slip faulting in the region between the Main Recent Fault to the south and the North Tabriz Fault to the north. The spatial pattern of strike-slip faulting over the northwest Iranian region (including the North Tabriz fault, the Ahar fault, Salmas and Maragheh fault zones) favors a distributed deformation model, which could help to advance our understanding of geodynamic processes and the level of seismic hazard in this part of the Iranian plateau.