North Tehran Fault Research Articles

First luminescence dating of exhumed fault-zone rocks of the North Tehran Fault, Iran

Here we report luminescence dating results on exhumed fault rocks from the North Tehran Fault (NTF, Iran), including the fault gouges. The NTF is an oblique-dip thrust fault expanding from west to east at the northern fringe of the megacity of Tehran. Although the fault is known to be active and a major threat to the city, only little is known about its earthquake history. We present first data on the timing of past fault motion using dating of fault rocks. Three sites have been selected for this study in which the fault damage zone is associated with Eocene volcaniclastic rocks (Karaj Formation). The fault gouge, transitional and damage zone were sampled for which we observed slip planes in the field. The fault rocks are composed of quartz and alkali feldspar favourable for luminescence dating. However, our study reveals that the quartz optically stimulated luminescence (OSL) signal of the Karaj Formation does not seem to have a measurable fast decaying signal component. Instead, the post-infrared stimulated luminescence at 225 °C (pIRIRSL225) of polymineral fine-grain fraction appears to be the most feasible signal for these samples. The first luminescence-based results presented here comprise an age range from 45 ± 5 ka to 72 ± 13 ka for fault gouges and transitional zone. Since dating the transitional zone close to the fault gouge led to a younger age than the fault gouge at one site, we conclude that the sampling location plays a crucial role in dating exhumed fault rock using luminescence dating. The obtained ages are far older than those of the previous palaeoseismological studies that dated earthquake-related sedimentary features in the region. Therefore, more research is required to shed light on the resetting mechanism and condition of these fault rocks due to the recent activity of the NTF.

Earthquake-induced paleo-landslides in the Tehran Region and its role in assessing the seismic hazard, Iran

In the central portion of the Arabia-Eurasia collision zone, the Tehran domain is positioned at a transitional boundary between seismotectonic zones of the Central Iranian lowland (to the south) and the Alborz highland (to the north). Consequently, numerous destructive seismic events have occurred in this active tectonic domain. This study delves into the tectonic geomorphology of the region within its northern highland domain, specifically focusing on the hanging wall of the E-striking north-dipping North Tehran fault (NTF) zone. Our findings in this northern domain emphasize several prominent topographic scars as significant co-seismic features. These include huge landslides, rockfalls, rock avalanches, and offset geomorphic surfaces and could be present as the main indirect co-seismic morphological features. Within this seismically active region, the extensive dimensions of these geomorphic pieces of evidence reveal the seismic potential of the Tehran Region to experience really strong earthquakes (i.e. M>7.5). These results contrast with the previous Maximum Credible Earthquake (MCE) magnitude estimated for the Tehran Region (i.e. M~7.2) through different approaches in Seismic Hazard Assessments (SHAs). Consequently, the previous SHAs of the Tehran Region might have underestimated the seismic risk, and therefore, it is necessary to conduct an updated and complementary deterministic SHA based on the more detailed seismogenic geological features in this crucial area.

Uncertainty and sensitivity assessments on the inputs of probabilistic seismic hazard assessment: A case study of the North Tehran fault

Probabilistic seismic hazard analysis (PSHA) often incorporates significant uncertainty in its inputs, which have the potential to substantially affect the estimated hazards. To improve the reliability of seismic hazards, the present work examines how these uncertainties impact the variability of PSHA and disaggregation results. For this purpose, uncertainty and sensitivity analyses have been performed for different sites in the Tehran region, with the seismic source of the North Tehran Fault as a case study. The results show that uncertainties in the input parameters have a moderate to significant effect on the PSHA and disaggregation results. The uncertainty and sensitivity analyses of this study provide a better understanding of the various PSHA parameters and their associated uncertainties. Therefore, such analyses establish confidence in the PSHA results and expose the main sources of uncertainty, which enable the prioritization of endeavors to reduce hazard variability.

Finite element simulation for elastic dislocation of the North-Tehran fault: The effects of geologic layering and slip distribution for the segment located in Karaj

Finite element simulation for elastic dislocation of the North-Tehran fault: The effects of geologic layering and slip distribution for the segment located in Karaj

Performance of geophysical methods in determining fault zone at Darakeh Area (Tehran Province; Iran)

Darakeh area is one of the major areas in terms of seismic hazards in Tehran. The North Tehran Fault has gone through the center of the studied area, thus creating fractures, displacements and folds of layers, forming anticlines and synclines. Considering the old residential texture understanding the tectonic characteristics and locating the hidden faults of the region can be quite useful in providing thematic maps and preventing damages caused by potential earthquakes. Nevertheless, no geophysical studies have been carried out on this area so far. To map the area, three GPR and two electric resistivity profiles were designed based on the identified tectonic lineations and previous seismic studies on the area. Each GPR profile, was 100 m in length and surveyed using a MALA GPR with an unshielded 50-MHz antenna. The geo-electric profiles were surveyed by Wenner-Schlumberger array. The results of the processed profiles demonstrate a severe drop in resistivity in some regions which could be due to the presence of fault zones and potential cavities in the region under study.

A backbone probabilistic seismic hazard analysis for the North Tehran Fault scenario

In this study, a comprehensive probabilistic seismic hazard analysis (PSHA) using both time-independent and time-dependent approaches is carried out for the North Tehran fault (NTF) scenario. We applied a novel backbone approach to consider the epistemic uncertainty associated with the ground motion estimates. For this purpose, a backbone ground motion model (GMM) is selected using the data-driven deviance information criterion (DIC) method, and the logic tree branches are populated with the backbone GMMs that are added/subtracted from a scale factor. The results show that the estimated ground motions follow the spatial pattern of the NTF and decrease in the far-field, but this spatial pattern is also influenced by the amplification from site effects, in the southern alluvium part where the sites are classified as the category D of NEHRP. Furthermore, the effect of the multi-segment rupture is investigated using a cascading model. The results show that the ground motion values are increased by 20–40% and 10–20% for the 10%-in-50 years and 2%-in-50 years, respectively, particularly at near-fault distances. The results of this study are generally compatible with the previous seismic hazard studies for the Tehran region. Therefore, the novel backbone approach used in this study provides a more reliable seismic hazard estimates for the Tehran metropolis.

Evaluation of GPR method in identification hidden faults of Alluvial deposits in north of Persian Gulf artificial lake, twenty-two district of Tehran

In this research, to detect hidden faults around Persian Gulf artificial lake (22 District of Tehran), Ground Penetrating Radar (GPR) was used. Three profiles were studied in this method. South of Persian Gulf artificial lake there is a trench of which first profile is designed on top. There are eight observable subsidiary faults which indicate a high seismic potential of the target area. Second and third profiles are close and parallel to each other. They are designed 260 m far from north of Persian Gulf artificial lake. The GPR data prove the existence of faults and fractures in layers. A fault zone with an approximate length of 200 m in the northern part of the lake is found out. Generally, results suggest that second and third profiles in comparison with first profile, have more severe changes in layers conditions. In addition, subsidiary faults recognized are in the same direction of North Tehran fault (most dangers fault of Tehran). Therefore, they are absolutely fault branches of North Tehran fault.

Three-Dimensional P-Wave Velocity Structure of Tehran from Local Micro-Earthquake Tomography

Tehran region is located at the southern foothills of central Alborz Mountains which is one of the most seismically active regions due to the convergence between the Arabian and the Eurasian plates. In this study, 3-D crustal velocity structure of Tehran region was investigated using first P-wave arrival times of events with magnitudes less than 4. Data used was recorded by the stations from Tehran Disaster Management and Mitigation Organization, Iranian Seismological Center and International Institute of Earthquake Engineering and Seismology from 2004 to 2018. In order to obtain the crustal velocity structure of Tehran, iterative, damped least-squares method was used to solve/obtain earthquake parameters and velocity structures, simultaneously. Final results show three tectonic characteristics in the study area including high velocity anomalies in northern and eastern Tehran Mountains, and low velocity anomaly in triangular Tehran basin, so that the separation of the eastern Tehran Mountains and Tehran basin is especially sharp in cross-section profiles. Moreover, some low velocity anomalies are appeared around major faults in the study area (e.g. North Tehran Fault). The tomographic maps also show that the Tehran region contains of an upper crust layer with the thickness of 6 km which is located over middle crust layer bedrock with constant velocity up to 15 km. This upper crust layer consists of a sedimentary layer (~ 3 km thickness) overlaid a basement layer. Moreover, the thick and thin upper crust layers are separated by North Tehran and Kosar/Ghasr-Firooz faultsystems from the Tehran basin, respectively.

Vulnerability evaluation of urban buildings to various earthquake intensities: a case study of the municipal zone 9 of Tehran

The municipal zone 9 in Tehran is highly vulnerable to earthquake owing to possessing a highly weathered residential fabric, proximity to North Tehran Fault, and existing industrial usages. In order to take preventive measures and reduce the damages caused by earthquake, it sounds essential to designate the vulnerable areas and make the required arrangements. In this connection, the present study aims at avaluating the vulnerability of urban buildings in zone 9 of Tehran to various earthquake intensities. For this purpose, 10 effective factors on vulnerability of the aforesaid zone were employed under weighting and fuzzification against earthquake, adopting Analitical Network Process (ANP) - Fuzzy planning models. The selected layers in GIS environment were composed and finally, the generalized vulnerability mapping for the zone was prepared. To predict the damage caused to the urban buildings, the earthquake scenarios in the modified Mercalli intensities of 6, 7, and 8 were developed and implemented on the generalized vulnerability mapping of the zone. Ultimately, the vulnerability degrees of the buildings were grouped into five categories of very low, low, average, high, and very high based on the obtained results. The results of this research indicated that the vulnerability degrees of the urban buildings in the abovesaid range of were respectively 26, 56, 17, 1, and 0% for an earthquake with modified Mercalli intensity of 6, and 21, 10, 52, 16, and 1% for an earthquake with modified Mercalli intensity of 7, and 7, 4, 10, 61, and 18% for an earthquake with modified Mercalli intensity of 8. The results of this research are useful in understanding the capability of GIS spatial anlysis for vulnerability mapping.The information provided by these maps could help citizens, planners and engineers to reduce losses caused by existing and future erthquick by means of prevention, mitigation, and avoidance.

An integrated approach of the analytic network process and fuzzy model mapping of evaluation of urban vulnerability against earthquake

The earthquake is one of the most devastating natural hazards that most of the Iranian cities. District 9 of Tehran will be vulnerable due to old residential texture, proximity to North Tehran fault and industrial land use in case of earthquake. Therefore, reducing the vulnerability to this natural disaster is one of the main goals of this study. In the present research, to evaluate vulnerability due to earthquake hazard, 10 indices are studied as effective factors in cities buildings vulnerability. These factors are selected on the basis of indices in previous studies. Indices involving materials type, type of facade building density, the age of building, the number of floors, ground area of buildings, compatibility of adjacent users, distance from the fault, geology formation and width of passageways are analyzed by using computational method of ANP scored by experts. The criteria weight is applied in effective layers in vulnerability. At last, by integrating the layers in GIS environments, general vulnerability map is extracted in the area. In order to evaluate the buildings vulnerability against earthquake, data obtained and from ANP analysis were made fuzzy. Finally, vulnerability map in district 9 of Tehran against earthquake was extracted. The research results show that if earthquake occurs, in district 9 of Tehran, 19.46% and 10.69% of buildings respectively have trivial and low vulnerability, while 50.29 percent of buildings have medium vulnerability. Also, 17.62% and 1.91% of building have high and very high vulnerability respectively, or they are completely damaged.

Shallow/upper crustal shear wave structure of the Tehran region (Central Alborz, Iran) from the inversion of Rayleigh wave dispersion measurements

Surface wave dispersion curves from microearthquakes are used to obtain group velocity dispersion maps. The calculation of the local dispersion curves for each grid point from these maps then produces the input data to retrieve the 3D shear wave velocity model of the Tehran region. The group velocity maps indicate that the tomographic results agree well with the three main tectonic features and the geological units in the study area. The tomographic maps generally possess high-velocity structures across most of the mountain belts (Central Alborz and east-southeast mountains), whereas the Tehran Basin correlates to a low-velocity structure. Increasing the period in the study area highlights four independent low-velocity zones that reflect faults and fault junction systems. The shear wave velocity profiles indicate that the depth to bedrock exhibits southward variation ranging from ~ 300 m to ~ 1500 m. We also focus our analysis on the existence of faults within the shear wave profiles and discuss the low shear wave velocity anomalies deeper than 2 km result from the main fault structures (e.g., North Tehran, North-South Rey and Parchin). Furthermore, we argue that the dip angle of the North Tehran fault varies along fault strike, whereas the North-South Rey fault possesses a constant dip angle. Moreover, initial model uncertainties and checkerboard resolution tests are used to identify reliable and robust anomaly features in the 3D shear wave velocity model and 2D tomographic maps, respectively. Microearthquake analysis provides an effective approach for studying the upper crustal structure heterogeneity, especially the fault structure, of the Tehran region.

Broad-band simulation of M7.2 earthquake on the North Tehran fault, considering non-linear soil effects

Broad-band simulation of M7.2 earthquake on the North Tehran fault, considering non-linear soil effects

Seismic hazard assessment of Tehran, Iran with emphasis on near-fault rupture directivity effects

Many destructive earthquakes happened in Tehran, Iran in the last centuries. The existence of active faults like the North Tehran is the main cause of seismicity in this city. According to past investigations, it is estimated that in the scenario of activation of the North Tehran fault, many structures in Tehran will collapse. Therefore, it is necessary to incorporate the near field rupture directivity effects of this fault into the seismic hazard assessment of important sites in Tehran. In this study, using calculations coded in MATLAB, Probabilistic Seismic Hazard Analysis (PSHA) is conducted for an important site in Tehran. Following that, deaggregation technique is performed on PSHA and the contribution of seismic scenarios to hazard is obtained in the range of distance and magnitude. After identifying the North Tehran fault as the most hazardous source affecting the site in 10000-year return period, rupture directivity effects of this fault is incorporated into the seismic hazard assessment using Somerville et al. (1997) model with broadband approach and Shahi and Baker (2011) model with narrowband approach. The results show that the narrowband approach caused a 27% increase in the peak of response spectrum in 10000-year return period compared with the conventional PSHA. Therefore, it is necessary to incorporate the near fault rupture directivity effects into the higher levels of seismic hazard assessment attributed to important sites.

Earthquake Hazard in the Tehran Region based on the Characteristic Earthquake Model

ABSTRACTTehran is the most vulnerable urban area in Iran. Here, the characteristic earthquake model for the major earthquakes was integrated with the background seismicity to conduct the PSHA. For a 2475-year return period earthquake, a maximum PGA of 725 cm/s2 and a maximum PGV of 60 cm/s were estimated. In next step, the simulated ground motions of the North Tehran Fault (NTF) were applied directly into the PSHA. Due to the fault rupture directivity effect considered through the simulations, the maximum PGA and PGV were estimated 845 cm/s2 and 100 cm/s respectively for a 2475 year return period. If we change location of hypocenter in our simulations, the distribution of highest hazard region will also change.

PHYSICAL SEISMIC VULNERABILITY ASSESSMENT OF TEHRAN USING THE INTEGRATION OF GRANULAR COMPUTING AND INTERVAL DEMPSTER- SHAFER

Abstract. Several faults exist in the vicinity of Tehran, the capital of Iran such as North Tehran, Ray, Mosha and Kahrizak. One way to assist reducing the damage caused by the earthquake is the production of a seismic vulnerability map. The study area in this research is Tehran, based on the assumption of the activation of North Tehran fault. Degree of Physical seismic vulnerability caused by the earthquake depends on a number of criteria. In this study the intensity of the earthquake, land slope, numbers of buildings’ floors as well as their materials are considered as the effective parameters. Hence, the production of the seismic vulnerability map is a multi criteria issue. In this problem, the main source of uncertainty is related to the experts’ opinions regarding the seismic vulnerability of Tehran statistical units. The main objectives of this study are to exploit opinions of the experts, undertaking interval computation and interval Dempster-Shafer combination rule to reduce the uncertainty in the opinions of the experts and customizing granular computing to extract the rules and to produce Tehran physical seismic vulnerability map with a higher confidence. Among 3174 statistical units of Tehran, 150 units were randomly selected and using interval computation, their physical vulnerabilities were determined by the experts in earthquake-related fields. After the fusion of the experts’ opinions using interval Dempster-Shafer, the information table is prepared as the input to granular computing and then rules are extracted with minimum inconsistency. Finally, the seismic physical vulnerability map of Tehran was produced with % 72 accuracy.

Dynamic simulation of ground motions from scenario earthquakes on the North Tehran Fault

Dynamic simulation of ground motions from scenario earthquakes on the North Tehran Fault

A Study on Vulnerability of Urban Neighborhoods to Earthquake (Case Study: Farahzad Neighborhood, Tehran)

Iran is considered as one of the most seismic countries in the world and its cities have been frequently damaged by this natural phenomenon. Tehran, as the first metropolis of the country, is no exception to this, and prone to damage also due to its compactness, and being located on three active faults (Mesha fault, North Tehran fault, Rey fault). If activated, Mesha fault, North Tehran fault and Rey fault will destroy 20%, 35% and 55% of the city, respectively. Farahzad neighborhood in northern Tehran is one of the most seismic parts of Tehran metropolis. Hence, the main objective of this study is to investigate the seismicity of the neighborhood in terms of the risk of earthquakes. For this purpose, descriptive analysis, GIS software and Euclidean distance analysis were used. The results of this study showed that 57 hectares of Farahzad (136 hectares) with a relative area of 41% are located in a zone with a high earthquake risk (less than 400 m to the fault line). The area with a high seismic risk (400 to 800 meters) covers an area of 39 hectares, 29 percent of the total neighborhood. Also, 20 hectares of total residential buildings (34 hectares), with a relative area of over 58 percent, are located in a zone with a high risk of earthquakes.

Modeling interseismic deformation field of North Tehran Fault extracted from precise leveling observation

The North Tehran Fault (NTF) stands out as a major active thrust fault running for approximately 110km north of Tehran, the capital province of Iran. It has been the source of several major historical earthquakes in the past, including those in 958, 1665, and 1830. In this paper, interseismic strain accumulation on the NFT was investigated using precise leveling measurements obtained over the time frame 1997–2005. The relationship between surface deformation field and interseismic deformation models was evaluated using simulated annealing optimization in a Bayesian framework. The results show that the NTF fault follows an elastic dislocation model creep at a rate of 2.5±0.06mm/year in the eastern part and 6.2±0.04mm/year in the western part. Moreover, the locking depth of the fault was evaluated to be ±1.1km in the eastern part and 1.3±0.2km in the western part.

Employing Minimum age model (MAM) and Finite mixture modeling (FMM) for OSL age determination of two important samples from Ira Trench of North Tehran Fault

AbstractIra trench site is in a point where, the surface trace of North Tehran Fault (NTF) joins the Mosha Fault (MF) in the north-eastern margin of Tehran and can provide important paleosismological information for Tehran. The Ira trench, were divided into 6 packages (I to VI), described, according to their composition, relative and absolute ages. Package I consists of units 23, 25, 26, 27, 28, 29, 30 and 31. The whole package I mainly belongs to Holocene, and provides essential constraints for the recent paleoearthquake activity of the EMF and NTF zone. Therefore, finding accurate ages for the units of this package is very important. Three colluvial wedges (units 23, 26, 28) are present between 20 and 36.5 m north in package I, which are assigned to 3 episodes of activity on Fault 13. Central age model (CAM) provided OSL ages of 35.0 ± 6.1, 7.3 ± 1.3, 6.4 ± 0.9 and 56 ± 6.5 ka for units 23, 26, 28 and 29, respectively.The conflicting ages of 56 ± 6.5 and 35.0 ± 6.1 ka (for units 23 and 29, respectively) as compared to the underlying younger units suggest that these ages are overestimated. MAM provided OSL ages of 13.1 ± 4.3 and 3.5 ± 0.4 ka for units 23 and 29, respectively. The contribution of the new statistical age model of sample IRA4 to the paleoseismic data is discussed.

UNCERTAINTY HANDLING IN DISASTER MANAGEMENT USING HIERARCHICAL ROUGH SET GRANULATION

Abstract. Uncertainty is one of the main concerns in geospatial data analysis. It affects different parts of decision making based on such data. In this paper, a new methodology to handle uncertainty for multi-criteria decision making problems is proposed. It integrates hierarchical rough granulation and rule extraction to build an accurate classifier. Rough granulation provides information granules with a detailed quality assessment. The granules are the basis for the rule extraction in granular computing, which applies quality measures on the rules to obtain the best set of classification rules. The proposed methodology is applied to assess seismic physical vulnerability in Tehran. Six effective criteria reflecting building age, height and material, topographic slope and earthquake intensity of the North Tehran fault have been tested. The criteria were discretized and the data set was granulated using a hierarchical rough method, where the best describing granules are determined according to the quality measures. The granules are fed into the granular computing algorithm resulting in classification rules that provide the highest prediction quality. This detailed uncertainty management resulted in 84% accuracy in prediction in a training data set. It was applied next to the whole study area to obtain the seismic vulnerability map of Tehran. A sensitivity analysis proved that earthquake intensity is the most effective criterion in the seismic vulnerability assessment of Tehran.