North Tehran Fault Research Articles

INTEGRATED ESTIMATION OF SEISMIC PHYSICAL VULNERABILITY OF TEHRAN USING RULE BASED GRANULAR COMPUTING

Abstract. Tehran, the capital of Iran, is surrounded by the North Tehran fault, the Mosha fault and the Rey fault. This exposes the city to possibly huge earthquakes followed by dramatic human loss and physical damage, in particular as it contains a large number of non-standard constructions and aged buildings. Estimation of the likely consequences of an earthquake facilitates mitigation of these losses. Mitigation of the earthquake fatalities may be achieved by promoting awareness of earthquake vulnerability and implementation of seismic vulnerability reduction measures. In this research, granular computing using generality and absolute support for rule extraction is applied. It uses coverage and entropy for rule prioritization. These rules are combined to form a granule tree that shows the order and relation of the extracted rules. In this way the seismic physical vulnerability is assessed, integrating the effects of the three major known faults. Effective parameters considered in the physical seismic vulnerability assessment are slope, seismic intensity, height and age of the buildings. Experts were asked to predict seismic vulnerability for 100 randomly selected samples among more than 3000 statistical units in Tehran. The integrated experts’ point of views serve as input into granular computing. Non-redundant covering rules preserve the consistency in the model, which resulted in 84% accuracy in the seismic vulnerability assessment based on the validation of the predicted test data against expected vulnerability degree. The study concluded that granular computing is a useful method to assess the effects of earthquakes in an earthquake prone area.

Microseismicity of the Tehran region based on the data recorded in a local monitoring network: 2004-2010

Evaluation of the seismicity of a region depends on records of earthquakes. This article assesses the microseismicity of Tehran region, bounded by the coordinates 34.43°-36.87° N and 49.07°-53.13° E. This was investigated by the Tehran Disaster Mitigation and Management Organization (TDMMO) network from 2004 to 2010. The main purpose of this study was to substantiate the current tectonic activity of the region. We checked whether the observed faults in the region are active or not. Some active trends were found with the strongest activity in the eastern part of the region, especially associated with the North Tehran fault. In addition, records exist of strong historical earthquakes in this zone. These confirm that the area east of Tehran is more active than the west. The magnitude of completeness in the E, NE and SE is Mc=2. Major faults criss-crossing Tehran are located in the foot of the Alborz mountain belt. The released seismic energy map of the region demonstrates that the main active zones with high energy values for microearthquakes are in the east of the region.

Kinematic links between the Eastern Mosha Fault and the North Tehran Fault, Alborz range, northern Iran

Kinematic interaction of faults is an important issue for detailed seismic hazard assessments in seismically active regions. The Eastern Mosha Fault (EMF) and the North Tehran Fault (NTF) are two major active faults of the southern central Alborz mountains, located in proximity of Tehran (population ~ 9 million). We used field, geomorphological and paleoseismological data to explore the kinematic transition between the faults, and compare their short-term and long-term history of activity. We introduce the Niknamdeh segment of the NTF along which the strike-slip kinematics of EMF is transferred onto the NTF, and which is also responsible for the development of a pull-apart basin between the eastern segments of the NTF. The Ira trench site at the linkage zone between the two faults reveals the history of interaction between rock avalanches, active faulting and sag-pond development. The kinematic continuity between the EMF and NTF requires updating of seismic hazard models for the NTF, the most active fault adjacent to the Tehran Metropolis. Study of offsets of large-scale morphological features along the EMF, and comparison with estimated slip rates along the fault indicates that the EMF has started its left-lateral kinematics between 3.2 and 4.7 Ma. According to our paleoseismological data and the morphology of the nearby EMF and NTF, we suggest minimum and maximum values of about 1.8 and 3.0 mm/year for the left-lateral kinematics on the two faults in their linkage zone, averaged over Holocene time scales. Our study provides a partial interpretation, based on available data, for the fault activity in northeastern Tehran region, which may be completed with studies of other active faults of the region to evaluate a more realistic seismic hazard analysis for this heavily populated major city.

Evaluation of relative tectonic activity in the Tehran basin, central Alborz, northern Iran

Recent deformations in the area studied control structural expansions influenced by tectonic activities, causing transformations of geologic features and morphological landforms. The Tehran basin is located at the southern edge of the central Alborz and is the result of the Arabian–Eurasian convergence and clockwise rotation of the south Caspian basin with respect to Eurasia. Hence, assessment of the drainage pattern permutations and mountain fronts appears necessary. We used six significant morphometric indices for this evaluation: stream length gradient (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley floor width to valley height (Vf), drainage basin shape (Bs), and mountain front sinuosity (Smf). The combined analyzed indices represented the relative active tectonics (Iat). The study area was divided into four regions according to the values of Iat. These classes include class 1 (very high activity), class 2 (high), class 3 (moderate), and class 4 (low). The regions with high relative tectonic activity mostly correspond with the active structures in the basin. The tectonic activity classes 1 and 2 coincide with the fault mountain fronts in the southern edge of the central Alborz especially the North Tehran fault. The parts of the central Mosha fault and the regions in the east, the southeast, and the west of the basin indicate the moderate class of tectonic activity (class 3). The low elevation plain in the south and southwest of the area shows the lowest relative tectonic activity (class 4).

Real-Time Mapping of PGA Distribution in Tehran Using TRRNet and peeqMap

Tehran megacity, the political and economical capital of Iran with population of more than eight million residents, is situated in the seismically active zone of Alborz. The seismicity pattern of this zone shows occurrence of large earthquakes in long time periods (Masson et al. , 2005). Several large earthquakes such as the 855 A.D. M s 7.1, the 958 A.D. M s 7.7, and the 1117 A.D. M s 7.2 in the historical seismic catalog of Tehran and surrounding area proves that the city has a high level of seismic risk (Fig. 1). The last disastrous example among these earthquakes was in 1830, and the city is waiting for the next large earthquake (Ambraseys and Melville, 1982; Ashtari‐Jafari, 2010). Several active faults surround Tehran including North Tehran fault, Eyvanekey fault, North and South Ray faults (Fig. 1). Apart from existence of several active faults around the city, fast growth of population and urbanization in previous decades, and lack of strong regulations for urban development increased the vulnerability of Tehran to moderate to large earthquakes (Amini‐Hosseini et al. , 2009). Figure 1. Map showing major active faults (Hessami et al. , 2003), and seismicity around Tehran. Circles, epicenters of M s>6 earthquakes; numbers, the year of earthquake occurrence. The historical earthquakes are from Ambraseys and Melville (1982). Star, the epicenter of the 17 October 2009 ( M w 4.0). NRF and SRF in the dashed square area, closely surrounding the city, refer to South Ray fault and North Ray fault, respectively. Topographic contours at 200 m intervals of the boxed area are shown in Figure 3. Mindful of the seismic risk faced by the city, the Tehran Rapid Response Network (TRRNet) has been installed in the Tehran metropolitan area …

SENSITIVITY ANALYSIS OF ORDERED WEIGHTED AVERAGING OPERATOR IN EARTHQUAKE VULNERABILITY ASSESSMENT

Abstract. The main objective of this research is to find the extent to which the minimal variability Ordered Weighted Averaging (OWA) model of seismic vulnerability assessment is sensitive to variation of optimism degree. There are a variety of models proposed for seismic vulnerability assessment. In order to examine the efficiency of seismic vulnerability assessment models, the stability of results could be analysed. Seismic vulnerability assessment is done to estimate the probable losses in the future earthquake. Multi-Criteria Decision Making (MCDM) methods have been applied by a number of researchers to estimate the human, physical and financial losses in urban areas. The study area of this research is Tehran Metropolitan Area (TMA) which has more than eight million inhabitants. In addition, this paper assumes that North Tehran Fault (NTF) is activated and caused an earthquake in TMA. 1996 census data is used to extract the attribute values for six effective criteria in seismic vulnerability assessment. The results demonstrate that minimal variability OWA model of Seismic Loss Estimation (SLE) is more stable where the aggregated seismic vulnerability degree has a lower value. Moreover, minimal variability OWA is very sensitive to optimism degree in northern areas of Tehran. A number of statistical units in southern areas of the city also indicate considerable sensitivity to optimism degree due to numerous non-standard buildings. In addition, the change of seismic vulnerability degree caused by variation of optimism degree does not exceed 25 % of the original value which means that the overall accuracy of the model is acceptable.

Rapid Estimation of Peak Ground Velocity and Earthquake Location Using Small Magnitude Earthquakes in the Tehran Region, Iran

Online Material: Supplemental tables. The Tehran metropolis is located in an extensive area between the Alborz mountain belt to the north and the central Iranian plateau to the south. Tehran, as the political and economic capital of Iran, is considered one of the most populated cities in the world. From the point of view of vulnerability to natural disasters, Tehran is of great concern because of its basic infrastructures and population concentration. The Alborz mountain belt is a part of the Himalayan–Alps orogenic belt with numerous active faults, including the Mosha reverse fault, the North Tehran thrust fault, the Parchin, the Kahrizak, and the South and North Rey faults, with high seismic potential in the study region (Fig. 1). The Mosha fault is one of the fundamental structures of the central Alborz mountains and is situated north of Tehran. This fault is concave to the north and extends from the edge of the mountain range in the west to the eastern Alborz mountains and can be considered an upthrust in some places and an overthrust in others (Moinfar et al. , 1994; Berberian and Yeats, 1999). The North Tehran fault is the most prominent tectonic structure in the immediate vicinity of Tehran for which the trace is east–west to east‐northeast–west‐southwest and slightly concave to the south (Berberian and Yeats, 1999). The Tehran urban district is extended across thick alluvium layers over bedrock with complex geological structure. Based on historic seismic documents, Tehran is surrounded by several specific faults with return periods of about 150 years, but no damaging earthquake has occurred since 1830 (Moinfar et al. , 1994; Berberian and Yeats, 1999), when an estimated 45,000 …

Paleoearthquakes of the past 30,000 years along the North Tehran Fault (Iran)

The North Tehran Fault (NTF) is located at the southernmost piedmont of Central Alborz and crosses the northern suburbs of the Tehran metropolis and adjacent cities, where ∼15 million people live. Extending over a length of about 110 km, the NTF stands out as a major active fault and represents an important seismic hazard for the Iranian capital after historical seismicity. In order to characterize the activity of the NTF in terms of kinematics, magnitude and recurrence intervals of earthquakes, we carried out a first paleoseismological study of the fault within its central part between Tehran and Karaj cities. We opened a trench across a 3 m‐high fault scarp affecting Quaternary deposits. Our study shows that the scarp is the result of repeated events along a main N115°E trending shallow dipping thrust fault, associated with secondary ruptures. From the trench analysis and Infrared Stimulated Luminescence (IRSL) dating of fault‐related sediments, we interpreted between 6 and 7 surface‐rupturing events that occurred during the past 30 kyrs. Their magnitudes (estimated from the displacements along the faults) are comprised between 6.1 and 7.2. The two last events – the largest ‐ occurred during the past 7.9 ± 1.2 ka, which yields a Holocene slip rate of ∼0.3 mm/yr. The 7 earthquakes scenario suggests a regular periodicity with a mean recurrence interval of ∼3.8 kyrs. However, the two most recent events could correspond to the two largest historical earthquakes recorded in the area (in 312–280 B.C. and 1177 A.D.), and therefore suggest that the NTF activity is not regular.

Seismic sources and neo-tectonics of Tehran area (North Iran)

This study records evidence of neo-tectonic activities in Tehran area. The aim of the study is to investigate the seismic sources in Tehran area and Mosha fault has introduced as the most active fault. The high seismicity potentials have appeared by integration of structural geology and active tectonics studies. Movement potential evaluation of the main faults in the current tectonic regime show that the North Tehran fault have 90% potential to movement. Also, geomorphic indexes indicate the presence of differential uplifting in the geological past. Recent activity of Tehran area is investigated by a large number of geomorphic indexes such as: drainage basin asymmetry, stream gradient. The stream network asymmetry was studied using morphometric measures of transverse topographic symmetry, asymmetry factor and drainage basin shape. Keywords: Geomorphic, Indexes, Tectonics, Tehran

Seismic sources and neo-tectonics of Tehran area (North Iran)

This study records evidence of neo-tectonic activities in Tehran area. The aim of the study is to investigate the seismic sources in Tehran area and Mosha fault has introduced as the most active fault. The high seismicity potentials have appeared by integration of structural geology and active tectonics studies. Movement potential evaluation of the main faults in the current tectonic regime show that the North Tehran fault have 90% potential to movement. Also, geomorphic indexes indicate the presence of differential uplifting in the geological past. Recent activity of Tehran area is investigated by a large number of geomorphic indexes such as: drainage basin asymmetry, stream gradient. The stream network asymmetry was studied using morphometric measures of transverse topographic symmetry, asymmetry factor and drainage basin shape.Keywords: Geomorphic, Indexes, Tectonics, Tehran, Hazard, Active

Left-lateral active deformation along the Mosha–North Tehran fault system (Iran): Morphotectonics and paleoseismological investigations

The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip–slip thrusting movements. The recent faulting mainly occurs on new traces trending E–W to ENE–WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike–slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike–slip motion is transferred along the ENE–WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics.

Estimating Blood Transfusion Requirements in Preparation for a Major Earthquake: The Tehran, Iran Study

Tehran, Iran, with a population of approximately seven million people, is at a very high risk for a devastating earthquake. This study aims to estimate the number of units of blood required at the time of such an earthquake. To assume the damage of an earthquake in Tehran, the researchers applied the Centre for Earthquake and Environmental Studies of Tehran/Japan International Cooperation Agency (CEST/JICA) fault-activation scenarios, and accordingly estimated the injury-to-death ratio (IDR), hospital admission rate (HAR), and blood transfusion rate (BTR). The data were based on Iran's major earthquakes during last two decades. The following values were considered for the analysis: (1) IDR = 1, 2, and 3; (2) HAR = 0.25 and 0.35; and (3) BTR = 0.05, 0.07, and 0.10. The American Association of Blood Banks' formula was adapted to calculate total required numbers of Type- O red blood cell (RBC) units. Calculations relied on the following assumptions: (1) no change in Tehran's vulnerability from CEST/JICA study time; (2) no functional damage to Tehran Blood Transfusion Post; and (3) standards of blood safety are secure during the disaster responses. Surge capacity was estimated based on the Bam earthquake experience. The maximum, optimum, and minimum blood deficits were calculated accordingly. No deficit was estimated in case of the Mosha fault activation and the optimum scenario of North Tehran fault. The maximum blood deficit was estimated from the activation of the Ray fault, requiring up to 107,293 and 95,127 units for the 0-24 hour and the 24-72 hour periods after the earthquake, respectively. The optimum deficit was estimated up to 46,824 and 16,528 units for 0-24 hour and 24-72 hour period after the earthquake, respectively. In most Tehran earthquake scenarios, a shortage of blood was estimated to surge the capacity of all blood transfusion posts around the country within first three days, as it might ask for a 2-8 times more than what the system had produced following the Bam earthquake.

Faulting and folding in quaternary deposits of Tehran’s piedmont (Iran)

Tehran lies on the southern flank of the Central Alborz, an active mountain belt characterized by many historical earthquakes, some of which have affected Tehran itself. The border between the Alborz Mountain and the Tehran’s piedmont (northern part of Tehran City) is marked by the North Tehran Fault (NTF), dividing the Eocene rock formation from the alluvial units of different ages (Early Pleistocene to the recent alluvium). A detail mapping of the piedmont, combined with structural study reveal that two active thrust faults (situated south of the NTF) are of importance for hazard assessment of the City. The geomorphological evidences along the NTF are not in agreement with an active fault, indicating that the fault activity may have been shifted southward. Furthermore differentiation of newly recognized alluvial units and their inferred ages, together with the mapped fault pattern permit us to characterize the Quaternary deformation. The Late Pleistocene alluvial deposits consist of three alluvial fans among them the youngest one together with the modern alluvial fan defines the Holocene deposit. The present deformation in the piedmont is accommodated along vertically left-lateral strike-slip faults and low-angle thrust faults trending in range from N070 to N110E.

Seismotectonic framework of the North Tehran Fault

The North Tehran Fault is the principal structure by which the southern flank of the Alborz range was raised about 2 1 2 km above the alluvium of the Tehran embayment. It forms part of a system of small blocks accommodating the NE-SW thrust of the Alborz. The fault is about 35 km long and seems to die out as a single structure in the west and joints the major Musha-Fasham Fault in the east. Displacements are by upthrusting of the Eocene volcanics of the Alborz southwards over the Pliocene-Quaternary alluvium of Tehran, accompanied by a minor left-lateral movement. These displacements started in the Late Pliocene and may still be continuing to-day. Two recent catastrophic earthquakes occurred in 1957 and 1962 in two regions about 135 km from Tehran, in tectonic systems not directly related to the North Tehran Fault. The nearest damaging earthquake occurred in 1930, not far from the point where the North Tehran Fault joins the Musha-Fasham Fault. Seismicity in the 20th century is not controlled by any single major fault, but seems to follow ‘seismotectonic provinces’. Though undamaged since the late 19th century, the Tehran region has experienced some major earthquakes in the past. As in other seismic countries, reverse and thrust-fault activity, is often more difficult to detect than strike-slip by topographic and epicentre locations alone. This was shown recently by the 1971 San Fernando earthquake, California. It is therefore essential that research be pursued, and that adequate geodetic and microseismic instrumentation be installed in the Tehran region and in particular near the North Tehran Fault.