Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
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.
ISSN: 0040-1951

hal-00617778
https://hal.archives-ouvertes.fr/hal-00617778
DOI : 10.1016/j.tecto.2010.09.013

Éditeur(s) : HAL CCSD
Résumé : The North Tehran Fault is located at the southernmost piedmont of Central Alborz, north of Iran. It stands out as a major active fault menacing directly the city of Tehran, a 12 million people metropolis, and would have been the source of several major historical earthquakes in the past. The fault zone extends up to 110km and corresponds mainly to a reverse fault mostly crossing the northern suburbs of the Tehran metropolis, although NTF in its eastern part is characterized more as a left lateral strike slip active fault. We carried out a paleoseismological study of the fault zone in order to determine whether the fault was activated during the Holocene, and to define the characteristics of its activity in terms of kinematics and magnitude. Here in this paper we present only a part of our paleoseismological investigations trench TE2. Observations fromtwo trenches dug across the North Tehran fault scarp reveal evidence for a maximum of six surface-rupturing events within the late quaternary. According to the empirical relationships among average displacement per event and Moment magnitude [25], we can estimate six events Mw~ 6.5 associated with these ruptures in TE2 trench.
Journal of Seismology and Earthquake Engineering

hal-00758375
https://hal.archives-ouvertes.fr/hal-00758375

Éditeur(s) : HAL CCSD
Résumé : This thesis aims to analyze the active tectonics and the seismic hazard for three main cities of NW Iran (Tehran, Tabriz and Zandjan) using morphotectonics and paleoseismology. Within the Tehran capital, we focused our analysis on the Mosha-North Tehran (M-NT) active fault system. Our investigations show that this fault system is mainly dominated by left-lateral faulting. Along the eastern part of the M-NT fault system, we found evidences of at least seven strong (M>7) paleoearthquakes during the past 10 ka (recurrence interval : 1100-1400 yrs). Our study along the central portion of the fault system (in Abali region) suggests that it corresponds probably to the source of the 1830 AD historical earthquake (M=7.1, Io= IX). Within Tabriz region, we studied the SE segment of the North Tabriz fault. We found evidences of at least three strong events, which occurred during the past 33.5 ka. The North Tabriz dextral fault corresponds to the central portion of a fault system (TFS), and contains two fault segments (NW and SE). Our paleoseismological analysis shows a variation of the slip rate, which decreases from NW to SE along the strike-slip fault. The western (Mishu) and eastern (Bozghush) terminations of the fault system correspond to oblique-compression zones. TFS belongs to the eastern portion of a regional fault system (GSKT), linking the active extension within the central part of the collision and the active compression to the East. Finally, we focus on the Zandjan area, where no important historical seismicitiy is recorded. There, based on morphotectonics analysis we discovered a large active fault network, whose southeastern part affects the Zandjan city. To conclude this work, we replace our observations within the general geodynamic framework of the Arabia- Eurasia collision. One of the striking pictures is the occurrence of opposite kinematics along the M-NT (and other range parallel faults within the south Central Alborz) and the North Tabriz fault systems that have the same trend. This shows the rapid variation of the regional stress field in the Northern Iran.
L'objectif de ce mémoire de thèse est l'étude de la tectonique récente et l'évaluation de l'aléa sismique pour trois villes importante, Téhéran, Tabriz et Zandjan, situées dans le nord-ouest de l'Iran. Dans la capitale de l'Iran, Téhéran, nous nous sommes concentrés sur le système de faille active de Mosha-Nord Téhéran. Nos travaux démontrent que ce système est essentiellement décrochant sénestre. Nos analyses paléosismologiques sur la portion est de ce système (dans la vallée de Tar) montrent au minimum les évidences de sept grands événements sismiques (M>7) pendant les derniers 10000 ans (l'intervalle de récurrence est de 1100 à 1400 ans). Les études que nous avons mené dans la partie centrale de ce système (région d'Abali) révèlent qu'il pourrait être la source du dernier événement sismique ayant affecté la ville de Téhéran en 1830 AD. Dans la région de Tabriz, nous nous sommes intéressés au segment SE de la faille décrochante dextre de Nord Tabriz où nous avons trouvé les évidences de trois grands séismes pendant les derniers 33500 ans. Nos études montrent que la faille Nord Tabriz qui est la portion centrale d'un système de faille (TFS) est constituée par deux segments NW et SE dextres. Notre étude paléosismologique suggère une variation de la vitesse qui diminue du NW vers SE le long de ces segments. Les extrémités ouest (Mishu) et est (Bozghush) de ce système correspondent à des zones compressives qui absorbent les déplacements horizontaux sur les segments NW et SE. D'un point de vue général la TFS est une partie d'un système de failles régionales (GSKT) qui relie une zone d'extension active dans la partie centrale de la collision Arabie-Eurasie et une zone de compression active à l'Est. Enfin, à Zandjan qui est une ville située dans une région de lacune sismique, nous avons découvert un important réseau de failles actives. Le tracé sud-est de ce réseau de failles passe par la ville de Zandjan. En conclusion, les localisations et les cinématiques des systèmes de faille étudiés sont discutées dans le cadre géodynamique général de la collision Arabie-Eurasie. On remarquera que la faille majeure de Nord Tabriz qui correspond essentiellement à un décrochement dextre a la même direction NW-SE que les décrochements sénestres présents dans la chaîne de l'Alborz (les failles de : Mosha, Talaghan et Manjil). Cette observation nécessite une variation de la direction de compression entre ces deux régions.
https://tel.archives-ouvertes.fr/tel-00539739

tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739/document
https://tel.archives-ouvertes.fr/tel-00539739/file/thesesoleymani.pdf

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
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.
ISSN: 0148-0227

hal-00757568
https://hal.archives-ouvertes.fr/hal-00757568
https://hal.archives-ouvertes.fr/hal-00757568v2/document
https://hal.archives-ouvertes.fr/hal-00757568/file/ritz2012.pdf
DOI : 10.1029/2012JB009147

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
P>Tehran is one of the largest cities in the world (12 million people) facing seismic hazard. Standing at the foothills of Alborz Mountains, the capital of Iran is exposed to potential earthquakes associated with several nearby active faults. Classically mentioned as active features, the Kahrizak, the North Rey and the South Rey scarps cross the town itself and would be the sources of several destructive historical earthquakes. However, the nature of these topographic scarps remains uncertain. To assess whether these features correspond to active faults, we carried out a morphological and stratigraphic study. Our results show that the three scarps define horizontal scarp lines that follow contour lines matching ancient shorelines further East. This point, associated with other morphological characteristics such as the flatness of the upper and the lower surfaces, the long and regular streams that incised the upslope upper surfaces and the fact that the deposits are horizontal and without deformations, suggests in fact that the Kahrizak, the North Rey and the South Rey scarps correspond most likely to ancient shore lines and are not fault scarps.
ISSN: 0954-4879

hal-00496390
https://hal.archives-ouvertes.fr/hal-00496390
DOI : 10.1111/j.1365-3121.2010.00938.x

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
In this paper, a combined approach of geomorphic analyses, detailed geological mapping on SPOT 5 satellite images and field surveys, complemented by radiometric dating (Ar-40/Ar-39) allows proposing a new and consistent tectonic configuration for the northeastern Arabia-Eurasia collision zone. It favors a simple strike-slip faulting mechanism in NE Iran accommodating the northward motion of central Iran with respect to Eurasia between the Binalud and Kopeh Dagh mountains. Our results demonstrate that similar to 2 mm/a (similar to 25%) of this northward motion has been transferred from the Binalud to the Kopeh Dagh through the Meshkan Transfer Zone since similar to 5 Ma. The modern state of stress deduced from fault kinematics analyses shows N30 degrees E trending maximum stress axis and confirms a dominant strike-slip faulting mechanism. Combining our geological data with other available data, we conclude that kinematics of deformation can be appropriately described by rigid block faulting in NE Iran; instead, the continuous deformation as it has been thought during the last 3 decades.
ISSN: 0278-7407

hal-00420909
https://hal.archives-ouvertes.fr/hal-00420909
DOI : 10.1029/2008TC002444

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The 856 A.D. Qumis earthquake (M7.9) is the most destructive earthquake to have occurred in Iran, killing more than 200,000 people and destroying the cities of Damghan and the old Parthian capital of Shahr-i Qumis (Hecatompylos). This study combines evidence of historical seismicity with observations of the geomorphology and paleoseismology to provide the first detailed description of active faulting in the Damghan region of the east Alborz mountains, Iran. Regional left-lateral shear is accommodated on the Astaneh, Damghan, and North Damghan faults. Quaternary alluvial fans have been displaced along the Astaneh fault, with 15–20 m stream offsets recording the cumulative displacement over the last two to five earthquakes. A paleoseismology study from a single trench along a 5–10 km segment of the Astaneh fault reveals a rupture prior to 1300 A.D. and significantly later than 600 B.C. Despite the limitations of a single trench in documenting the spatial and temporal evolution of the fault over the late Quaternary, we are nevertheless able to bracket the last event to a time period consistent with the 856 A.D. earthquake. Two older earthquakes were also identified during the Holocene occurring between 600 B.C. and 4600 B.C. and between 4600 B.C. and 9600 B.C. The location of our trench within a bend on the Astaneh fault, which could act as a barrier to rupture propagation, means the three earthquakes recovered from our trench over the Holocene may represent a minimum. Further trenching will reveal how the Astaneh fault ruptures over repeated earthquakes and, consequently, the magnitude and extent of slip during the 856 A.D. earthquake.
ISSN: 0148-0227

hal-00551330
https://hal.archives-ouvertes.fr/hal-00551330
https://hal.archives-ouvertes.fr/hal-00551330v2/document
https://hal.archives-ouvertes.fr/hal-00551330/file/Hollingsworth2010.pdf
DOI : 10.1029/2009JB007185

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Northwest Iran is characterized by a high level of historical and instrumental seismicity related to the ongoing convergence between the Arabian and Eurasian plates. In this region, the main right-lateral strike-slip fault known as the North Tabriz fault (NTF) forms the central portion of a large crustal fault system called the Tabriz fault system (TFS). The NTF is a major seismic source along which at least three strong and destructive earthquakes have occurred since 858 AD. The two most recent destructive seismic events occurred in 1721 AD and 1780 AD, rupturing the SE and NW fault segments, respectively. This paper reports paleoseismological and quantitative geomorphologic investigations on the SE segment of the NTF, between the cities of Bostanabad and Tabriz. These observations help to improve our understanding of the seismic hazard for Tabriz city and its surrounding areas. Our field investigations revealed evidence of successive faulting events since the Late Quaternary. Paleoseismic investigations indicate that since 33.5 kyr, the SE segment of the NTF has experienced at least three major (M>7.5) seismic events, including the 1721 AD earthquake (M=7.6–7.7). Along the NW segment of the fault, however, our results suggest that the amount of strong (M~7.5) seismic events during the same period is significantly greater than along the SE segment. One possible explanation of such a difference in seismic activity is that the Late Quaternary-Holocene coseismic slip rate is decreasing along the NTF from the northwest to the southeast. This explanation contradicts the former hypothesis of a constant slip rate along the whole length of the NTF. In addition, more distributed deformation along several parallel fault branches, in a wider fault zone of the SE segment of the NTF may be considered as additional evidence for the estimation of lower rate of deformation along the fault segment. Such a slip distribution pattern can explain the existence of smaller (~300 m) Pliocene-Quaternary cumulative dextral offsets along the SE fault segment than the measured cumulative offsets along the NW segment (~800 m) of the NTF.
ISSN: 0040-1951

hal-01089420
http://hal.upmc.fr/hal-01089420
http://hal.upmc.fr/hal-01089420/document
http://hal.upmc.fr/hal-01089420/file/Solaymani%20Azad%20et%20al.%2C%202014%20%28accepted%29.pdf
DOI : 10.1016/j.tecto.2014.11.010