articles by Faramarz Nilfouroushan
The switch in direction of convergence between Central Iran and the Eurasian Plate is believed to... more The switch in direction of convergence between Central Iran and the Eurasian Plate is believed to have a significant impact on the structural style in the Alborz Mountains, in the north of Iran. To understand the deformation pattern and investigate the influence of the South Caspian Basin kinematics since the middle Miocene on the structural styles and active tectonics of the Alborz Mountains, a series of scaled analogue models were prepared, in which passively layered loose sand simulating the sedimentary units were subjected to orthogonal and subsequently oblique shortening by a rigid indenter. Model results indicate that during the shortening, an arcuate-shaped foreland-vergent imbricate stack forms in front of the indenter. The orthogonal shortening is characterized by a prevailing right-lateral and left-lateral oblique-slip motion in the east and west of the model, respectively. This shift in kinematics contradicts the proposed preneotectonic (orthogonal) model of the Alborz. However, during oblique shortening, model results show that deformation is mainly accommodated by left-lateral transpression within the sand wedge and internal deformation. Oblique shortening is consistently accommodated by continued left-lateral motion on the west-northwest-trending oblique thrusts, whereas the east–west-trending thrusts and the preexisting east-northeast-trending right-lateral oblique thrusts reactivate as left-lateral oblique faults. Precise monitoring of the model surface also illustrates partitioning of shortening into the foreland-vergent left-lateral thrusting in the south and hinterland-vergent back thrusting in the north. These model results are generally consistent with field observations and GPS data of structure and kinematics of the Alborz Mountains.
We use historical and recent major earthquakes and GPS geodetic data to compute seismic strain ra... more We use historical and recent major earthquakes and GPS geodetic data to compute seismic strain rate, geodetic slip deficit, static stress drop, the parameters of the magnitude--frequency distribution and geodetic strain rate in the Iranian Plateau to identify seismically mature fault segments and regions. Our analysis suggests that 11 fault segments are in the mature stage of the earthquake cycle, with the possibility of generating major earthquakes. These faults primarily are located in the north and the east of Iran. Four seismically mature regions in southern Iran with the potential for damaging strong earthquakes are also identified. We also delineate four additional fault segments in Iran that can generate major earthquakes without robust clues to their maturity.The most important fault segment in this study is the strike-slip system near the capital city of Tehran, with the potential to cause more than one million fatalities.
Papers by Faramarz Nilfouroushan
Geological Society, London, Special Publications, 2006
We report a direct comparison of scaled analogue experiments to test the reproducibility of model... more We report a direct comparison of scaled analogue experiments to test the reproducibility of model results among ten different experimental modelling laboratories. We present results for two experiments: a brittle thrust wedge experiment and a brittleviscous extension experiment. The experimental set-up, the model construction technique, the viscous material and the base and wall properties were prescribed. However, each laboratory used its own frictional analogue material and experimental apparatus. Comparison of results for the shortening experiment highlights large differences in model evolution that may have resulted from (1) differences in boundary conditions (indenter or basal-pull models), (2) differences in model widths, (3) location of observation (for example, sidewall versus centre of model), (4) material properties, (5) base and sidewall frictional properties, and (6) differences in set-up technique of individual experimenters. Six laboratories carried out the shortening experiment with a mobile wall. The overall evolution of their models is broadly similar, with the development of a thrust wedge characterized by forward thrust propagation and by back thrusting. However, significant variations are observed in spacing between thrusts, their dip angles, number of forward thrusts and back thrusts, and surface slopes. The structural evolution of the brittle-viscous extension experiments is similar to a high degree. Faulting initiates in the brittle layers above the viscous layer in close vicinity to the basal velocity discontinuity. Measurements of fault dip angles and Angles of peak friction, stable-dynamic friction and inferred cohesion determined with a ring-shear tester (Schulze 1994) at GFZ Potsdam. † Angles of peak friction and stable-dynamic friction determined with a Casagrande shear box (Casagrande 1932) at high normal loads; these normal loads are much higher than those in the experiments. Values of cohesion obtained by linear regression of high normal stress Casagrande tests are questionable (Pavia: 2686
Abstract We performed a quantitative comparison of brittle thrust wedge experiments to evaluate t... more Abstract We performed a quantitative comparison of brittle thrust wedge experiments to evaluate the variability among analogue models and to appraise the reproducibility and limits of model interpretation. Fifteen analogue modeling laboratories participated in this benchmark initiative. Each laboratory received a shipment of the same type of quartz and corundum sand and all laboratories adhered to a stringent model building protocol and used the same type of foil to cover base and sidewalls of the sandbox. Sieve structure, sifting height, filling rate, and details on off-scraping of excess sand followed prescribed procedures. Our analogue benchmark shows that even for simple plane-strain experiments with prescribed stringent model construction techniques, quantitative model results show variability, most notably for surface slope, thrust spacing and number of forward and backthrusts. One of the sources of the variability in model results is related to slight variations in how sand is deposited in the sandbox. Small changes in sifting height, sifting rate, and scraping will result in slightly heterogeneous material bulk densities, which will affect the mechanical properties of the sand, and will result in lateral and vertical differences in peak and boundary friction angles, as well as cohesion values once the model is constructed. Initial variations in basal friction are inferred to play the most important role in causing model variability. Our comparison shows that the human factor plays a decisive role, and even when one modeler repeats the same experiment, quantitative model results still show variability. Our observations highlight the limits of up-scaling quantitative analogue model results to nature or for making comparisons with numerical models. The frictional behavior of sand is highly sensitive to small variations in material state or experimental set-up, and hence, it will remain difficult to scale quantitative results such as number of thrusts, thrust spacing, and pop-up width from model to nature.
"AbstractA series of scaled analogue models are used to study (de)coupling between basement and c... more "AbstractA series of scaled analogue models are used to study (de)coupling between basement and cover deformation. Rigid basal blocks were rotated about a vertical axis in a ‘bookshelf’ fashion, which caused strike-slip faulting along the blocks and in the overlying cover units of loose sand. Three different combinations of cover–basement deformations are modelled: (i) cover shortening before basement fault movement; (ii) basement fault movement before cover shortening; and (iii) simultaneous cover shortening with basement fault movement. Results show that the effect of the basement faults depends on the timing of their reactivation. Pre- and syn-orogenic basement fault movements have a significant impact on the structural pattern of the cover units, whereas post-orogenic basement fault movement has less influence on the thickened hinterland of the overlying belt. The interaction of basement faulting and cover shortening results in the formation of rhombic structures. In models with pre" # "- and syn-orogenic basement strike-slip faults, rhombic blocks develop as a result of shortening of the overlying cover during basement faulting. These rhombic blocks are similar in appearance to flower structures, but are different in kinematics, genesis and structural extent. We compare these model results to both the Zagros fold-and-thrust belt in southwestern Iran and the Alborz Mountains in northern Iran. Based on the model results, we conclude that the traces of basement faults in cover units rotate and migrate towards the foreland during regional shortening. As such, these traces do not necessarily indicate the actual location or orientation of the basement faults which created them."
AGU Fall Meeting …, Dec 1, 2004
Several GPS networks have been installed in Iran and Northern Oman to measure the active tectonic... more Several GPS networks have been installed in Iran and Northern Oman to measure the active tectonic deformation of this part of the Alpine-Himalayan mountain belt. These studies confirm the rigidity of the Northern part of the Arabian plate and a northward motion relative to ...
AGU Fall Meeting Abstracts, Dec 1, 2002
Iran is wedged up between Eurasia and Arabia. This northward convergence of the Arabian platform ... more Iran is wedged up between Eurasia and Arabia. This northward convergence of the Arabian platform relative to Eurasia involves continental collision in several belts (Zagros, Alborz, Talesh, Kopet Dag), and oceanic subduction of the Gulf of Oman under the Makran accretionary wedge. All these deformation areas are surrounding relative aseismic blocks (South Caspian block, Central Iran). Some of them are bordered by great NS strike slip faults (Lut, Helmand). As GPS is providing a precise tool to quantify the deformation, a network ...
The Alborz range is an active mountain belt south of the Caspian sea. The main tectonic structure... more The Alborz range is an active mountain belt south of the Caspian sea. The main tectonic structures of Alborz are generally overthrusting range-parallel faults northward dipping in the south and southward dipping in the north. The regular occurrence of large historical earthquakes in this range suggests an important activity of the faults. To study the internal deformation (horizontal and vertical movements) of the Alborz range, we have installed a GPS network of 12 sites crossing the Alborz range 50 km east of Tehran. Three ...
Earth and Planetary Science Letters, 2004
The Alborz is a narrow (100 km) and elevated (3000 m) mountain belt which accommodates the differ... more The Alborz is a narrow (100 km) and elevated (3000 m) mountain belt which accommodates the differential motion between the Sanandaj -Sirjan zone in central Iran and the South Caspian basin. GPS measurements of 12 geodetic sites in Central Alborz between 2000 and 2002 allow to constrain the motion of the belt with respect to western Eurasia. One site velocity on the Caspian shoreline suggests that the South Caspian basin moves northwest at a rate of 6 F 2 mm/year with respect to western Eurasia. North -South shortening across the Alborz occurs at 5 F 2 mm/year. To the South, deformation seems to extend beyond the piedmont area, probably due to active thrusting on the Pishva fault. We also observe a left-lateral shear of the overall belt at a rate of 4 F 2 mm/year, consistent with the geological motion observed along E -W active strike-slip faults inside the belt (e.g., the Mosha fault).
Geophysical Journal International, 2006
The Bandar Abbas-Strait of Hormuz zone is considered as a transition between the Zagros collision... more The Bandar Abbas-Strait of Hormuz zone is considered as a transition between the Zagros collision and the Makran oceanic subduction. We used GPS network measurements collected in 2000 and 2002 to better understand the distribution of the deformation between the collision zone and the Makran subduction. Analysing the GPS velocities, we show that transfer of the deformation is mainly accommodated along the NNW-SSE-trending reverse right-lateral Zendan-Minab-Palami (ZMP) fault system. The rate is estimated to 10 ± 3 mm yr −1 near the faults. Assuming that the ZMP fault system transfers the motion between the Makran-Lut Block and the Arabian plate, we estimate to 15 mm yr −1 and 6 mm yr −1 , respectively, the dextral strike-slip and shortening components of the long-term transpressive displacement. Our geodetic measurements suggest also a 10-15 km locking depth for the ZMP fault system. The radial velocity pattern and the orientation of compressive strain axes around the straight of Hormuz is probably the consequence of the subducting Musandam promontory. The N-S Jiroft-Sabzevaran (JS) fault system prolongates southwards the dextral shear motion of the Nayband-Gowk (NG) fault system at an apparent rate of 3.1 ± 2.5 mm yr −1 . The change from strong to weak coupling for underthrusting the Arabian plate beneath the Zagros (strong) and the Makran (weak) may explain the dextral motion along the ZMP, JS/NG and Neh-Zahedan fault systems which transfer the convergence from a broad zone in the western Iran (Zagros, Tabriz fault system, Alborz, Caucasus and Caspian sea surroundings) to Makran subduction.
We report on the first results of a French-Iranian GPS project designed for quantify the inter-an... more We report on the first results of a French-Iranian GPS project designed for quantify the inter-and intra-plate deformation in Iran and constrain the Arabian-Eurasian plate motions. The main purpose is to understand how the deformation is distributed in the whole country, that is to say,(1) how much shortening is accommodated by the Alborz, Kopet-Dag and Zagros mountain ranges?(2) how is accommodated the deformation along the faults bordering the stable blocks as the Lut block?(3) what is the relation between seismicity ...
We present in this poster the French-Iranian GPS project designed to quantify the de-formation in... more We present in this poster the French-Iranian GPS project designed to quantify the de-formation in Iran. Another presentation (Vernant et al., this session) details the tectonic implications of the first results of GPS measurements in Iran. To study the deforma-tion in Iran and to constrain the Arabian-Eurasian plate motions, a GPS network was installed by Iranian (NCC, IIEES) and French (LGTS Montpellier, LGIT Grenoble, ENS Paris) scientific institutions in 1999. The network covers the whole country with 25 stations (15 pillars and ...
Geophysical Journal International, 2004
Journal of Geodesy, 2003
The rate of crustal deformation in Iran due to the Arabia-Eurasia collision is estimated. The res... more The rate of crustal deformation in Iran due to the Arabia-Eurasia collision is estimated. The results are based on new global positioning system (GPS) data. In order to address the problem of the distribution of the deformation in Iran, Iranian and French research organizations have carried out the first large-scale GPS survey of Iran. A GPS network of 28 sites (25 in Iran, two in Oman and one in Uzbekistan) has been installed and surveyed twice, in September 1999 and October 2001. Each site has been surveyed for a minimum observation of 4 days. GPS data processing has been done using the GAMIT-GLOBK software package. The solution displays horizontal repeatabilities of about 1.2 mm in 1999 and 2001. The resulting velocities allow us to constrain the kinematics of the Iranian tectonic blocks. These velocities are given in ITRF2000 and also relative to Eurasia. This last kinematic model demonstrates that (1) the north-south shortening from Arabia to Eurasia is 2-2.5 cm/year, less than previously estimated, and (2) the transition from subduction (Makran) to collision (Zagros) is very sharp and governs the different styles of deformation observed in Iran. In the eastern part of Iran, most of the shortening is accommodated in the Gulf of Oman, while in the western part the shortening is more distributed from south to north. The large faults surrounding the Lut block accommodate most of the subduction-collision transition.
Geophysical Journal International, 2006
Interferometric Synthetic Aperture Radar (InSAR) has become a geodetic method of choice to assess... more Interferometric Synthetic Aperture Radar (InSAR) has become a geodetic method of choice to assess ground deformation associated with seismic and volcano activity. InSAR observations suffer from error sources such as inaccurate orbital information and in particular from variation in the refractive index of the atmosphere, which can compromise the accuracy of repeat-pass interferometry. Because of spatial variation in vertical stratification of the lower part of atmosphere (troposphere), interferometric phase component is often correlated with elevation, mainly in mountainous area. Previous studies have used a linear relationship between phase and topography to reduce atmospheric effects. This assumption is only valid for simplified cases , where only static tropospheric delay prevails. However, there are always other factors in an InSAR measurement that can affect the phase, including deformation due to tectonic/non-tectonic processes and effects of orbital errors and atmospheric del...
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2013
InSAR capacity to detect slow deformation over terrain areas is limited by temporal and geometric... more InSAR capacity to detect slow deformation over terrain areas is limited by temporal and geometric decorrelations. Multitemporal InSAR techniques involving Persistent Scatterer (Ps-InSAR) and Small Baseline (SBAS) are recently developed to compensate the decorrelation problems. Geometric decorrelation in mountainous areas especially for Envisat images makes phase unwrapping process difficult. To improve this unwrapping problem, we first modified phase filtering to make the wrapped phase image as smooth as possible. In addition, in order to improve unwrapping results, a modified unwrapping method has been developed. This method includes removing possible orbital and tropospheric effects. Topographic correction is done within three-dimensional unwrapping, Orbital and tropospheric corrections are done after unwrapping process. To evaluate the effectiveness of our improved method we tested the proposed algorithm by Envisat and ALOS dataset and compared our results with recently developed PS software (StaMAPS). In addition we used GPS observations for evaluating the modified method. The results indicate that our method improves the estimated deformation significantly.
ABSTRACT Iranian plateau, as part of Eurasian plate wedged between Arabian and Indian plates, is ... more ABSTRACT Iranian plateau, as part of Eurasian plate wedged between Arabian and Indian plates, is a zone of active tectonic where experiences destructive earthquakes frequently. Quantitative interpretation of seismicity and their comparison with measured geodetic strain rate can provide invaluable information to assess the seismic hazard potential in Iran. We used seismicity recoded by national (2006-Present) and international (1909- Present) networks as well as geodetic data (1999-2011) to compute seismic strain rate, variation in source strength (Potency), rock mass resistance to the flow of coseismic inelastic deformation (Seismic viscosity) and their correlation with measured geodetic strain rate. Our results suggest lower seismic strain rate along North Tabriz fault, central and NE Alborz and distinct areas in NE of Iran. These areas are associated with higher seismic viscosity suggesting quiescence time, however surrounded by lower seismic viscosity, which implies the easier flow of seismic inelastic deformation or greater stress transfer due to seismicity. Major historical earthquakes (more than 10 earthquakes with M>7, occurred before 1909) associated with suggested area in the northern Iran and the observed seismo-tectonic behavior may imply the potential seismic hazard in these regions.
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articles by Faramarz Nilfouroushan
Papers by Faramarz Nilfouroushan