Many papers refer in a revised way to the two-step scenario of the Messinian Crisis conceived by Clauzon et al. (1996). The present paper recalls the basis for the two-step scenario and discrepancies with the later modified version, completed by new data supported by extensive micropaleontological analyses. Our interpretation of the Sicilian Eraclea Minoa section as belonging to a peripheral basin is the centre of the debate. We show the great amplitude of fluvial erosion during the peak of the crisis, which for the Rhône River, exceeded 400 km upstream of the present shoreline. Based on dinoflagellate cysts, we also recall the reasons for supporting the occurrence of three successive Lago Mare episodes of two different origins. The first and third episodes constitute phases of high sea-level exchanges between the Mediterranean and the Paratethys respectively just before the onset of paroxysm and after it. The second episode is due to overflowing Paratethyan waters from the Aegean Basin just before the end of paroxysm. Similarly, the demonstration of the marine reflooding of the Mediterranean Basin prior to the Zanclean is repeated. We emphasize dissimilarity between basins, focussing in particular on those, isolated or perched ones, which were continuously filled by waters during the desiccation phase: western part of the Alboran Sea and southeastern part of the Levantine Basin (marine waters), Apennine Foredeep (fresh waters), and Aegean Basin (brackish waters). The Apennine Foredeep cannot be the reference for the entire Mediterranean with respect to its evolution during the crisis. During the crisis, water exchanges between the Aegean Basin and the Eastern Paratethys (Dacic Basin, Black Sea) were impossible through the Marmara region because of the development of two opposed fluvial networks. Such exchanges existed thanks to a gateway that was probably located within the Balkans. Investigations around the Levantine Basin point to areas submitted to fluvial erosion during the crisis paroxysm and nearby areas, which might have received marine waters from the Red Sea. Much information is still to be discovered and that more progress is still needed in order to fully decipher this outstanding event.
The Betics are a key area to study an orogenic landscape disrupted by late‐orogenic extension. New low‐temperature thermochronology (LTT) data (AHe and AFT) coupled with geomorphic constraints in the Sierra de Gador (Alpujarride complex) are used to reconstruct the cooling history and evolution of relief during the Neogene. We document three stages: (1) a fast cooling event between 23 and 16 Ma associated with the well‐known extensive tectonic exhumation of the Alpujarride unit, (2) a period of slow cooling between 16 and 7.2 Ma related to a planation event and (3) a post‐7.2 Ma surface uplift associated with the inversion of the Alboran domain undetected by LTT. The planation event followed by this late uplift can explain the occurrence of inherited low‐relief surfaces overlain by Tortonian–Messinian platform deposits at the top of the range. Finally, we propose that the Sierra de Gador is a more transient landscape than the nearby Sierra Nevada.
Lors de la construction orogenique, les processus internes entrainent une croissance de la topographie, tandis que les processus de surface tendent a la detruire par erosion. Le systeme tend alors vers un etat dit d’equilibre, pour lequel l’erosion contrebalance la surrection. La presence de formes transitoires de relief (surfaces planes, knickpoints dans les rivieres) est generalement associee a des changements de conditions aux limites du systeme orogenique. La chaine des Betiques est un exemple d’orogene ou se sont succedes de multiples changements de conditions aux limites au cours du Cenozoique (collision eo-oligocene, effondrement postorogenique oligo-miocene, inversion tortonienne) qui en font un terrain-cle pour evaluer l’etat d’equilibre des reliefs et leur evolution spatiale et temporelle. Dans cette etude, nous montrons que la topographie betique presente de larges surfaces aplanies au sommet de certains chainons comme celui de la Sierra de Gador, situee dans les zones internes des Betiques. Afin de contraindre l’exhumation de ce chainon et son couplage avec les processus en surface, des datations de thermochronologie basse temperature (U-Th)/He et traces de fission sur apatites ont ete realisees sur les roches du complexe metamorphique Alpujarride qui constitue le socle emousse de la Sierra de Gador. Les resultats montrent un âge de refroidissement AHe d’environ 9 Ma et environ 16 Ma pour les AFT. Ces âges ont ete inverses dans un modele thermique permettant de reconstituer l’histoire du refroidissement de ces roches au cours du Neogene. Apres un refroidissement rapide associe a l’exhumation d’un dome extensif entre 20 et 16 Ma, le modele montre une periode de fort ralentissement du refroidissement entre 16 et 7 Ma. Nous relions cette derniere phase a l’initiation de l’aplanissement responsable des surfaces emoussees observees aujourd’hui au sommet de la Sierra de Gador. Cette surface peut s’assimiler a une peneplaine formee a proximite du niveau de base du Tortonien (depots marins dates a 7 Ma par Braga et al., 2003). Les donnees thermochronologiques ne montrent pas de recuit post 7 Ma indiquant une epaisseur deposee et erodee tres faible, et ce malgre une reprise en compression et un soulevement important (jusqu’a 1600 m) depuis cette periode. Ce resultat contraste avec les roches de l’unite metamorphique inferieure (Nevado-Filabride) affleurant au Nord en Sierra Nevada qui, elles, continuent d’etre exhumees pendant l’inversion tectonique. Ceci est vraisemblablement a mettre en relation avec les variations d’amplitude de plissement du socle et de soutien dynamique de la topographie enregistrees par ces deux sierras depuis le Tortonien.
Transpressive deformation at the northern Caribbean plate boundary is accommodated mostly by two major strike-slip faults, but the amount and location of accommodation of the compressional component of deformation are still debated. We collected marine geophysical data including multibeam bathymetry and multichannel seismic reflection profiles along this plate boundary around Hispaniola, in the Jamaica Passage, and in the Gulf of Gonave. The data set allows us to image the offshore active strike-slip faults as well as the compressional structures. We confirm that the Enriquillo-Plantain-Garden Fault Zone (EPGFZ) in the Jamaica Passage has a primary strike-slip motion, as indicated by active left-lateral strike-slip-related structures, i.e., restraining bend, asymmetrical basin, en echelon pressures ridges, and horsetail splay. Based on topographic cross sections across the EPGFZ, we image a very limited compressional component, if any, for at least the western part of the Jamaica Passage. Toward the east of the Jamaica Passage, the fault trace becomes more complex, and we identify adjacent compressional structures. In the Gulf of Gonave, distributed folding and thrust faulting of the most recent sediments indicate active pervasive compressional tectonics. Estimates of shortening in the Jamaica Passage and in the Gulf of Gonave indicate an increase of the compressional component of deformation toward the east, which nonetheless remains very small compared to that inferred from block modeling based on GPS measurements.
Multibeam bathymetry data and multichannel seismic reflection profiles have been collected at the end of 2012 along the Enriquillo-Plantain-Garden Fault Zone (EPGFZ) in the Jamaica Passage, between Jamaica and Hispaniola. Analysis of the data set reveals the tectonic evolution and the stratigraphic complexity of the northern Caribbean boundary. Stratigraphic correlations with previous marine and on land studies are proposed to place the identified seismic sequences in their regional tectonic history. Two distinct crustal domains are interpreted. Typical stratigraphic sequences for the rifted blocks of the Eastern Cayman Trough margin are identified in five basins of the Jamaica Passage, highlighting the eastward limit of the Cayman Trough margin. These inherited basins are deformed and folded during a first phase of compression that could correspond to the regional tectonic rearrangement recorded in the early Miocene (about 20 Ma). A distinct crustal domain that we propose to relate to the Carib Beds (Caribbean typical reflectors A″, B″ and V) is identified in the southern part of the Jamaica Passage, indicating that the Caribbean Large Igneous Province could extend up to the extreme northeast part of the Lower Nicaragua Rise. The left-lateral EPGFZ currently cuts across two pre-existing basins, the Morant and Matley basins. During the activity of the EPGFZ, these basins are deformed and folded indicating a second phase of compression. In contrast, the Navassa basin, located in the middle of the Jamaica Passage, results from the strike-slip motion of the EPGFZ and is interpreted as an asymmetrical basin bordered by the EPGFZ only on its northern side.
We explored the submarine portions of the Enriquillo-Plantain Garden Fault zone (EPGFZ) and the Septentrional-Oriente Fault zone (SOFZ) along the Northern Caribbean plate boundary using high-resolution multibeam echo-sounding and shallow seismic reflection. The bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between Haiti and Jamaica (EPGFZ) and 300 km between the Dominican Republic and Cuba (SOFZ). The primary plate-boundary structures are a series of strike-slip fault segments associated with pressure ridges, restraining bends, step overs and dogleg offsets indicating very active tectonics. Several distinct segments 50-100 km long cut across pre-existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike-slip regime. Along the most recent trace of the SOFZ, we measured a strike-slip offset of 16.5 km, which indicates steady activity for the past similar to 1.8 Ma if its current GPS-derived motion of 9.8 +/- 2 mm a(-1) has remained stable during the entire Quaternary.
Since the discovery of calcareous nannofossils, dinoflagellate cysts and planktonic foraminifers in deposits from the Dacic Basin, intensive research has been performed in order to evidence which gateway this microplankton used to connect Paratethys and the Mediterranean prior and after the Messinian Salinity Crisis (MSC). Such a gateway is also to be regarded at the origin of successive influxes of Paratethyan organisms (molluscs, ostracods, dinoflagellates) into the Mediterranean Basin (“Lago Mare” events). Observing that the İstanbul area, usually proposed for this purpose, was inefficient, we examine the succession of marine well-dated pre-MSC and post-MSC deltaic deposits through the Balkans, from northern Greece to southern Romania, that constitutes a reliable candidate for such a marine corridor, the origin of which was caused by the regional tectonic extension. The reconstructed palaeogeography for high sea level episodes that encompassed the MSC clarifies the context of the so-called North Aegean Lake. This marine gateway probably evolved as a powerful river during the peak of the MSC, contributing to the deposition of clastics in the hydrocarbon Prinos Field. A tectonically controlled subsidence to the north and south of the Skopje region caused the closure of such a gateway.
The two sides of the Strandja Sill show a highly discontinuous stratigraphic succession since the Late Oligocene. This area, together with the Sea of Marmara Basin, is usually proposed as the gateway for the Paratethyan freshwaters and organisms that constituted the Lago Mare facies in the Mediterranean Sea during the Messinian Salinity Crisis (MSC). Our investigations involving new field observations and datings, together with previous studies, suggest that the sill has possibly experienced such a connection at around 8Ma, i.e. significantly before the crisis. The proposal of a sea-level drop of the Black Sea before 7Ma is not supported by our data on dinoflagellate cysts. Consistency of calcareous nannofossil succession at DSDP Site 380 is reinforced, allowing to reassert that subaerial erosion impacted both the southwestern Black Sea and the central Marmara – Dardanelles area during the peak of the MSC. At that time, this region was crossed by two oppositely directed fluvial networks, further supporting the absence of a marine gateway through the Strandja Sill. It is concluded that none of the Lago Mare events recorded in the Mediterranean during the MSC were the consequence of the passage of Paratethyan waters and organisms through this area. In the Black Sea, the well-dated Messinian fluvial erosion can be followed offshore. The overlying prograding deltaic deposits attest to a fast marine reflooding after the crisis. This constitutes a comprehensive erosion – sedimentation model in an area intensively explored for hydrocarbons.
The Iranian plateau is a vast inland region with a smooth average elevation of c. 1.5 km formed at the rear of the Zagros orogen as a result of the Arabia‐Eurasia collision (i.e., over the last 30–35 Myr). This collision zone is of particular interest due to its disputed resemblance to the faster Himalayan collision, which gave birth to the Tibetan plateau around 50 Myr ago. Recent studies have suggested that a recent (10–5 Ma) slab break‐off event below Central Iran caused the formation of the Iranian plateau. Here, we test several hypotheses through large‐scale (3082 × 590 km) numerical models of continental subduction models that incorporate a free upper surface erosion, rheological stratification, brittle‐elastic‐ductile rheologies, and metamorphic phase changes (density and physical properties) and account for the specific crustal and thermal structure of the Arabian and Iranian continental lithospheres. We test the impact of the transition from oceanic to continental subduction and the topographic consequences of the progressive slowdown of the convergence rate during continental subduction. Our results demonstrate the role of mantle flow beneath the overriding plate, initiated as an indirect consequence of slab break‐off. This flow creates a dynamic topography support during continental subduction and results in delamination of the overriding plate lithospheric mantle followed by isostatic readjustment, hence of further uplift and maintenance of a plateau‐like topography without significant crustal thickening. The slowdown of the convergence rate during the development of the continental subduction/collision phase largely contributes to this process by controlling the timing and depth of slab break‐off.
Geodetic observations across most of the major strike-slip faults show an interseismic strain rate, which presents a sharp localization of elastic shear strain in the fault vicinity (20-60 km). The screw dislocation model of Savage & Burford is commonly used to fit these geodetic data and to retrieve the far field velocity and the locking depth. This model is very popular because of its inherent simplicity to derive fault slip rates, and mostly because it predicts locking depths, which are of the same order of magnitude as the base of the seismogenic zone (5-20 km). A first issue with the screw dislocation model is that localization is paradoxically introduced by imposing a step function in the velocity field at a depth where the crust is otherwise recognized to behave following a viscous rheology. A second issue with this model is that it is not consistent with the rheological model of the crust that is valid for both post-seismic (1-10 yr), interseismic (several thousand years) and long-term geodynamic (several thousand to several million years) timescales. Here we use numerical models to study how alternative and more geologically realistic boundary conditions and rheological structures can lead to the localization of elastic strain at the Earth's surface during the interseismic period. We find that simple elastic models resembling the Savage & Burford model but driven by far field plate velocity are inefficient at localizing strain unless this driving velocity is transmitted by a rigid indentor. We also find that models including a weak viscous heterogeneity beneath the fault zone are able to produce appropriate localization of the deformation near the fault. This alternative class of model is shown to be pertinent in regards to the boundary conditions and geological observations along exhumed ductile strike-slip shear zone.
While subduction of crustal rocks is increasingly accepted as a common scenario inherent to convergent processes involving continental plates and micro-continents, its occurrence in each particular context, as well as its specific mechanisms and conditions is still debated. The presence of ultra-high pressure(UHP) terranes is often interpreted as a strong evidence for continental subduction (subduction of continental crust) since the latter is seen as the most viable mechanism of their burial to UHP depths, yet if one admits nearly lithostatic pressure conditions in the subduction interface (or "channel"). The presumed links of continental subduction to exhumation of high- and ultra-high-pressure (HP/UHP) units also remain a subject of controversy despite the fact that recent physically consistent thermo-mechanical numerical models of convergent processes suggest that subduction can create specific mechanisms for UHP exhumation. We hence review and explore possible scenarios of subduction of continental crust, and their relation to exhumation of HP and UHP rocks as inferred from last generation of thermo-mechanical numerical models accounting for thermo-rheological complexity and structural diversity of the continental lithosphere. The inferences from these models are matched with the petrology data, in particular, with P–T–t paths, allowing for better understanding of subtleties of both subduction and burial/exhumation mechanisms. Numerical models suggest that exhumation and continental subduction are widespread but usually transient processes that last for less than 5–10Myr, while long-lasting (>10–15Myr) subduction can take place only in rare cases of fast convergence of cold strong lithospheres (e.g. India). The models also show that tectonic heritage can play a special role in subduction/exhumation processes. In particular, when thicker continental terrains are embedded in subducting oceanic plate, exhumation of UHP terranes results in the formation of versatile metamorphic belts and domes and in series of slab roll-back and exhumation events with remarkably different P–T–t records.
The Iranian plateau is a flat ~ 1.5–2 km high plateau thought to result from the collision between the Arabian and Eurasian plates since ~ 30 ± 5 Ma, and may represent a young analogue to the so far better studied Tibetan plateau. In order to constrain the exhumation history of the internal Zagros and of the Iranian plateau, we herein present apatite (U-Th)/He (AHe) and apatite (AFT) and zircon fission-track (ZFT) data on plutonic rocks from the Sanandaj–Sirjan Zone (SSZ), Urumieh–Dokhtar magmatic arc (UDMA), Central Iran and Kopet Dagh. Thermochronologic data show that the SSZ was exhumed early in the collision process (essentially before 25–20 Ma), with a likely acceleration of cooling during the late Eocene, from 0.04 to 0.3 mm/year. Results suggest that cooling of the internal Zagros migrated from the SSZ to the UDMA during a more mature stage of the continental collision, after ~ 17 Ma (i.e., coeval with the outward propagation of deformation and topography fronts in the external Zagros). Constant exhumation rates in the UDMA (~ 0.3 mm/year) suggest that no significant variation of erosion rates occurred since the onset of continental collision. In Central Iran, the overlap of ZFT, AFT and AHe ages from gneissic samples points to rapid cooling during the late Eocene (~ 42 °C/Myr), which is consistent with previous reports on the formation of Eocene metamorphic core-complexes.
The 290 km long Nayband right‐lateral fault cuts across a region seismically quiescent during the last few millennia. Chlorine‐36 and optically stimulated luminescence (OSL) dating of cumulative geomorphic offsets between 9 ± 1 m and 195 ± 15 m with ages from 6.8 ± 0.6 ka to ∼ 100 ka allow deriving a slip rate of 1.8 ± 0.7 mm yr‐1. The paleoseismic record retrieved from the first trench excavated across the fault combined with 18 OSL ages demonstrates the occurrence of at least four large (Mw ∼ 7) earthquakes during the last 17.4 ± 1.3 ka and two older earthquakes (before ∼ 23 ka and 70 ± 5 ka). Sediments from the last ∼ 7 ka contain evidence of the three younger earthquakes. Penultimate and antepenultimate events occurred between 6.5 ± 0.4 ka and 6.7 ± 0.4 ka within at most 1 ka whereas the most recent earthquake occurred within the last millennium. Such an irregular earthquake occurrence may suggest seismic clustering. Therefore, the imminence of an earthquake along the fault cannot be discarded even if the most recent earthquake occurred within the last 800 years. This event went unnoticed in the historical records demonstrating the incompleteness of the historical seismic catalogs in Central Iran, challenging any assessment of seismic hazard without geologic information. Infrequent large earthquakes typify the slow‐slipping strike‐slip faults slicing Central and Eastern Iran. Also, the slip rates summed from the Iran Plateau up to the Afghan lowlands appear in fairly good agreement with the most recent GPS data.
We use thermo-mechanical numerical models to explore the impact of rheological structure, brittle-elastic-ductile rheology and metamorphic reactions on localization and style of deformation in convergent contexts, during oceancontinent or continent-continent interactions. Even though continental subduction may occur in most cases of strong lithospheres with competent mantle at sufficiently high initial convergence rates (>1-1.5 cm/y), the subduction/ collision styles and topography evolution are quite different depending on the initial configuration and preceding tectonic history but also on the particular structure of the continental crust, eventually affected by tectonic heritage, and localising properties of the subduction channel. Depending on lower and intermediate crustal rheology, the entire (upper, intermediate, lower) crust, intermediate or only the lower crust can deform independently of the mantle lithosphere. This results in different characteristic tectonic styles (leading, for example, to development of thin-sheet to thick-sheet tectonics structures), wavelengths, altitudes of surface topography and slab geometries. Certain rheological structures of the continental crust, while looking plausible from the geological and experimental rock mechanics point of view, are not compatible with the development of continental subduction, resulting in either blockage of the subduction channel and transition to folding and collision, or in gravitationally instable behaviours. Phase changes leading to material softening significantly improve chances for stable subduction, which is marked by exhumation of UHP-HP rocks to the surface that is particularly favoured if the crustal rheological profile has internal ductile decolement levels between the upper and lower or intermediate crust and the lower crust and mantle lithosphere. Pure shear or unstable RT-type collision is dominant when the mantle is rheologically weak or at convergence rates lower than 1-1.5 cm/yr. In continent-continent convergence settings, formation of high plateaux instead of rather narrow mountain ranges is conditioned by the degree of locking of the subduction channel, slow-down of the convergence causing slab retreat and by the rheological structure of both the upper and lower plates. Similarly, obduction and the associated exhumation processes appear to be largely dependent on the rheological properties of both the continental and oceanic crust, so that obduction is only possible for very specific combinations of rheological properties, requiring, in particular, relatively weak lower crust of the continental counterpart and presence of a weak serpentinized layer between the oceanic crust and mantle. These conditions drastically narrow the range of the rheological parameters compatible with tectonically realistic scenario of evolution of convergent zones allowing us to put a number of quantified constraints on the ductile rheology laws for crustal and mantle materials, and hence providing new possibilities for extrapolation of laboratory based rheology laws to geodynamic spatial and temporal scales.
Modelling the evolution of the concentration of in-situ produced cosmogenic nuclides as a function of depth (depth-profile) has been developed to allow determining both the exposure duration and the denudation rate affecting geomorphic features. However, material sampled through surficial deposits may exhibit an inherited component resulting from exposure to cosmic rays before deposition. In case of homogeneous inheritance, this inherited component may be estimated through sampling at increasing depths and subsequently subtracted. In case of variable inheritance, the measured concentrations are scattered and the random distribution of the depth-profile concentrations prevents modelling confidently a depth-profile and precludes constraining an exposure duration. Often observed in desert and endorheic regions, this greatly restricts the possibilities to determine an accurate abandonment age of alluvial surfaces in such environments. Provided the denudation is demonstrated negligible, a method for determining a more accurate range of minimum inheritance, hence a more accurate maximum abandonment age for a given alluvial surface, is proposed. This method, based on the rejuvenation of depth-profile samples, relies on the simple hypothesis that at least one of the depth-profile samples would be emplaced with no or negligible inherited component and on the obvious principle that none of analysed sample has been emplaced with a negative cosmogenic nuclide concentration. The method consists then in determining which of the measured depth-profile sample may have been emplaced with a null CRE concentration; i.e., with a zero inheritance value. This requires to calculate the in-situ duration of exposure needed to reach the concentration measured for each depth-profile sample and to retain the one that provides the smallest in-situ exposure duration. Several examples from alluvial surfaces of central Iran illustrate the profile rejuvenation method and highlight a variable inheritance ranging between 1.5×105 and 16.1×105at/g (SiO2) for terraces whose abandonment ages range from ten to several hundreds of ka.
The M essinian S alinity C risis is well known to have resulted from a significant drop of the M editerranean sea level. Considering both onshore and offshore observations, the subsequent reflooding is generally thought to have been very sudden. We present here offshore seismic evidence from the G ulf of L ions and re‐visited onshore data from I taly and T urkey that lead to a new concept of a two‐step reflooding of the M editerranean B asin after the M essinian S alinity C risis. The refilling was first moderate and relatively slow accompanied by transgressive ravinement, and later on very rapid, preserving the subaerial M essinian E rosional S urface. The amplitude of these two successive rises of sea level has been estimated at ≤500 m for the first rise and 600–900 m for the second rise. Evaporites from the central M editerranean basins appear to have been deposited principally at the beginning of the first step of reflooding. After the second step, which preceeded the Z anclean G lobal S tratotype S ection and P oint, successive connections with the P aratethyan D acic B asin, then the A driatic foredeep, and finally the E uxinian B asin occurred, as a consequence of the continued global rise in sea level. A complex morphology with sills and sub‐basins led to diachronous events such as the so‐called ‘ L ago M are’.This study helps to distinguish events that were synchronous over the entire M editerranean realm, such as the two‐step reflooding, from those that were more local and diachronous. In addition, the shoreline that marks the transition between these two steps of reflooding in the P rovence B asin provides a remarkable palaeogeographical marker for subsidence studies.
The Central Iran plateau appears aseismic during the last few millenniums based on instrumental and historical seismic records. Nevertheless, it is sliced by several strike-slip faults that are hundreds of kilometres long. These faults display along-strike, horizontal offsets of intermittent gullies that suggest the occurrence of earthquakes in the Holocene. Establishing this is crucial for accurately assessing the regional seismic hazard. The first palaeoseismic study performed on the 200-km long, NS striking Anar fault shows that this right-lateral fault hosted three large (Mw similar to 7) earthquakes during the Holocene or possibly Uppermost Pleistocene for the older one. These three seismic events are recorded within a sedimentary succession, which is not older than 15 ka, suggesting an average recurrence of at most 5 ka. The six optically stimulated luminescence ages available provide additional constraints and allow estimating that the three earthquakes have occurred within the following time intervals: 4.4 +/- 0.8, 6.8 +/- 1 and 9.8 +/- 2 ka. The preferred age of the more recent event, ranging between 3600 and 5200 yr, suggests that the fault is approaching the end of its seismic cycle and the city of Anar could be under the threat of a destructive earthquake in the near future. In addition, our results confirm a previous minimum slip rate estimate of 0.8 +/- 0.1 mm yr-1 for the Anar fault indicating that the westernmost prominent right-lateral faults of the Central Iran plateau are characterized by slip rates close to 1 mm yr-1. These faults, which have repeatedly produced destructive earthquakes with large magnitudes and long recurrence interval of several thousands of years during the Holocene, show that the Central Iran plateau does not behave totally as a rigid block and that its moderate internal deformation is nonetheless responsible for a significant seismic hazard.