landslide hazard assessment in the three gorges area china using aster imagery wushan badong abstract the objectives of this study are to develop a methodology for regional scale assessment of landslide hazard using remotely sensed data and to produce a landslide hazard map of the wushan badong area in the three gorges china from advanced spaceborne thermal emission and reflection radiometer aster images the area is undergoing rapid urban development with slope instability causing a widespread natural hazard landslide related parameters were largely estimated through image processing and visual interpretation of aster multi spectral and topographic data we used field measurements to define the quantification for three parameters a slope angle in relation to lithology b distance to drainage network in relation to stream order and c distance to tectonic lineament in relation to lineament length we employed a multi parameter elimination and characterization model based on estimation of the geometric mean to remove areas where landslides are not expected to occur and classify the remaining areas into landslide hazard categories our results show increased landslide hazard in and around wushan and badong towns as well as other populated areas along the yangtze and its tributaries we used field data on landslide distribution to identify typical geomorphological settings for different landslide types and to provide ground control for the hazard assessment the results indicate good correlation between classified high hazard areas and field confirmed slope failures and show the usefulness of aster imagery for landslide hazard assessment at a regional scale

higher himalaya in the bhagirathi section nw himalaya india its structures backthrusts and extrusion mechanism by both channel flow and critical taper mechanisms the higher himalayan crystalline hhc in the bhagirathi river section india on fieldwork reveals two extensional ductile top to n ne shear sub zones the south tibetan detachment system and the basal detachment besides a preceding top to s sw ductile shear a top to n ne brittle shear was identified as backthrusts from the hhc except its northern portion that occur repeatedly adjacent to numerous top to s sw brittle shears as fore thrusts the northern portion of the hhc the gangotri granite exhibits infrequent total six extensional and compressional brittle shear senses the backthrusts could be due to a low friction between the lower boundary of the hhc i e the main central thrust zone and the partially molten hot rock materials of the hhc subduction of the eurasian plate towards s sw below the indian plate more extensively in the garhwal sector could be the second possible reason presence of two ductile extensional shear sub zones may indicate channel flow or several exhumation mechanisms of the hhc in a shifting mode similar to mukherjee et al in int j earth sci 101 253 272 2012 the top to s sw extensional brittle shear exclusively within the upper northern portion of the hhc and a top to s sw brittle shear within the remainder of it is a possible indicator of critical taper deformation mechanism thus this work provides the field evidences of possibly both channel flow and critical taper conditions from a higher himalayan section besides that by larson et al geol soc am bull 122 1116 1134 2010

detachment folding fold amplification and diapirism in thrust wedge experiments 1 the relations between detachment folding fold amplification and salt diapirism in contractional settings have been investigated by means of scaled analogue models the viscosity of the silicone layer simulating salt in nature and the shortening rates were combined in order to reproduce weak type 1 models and strong type 2 models decollements deformation patterns in the roof sequence exhibited two contrasting styles 1 outward propagation of detachment folding along the decollement ofp mode and 2 passive roof duplex prd mode in type 2 models detachment folding propagated away from the most external thrust in the floor sequence while in type 1 models long lived detachment folds almost invariably localized amplified above a floor thrust tip as a result of strain localization a silicone wall intruded occasionally into the crestal graben of detachment folds in type 1 and ofp models best fitting of transition models data points indicates nonlinear relations with regression curves close to the equilateral hyperbola equation for both ofp prd and amplified detachment folds box folds transitions a quantitative comparison of model results with nature has been attempted by plotting salt based fold and thrust belts data points on the scaled transition curves obtained from the modeling such a comparison relates shear stress products and ratios to the conditions favoring the amplification of detachment folds and the potential emplacement of ductile diapirs in their core by reducing the roof sequence strength pore fluid pressure b is inferred to shift the equilibrium of fold and thrust belts toward the field of ofp and diapirism

central zagros fold thrust belt iran new insights from seismic data field observation and sandbox modeling 1 we present five generalized cross sections across the central zagros fold and thrust belt iran these sections show that the fold geometry varies significantly both horizontally and vertically the style is closely related to the changes in the mechanical behavior of the lithostratigraphic horizons and in particular to the presence of intermediate decollements within the sedimentary pile restoration of the sections shows amounts of shortening of the same order from one section to the other however it appears to be unequally distributed suggesting variations in basal decollement shear strength analogue modeling has been performed to systematically investigate the effect of an intermediate decollement level at different depths on the style of folding the models demonstrate that the position of intermediate decollements is an important factor controlling both structural style and fold wavelength models with shallow intermediate decollement show regularly and widely spaced anticlines in these models the fold wavelength depends directly on the thickness of the dominant competent layer and short wavelength superficial structures mask broad anticlines at depth models with deep intermediate decollement are characterized by the rapid propagation of deformation with small rate of shortening along this decollement influencing localization of forthcoming anticlines in the upper levels such propagation favors the development of duplexes and multiwavelength folds on this basis fold kinematics in central zagros is discussed using the variation of structural style along different folds as an indicator of the sequence of deformation detachment folding is the main folding style at least for the initial stages of deformation and thrust faults developed only at later stages some of these faults branched on decollement levels express the progression of folding whereas others are linked to late basement faults cutting through early structures in general the decollement levels are activated sequentially from deeper horizons to shallower ones however in one case gachsaran decollement a shallow decollement is activated during the early stages of folding and then abandoned during the subsequent evolution

fold patterns and multilayer rheology of the lurestan province zagros simply folded belt iran abstract anticlines of the lurestan province in the zagros fold thrust belt have been studied by integrating field based analysis with the use of high resolution satellite images and data available from the literature the distribution of folds in the southeastern lurestan province expressed in terms of axial length and wavelength distribution shows a direct link with the characteristics of the sedimentary multilayer in which the folds developed within the carbonate deposits of the late cretaceous bangestan group the transition from pelagic to neritic facies determines a threefold increase in anticline spacing and promotes the development of thrust structures in the forelimb of anticlines the oligocene miocene shahbazan asmari unit folds harmonically with the bangestan group except in the areas where the palaeogene deposits interposed between the two units exceed 1300 m of thickness in these areas the shahbazan asmari carbonates display short wavelength folds indicating a complete decoupling from the underlying folds of the bangestan group it is suggested that this decoupling occurs because the summed thickness of the incompetent units separating the two carbonate units exceeds the extension of the zone of effective contact strain of the bangestan group folds

susceptibility and risk assessment of earthquake induced landslides based on landslide response units in the subao river basin china generally pixels are the basic unit for assessment of landslide susceptibility however even if the results facilitate the comparison a pixel based analysis does not clearly illustrate the distribution relationships to eliminate this deficiency the concept of the landslide response unit lru is proposed in this study for which adjacent pixels that have similar properties are combined as a basic unit for susceptibility assessment the subao river basin seriously impacted by the wenchuan earthquake was selected as the study area and three factors including slope gradient slope aspect and slope shape which have a significant impact on landslides were chosen to divide the basin into 25 984 lrus then topographic geologic and distance factors were applied for the landslide susceptibility evaluation the logistic regression method was used to establish the susceptibility assessing model by analyzing 2 000 susceptible lrus and 2 000 un susceptible lrus the model accuracy was defined in terms of the roc curve value and the value 0 531 and 0 84 respectively the susceptibility of landslides was divided into low moderate high and very high in subao river basin and 73 of historical landslides and all four new landslides are in the highly susceptible zone and very highly susceptible zones finally the lrus with houses farmlands and roads prone to sliding and burial hazard were assessed separately on the basis of considering the potential movement directions of the lrus the result found that 1 001 and 835 lrus probably would be destroyed by slope sliding and landslide burial respectively

the impact of cover rock rheology on the style of folding in the zagros fold thrust belt abstract the present day morphology of the zagros fold thrust belt is dominated by magnificent exposures of nw se trending folds these folds differ in their size and geometry and these differences are related mainly to the rheological profile of the cover rock the cover rock succession of the zagros consists of a sequence of competent and incompetent units which vary both along and across the belt field based study combined with the use of satellite images reveals that the thickness and facies distribution of the cover rock succession has a significant impact on the style of deformation during the shortening linked to the current convergence of the arabian and iranian plates the incompetent units act as detachment horizons which localise thrusting and which act as decollement above which detachment folds form in addition where these incompetent units are thick e g 1 km they allow the deformation above and below them to become completely decoupled enabling disharmonic folding to occur as a result the folds above and below the incompetent units in the central part of the zagros folded belt have significantly different geometries and wavelengths as the zagros folds host the majority of the hydrocarbon reserves in iran and iraq an understanding of the processes that influence their geometry and spatial organization at different levels in the cover rock is crucial for the future exploration in the region

epicenter distribution and magnitude of earthquakes in fold thrust belts insights from sandbox models scaled analogue models are used to illustratethe eect of basal friction and erosion on fault activity andhence on epicentre distribution and magnitude of earth quakes in the sedimentary cover of active fold thrust belts model results suggest that in fold thrust belts shortenedabove low friction ductile decollements rock salt or over pressured mudstone low to moderate magnitude earth quakes mw 5 3 5 6 distributed over a wide area occuralong several long lived thrust faults conversely in areasshortened above high friction decollements large magnitudeearthquakes mw 6 6 6 8 distributed over a narrowzone are likely to occur along few short lived thrust ramps calculated magnitude of earthquakes from models and theirdistribution are in agreement with recorded earthquake pat tern from the zagros mountain belt which is partially short ened above a ductile decollement of hormuz salt formation model results also showed that erosion reactivates older in active thrusts and promotes formation of out of sequencethrusts

centrifuged models of gulf of mexico profiles abstract physical models dynamically scaled in a centrifuge are used to explore the importance of slope progradation in driving internal salt structures much further horizontally than they rise large increments of ductile plastic overburden added at normal gravity values simulated primary clastic sedimentary progradation of a clastic slope over a layer of buoyant fluid simulating salt during load increments at a nominal 800 g in a centrifuge this ductile topographic slope spread over the ductile decollement except for down to basin growth faults all the structures considered to be distinctive in the northern gulf of mexico are simulated in the models that are scaled such that 1 mm and 60 s in the model correspond to 1 1 5 km and 2 6 ma in the prototype ratios of the rate of advance to the rate of rise of the shelf break compared with the rate of advance and increase in relief of salt structures control how much of the deep autochthonous salt is squeezed ahead of the advancing shelf and the paths this salt takes to shallow structural levels the few three dimensional diapiric stocks which developed from many two dimensional mullions in the models spread stock canopies which advanced huge distances before some became tongue canopies by climbing over clastic sediments already aggraded in front of them the models emphasize the significance of ductile spreading of the clastic sediments now being discerned by backstripping

passive roof thrusting and forelandward fold propagation in scaled brittle ductile physical models of thrust wedges a set of scaled analogue models was performed to investigate the role of a decollement layer in the structural style of fold and thrust belts silicone putty sgm 36 has been employed to represent the ductile decollement while frictional material quartz sand has been used to simulate the brittle behavior of roof and floor sequences situated above and below the decollement respectively in order to explore a wide combination of strength profiles models have been deformed under five distinct rates of compression 0 15 0 3 0 45 0 6 and 1 5 cm h 1 employing four different thicknesses for the silicone layer 0 1 0 2 0 4 and 0 8 cm experimental results indicate that roof sequences exhibit two distinct styles of deformation 1 passive roof duplex prd geometry e g banks and warburton 1986 and 2 outward propagation of folding ofp along the decollement e g davis and engelder 1985 in prd geometry the roof sequence remains relatively stationary being underthrust by a wedge shaped floor duplex while in ofp displacement along the floor thrusts is transferred horizontally along the decollement layer experiments suggest the occurrence of a genetic relationship between shear stresses at the base of the roof sequence b and within the ductile layer d and the development of prd or ofp geometry for a given strain rate the deformation pattern of roof sequences depends upon the b d ratio as well as the absolute b and d values the transition field between ofp and prd styles has been approximated by curvilinear regression of transition style experimental data points with a minimum value of d varying between about 112 and 160 pa to enter the prd field syntectonic sedimentation in the molasse basin is found to inhibit development of folding into the foreland but to promote prd style experiments simulate many of the principal characteristics of fold and thrust belts developed above a basal evaporite decollement as well as the development of passive roof duplexes at mountain fronts shear stress values inferred for many fold and thrust belts correlate well the deformation fields predicted by the present experimental study allowing to propose a simple model describing the mechanical behavior of natural roof sequences underlain by a decollement layer

effect of basal friction on surface and volumetric strain in models of convergent settings measured by laser scanner abstract this paper uses measurements by a high accuracy laser scanner to investigate the role of basal friction on surface and volumetric strains in sandbox models simulating fold thrust belts and accretionary wedges we monitor progressive deformation wedge growth and strain distribution in three models with similar initial boundary conditions but with different basal frictions our analyses show that in addition to influencing the kinematics and geometry of model wedges basal friction also governs both the surface and volumetric strains of the wedge after 16 3 bulk shortening the volume decreased 5 0 5 9 5 0 5 and 12 5 0 5 in the models shortened above low intermediate and high friction decollements respectively applied to nature our model results suggest that more compaction and penetrative strain is expected in convergent settings with a high friction decollement than those shortened above a low friction decollement or a weak basal bed like the salt formation under parts of the zagros fold thrust belt this volume decrease probably reduces the porosity in the deformed lithologies

systematics of the equatorward diffuse auroral boundary dmsp f2 and dmsp f4 precipitating electron data are used to determine statistically the systematic variations of the equatorward diffuse auroral boundary with kp as a function of local time this work extends a previous study of dawn and dusk boundaries to the noon and midnight regions the boundaries are well ordered by kp in the night sector but show increasingly greater scatter from dawn to postnoon in the noon sector it is often the case that no diffuse aurora is discernible within detector sensitivity the equatorward diffuse auroral boundary is well fit by a circle at each activity level the center of the circle is offset from the geomagnetic pole and the radius of the circle increases with increasing magnetic activity the circular fits are projected to the ecliptic plane by using the mead fairfield magnetic field model where they are identified with the inner edge of the plasma sheet in order to make comparison with volland stern type convection electric field predictions previously found variations of the electric field with kp are confirmed including a rotation of the axis of symmetry away from the dawn dusk meridian all equatorward auroral boundaries from dmsp for 1978 were compiled using the equations for boundary variations with kp each evening sector boundary was projected to a midnight boundary the projected midnight boundary serves as an index of auroral activity and an indicator of the strength of the large scale magnetospheric convection electric field the auroral boundary index is given in monthly plots for 1978

magnetostratigraphy of miocene pliocene zagros foreland deposits in the front of the push e kush arc lurestan province iran abstract the timing of the deformation in the zagros simply folded belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences the foreland basin infill at the front of the push e kush arc is composed of fine grained fluvial plain deposits agha jari fm and coarse conglomerates at the top of the section bakhtyari fm a magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata and to constrain the timing of the deformation in the mountain front flexure mff magnetostratigraphic correlation of the base of the agha jari fm with chron c5a yields an age of 12 8 to 12 3 ma for this base the transition to the conglomerates of the bakhtyari fm correlates with the upper gauss chron c2an at approximately 3 ma the deposition age of the top of the preserved bakhtyari fm is extrapolated around the pliocene pleistocene boundary the base of the agha jari fm growth strata and thus the beginning of the deformation in the front of the push e kush arc is dated at 8 1 7 2 ma the topmost preserved bakhtyari is folded in the ne flank of the changuleh anticline and is unconformably overlying the sw flank of the anaran anticline this indicates that the tectonic deformation in the front of the push e kush arc was active at least during 5 my the mff is a relatively long lived structure active from 8 1 to 7 2 ma to about the pliocene pleistocene boundary partly synchronous with the changuleh anticline to the foreland after mff tectonic cessation only the changuleh anticline remained active

sandbox experiments of inverted listric and planar fault systems abstract the kinematic and geometric evolution of basement controlled inversion structures has been analyzed using a plane strain sandbox apparatus the results of two representative scaled analogue models comprising rigid listric and planar detachment faults that both have cut off angles of 60 to the horizontal are described in detail the hangingwall above these detachment geometries was constructed from alternate layers of sand and mica in order to simulate an anisotropic sedimentary sequence in both experiments initial shortening at the onset of inversion was accommodated by bulk strain this was followed by reactivation of the basal detachment together with the main basin controlling planar and listric faults which propagate upwards through the post rift sequence at approximately the same angle as the upper part of the detachment fault i e 60 reactivation of relatively steep intra basinal extensional faults within the cover was restricted to nucleation of reserve faults and thrusts in the region of the tips during approximately the first 10 to 15 contraction this resulted in gently dipping thrusts that propagated upwards through the post rift sequence to produce harpoon shaped structures later in the inversion phase after approximately 15 contraction backthrusts cut through and displaced the original antithetic extensional graben faults producing downward tapering wedge shaped structures at the margins of the basin although deformation in these experiments was limited to purely dip slip displacement the nature of the original extensional faults and their reactivated tip regions resulted in cross sectional geometries that have a marked resemblance to strike slip induced flower structures uplift was asymmetric and centred above the upper part of the main detachment above the listric fault but was more symmetrical and centred above the soling out point of the detachment in the case of the planar fault geometry the results of these experiments show distinct similarities to structures seen on seismic sections form the southern north sea and other inverted sedimentary basins

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

how to build an extensional basin in a contractional setting numerical and physical modelling applied to the mejerda basin at the front of the eastern tell of tunisia abstract in tunisia africa eurasia convergence resulted in the tell fold and thrust belt ftb part of the tell rif or maghrebides associated to the south to the atlas intra continental belt the mejerda rift basin is developed over the compressional boundary between the tell and the atlas the main objective of this study is to identify the mechanism responsible for such a basin development the abundance of triassic salt structures in the northern atlas compared to the tell suggests a friction change along the basal decollement formed by the salt level this frictional contrast is expected to produce a heterogeneous deformational response and complex structures on this basis numerical and analogue modelling were used to investigate the impact of a friction change on the deformation style the kinematic approach of the limit analysis theory was applied here via the software optum g2 the onset of faulting in all numerical tests reveals extensional faults appear at the friction boundary beyond the onset of faulting sandbox experiments show extensional features such as collapsing blocks and extensional faults overall the adopted numerical and physical approaches showed evidences of extension in particular the experiment using sandpaper and silicon putty pdms for the decollement transition shows viscous deformation mimicking diapiric movement these observations of numerical and physical model behaviors highlight that compression can produce an extensional basin at the top of a thrust wedge as expression of a strong basal friction change hence the mejerda basin is interpreted as a wedge top basin it developed during the growth of the tell and atlas ftbs the same configuration likely exists in other mountain belts the case of the molasse basin between the jura and the western alps is advocated

effect of lateral thickness variation of an intermediate decollement on the propagation of deformation front in the lurestan and izeh zones of the zagros fold thrust belt insights from analogue modeling although the role of various basal decollement levels on structural style and deformation propagation is well documented in many folded belts the effect of lateral variation in intermediate decollements is poorly constrained this work uses results of three scaled sand box models shortened from one end to study the variation in structural development between areas with a ductile intermediate decollement and areas without or with a thinner intermediate decollement combined results of scaled models with field observations are used to argue that the presence of mechanically different intermediate decollement horizons within the zagros stratigraphy has resulted in deformation partitioning between the lurestan and izeh zones a thick intermediate decollement facilitates a faster propagation of deformation front and a lower taper in comparison with a thinner or non existing intermediate decollement during compression however the effect of lateral thickness variation in the intermediate decollement on propagation of deformation is less profound than the effect of mechanical differences in basal decollements

tertiary sequence of deformation in a thin skinned thick skinned collision belt the zagros folded belt fars iran 1 we describe how thin skinned thick skinned deformation in the zagros folded belt interacted in time and space homogeneous fold wavelengths 15 8 5 3 km tectono sedimentary evidence for simultaneous fold growth in the past 5 5 2 5 ma drainage network organization and homogeneous peak differential stresses 40 15 mpa together point to buckling as the dominant process responsible for cover folding basin analysis reveals that basement inversion occurred 20 ma ago as the arabia eurasian plate convergence reduced and accumulation of neogene siliciclastics in foreland basin started by 10 ma ongoing contraction occurred by underplating of arabian crustal units beneath the iranian plate this process represents 75 of the total shortening it is not before 5 ma that the zagros foreland was incorporated into the southward propagating basement thrust wedge folds rejuvenated by 3 2 ma because of uplift driven by basement shortening and erosion since then folds grew at 0 3 0 6 mm yr and forced the rivers to flow axially a total shortening of 65 78 km 16 19 is estimated across the zagros this corresponds to shortening rates of 6 5 8 km ma consistent with current geodetic surveys we point out that although thin skinned deformation in the sedimentary cover may be important basement involved shortening should not be neglected as it requires far less shortening moreover for such foreland folded belts involving basement shortening underplating may be an efficient process accommodating a significant part of the plate convergence

intermediate decollement activation in response to the basal friction variation and its effect on folding style in the zagros fold thrust belt an analogue modeling approach although the role of various basal and intermediate decollement levels on structural style is well documented individually in many folded terrains the interaction between basal and intermediate de

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

variation of structural style and basin evolution in the central zagros izeh zone and dezful embayment iran abstract structural style and its relationship to sedimentary facies and the evolution of sedimentary depocenters since late cretaceous times have been studied on the basis of one regional balanced transect and several updated isopach maps in the izeh zone and the dezful embayment central zagros this study relies on fieldwork data existing geological maps seismic data and well information a new structural classification for part of the zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column it shows the existence of several local decollement levels activated during folding these decollement levels separate lithotectonic units which accommodate shortening in different ways the lower paleozoic is the basal decollement level throughout the studied area triassic evaporites albian shales eocene marls and miocene evaporites can act as intermediate decollement levels and present variable facies in the central zagros lateral facies and thickness variations the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength amplitude and style of folding in the study area furthermore surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding the evolution of sedimentary depocenters from the late cretaceous obduction episode until early miocene collision is described based on updated isopach maps and tectonic subsidence curves this analysis shows continuous compression and movements along n s and nw se trending faults in the zagros basement which predate the neogene zagros folding and influence sedimentation history it also indicates a southwestward migration of the depocenters through time in addition to the basement involvement below some folds during the zagros orogeny

the effect of basement step topography on the geometry of the zagros fold and thrust belt sw iran an analog modeling approach systematic analog models are run to study the variation in deformation across basement steps in the zagros fold thrust belt our model results demonstrate that basement configuration topography influences the sedimentation thickness and hence the kinematics and geometric evolution of the fold and thrust belt the greater the difference in thickness between the adjacent cover units across a basement step the sharper and clearer will be the offset of the deformation front based on model results we conclude that in a fold thrust belt where basement step topography is covered by a layer of ductile salt acting as a decollement the effect of the salt decollement on the evolution of the belt is far greater than the effect of thickness variation of the cover units

structural styles and decoupling in stratigraphic sequences with double decollements during thin skinned contractional tectonics insights from numerical modelling abstract six series of particle based numerical experiments were performed to simulate thin skinned contractional tectonics in stratigraphic sequences with double decollements during horizontal shortening the models were assigned with varying rock competence depth and thickness of the upper decollement which resulted in significantly different styles of deformation and decoupling characteristics above and below the upper decollement the models composed of the least competent material produced distributed sinusoidal detachment folds with many shallow structures profoundly decoupled from the deep seated folds the models composed of a more competent material are dominated by faulted box folds with minor disharmonic folds developed in their limbs in contrast the results of models composed of the most competent material are characterised by localised piggyback thrusts fault bend folds and pop up structures with tensile fractures developed in fold hinges depth of the upper decollements also plays an important role in controlling structural decoupling i e the shallower the upper decollements the higher the degree of decoupling becomes thicker upper decollements can provide sufficient mobile materials to fill fold cores and contribute to the formation of secondary disharmonic folds helping enhance structural decoupling our modelling results are comparable to the structural features exhibited in the dezful embayment of the zagros fold and thrust belt with the miocene gachsaran formation acting as the shallow upper decollement and the fars with the triassic dashtak formation as its intermediate decollement this study demonstrates that rock competence depth and thickness of the upper decollements can jointly affect the structural styles and decoupling our modelling results are instructive for structural interpretation of deep zones in fold and thrust belts that exhibit distinct structural decoupling features

experimental insights on the geometry and kinematics of fold and thrust belts above weak viscous evaporitic decollement abstract this paper discusses the differences in mechanical properties and kinematics between fold and thrust belts detaching on evaporitic decollements and those detaching on stronger detachments physical experiments are described that model shortening of a thick brittle cover overlying a weak viscous decollement to gain a better understanding of these differences we tested the influence of 1 the decollement layer thickness and 2 the presence of a deformable backstop on the hinterland side and of a decollement pinch out on the foreland side because of the very low shear strength of the viscous decollement folds and thrusts did not propagate according to a piggy back sequence but by centripetal back and forth propagation additional shortening was accommodated by growth of all existing structures fold symmetry and thrust vergence varied between experiments models confined between two rigid vertical endwalls always deformed by symmetric folding and thrusting in models having a deformable backstop and a foreland decollement pinch out forethrusting initially dominated folds were asymmetric and fault blocks rotated in models having a thick decollement layer folds kept growing asymmetrically diapirism also depended on the initial decollement geometry diapirs formed only in models having a deformable backstop and were restricted to the hanging wall of a fault related fold finally the implications of such kinematics on the thermal history are discussed as well as the likelihood of hydrocarbon maturation and preservation

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

effect of basement structure and salt tectonics on deformation styles along strike an example from the kuqa fold thrust belt west china abstract the kuqa fold thrust belt kftb has a complex thrust system geometry and comprises basement involved thrusts decollement thrusts triangle zones strike slip faults transpressional faults and pop up structures these structures combined with the effects of paleogene salt tectonics and paleozoic basement uplift form a complex structural zone trending e w interpretation and comprehensive analysis of recent high quality seismic data field observations boreholes and gravity data covering the kftb has been performed to understand the characteristics and mechanisms of the deformation styles along strike regional sections fold thrust system maps of the surface and the sub salt layer salt and basement structure distribution maps have been created and a comprehensive analysis of thrust systems performed the results indicate that the thrust fold system in paleogene salt range can be divided into five segments from east to west the kela 3 keshen dabei bozi and awate segments in the easternmost and westernmost parts of the paleogene salt range strike slip faulting and basement involved thrusting are the dominant deformation styles as basement uplift and the limits of the cenozoic evaporite deposit are the main controls on deformation salt core detachment fold thrust systems coincide with areas of salt tectonics and pop up imbricate and duplex structures are associated with the main thrust faults in the sub salt layer distribution maps of thrust systems basement structures and salt tectonics show that paleozoic basement uplift controlled the paleozoic foreland basin morphology and the distribution of cenozoic salt in the kftb and thus had a strong influence on the segmented structural deformation and evolution of the fold thrust belt three types of transfer zone are identified based on the characteristics of the salt layer and basement uplift and the effects of these zones on the fault systems are evaluated basement uplift and the boundary of the salt deposit generated strike slip faults in the sub salt layer and supra salt layers at the basin boundary model a when changes in the basement occurred within the salt basin strike slip faults controlled the deformation styles in the sub salt layer and shear zone dominated in the supra salt layer model b a homogeneous basement and discontinues salt layer formed different accommodation zones in the sub and supra salt layers model c in the sub salt layer the thrusts form imbricate structures on the basal decollement whereas the supra salt layer shows overlapping discontinuous faults and folds with kinds of salt tectonics and has greater structural variation than the sub salt layer

controlling factors of loess landslides in western china based on detailed field data from recent geo hazards surveys in the loess plateau region of western china this study analyzes the key factors that control loess landslides the evolution phase of river valleys the geological structure of slopes and the geometry of slopes are all found to play a role in determining the occurrence distribution and other characteristics of loess landslides groundwater and vegetation also contribute to their formation a combination of human engineering activities and precipitation events are the principal triggering factors for the instability of loess slopes

modeling the evolution of loess covered landforms in the loess plateau of china using a dem of underground bedrock surface the evolution of loess covered landforms is largely controlled by the pre quaternary underlying bedrock terrain which is one of the most important factors in understanding the formation mechanism of the landforms this study used multiple data sources to detect 1729 outcropping points of underlying terrain in order to construct a digital elevation model dem of the paleotopography of an area of the loess plateau subject to severe soil erosion four terrain characteristics including terrain texture slope gradient the hypsometric curve and slope aspect were used to quantify topographic differences and reveal the loess deposition process during the quaternary a loess thickness map was then created to show the spatial distribution of loess deposits in the test area finally the geomorphological inheritance characteristics of the loess covered landforms were evaluated in different landform divisions the results showed the significant inheritance of modern topography from the underlying topography with a similar general relief trends the average thickness of loess deposits was computed to be 104 6 m with the thickest part located in the xifeng loess tableland area in addition the slope aspects of the north and northwest seem to have favored quaternary loess deposition which supported the hypothesis of an eolian origin for loess in china the modem surface has lower topographic relief compared to the underlying terrain due to loess deposition crown copyright c 2013 published by elsevier b v all rights reserved

suitability analysis for topographic factors in loess landslide research a case study of gangu county china loess plateau is one of the ecologically fragile regions in china it is one of the slippery strata of which landslides often developed the formation and development of landslides are mainly affected by various natural environments triggering factors the vulnerability of landslide bearing bodies and topography has a controlling effect on landslides and determines landslide distribution as important environmental elements the selection and reclassification of topographic factors are the basis for loess landslide vulnerability map in this study our research suggests an effective workflow to select and analyze the topographic factors in the loess landslides nine hazard formative environmental factors e g slope aspect slope shape ss slope of slope sos slope of aspect soa surface amplitude sa surface roughness sr incision depth id and elevation variation coefficient evc are prepared for landslide suitability analysis the models of certainty factor sensitivity index and correlation coefficient are combined to select and analyze the suitability of these factors four topographic factors i e slope sos ss and sr were ultimately selected to carry out the landslide vulnerability mapping with other factors our results showed that most of the landslides were located in medium and high classes and accounting for 75 3 and these places also coincided with higher economies and intense human activities our research also suggested that in situ measurements are necessary to determine how to reclassify these topographic factors and how many grades these topographic factors divided which would further improve the reliability of landslide vulnerability map for the decision makers to deal with the possible future landslides in terms of safety and human activities

gps scintillation and irregularities at the front of an ionization tongue in the nightside polar ionosphere in this paper we study a tongue of ionization toi on 31 october 2011 which stretched across the polar cap from the canadian dayside sector to svalbard in the nightside ionosphere the toi front arrived over svalbard around 1930 ut we have investigated gps scintillation and irregularities in relation to this toi front this is the first study presenting such detailed multi instrument data of scintillation and irregularities in relation to a toi front combining data from an all sky imager the european incoherent scatter svalbard radar the super dual auroral radar network hankasalmi radar and three gps scintillation and total electron content tec monitors in longyearbyen and ny alesund we observe bursts of phase scintillation and no amplitude scintillation in relation to the leading gradient of the toi spectrograms of 50hz phase measurements show highly localized and variable structuring of the toi leading gradient with no structuring or scintillation within the toi or ahead of the toi

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

deformation transfer in viscous detachments comparison of sandbox models to the south pyrenean triangle zone deformation transfer in viscous detachments comparison of sandbox models to the south pyrenean triangle zone

structural evolution of a fold and thrust belt generated by multiple decollements analogue models and natural examples from the northern apennines italy this study analyses the role played by the mechanical proprieties of the rocks involved in a thrust system focusing on the problem of multiple decollements and of related compressional structures integration of geophysical seismic reflection profiles and geological data and scaled sandbox models are used to study the deformation style of two areas of the northern apennines italy the po plain and the umbria marche apennines both areas are characterised by a complex stratigraphy consisting of decollements located at different depths that influence the geometry and kinematics of the thrust system the main characteristic of the models presented here is the presence of two decollement horizons situated at the base and in an intermediate level of the models during deformation of the models these two decollement horizons generate two sets of structures with different geometrical characteristics and significance through the joint analysis of geophysical and geological data and model results wavelengths of the compressional structures analysed show that the structural style of the two analysed areas is almost similar moreover model results prove that the final configuration of the thrust system follows the general rules of evolution of a wedge deformed above a weak decollement and is largely governed by the larger deep seated structures

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

landslide susceptibility assessment what are the effects of mapping unit and mapping method landslide susceptibility assessment forms the basis of any hazard mapping which is one of the essential parts of quantitative risk mapping for the same study area different susceptibility maps can be achieved depending on the type of susceptibility mapping methods mapping unit and scale although there are various methods of obtaining susceptibility maps the efficiency and performance of each method should be evaluated in this study the effect of mapping unit and susceptibility mapping method on landslide susceptibility assessment is investigated when analyzing the effect of susceptibility mapping method logistic regression lr which is widely used in landslide susceptibility mapping and spatial regression sr which have not been used for landslide susceptibility mapping are selected the susceptibility maps with logistic and spatial regression models are obtained using two different mapping units namely slope unit based and grid based mapping units the procedure for investigation of effect of mapping unit on different susceptibility mapping methods is applied to kumluca watershed in bartin province of western black sea region turkey 18 factor maps are prepared for landslide susceptibility assessment in the study region geographic information systems and remote sensing techniques are used to create the landslide factor maps to obtain susceptibility maps and to compare the results the relative operating characteristics roc curve is used to compare the predictive abilities of each model and mapping unit and also the accuracy is evaluated depending on the observations made during field surveys by analyzing the area under the roc curve for grid based and slope unit based mapping units it can be concluded that sr model provide better predictive performance 0 774 in grids and 0 898 in slope units as compared to the lr model 0 744 in grids and 0 820 in slope units this result is also supported by the accuracy analysis for both mapping units the sr model provides more accurate result 0 55 for grids and 0 57 for slope units than the lr model 0 50 for grids and 0 48 for slopes the main reason for this better performance is that the spatial correlations between the mapping units are incorporated into the model in sr while this fact is not considered in lr model

viscosity estimates of salt in the hormuz and namakdan salt diapirs persian gulf the parabolic surface profiles of the hormuz and namakdan salt diapirs in the persian gulf suggest that they have been extruding with newtonian viscous rheologies for the last 10 4 years we derive velocity profiles for these diapirs neglecting gravitational spreading and erosion dissolution while assuming incompressible newtonian rheology of the salt fitting known rates of extrusion at specific points in its elliptical cross section the dynamic viscosity of the salt of the hormuz diapir is found to range between 10 18 and 10 21 pa s approximating its sub circular cross section to a perfect circle the range of viscosity of the salt of the namakdan diapir is obtained as 10 17 10 21 pa s these calculated viscosities fall within the range for naturally flowing salts elsewhere and for other salt diapirs but are broader than those for salts with newtonian rheology deforming at room temperatures the salts of the hormuz and namakdan diapirs are expected to exhibit a broader range of grain size which matches the limited existing data

folding style of the dezful embayment of zagros belt signatures of detachment horizons deep rooted faulting and syn deformation deposition abstract defining the governing factors on the geometry of the dezful embayment folds a major oil province in the zagros fold thrust belt in sw iran reduces the risks inherent in hydrocarbon exploration the goal of the current study is to find a reasonable relationship between folding and faulting in the northern part of the dezful embayment the role of major and minor detachment horizons and deep rooted faults on structural style is also a matter of investigations to achieve these goals geological surface information and the available well and 2d and 3d seismic data were used to construct a balanced structural cross section the area is subdivided into ne and sw sectors based on dissimilar physiographic features of the surface and structural and stratigraphic characteristics in the both sectors the miocene gachsaran formation acted as the upper detachment horizon in the ne sector the role of the gachsaran formation as major detachment horizon in decoupled folding styles of overlying and underlying units is prominent the gachsaran formation becomes less effective as a detachment horizon towards the sw as its thickness decreases and its facies change the triassic dashtak formation is most probably a major detachment horizon in the study area and evidence of another deeper detachment horizon such as the pre cambrian cambrian hormuz series is not apparent based on available data the lower cretaceous garau upper cretaceous gurpi and paleocene eocene pabdeh formations and the oligocene kalhur member are subordinate detachment horizons the role of major faults in the area such as the mountain front fault in driving thick skinned deformation is taken into account along with the dominant thin skinned deformation in the study area the kuh e asmari anticline is the only emergent anticline exposing the paleocene strata due to the activity of the deep rooted lahbari thrust this study reveals the commanding role of the upper detachment gachsaran formation and the overlying syn deformation fluvial clastics of the aghajari miocene and bakhtyari pliocene formations on disharmonic folding styles

tectono sedimentary framework of the gachsaran formation in the zagros foreland basin abstract continental collision between iranian and arabian plates resulted in the formation of the zagros fold thrust belt and its associated foreland basin during convergence pre existing faults in the basement were reactivated and the sedimentary cover was shortened above two different types of basal decollement viscous frictional this led to heterogeneous deformation which segmented not only the zagros fold thrust belt but also its foreland basin into different compartments resulting in variation in facies thickness and age of the sediment infill based on this concept a new tectono sedimentary model is proposed for one of the most important syn tectonic sedimentary unit the gachsaran salt in the zagros foreland basin in this proposed model it is argued that differential propagation of the deformation front above decollements with different mechanical properties viscous versus frictional results in along strike irregularity of the zagros deformation front whereas movement along pre existing basement faults leads to development of barriers across the zagros basin the irregularity of the deformation front and the cross basin barriers divided the zagros foreland basin into six almost alternating sub basins where gachsaran salt and its non salt equivalents are deposited in the salt sub basins two different processes were responsible for the deposition of gachsaran salt 1 evaporation and 2 dissolution of extruding hormuz salt and its re precipitation as gachsaran salt re precipitation was probably the most significant process responsible for the huge deposit of gachsaran salt in the extreme south east part of the zagros foreland basin

experimental modeling of role of gravity and lateral shortening in zagros mountain belt dynamically scaled analogs of the geologic structures of the zagros mountain belt are used to argue that different parts of the zagros mountains of iran record different combinations of the effects of a gravity driven overturn and a southwest northeast lateral shortening superimposed on the zagros overturn partially scaled material models have been used to simulate the zagros geodynamics which involve layer parallel compression of a 6 to 7 km thick phanerozoic carbonate cover containing a pattern of preshortening diapirs the folds in the zagros form rapidly 1 5 mm yr in a 20 to 30 km wide zone reactive some of the preshortening diapirs and generate new synshortening listric diapirs a third set of postshortening diapirs rises from the hormuz decollement behind the fold thrust front model buckle folds superimposed on diapirs or pillows tend to avoid and curve around preshortening diapirs which flatten in the synclines model profiles show that lateral shortening induces residual salt at depth to flow toward and rise through the anticlinal cores as synshortening or postshortening diapirs i suggest that any salt pillows in currently diapir free zones of the zagros fold thrust belt may surface as diapirs through the anticlines in the future in the absence of well data seismic and field observations i have used only three map pattern criteria to recognize the timing of diapirs these are locally obscured by extrusive salt sheets preshortening diapirs are generally small and elongate parallel to fold axes and are restricted to synclines synshortening diapirs are elongate perpendicular to the fold axes and are restricted to anticlines postshortening diapirs can be the same size as synshortening diapirs or larger and can be circular they are more common in the anticlines

mechanical stratigraphy and folding style of the lurestan region in the zagros fold thrust belt iran abstract the structural style of the folds from the central part of the lurestan salient located in the nw portion of the zagros fold thrust belt has been studied by constructing a regional balanced cross section from field data existing geological maps seismic profiles stratigraphic surface sections and well data the regional balanced structural cross section that is constructed from the high zagros fault to the mountain front fault highlights the difference in the folding style across the area the vertical and lateral changes in the style of the folding indicate the influence of mechano stratigraphic contrast between the sedimentary units three main decollement levels the basal lower palaeozoic the intermediate triassic and the upper upper cretaceous lower palaeocene have been interpreted folds developed during the zagros fold thrust belt evolution above and below these decollement horizons are decoupled from each other and are different in both geometry and size similarly thickness and facies changes of some formations across the region cause lateral variation in folding pattern from the north to the south polyharmonic folds exist in the south where the different structural levels are relatively strongly coupled to the north however strongly disharmonic folding occurs where a combination of increased decollement thickness and decreased mechanical competence has led to decoupling at different structural levels this change in folding style has a direct impact on hydrocarbon exploration in the area to reduce structural risk in exploration the incorporation of high resolution deep seismic data with the surface geology is recommended for future hydrocarbon exploration activities within the lurestan region

displacement fields and finite strains in a sandbox model simulating a fold thrust belt this thesis uses geodetic satellite data to measure present day crustal deformation in the zagros fold thrust belt sw iran geodetic type measurements are also used in down scaled models that simulate the surface deformations seen in convergent settings like the zagros fold thrust belt global positioning system gps measurements of three surveys between 1998 and 2001 indicate 9 3 mm yr and 5 3 mm yr shortening across the se and nw zagros respectively gps results show that in addition to the different rates and directions of shortening on either side of the ns trending kazerun fault local along belt extension occurs to the east differential sar interferograms of ers1 2 images between 1992 and 1999 detect 8 4 mm yr uplift rate across a newly recognized fault in sw qeshm island this can be attributed to a steep imbricate thrust that may still represent the local zagros deformation front the salt diapirs in the zagros rise from a source layer that acts as a low frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern zagros whereas the cover to the west deforms above a high friction decollement physical models were prepared to simulate cover deformation in the zagros by shortening a sand pack above adjacent high and low frictional decollements represented by a ductile layer the strain distributions differed above the two types of decollements it was more heterogeneous above the salt where local extension in the shortening direction was dominant a separate work also investigated systematically the role of basal friction on cover deformation in convergent settings accurate height measurements of the model surface by laser scanner indicated a deformation front more distal than usual particularly in the low basal frictional models the volume reduction in our shortened sand models correlated directly with their basal friction

effect of spatial distribution of hormuz salt on deformation style in the zagros fold and thrust belt an analogue modelling approach scaled analogue models of thin skinned simultaneous shortening above adjacent viscous and frictional decollements simulate the effect of hormuz salt on the shortening in the zagros fold and thrust belt the models consisted of sand layers that partly overlay a viscous layer of silicone and were shortened from one end spatial distribution of the viscous decollement varied along strike and dip as occurs in part of the zagros fold and thrust belt in this belt phanerozoic sedimentary cover was shortened partly above the hormuz salt lying on the precambrian crystalline basement behaving as a basal viscous decollement model results display how the nature of the decollement affects the evolution of an orogenic belt using model results we explain the development of deflection zones and discuss strain partitioning formation of different topographic wedges and differential sedimentation along the zagros fold and thrust belt model results suggest the formation of a gentle taper consisting of both foreward and backward thrusts above a viscous decollement and a relatively steeper taper consisting only of forward vergent imbricates above a frictional decollement however in our models the steepest wedge with the highest topography formed where the viscous substrate had a limited extent with a transitional boundary pinch out perpendicular to the shortening direction shortening of this boundary led to development of frontal ramps associated with significant uplift of the area behind the deformation front

influence of basement faults on the development of salt structures in the danish basin scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the danish basin the models consisted of a viscous layer simulating rock salt overlain by layers of cohesive sand that mimic brittle failure in natural overburdens model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the danish basin in plan view model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement with further burial single diapirs rose from these buoyant walls some of the diapirs surfaced through the faulted overburden a few were trapped beneath the competent cretaceous units and others were starved due to lack of supply from below in section model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south where they rise diapirically in the model the pressure due to loading by overburden layers changed from 1 3 102 pa in the south to 2 3 102 pa in the northern part of the basin in general the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half grabens and introducing a slope and steps at the base of the buoyant layer weakening its overburden and causing differential loading and compaction the spreading overhangs of salt diapirs beneath the cretaceous chalk in the danish basin would seal any potential pre cretaceous reservoir rocks

progressive unconformities within an evolving foreland fold thrust belt zagros mountains a major angular unconformity between the bakhtyari conglomerates and the underlying agha jari formation has long been interpreted as indicating that orogeny in the zagros simply folded zone took place in plio pleistocene times this study uses field evidence of unconformities between older units in conjunction with geological maps and cross sections to argue that the front of the zagros simply folded zone has propagated in time and space these unconformities indicate that deformation started as early as end eocene in the northeast of the simply folded zone and propagated progressively to the southwest where unconformable contacts are only seen between younger units as shortening continued the southwest migration of the deformation front drove the foreland basin in front of it to its present position along the persian gulf and mesopotamia the climax of orogeny took place at end pliocene time when the most extensive unconformity in the zagros simply folded zone developed between the upper bakhtyari formation and older units active seismicity and documented present uplift imply that the simply folded zone is still propagating southwestward

detachment folding in the central and eastern zagros fold belt iran salt mobility multiple detachments and late basement control abstract detachment folding has been studied on the basis of field and subsurface examples from the central and eastern zagros iran we discuss different aspects of detachment folding well illustrated in the studied area in particular we focus on salt mobility multiple decollements and late basement control salt mobility concerns the hormuz basal detachment and the gachsaran upper detachment for the latter it is shown that mobility results not only from folding related diapirism but also from early gravity driven migration from growing anticlines towards intervening synclines concentric folding between two detachment levels is directly observed in the izeh zone central zagros where it is shown that the wave length depends on the distance between the two active decollements and that the fold shape is a function of the level of erosion throughout the zagros detachment folds mainly developed during an initial thin skinned phase of deformation which was followed by the current thick skinned stage this succession is particularly well expressed in the eastern zagros where basement faults cut early detachment folds obliquely

intermediate scale plasma irregularities in the polar ionosphere inferred from gps radio occultation we report intermediate scale plasma irregularities in the polar ionosphere inferred from high resolution radio occultation ro measurements using gps global positioning system to cassiope cascade smallsat and ionospheric polar explorer satellite radio links the high inclination of cassiope and the high rate of signal reception by the gps attitude positioning and profiling ro receiver on cassiope enable a high resolution investigation of the dynamics of the polar ionosphere with unprecedented detail intermediate scale scintillation producing irregularities which correspond to 1 to 40 km scales were inferred by applying multiscale spectral analysis on the ro phase measurements using our multiscale spectral analysis approach and satellite data polar operational environmental satellites and defense meteorological satellite program we discovered that the irregularity scales and phase scintillations have distinct features in the auroral oval and polar cap we found that large length scales and more intense phase scintillations are prevalent in the auroral oval compared to the polar cap implying that the irregularity scales and phase scintillation characteristics are a function of the solar wind and magnetospheric forcings

bias due to side wall friction in sand box experiments abstract the principal concern of this paper is with the accuracy and validity of experimental sand box models of geological structures and of thrust faults in particular as influenced by side wall friction side wall friction can produce undesirable artifacts in particular in experiments aimed at reproducing plane deformations the importance of such artifacts is revealed in the present study by the results of experiments that are affected in opposite ways by side wall friction two distinct experimental configurations have been chosen for this purpose for a set up that comprises a body of sand placed between vertical side walls on a basal plate against a back wall and a front wall all made of glass in configuration m the bottom plate and attached front wall move relative to the side walls towards a fixed back wall while in configuration f the back wall moves relative to the side walls and attached bottom plate towards a fixed front wall fixed fixed relative to the side walls in both configurations thrust traces on the top surface of the sand become curved near the side walls because of wall friction the outcome of altogether 31 experiments in the two configurations shows that the magnitude of the experimental bias depends on the ratio s l s b of the area of contact of the sand body with the side walls s l to its area of contact with the basal surface s b the bias is the difference in thrust locations in the two configurations it is measured on photographs taken through the side walls during the experiments away from the side walls the bias is estimated by the thrust curvatures observed in top views for s l s b 0 1 i e very little contact with side walls there is no identifiable bias furthermore a 2d theoretical solution reproduces well the results for s l s b increasing to 0 25 curvatures increase yielding rather different cross sections at the side walls but still similar cross sections in the central part of the sand body for s l s b 0 3 thrust planes occupy different regions of the box for each configuration although their curvature is decreasing at s l s b 0 9 curvatures have almost disappeared but the location of the thrusts and the length of the decollement depend strongly on the experimental configuration departures from the 2d theoretical solution are clearly stronger with configuration m than f another important conclusion is that the absence of curvature of the thrust traces is not a proof of the 2d character of the experiment mechanical equilibrium of the total forces recorded at both front and back walls during shortening shows that the thrust locations are controlled by the difference between basal and side wall shear forces

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

analogue modeling of the role of multi level decollement layers on the geometry of orogenic wedge an application to the zagros fold thrust belt sw iran the presence of evaporate and incompetent formations i e decollement horizons within the sedimentary sequence of fold thrust belts can control their structural style and deformation evolution in the present study the influence of the decollement layers e g basal and internal decollement layers on the deformation style of several segments of the zagros fold thrust belt zftb sw iran e g fars arc dezful embayment and izeh zone was investigated using a series of analogue models of accretionary wedges the study of seismic profiles to understand the structural evolution of these segments of the belt where several decollement intervals acted as basal and internal decollements is complemented by the analogue model results the experimental results reveal that the thickness of the internal decollement layers influences the creation of fold dominated or thrust dominated deformations respectively experimental models and seismic data highlight that incompetent layers act as barrier units against fault propagation in sequence and or out of sequence faults into overlying strata towards southwest by fore deformation and control the rate of deformation propagation in the zftb the presence of both the basal and internal decollement layers located at different stratigraphic levels is required to form disharmonic decollement folds in the foreland of the zftb in addition the geometry spacing activity and propagation of faults as well as the topographic height of the critical wedges are directly controlled by low frictional decollements geophys j int 165 1 336 356 2006 geochem geophys geosyst 14 1131 1155 2013 the seismic profiles of the zftb showed that in addition to lithological contrasts the existence and activity of deep seated and basement faults had a big impact on the structural styles of the region