the eastern termination of the zagros fold and thrust belt iran structures evolution and relationships between salt plugs folding and faulting 1 the zagros mountains result from the ongoing collision between the arabian and central iran plates the main features of the eastern zagros are 1 numerous emerged or buried salt diapirs made up of late precambrian hormuz salt and 2 the irregular along strike shape of the collision related detachment folds with frequent bending to understand this layout four geological cross sections have been constructed from the persian gulf foreland basin to the inner part of the zagros fold and thrust belt shortening in the deformed parts of the sections is less than 10 and is mainly accommodated by detachment folding we show that late cenozoic folding occurred in a region that was already punctuated by salt domes and diapirs in fact almost continuous halokinesis developed since the earlier paleozoic i e just short time after the deposition of the hormuz salt and continued up to the present these preexisting salt structures and their relevant local thickening strongly influenced both the localization and the direction of folds

radar interferometric mapping of deformation in the year after the landers earthquake although the 1992 landers california earthquake sequence occurred in an area well sampled by geodetic networks1 3 the postseismic deformation in the months following the earthquake has been measured at only 15 geodetic stations4 another shortcoming in the geodetic coverage occurs west of the primary rupture where the existing geodetic observations suggest but cannot resolve sympathetic slip on secondary faults1 such measurements which are needed to place the landers earthquake sequence in the context of a recurring seismic cycle in california can be obtained with the dense spatial coverage provided by satellite radar interferometry5 9 here we present radar maps of the surface deformation field which reveal features that would otherwise have been poorly sampled particularly if the earthquake had occurred in a less accessible area we see triggered slip at the level of several centimetres as far as 100 km from the primary rupture and can resolve the geodetic signal of at least one small magnitude 5 aftershock the amount of surface slip following the main shock is less than a decimetre and is consistent with an exponential decay time of several months for the postseismic deformation

drained and undrained anisotropic elastic stiffness parameters equations that map drained to undrained elastic stiffness parameters in a cross anisotropic material are presented graphs of various anisotropic stiffness ratios are used to illustrate the important trends a new 2 d graph showing the elastic bound enables measured elastic parameters to be plotted which all lie well within it the 2 d graph enables uncoupled and incompressible materials to be shown plus materials with particular initial effective stress path slopes in an undrained triaxial test bounds more restrictive than the elastic one are also discussed and the likely ranges of various anisotropic stiffness ratios are presented in general undrained anisotropy is much less than drained that is closer to isotropic in undrained plane strain conditions vertical and horizontal moduli are found to be the same in drained plane strain conditions the ratios of the moduli are almost the same as the young s moduli

effect of fabric on the behaviour of reservoir sandstones a laboratory investigation was undertaken on the mechanical behaviour of two sandstones that are commonly used as analogous hydrocarbon reservoir sandstones using triaxial apparatuses with a capacity of up to 70 mpa confining pressure both materials are lightly cemented but show a mechanical behaviour at large strains that is similar to that seen in rocks with much stronger cementation at small strains however these materials behave more like uncemented sands in that they show a strong stress dependency of the shear modulus and yield takes places at relatively small strains it is believed that fabric plays a fundamental role in the observed behaviour and this is supported by the experimental evidence so that the concept of strong fabric in sandstones is introduced

rheology of synthetic polycrystalline halite in torsion abstract motivated by the need for halite rheology we investigated the stress strain strain rate behaviour of halite to high shear strains in torsion using polymer jackets whose strength does not influence halite rheology the experimental results show that 1 halite strength decays exponentially with temperature increase being very weak at 300 c ca 2 nm 2 power laws fit the stress strain rate data from which we determined the stress exponent n between ca 13 60 c and ca 3 200 c indicating that n decreases exponentially with temperature increase 3 the activation energy q decreases exponentially with temperature increase from ca 159 kj mol 38 kcal mol at 60 c to ca 59 kj mol 14 kcal mol at 200 c 4 q depends linearly on n with a slope of ca 10 the empirical constitutive equation 12 1 exp 9 6 7 1 e 6 exp 1 t 1 9 e 4 2 5 9 3 e6exp t 24 3 describes the experimental results comparison of the present and previous experimental results shows that halite is much weaker in shear than in axial compression or extension this difference likely results from the rotational component of simple shear

the ayers rock australia earthquake of 28 may 1989 a temporally isolated mb 5 8 intraplate event abstract at 0255 utc on 28 may 1989 an m b 5 8 earthquake shook the yulara resort and uluru national park in the northern territory of australia the epicenter lay 40 km west of ayers rock in an area where moderate size earthquakes had not previously been recorded within 215 km although many people at yulara and uluru were alarmed damage to buildings was minimal the australian national university anu installed an array of 11 seismographs in the epicentral area 6 days after the m b 5 8 event no aftershocks were detected by the anu network during 2 weeks of recording with an estimated detection threshold of magnitude 1 to 0 another group of seismologists who operated a single recorder near uluru beginning 59 hours after the main shock and continuing through july and 6 other recorders for 6 days in early june also failed to observe any aftershocks within the sensitivity of the arrays the ayers rock event was a temporally isolated earthquake the absence of aftershock activity is in sharp contrast to the seismicity pattern following two magnitude 5 2 earthquakes near tennant creek in january 1987 and to other earthquakes of magnitude 4 2 to 6 3 observed in continental intraplate settings worldwide

on the role of bond breakage due to unloading in the behaviour of weak sandstones a laboratory investigation was made of the effects of isotropic unloading on the mechanical behaviour of cemented sandstones modelling in a simple way the influence of sampling on hydrocarbon reservoir sandstones that have been cemented at depth artificial samples of sandstone were created by allowing a cement to hydrate while a sand sample was under a high confining stress in a triaxial apparatus comparisons were then made between the behaviour of samples that had been unloaded to zero confining stress with that of samples tested at stress levels around that during cementing it was found that the isotropic unloading damaged the cement which had a significant effect on the small strain and yielding behaviour but not on the strength and large strain behaviour comparisons were also made with tests on natural samples of reservoir and analogue sandstones and it was found that the artificial sandstone had reproduced the key elements of their behaviour the intrinsic properties of all of the sandstones t

the measurement of local axial strains in triaxial tests using lvdts in this technical note the author describes an experiment in the use of linear variable differential transformer lvdt to allow accurate measurement of axial displacement over the complete range of strains of interest to geotechnical engineers

depth segmentation of the seismogenic continental crust the 2008 and 2009 qaidam earthquakes 1 the seismic hazard in the immediate vicinity of an earthquake is usually assumed to be reduced after rupture of a continental fault with along strike portions being brought closer to failure and aftershocks being significantly smaller this period of reduced hazard will persist as strain re accumulates over decades or centuries however this is only realised if the entire seismogenic layer ruptured in the event here we use satellite radar measurements to show the ruptures of two mw 6 3 earthquakes occurring in almost the same epicentral location ten months apart in the qaidam region china were nearly coplanar the 2008 earthquake ruptured the lower half of the seismogenic layer the 2009 event the upper half fault segmentation with depth allows a significant seismic hazard to remain even after a moderate and potentially devastating earthquake this depth segmentation possibly exists in the case of the 2003 bam earthquake where satellite radar and aftershock measurements showed that it ruptured only the upper half of the 15 20 km deep seismogenic region jackson et al 2006 and that the lower unruptured part may remain as a continuing seismic hazard

yielding and pre failure deformation of structured sands many natural sands have a structure that is imparted to them during their geological life and that significantly modifies their pre failure behaviour when compared with that of the reconstituted material unlike clays for which emphasis has been given to both the bonding and fabric components of structure for sands structure has generally been simply identified with bonding whereas the effects of fabric have often been overlooked an understanding of the way in which these components of structure influence the yielding and stiffness of these materials is required to formulate constitutive models that can adequately predict their response the paper examines the pre failure behaviour of two structured sands in triaxial compression performed over a wide range of pressures since yielding occurred at small strains laboratory techniques were developed to produce reliable and accurate determinations of stiffness ranging from 1 microstrain to failure the influence of structure on the shear stiffness was in

discrete element method simulations of analogue reservoir sandstones abstract the discrete element method was used to model the behaviour of two natural sandstones that are commonly used as analogues for oil reservoir sandstones with a relatively large number of parameters needed to define the model and few micro scale data on which to base them a parametric study was first carried out to identify how each parameter affects the overall macroscopic behaviour this study highlighted the importance of the load share between the particle contacts and the bonds the model for the more strongly cemented sandstone was calibrated against the response observed at a single stress level and predictions at other stress levels were then found to be good a second more weakly cemented sandstone was also modelled it was found that while this sandstone had a very much lower cement content by weight only minor modifications were needed to the bond strengths and the proportion of bonded contacts compared to the more strongly bonded material this may be because of the failure to model the natural fabric of the sandstones in general the post peak regime was not modelled well nor was the volumetric response the latter as a result of the failure to achieve the in situ porosities in the model

zagros phantom earthquakes reassessed the interplay of seismicity and deep salt flow in the simply folded belt unraveling the contributions of main shock slip aftershocks aseismic afterslip and postseismic relaxation to the deformation observed in earthquake sequences heightens our understanding of crustal rheology triggering phenomena and seismic hazard here we revisit two recent earthquakes in the zagros mountains iran which exhibited unusual and contentious aftereffects the mw 6 earthquakes at qeshm 2005 and fin 2006 are both associated with large interferometric synthetic aperture radar insar signals consistent with slip on steep reverse faults in carbonate rocks of the middle sedimentary cover but small aftershocks detected with local seismic networks were concentrated at significantly greater depths this discrepancy can be interpreted in one of two ways either 1 there is a genuine vertical separation between main shock and aftershocks reflecting a complex stress state near the basement cover interface or 2 the aftershocks delimit the main shock slip and the insar signals were caused by shallow updip afterslip phantom earthquakes with very similar magnitudes mechanisms and geographical positions as the original earthquakes here we show that main shock centroid depths obtained from body waveform modeling which in this instance is the only method that can reveal for certain the depth at which seismic slip was centered strongly support the first interpretation at qeshm microseismic aftershock depths are centered at the level of the hormuz formation an infracambrian sequence of intercalated evaporitic and nonevaporitic sediments these aftershocks may reflect the breaking up of harder hormuz sediments and adjacent strata as the salt flows in response to main shock strain at the base of the cover this work bolsters recent suggestions that most large earthquakes in the zagros are contained within carbonate rocks in the midlower sedimentary cover and that the crystalline basement shortens mostly aseismically

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

macroseismic field generated by 29 march 1999 chamoli earthquake and its seismotectonics abstract a damaging earthquake of magnitude 6 4 mb usgs rocked the garhwal region on 29 march 1999 at 00 35 00 hours ist maximum intensities of viii and vii on the medvedev sponheaer karnik msk 64 scale and the european macroseismic scale 98 ems 98 were observed in the affected region extensive damage was noticed both in the chamoli and rudraprayag regions of the garhwal himalaya in the chamoli region damage of intensity viii was confined to the right bank of the river alaknanda in the rudraprayag region the damage was widespread between chandrapuri and cantha villages an isoseismal map prepared on the basis of a damage survey shows a nw se trend with its major axis in the nw se direction and minor axis in the ne sw direction in the rudraprayag region the major axis is 11 km long and minor axis 8 km long thus the viii isoseismal zone covers an area of approximately 88 km2 the damage survey revealed that maximum damage has been either along major faults or to adobe houses locally called pathal houses the damage was also higher than expected because of the use of undressed stones and heavy pathal slate roofing the villages of kansali pingalpani akhori kiyunja sena cantha tewri talsari and chamoli were the most affected in the rudraprayag and chamoli regions grade 4 and grade 3 damage has been observed in many adobe houses in the intensity zone vii the study of damage distribution and intensity attenuation has demonstrated an asymmetric distribution and heterogeneous behaviour the heterogeneous pattern could be related to rupture asperity distribution a noteworthy feature of this earthquake was that it has produced a lot of ground fissures some traceable for many tens to hundreds of meters affecting both rocks and overburden one such fissure was traced for nearly 500 m trending nw se with a downthrow of 20 25 cm this fissure shows thrust faulting with the foot wall having moved down towards the ne and the hanging wall upwards toward the sw side this is in conformity with the fault plane solution given by the usgs using the moment tensor technique which indicates that the earthquake originated by slip along a low angle thrust fault dipping ne changes in hydrological conditions have been noticed in a number of villages for example kiyunja kansali talsari pingalpani mukku sena akhori tewri gurpunga and bhatwari etc

the measurement of soil stiffness in the triaxial apparatus this paper describes a simple technique for accurately measuring the mean local axial strains of triaxial samples over a central gauge length the technique makes use of an axial displacement gauge which is a development of one devised by burland symes 1982 which makes use of electrolytic levels the device can resolve to less than 1 m over a range of 15 mm is simple to mount on the specimen and is not damaged when the sample is taken to failure the results of undrained triaxial tests are presented for a wide spectrum of soil types ranging from sands through intact reconstituted and remoulded low plasticity till undisturbed london clay to intact unweathered chalk the test results show that conventional external measurements of displacement contain errors which are frequently so large that their use in the determination of soil stiffness at working levels of stress is invalid the errors mainly result from tilting of the sample bedding at the end platens and the effects of compliance in the app

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

regional trends in active diapirism revealed by mountain range scale insar time series 1 we construct an orogen wide insar time series over the zagros mountains and eastern markan subduction zone in southern iran from 19 envisat tracks spanning 2003 2010 we observe active salt diapirism of the infra cambrian hormuz salt at 20 locations and identify several diapirs that are not moving all active diapirs reach the surface within the asmari limestone or older rock units while we do not observe any active diapirism occurring within younger exposures reflecting a complex vertical accumulation of the basal salt and reactivation of diapirs by erosion diapir reactivation of this sort may be a critical factor affecting the feasibility of sequestering nuclear waste and co2 in evaporite sequences over geologic time scales the distribution of active diapirism is indifferent to increases in mean elevation suggesting a relatively uniform thickness of the zagros fold belt above the basal salt with steps in topography driven by basement thickening we do not observe aseismic uplift of anticlines because rates are likely below the detection threshold of our time series this suggests that uplift is accommodated at small rates 2 3 mm yr over numerous structures instead of focused at the deformation front

the mechanics of cemented carbonate sands the behaviour of artificially cemented carbonate sand was investigated in triaxial tests at confining pressures of up to 9 mpa the results show that an important effect of cementing is a reduction in specific volume resulting from the increase in fines content this influences both the stress strain behaviour and the peak strength at strains beyond those required to fracture the cement bonding comparisons between the behaviour of cemented and uncemented soils should therefore be carried out on samples with the same gradings for cemented samples it is possible to identify a yield curve outside the state boundary surface of the uncemented soil a framework for the behaviour has been defined which depends on the relative magnitudes of the confining pressure and cement bond strength the behaviour of a natural cal carenite agreed well with this framework which is also likely to be applicable to other cemented soils le comportement d un sable carbonate artificiellement cimente a ete etudie a l aide d essa

on the mechanics of structured sands to date the effect of structure on the behaviour of natural sands has focused almost exclusively on the component of bonding and the effect of fabric has been largely overlooked the paper describes a detailed investigation of the behaviour of two natural sands by means of triaxial testing over a wide range of pressures one material had bonding as the principal element of its structure and the other fabric following on from a paper of cuccovillo and coop which examined the influence of the two structural elements on the small strain stiffness the current paper develops a new framework for the yielding and large strain behaviour it is suggested that structure should be considered as an element of the nature of a sand in addition to properties such as mineralogy particle shape and grading the resulting framework is then capable of encompassing the patterns of behaviour seen for both bonding and fabric dominated sands while bonding results in a cohesive mode of shearing it is demonstrated that when

spatial relation between main earthquake slip and its aftershock distribution 1 we examine where aftershocks occur relative to the spatial distribution of the main shock slip using data from several recent large earthquakes no universal relation between high and low moment regions and high or low aftershock occurrence or vice versa is found we generally find that few and usually the smaller aftershocks occur in the high slip regions of the fault a notable exception to this being the great 1996 biak indonesia subduction zone earthquake in all cases aftershocks occur on favorably oriented planes of weakness in regions of increased postseismic stress generally they are clustered at both ends of faults but examples where aftershocks occur only at one end or where there is no clustering at the ends are found aftershock clusters are also found at the edge of unbroken barriers and regions of rapid transition from high to low slip within the main fault area we identify examples of geometrical and inhomogeneous barriers and sharp and dull stress concentrations rupture in the main shock is generally found to nucleate in the region of low slip or at the edge of high slip regions the 1996 biak earthquake again being the only exception nucleating in a very high slip region off fault aftershocks are found for all earthquakes in this study and they sometimes rupture the nodal plane conjugate to the main shock fault plane

effect of cementation on the small strain parameters of sands natural cementation affects the properties of soils the interpretation of in situ and laboratory test results and the selection of criteria for geotechnical design in this paper published exper

phantom earthquakes and triggered aseismic creep vertical partitioning of strain during earthquake sequences in iran 1 we present evidence for significant aseismic fault slip at shallow depth above a pair of mainshock aftershock sequences in the zagros mountains of iran the two mw 5 9 earthquakes are each spanned by high quality geodetic imagery and have well recorded sequences of aftershocks that occurred beneath a salt decollement earlier studies of the geodetic data inferred that the mainshocks were located above the decollement requiring a 10 km spatial separation between aftershock cluster and earthquake centroid we find that the geodetic data simultaneously allow two slip sources of similar magnitude one within the basement collocated with aftershocks and one shallow source also equivalent to mw 6 responsible for the primary signal apparent in the geodetic imagery should this phenomenon be widespread in the zagros it would partially explain a previously noted discrepancy between observed seismic moment release in the zagros and current convergence rates between the arabian and eurasian plates

miocene to holocene exhumation of metamorphic crustal wedges in the nw himalaya evidence for tectonic extrusion coupled to fluvial erosion the himalayan crystalline core zone exposed along the sutlej valley india is composed of two high grade metamorphic gneiss sheets that were successively underthrusted and tectonically extruded as a consequence of the foreland directed propagation of crustal deformation in the indian plate margin the high himalayan crystalline sequence hhcs is composed of amphibolite facies to migmatitic paragneisses metamorphosed at temperatures up to 750 c at 30 km depth between eocene and early miocene during early miocene combined thrusting along the main central thrust mct and extension along the sangla detachment induced the rapid exhumation and cooling of the hhcs whereas exhumation was mainly controlled by erosion since middle miocene the lesser himalayan crystalline sequence lhcs is composed of amphibolite facies para and orthogneisses metamorphosed at temperatures up to 700 c during underthrusting down to 30 km depth beneath the mct the lhcs cooled very rapidly since late miocene as a consequence of exhumation controlled by thrusting along the munsiari thrust and extension in the mct hanging wall this renewed phase of tectonic extrusion at the himalayan front is still active as indicated by the present day regional seismicity and by hydrothermal circulation linked to elevated near surface geothermal gradients in the lhcs as recently evidenced in the himalayan syntaxes active exhumation of deep crustal rocks along the sutlej valley is spatially correlated with the high erosional potential of this major trans himalayan river this correlation supports the emerging view of a positive feedback during continental collision between crustal scale tectono thermal reworking and efficient erosion along major river systems

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

seismic site classification and correlation between standard penetration test n value and shear wave velocity for lucknow city in indo gangetic basin subsurface lithology and seismic site classification of lucknow urban center located in the central part of the indo gangetic basin igb are presented based on detailed shallow subsurface investigations and borehole analysis these are done by carrying out 47 seismic surface wave tests using multichannel analysis of surface waves masw and 23 boreholes drilled up to 30 m with standard penetration test spt n values subsurface lithology profiles drawn from the drilled boreholes show low to medium compressibility clay and silty to poorly graded sand available till depth of 30 m in addition deeper boreholes depth 150 m were collected from the lucknow jal nigam water corporation government of uttar pradesh to understand deeper subsoil stratification deeper boreholes in this paper refer to those with depth over 150 m these reports show the presence of clay mix with sand and kankar at some locations till a depth of 150 m followed by layers of sand clay and kankar up to 400 m based on the available details shallow and deeper cross sections through lucknow are presented shear wave velocity swv and n spt values were measured for the study area using masw and spt testing measured swv and n spt values for the same locations were found to be comparable these values were used to estimate 30 m average values of n spt n30 and swv vs30 for seismic site classification of the study area as per the national earthquake hazards reduction program nehrp soil classification system based on the nehrp classification the entire study area is classified into site class c and d based on vs30 and site class d and e based on n30 the issue of larger amplification during future seismic events is highlighted for a major part of the study area which comes under site class d and e also the mismatch of site classes based on n30 and vs30 raises the question of the suitability of the nehrp classification system for the study region further 17 sets of spt and swv data are used to develop a correlation between n spt and swv this represents a first attempt of seismic site classification and correlation between n spt and swv in the indo gangetic basin

extension on the tibetan plateau recent normal faulting measured by insar and body wave seismology we use insar and body wave modelling to determine the faulting parameters for a series of five mw 5 9 7 1 normal faulting earthquakes that occurred during 2008 including the march 20 yutian earthquake mw 7 1 one of the largest normal faulting events to have occurred recently on the continents we also study three earlier normal faulting earthquakes that occurred in southern tibet between 1992 and 2005 coseismic deformation for each of these eight events is measured with ascending and descending interferograms from envisat ers and alos sar data elastic dislocation modelling of the line of sight insar displacements and body wave seismological modelling of p and sh waves are used to estimate fault parameters and are found to be in good agreement for all the events studied the use of insar to measure deformation allows a relatively precise determination of the fault location in addition to resolving the focal plane ambiguity only five of the eight events are associated with a clear surface topographic feature suggesting that an underestimation of the amount of extension would result from using the surface expressions of normal faulting alone the observations in all cases are consistent with slip on planar surfaces with dips in the range 40 50 that penetrates the uppermost crust to a depth of 10 15 km we find no evidence for active low angle dip less than 30 normal faulting the contribution of the normal faulting to overall extension estimated by summing seismic moments over earthquakes for the past 43 yr is 3 4 mm yr 1 or 15 20 per cent of the rates of extension measured across the plateau using gps 85 per cent of the moment release in normal faulting over the past 43 yr has occurred in regions whose surface height exceeds 5 km this observation adds weight to the suggestions that the widespread normal faulting on the plateau is the result of variations in the gravitational potential energy of the lithosphere

source parameters for moderate earthquakes in the zagros mountains with implications for the depth extent of seismicity six earthquakes within the zagros mountains with magnitudes between 4 9 and 5 7 have been studied to determine their source parameters these events were selected for study because they were reported in open catalogs to have lower crustal or upper mantle source depths and because they occurred within an area of the zagros mountains where crustal velocity structure has been constrained by previous studies moment tensor inversion of regional broadband waveforms has been combined with forward modeling of depth phases on short period teleseismic waveforms to constrain source depths and moment tensors our results show that all six events nucleated within the upper crust 11 km depth and have thrust mechanisms this finding supports other studies that call into question the existence of lower crustal or mantle events beneath the zagros mountains

assessment of the structural representativeness of sample data sets for the mechanical characterization of deep formations accurate characterization of the mechanical behavior of geomaterials at depth is a fundamental need for geologic and engineering purposes laboratory tests on samples from well cores provide the material characterization in terms of mechanical response and other relevant properties representativeness of a sample data set with respect to the in situ conditions at depth is a key issue which needs to be addressed to extrapolate the laboratory response to the whole rock mass we have developed a procedure aimed at quantitatively evaluating the representativeness of laboratory samples the methodology is based on joint processing of laboratory ultrasonic tests and wellbore sonic logs a structural index is used to quantify the difference between the average structure of the laboratory sample and the structure of the formation at the wellbore scale this index could be used to identify different causes of discrepancies between the behavior of the cored samples and the behavior of the rock formation as documented by well logs then it could also be used to integrate laboratory data for the construction of a reliable geomechanical model with reference to the real in situ state the methodology was applied to three different experimental data sets showing the effectiveness of the method

behavior of hydrocarbon reservoir sands and sandstones most new oil and gas reservoirs are discovered in sands and weak sandstones and the petroleum industry has therefore generated an extensive amount of data from laboratory tests on these materials some of these data are reexamined in this paper within the context of recent soil mechanics research of key importance to petroleum engineers is the compressibility of the sands and this is shown to be related both to the current density and stress level of the soil and to the location of its normal compression line when present the cement bonds between the particles appear to be weaker than the particles themselves so that the major yield point during compression is still associated with breakage of the particles rather than of the cement bonds the paper also examines the behavior of the sands and sandstones in shearing allowing a more general understanding of the mechanics of the materials to be developed

deformation characteristics at small strains of sedimentary soft rocks by triaxial compression tests it is shown that in triaxial compression tests of sedimentary soft rocks axial strains from the axial displacement of the loading piston or specimen cap could be totally unreliable due to bedding errors at the top and bottom ends of a specimen a local deformation transducer was used to measure axial strains free from the bedding error continuously from less than 0 001 to about 1 at strains less than about 0 001 the deformations are virtually linear recoverable and strain rate independent and their values of young s modulus are virtually the same as those obtained from field shear wave velocities the deformations become non linear before strain reaches 0 01 at a strain of 0 1 and at the stress level of half the peak strength which are the typical largest strain and stress levels in soft rock at working load levels the secant young s moduli are still about half of m the ratio of m x to the compressive strength ranges from about 400 to 1000 about 100 is suggested by many previous studi

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

plio plistocene in sequence thrust propagation along the main central thrust zone kumaon garhwal himalaya india new thermochronological data abstract the kumaon and garhwal himalayas nw india have similar geologic tectonic topographic and precipitation pattern however low temperature thermochronological age pattern varies significantly along the strike as well as across the strike of major faults here we interpret the new set of thermochronological age data across the strike of major faults namely vaikrita thrust vt munsiari thrust mt berinag thrust bt and the baijnath nappe along pindari valley in the kumaon garhwal himalaya in the present work 18 new apatite fission track aft ages of samples collected along a north south transect have been reported ages in the hanging wall of vt which range from 2 1 0 2 to 4 2 0 7 ma have been found to be becoming younger linearly with distance from north to the vt this trend crosses the vt with significant jump in ages in the south of the vt ages are lying between 0 3 0 1 and 3 9 0 8 ma and show linear variation with distance from the vt to bt no significant jump in ages across the mt is observed and the linear trend of younging southward is continuing till the bt the break and displacement in age pattern with youngest ages close to thrusts possibly indicate progressive late thrust movement it reflects sequential uplift and cooling towards the south from the vt to bt which is consistent with an in sequence style of thrust propagation we compare our new data to the published thermochronological data from its adjacent traverses along the goriganga and dhauliganga valleys 25 km away from the present traverse towards east and west respectively in the kumaon garhwal himalaya in order to understand potential along strike variations in the kinematics our observations indicate a dynamic coupling between tectonic and surface processes in the garhwal kumaon himalaya and support that the geometry of crustal scale faults and their associated kinematics control exhumation pathways of rocks

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

new views on earthquake faulting in the zagros fold and thrust belt of iran the zagros fold and thrust belt is amongst the world s most seismically active mountain ranges and is influential in our understanding of continental collisions the presence of hormuz salt at the base of the 10 km thick folded sedimentary cover together with the general absence of coseismic surface rupturing have led to an assumption that earthquakes are concentrated within the basement here we reinterpret the seismicity of the zagros in light of insar studies that show some recent earthquakes ruptured the competent group of mechanically strong strata in the lower sedimentary cover local network data demonstrate that microseismicity occurs within the basement reaching depths of 20 km and in places 30 km centroid depths of larger mw 5 earthquakes are mostly 4 14 km with rare events up to 20 km and 28 km along the oman line within the simply folded belt most of these events are contained within the competent group and are limited to mw 6 5 earthquakes occur earthquakes within the competent group can account for much of the overall shortening at this level but the seismic strain rate in the basement is much lower it is unclear whether the basement deforms by aseismic creep or folding beneath the sfb or by ductile shortening beneath the high zagros or iranian plateau

orogenic plateau growth expansion of the turkish iranian plateau across the zagros fold and thrust belt 1 this paper shows how the turkish iranian plateau grows laterally by incrementally incorporating adjacent parts of the zagros fold and thrust belt the limit of significant seismogenic thrusting in the zagros mw 5 occurs close to the regional 1250 m elevation contour the seismicity cutoff is not a significant bedrock geology boundary elevations increase northward toward regional plateau elevations of 2 km implying that another process produced the extra elevation between the seismogenic limit of thrusting and the suture this process is a plausibly ductile thickening of the basement suggesting depth dependent strain during compression similar depth dependant crustal strain may explain why the tibetan plateau has regional elevations 1500 m greater than the elevation limit of seismogenic thrusting at its margins we estimate 68 km shortening across the zagros simply folded belt in the fars region and 120 km total shortening of the arabian plate the dezful embayment is a low strain zone in the western zagros deformation is more intense to its northeast in the bakhtyari culmination the orogenic taper across strike topographic gradient across the dezful embayment is 0 0004 and across the bakhtyari culmination 0 022 lateral plateau growth is more pronounced farther east fars where a more uniform structure has a taper of 0 010 up to elevations of 1750 m a 100 km wide region of the zagros further northeast has a taper of 0 002 and is effectively part of the turkish iranian plateau internal drainage enhances plateau development but is not a pre requisite aspects of the seismicity structure and geomorphology of the zagros do not support critical taper models for fold and thrust belts

active accommodation of plate convergence in southern iran earthquake locations triggered aseismic slip and regional strain rates 1 we present a catalog of interferometric synthetic aperture radar insar constraints on deformation that occurred during earthquake sequences in southern iran between 1992 and 2011 and explore the implications on the accommodation of large scale continental convergence between saudi arabia and eurasia within the zagros mountains the zagros mountains a salt laden fold and thrust belt involving 10 km of sedimentary rocks overlying precambrian basement rocks have formed as a result of ongoing continental collision since 10 20 ma that is currently occurring at a rate of 3 cm yr we first demonstrate that there is a biased misfit in earthquake locations in global catalogs that likely results from neglect of 3 d velocity structure previous work involving two m 6 earthquakes with well recorded aftershocks has shown that the deformation observed with insar may represent triggered slip on faults much shallower than the primary earthquake which likely occurred within the basement rocks 10 km depth we explore the hypothesis that most of the deformation observed with insar spanning earthquake sequences is also due to shallow triggered slip above a deeper earthquake effectively doubling the moment release for each event we quantify the effects that this extra moment release would have on the discrepancy between seismically and geodetically constrained moment rates in the region finding that even with the extra triggered fault slip significant aseismic deformation during the interseismic period is necessary to fully explain the convergence between eurasia and saudi arabia

finite element inversion of dinsar data from the mw 6 3 l aquila earthquake 2009 italy 1 fault slip distribution is usually retrieved from geodetic data assuming that the local crust is an elastic homogeneous and isotropic half space in the last decades spatially dense geodetic data e g dinsar maps have highlighted complex patterns of coseismic deformation that require new modeling tools such as numerical methods able to represent rheological and geometrical complexities of the earth s crust in this work we develop a procedure to perform inversion of geodetic data based on the finite element method accounting for a more realistic description of the local crust the method is applied to the 2009 l aquila earthquake mw 6 3 using dinsar images of the coseismic displacement results highlight the non negligible influence of the medium structure homogeneous and heterogeneous models show discrepancies up to 20 in the fault slip distribution values furthermore in the heterogeneous models a new area of slip appears above the hypocenter we also perform a resolution study showing that the information about fault slip distributions retrieved from geodetic data should be considered as averaged on surrounding patches