the 2008 nura earthquake sequence at the pamir tian shan collision zone southern kyrgyzstan this research was funded by dfg bundle tipage pak 443 the came project bundle tiptimon funded by the german federal ministry of education and research support code 03g0809 and gfz we acknowledge funding for the earthquake task force deployment by gfz and the hannover ruck reinsurance company

the liquefaction of clayey soils under cyclic loading abstract this paper seeks to investigate the liquefaction of clayey soils a phenomenon that has been the trigger for many natural disasters in the last few decades including landslides research was conducted on artificial clay sand mixtures and natural clayey soils collected from the sliding surfaces of earthquake induced landslides the undrained response of normally consolidated clayey soils to cyclic loading was studied by means of a ring shear apparatus for the artificial clay sand mixtures it was found that the presence of a small amount of bentonite 7 would cause rapid liquefaction while a further increase in bentonite content 11 produced the opposite effect of raising soil resistance to liquefaction by a significant degree it was demonstrated that the bentonite sand mixture was considerably more resistant to liquefaction than the kaolin and illite mixtures given the same clay content the test results of plastic soils revealed the significant influence of plasticity on the liquefaction resistance of soil the microfabric of clayey soil was investigated by means of a scanning electron microscope the analysis showed that the liquefaction potential of soil was strongly related to certain particle arrangements for example soil vulnerable to liquefaction had an open microfabric in which clay aggregations generally gathered at the sand particle contact points forming low strength clay bridges that were destroyed easily during cyclic loading on the other hand the microfabric of soil that was resistant to liquefaction appeared to be more compact with the clay producing a matrix that prevented sand grains from liquefying in the case of the natural soils the obtained results indicated that their cyclic behavior was similarly influenced by factors such as clay content clay mineralogy and plasticity the relation between the liquefaction potential of natural soil and its microfabric was thus also established on the basis of the obtained results the authors posited an explanation on the mechanism of liquefaction for clayey soil

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

effects of confining stress density and initial static shear stress on the cyclic shear response of fine grained unclassified tailings a constant volume direct simple shear apparatus was used to investigate the effects of confining stress initial static shear stress and void ratio on the liquefaction resistance of fine grained tailings the cyclic resistance ratio also expressed as the overburden stress correction factor was found to decrease with increasing confining stresses in the range 100 400 kpa and to gradually increase from 400 kpa onwards when samples were tested at the same initial void ratio the presence of an initial static shear stress decreased the liquefaction resistance a key outcome of the work was to reveal the critical importance of density on liquefaction susceptibility of compressible tailings thus a combined correction factor to account for overburden stress and density on cyclic resistance was proposed

undrained cyclic shear behaviour of weathered tephra weathered tephra is prevalent across volcanic islands like the north island of new zealand and is composed of volcanic airfall materials that have been subjected to various soil processes understa

surface motions and intraplate continental deformation in alaska driven by mantle flow the degree to which the lithosphere and mantle are coupled and contribute to surface deformation beneath continental regions remains a fundamental question in the field of geodynamics here we use a new approach with a surface deformation field constrained by gps geologic and seismicity data together with a lithospheric geodynamic model to solve for tractions inferred to be generated by mantle convection that 1 drive extension within interior alaska generating southward directed surface motions toward the southern convergent plate boundary 2 result in accommodation of the relative motions between the pacific and north america in a comparatively small zone near the plate boundary and 3 generate the observed convergence within the north american plate interior in the mackenzie mountains in northwestern canada the evidence for deeper mantle influence on surface deformation beneath a continental region suggests that this mechanism may be an important contributing driver to continental plate assemblage and breakup

index properties based criteria for liquefaction susceptibility of clayey soils a critical assessment the cooper marl in charleston s c a deep layer of clayey soils approximately 5 21 m below the ground surface is generally recognized as nonliquefiable material data from field cone penetration tests and laboratory tests of samples taken from the cooper marl are used to investigate the adequacy of index properties based criteria for assessing liquefaction susceptibility of clayey soils in particular the criterion based on soil behavior type index ic and that based on atterberg limits are examined the results show that the atterberg limits based criterion adequately reflected the characteristics of the marl whereas the ic based criterion erroneously identified the marl as being liquefiable a possible reason for the deficiency of ic and a modification to overcome this deficiency are presented

deep burial of asian continental crust beneath the pamir imaged with local earthquake tomography an inclined zone of intermediate depth seismicity beneath the pamir orogen in central asia has been interpreted as southward subduction of a slab of asian lithosphere however it is not known whether asian lithosphere subducts intact or only partially we used arrival times of shallow and intermediate depth earthquakes recorded with a temporary 2008 2010 seismic network in this region to invert for 3d models of seismic velocities in an attempt to answer this question with local seismicity reaching depths of up to 240 km the deep structure of the pamir could be illuminated with high resolution the resulting velocity models show a north south contrast in crustal seismic velocities in the pamir with very low p velocities 5 7 5 9 km s at 15 30 km depth coupled with relatively low vp vsvp vs 1 70 at mid crustal levels in the southern part of the orogen at sub moho depths we image an arcuate high velocity 8 2 8 6 km s slab dipping south in the eastern pamir and east in the pamir s southwest underlying the intermediate depth earthquakes on top of the high velocity slab and just above the onset of deep seismicity between a depth of 60 to 100 km very low compressional wavespeeds around 7 1 km s and high vp vsvp vs ratios 1 80 attest to subducted crustal rocks additionally we carried out 2d numerical thermomechanical modeling of the continental collision in the pamir focusing on the fate of the crust and mantle lithosphere of the asian and indian plates seismic velocities were computed from the modeling results and the resulting images were compared with the velocity distributions obtained from seismic traveltimes combining tomography and modeling results we infer that a substantial amount of crustal material is pulled down beneath the pamir by cold mantle lithosphere to depths of at least 80 100 km from there on only lower crust and mantle lithosphere continue their subduction and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions the buoyant asian upper and middle crust does not penetrate deeper into the mantle but pools at this depth level from where it might eventually exhume or relaminate

lithospheric structure and crust mantle decoupling in the southeast edge of the tibetan plateau abstract convergence between the indian plate and the eurasian plate has resulted in the uplift of the tibetan plateau and understanding the associated dynamical processes requires investigation of the structures of the crust and the lithosphere of the tibetan plateau yunnan is located in the southwest edge of the plateau and adjacent to myanmar to the west previous observations have confirmed that there is a sharp transition in mantle anisotropy in this area as well as clockwise rotations of the surface velocity surface strain and fault orientation we use s receiver functions from 54 permanent broad band stations to investigate the structures of the crust and the lithosphere beneath yunnan the depth of the moho is found to range from 36 to 40 km beneath southern yunnan and from 55 to 60 km beneath northwestern yunnan with a dramatic variation across latitude 25 26 n the depth of the lithosphere asthenosphere boundary lab ranges from 180 km to less than 70 km also varying abruptly across latitude 25 26 n which is consistent with the sudden change of the fast s wave direction from nw se to e w across 26 28 n in the north of the transition belt the lithosphere is driven by asthenospheric flow from tibet and the crust and the upper mantle are mechanically coupled and moving southward because the northeastward movement of the crust in the burma micro plate is absorbed by the right lateral sagaing fault the crust in yunnan keeps the original southward movement however in the south of the transition belt the northeastward mantle flow from myanmar and the southward mantle flow from tibet interact and evolve into an eastward flow by momentum conservation as shown by the structure of the lab this resulting mantle flow has a direction different from that of the crustal movement it is concluded that the sagaing fault causes the west boundary condition of the crust to be different from that of the lithospheric mantle thus leading to crust mantle decoupling in yunnan

geometry of the pamir hindu kush intermediate depth earthquake zone from local seismic data 1 we present new seismicity images based on a two year seismic deployment in the pamir and sw tien shan a total of 9532 earthquakes were detected located and rigorously assessed in a multistage automatic procedure utilizing state of the art picking algorithms waveform cross correlation and multi event relocation the obtained catalog provides new information on crustal seismicity and reveals the geometry and internal structure of the pamir hindu kush intermediate depth seismic zone with improved detail and resolution the relocated seismicity clearly defines at least two distinct planes one beneath the pamir and the other beneath the hindu kush separated by a gap across which strike and dip directions change abruptly the pamir seismic zone forms a thin approximately 10 km width curviplanar arc that strikes east west and dips south at its eastern end and then progressively turns by 90 to reach a north south strike and a due eastward dip at its southwestern termination pamir deep seismicity outlines several streaks at depths between 70 and 240 km with the deepest events occurring at its southwestern end intermediate depth earthquakes are clearly separated from shallow crustal seismicity which is confined to the uppermost 20 25 km the hindu kush seismic zone extends from 40 to 250 km depth and generally strikes east west yet bends northeast toward the pamir at its eastern end it may be divided vertically into upper and lower parts separated by a gap at approximately 150 km depth in the upper part events form a plane that is 15 25 km thick in cross section and dips sub vertically north to northwest seismic activity is more virile in the lower part where several distinct clusters form a complex pattern of sub parallel planes the observed geometry could be reconciled either with a model of two sided subduction of eurasian and previously underthrusted indian continental lithosphere or by a purely eurasian origin of both pamir and hindu kush seismic zones which necessitates a contortion and oversteepening of the latter

investigation of the effect of surface heterogeneity and topography on the radiation environment of palmer station antarctica with a hybrid 3 d radiative transfer model we have developed and used a monte carlo radiative transfer code to investigate how surface topography and heterogeneous snow ice distributions affect the downwelling irradiance at palmer station antarctica 64 76 s 64 07 w the monte carlo calculations treat a three dimensional 3 d atmospheric volume which extends from the surface to 100 km altitude and has a 20 km 20 km footprint on the southwest coast of anvers island the radiative transfer calculations include the effects of molecular absorption rayleigh scattering and clouds the surface interaction is modeled explicitly the trajectories of reflected photons are computed from stochastic bidirectional directional reflectance functions and their paths are traced through multiple interactions with complex surface features computed results for a range of cloud optical depth solar zenith angle and surface albedo are presented comparisons of the 3 d model calculations to plane parallel model predictions show that the effective albedo which characterizes a given ice distribution is affected by regions surprisingly far from the point of interest under low clouds zcloud 1 km surface irradiance measurements over a snow surface are significantly affected by the dark ocean surface more than 7 km away for the opposite case of irradiance observations over ocean the effect of a distant snow surface is not significant at ranges greater than 2 or 3 km since the radius of influence depends on atmospheric transmission and surface albedo the effective albedo varies spectrally neglect of this nonlocal albedo effect may significantly degrade the accuracy of radiation diagnostics that depend on spectral intensity ratios

seismic domains within the gissar kokshal seismic zone soviet central asia by evaluating seismological data from the belt of shallow intraplate seismicity known as the gissar kokshal seismic zone in soviet central asia in conjunction with recent data on the shallow crustal structure and longer term geologic deformation we show that certain size classes of earthquakes are characteristic of adjacent and in some places overlapping geologic tectonic settings we call these settings seismic domains they are both geologically and seismologically distinct i e they contain different rocks and structures and have different frequency magnitude relationships for example in terms of number of events gissar kokshal seismicity is dominated by the microearthquakes that have occurred within the sedimentary rocks of the vakhsh fold thrust belt these are all shallow and have occurred mostly within the frontal portions of the thrust sheets more rarely moderate size m 5 5 earthquakes have ruptured the thrust ramps on the other hand the major strain release in this region has accompanied the large 5 5 m 8 1 shallow earthquakes on basement faults in the southern gissar range adjacent to the fold thrust belt within these ranges there is relatively little microearthquake activity that dichotomy indicates that a significantly different seismic hazard is associated with each of these areas but the seismological distinction is obscured along the front of the fold thrust belt where the domain of small shocks in the sedimentary rocks overlaps the domain of large earthquakes on basement faults to explain the localization of the large basement events along the southern flank of the fold thrust belt adjacent to the fold thrust belt we hypothesize a mechanism of thrust sheet loading thrust loads are greatest in this region since thrust sheets have overridden large basement block uplifts beneath the illiac and peter the first range faults

effect of sastrugi on snow bidirectional reflectance and its application to modis data 1 snow surface roughness such as sastrugi on the antarctic ice sheet can be a cause of error for remote sensing of snow parameters the effect of sastrugi on snow bidirectional reflectance was assessed by a field experiment model simulations and satellite measurements the hemispherical directional reflectance factor hdrf of artificial sastrugi like linear ridges measured at nakasatsunai hokkaido japan exhibited different patterns from that of a flat surface with the difference of more than 50 for some geometries a 3 d monte carlo radiative transfer model mc model reproduced both the hdrf measurements for the artificial ideal sastrugi and previous measurements for natural sastrugi at the south pole furthermore the sastrugi effect was applied to remote sensing failure to include the surface roughness in models for developing snow grain size lookup tables can lead to order of magnitude retrieval errors using the mc model and multiangle data derived from the moderate resolution imaging spectrometer over the south pole during the 2003 2004 summer the sastrugi and snow parameters were retrieved the height to width ratio of sastrugi reduced from 0 1 to 0 02 whereas the azimuth angle was nearly constant within the range of 0 30 during the summer the snow grain size showed a seasonal variation which depended on the spectral channel these retrieved parameters were consistent with existing ground measurements the results suggest that a combination of multiangle data and a 3 d radiative transfer model can be used to quantitatively estimate surface roughness along with snow grain size on ice sheets

modeling the evolution of continental subduction processes in the pamir hindu kush region several geological and geophysical studies suggest the presence of two converging subduction zones in the western syntaxis of the india eurasia collision zone with steep northward subduction of indian lithosphere beneath the hindu kush and southward subduction of asian lithosphere under the pamir we investigate the geometry and the timing of these subduction processes seismic tomography images are used to constrain the geometry of the two slabs under the pamir and the hindu kush by measuring the tomographically inferred length of the indian slab under the hindu kush region and by comparison with paleomagnetic reconstructions we estimate that the process of indian slab break off most likely occurred at the early stage of the collision at ca 44 48 ma we infer that after slab break off western india continued its northward motion until its northern boundary reached the present hindu kush region where it began to subduct we estimate an age for the initiation of subduction in this region of about 8 ma we apply 2d thermo kinematic and rheological numerical modeling to compute the temperature distribution and brittle field along two vertical sections across the hindu kush and pamir regions for the hindu kush we introduce parameters reproducing fast and near vertical subduction whereas in the pamir region we use the results from published studies to reproduce slower subduction modeling results indicate that faster subduction under the hindu kush results in a deeper brittle region which is consistent with observed deeper seismicity than in the pamir region

cenozoic thermo tectonic evolution of the northeastern pamir revealed by zircon and apatite fission track thermochronology abstract the northeastern pamir is a key location to explore asian intracontinental tectonic processes during the cenozoic new zircon fission track zft data show a 20 to 50 km wide region of partially reset ages on the northeastern margin of the pamir salient interpreted as an exhumed and tilted partial annealing zone paz widespread zft age peaks at 50 ma within the zft paz likely date early motion of the kashgar yecheng transfer system kyts but suggest this fault system was narrower in the early cenozoic than it is today apatite fission track aft ages of 10 6 ma combined with field observations across the kyts hint at an episode of strong thrusting related exhumational cooling which indicates that the modern fault system probably formed at this time to the southwest of the kyts the combination of new fission track and existing thermochronology data allows establishing temperature time trajectories that present diachronous rapid cooling from 450 to 120 c in the sares 13 10 ma muztagata 10 7 ma and kongur shan 3 1 ma domes rapid cooling in the eastern sares and southern muztagata massifs is driven by doming as supported by kinematic analyses of the shen ti fault successive rapid cooling of these massifs confirms eastward propagation of doming processes shortly postdating magma emplacement at 11 ma we propose that the synchronicity of regional tectonism magmatism and metamorphism implies that strong crustal thickening and contraction occurred beneath the northeastern pamir during the middle late miocene possibly associated with initial collision between the pamir and tian shan

cyclic resistance ratio of pleistocene age sands from the south carolina coastal plain abstract field and laboratory tests were performed on sandy soils from three pleistocene age sites in the south carolina coastal plain to investigate the age related resistance to liquefaction reported research indicates that liquefaction resistance of sands increases with the age of the deposit and that liquefaction may reset the aging clock the stress controlled cyclic triaxial test was used to determine the cyclic strength of soil deposits with geologic ages of approximately 200 000 450 000 and 1 400 000 years and evidence of sand blows that are 467 to 4185 years old specimens were obtained using a fixed piston sampler frozen ex situ and include naturally occurring differences in fabric cyclic stress ratios ranging from 0 135 to 0 225 were used to determine the peak deviator stress applied during the cyclic triaxial test and were initially estimated from two age based methods which were found to over estimate the laboratory cyclic stress ratio estimates of the at rest earth pressure coefficient were applied to the laboratory cyclic resistance ratio which resulted in field cyclic resistance ratios that ranged from 0 100 for the oldest deposit 1 400 000 years to 0 131 for the mid aged deposit 450 000 years for initial liquefaction occurring when the generated excess pore pressure was equal to the effective confining stress of 100 kpa ru 1 0 at n equal to 15 cycles the carbon dated age of the sand blow events correlated with the field cyclic resistance ratios the geologic ages of the soil deposits did not a correlation between the clay content not the fines content was observed

influence of silt size and content on liquefaction behavior of sands this study investigates the fines content influence on liquefaction potential of a single base sand mixed with three different essentially nonplastic silts through strain controlled monotonic undra

earthquake induced liquefaction features in a late quaternary fine grained lacustrine succession fucino lake italy implications for microzonation studies abstract the fucino lacustrine basin in central italy is a large flat area mostly devoted to agriculture with urbanization along the perimeter of the ancient lake in 1915 a strong earthquake struck the area mw 7 0 producing large damages and geological effects including surface faulting ground failures and liquefaction a channel excavated in the lacustrine sediments exposed ground failure with dykes of fine grained sediment that we interpret as the result of earthquake induced liquefaction we present the results of a multidisciplinary work aimed at characterizing in detail the geology of the buried stratigraphic succession its susceptibility to liquefaction and the likely source of the fine grained liquefied material the succession down to 20 m deep is formed by fine grained sediments younger than 170 180 kyrs mostly late pleistocene holocene prevailingly silt or silt clay mixtures the geological field analysis indicates that the dykes are filled by prevailing silt liquefied and transported by upward directed flow of short duration as for earthquake induced liquefaction tilting and lateral spreading accompanied the process the overall liquefaction potential derived from the simplified methods is high correlations of x ray powder diffraction mineralogy of samples from drilling cores with those from dykes allowed us to identify the most likely source layer filling dykes corresponding to a silt layer at 7 8 m depths this layer and the dykes lack illite and montmorillonite clay particles these results contribute to improve studies of liquefactions in sediments that differ from typical liquefiable loose sands they have also implications for microzonation studies most samples show grain size curves that do not fit within the field of potentially liquefiable soils suggesting that criteria based on grain size can be poorly significant in seismic microzonation studies of recent late pleistocene holocene lacustrine fine grained successions

measurements of erythemal irradiance near davis station antarctica effect of inhomogeneous surface albedo to examine effects of inhomogeneous surface albedo on uv irradiance measurements were taken near davis station 68 58 s 77 97 e east antarctica during november december 1997 data were collected in transects perpendicular to an ice water boundary while one instrument continuously measured at the ice edge irradiances along transects were normalised by coincident measurements at the ice edge systematic differences in downwelling irradiance near the ice edge were observed over the highly reflective surface and open water for cloudless conditions the relative change in irradiance reached limiting values of about 5 from the ice edge to a point 2 5 km over snow covered ice and about 5 from the ice edge to a point 2 5 km over water in overcast conditions higher relative changes were observed about 30 from the ice edge to a point 2 5 km over ice on 17 november 1997 with no sign of a constant relative change being reached

active tectonics of the pamirs and karakorum the source parameters of moderate to large sized earthquakes and the spatial distribution of earthquake hypocenters are used to investigate the active tectonics and three dimensional configuration of the subducted lithosphere in the pamir karakorum intracontinental convergence zone the continental collision has resulted in intense deformation in the upper crust the deformation is distributed over a broad area and is absorbed by thrust and strike slip faulting along the northern margin of the pamirs where the deformation due to continental collision is most intense the northern pamir thrust and several major fault zones mark the present boundary most of the earthquakes that occurred in these fault zones are shallow crustal events with focal mechanism solutions correlated with the tectonic features of the region along the pamir front thrust faulting dominates while on the western and eastern edges of the pamirs the style of deformation is characterized by oblique thrusting with a component of strike slip motion thrust type events beneath the tadjik depression indicate that both the sedimentary rocks and the basement are involved in shortening right lateral strike slip motion is observed on the eastern edge of the pamirs where they border the tarim basin and in the talas fergana kun lun fault zone a southward dipping seismic zone beneath the pamirs and karakorum indicates that the asian lithosphere has been subducted along the pamir front to a depth of at least 200 km this interpretation is consistent with published geological and geophysical data focal mechanism solutions of some intermediate depth events beneath the pamirs show strike slip faulting with approximately n s horizontally oriented p axes indicating that nearly horizontal compression at the intermediate depth is the predominant mode of deformation a 90 km deep event beneath the karakorum is interpreted as occurring in the subducted asian lithosphere the fact that the p axis of this event is oriented parallel to the descending plate suggests downdip compression within the asian lithosphere the overall tectonics of the region is interpreted as a consequence of the underthrusting asian lithosphere being impinged upon by the shallow northward underthrusting indian lithosphere

earthquake focal mechanisms deformation state and seismotectonics of the pamir tien shan region central asia this paper presents a review of the seismotectonics of the pamir tien shan collision zone in the garm region tajikistan based on geological structure seismicity and focal mechanism solutions the region is dominated by horizontal compression manifested by imbricate low angle thrust faults that separate the upper crust into a series of tectonic sheets these thrust systems verge northward from the tajik depression toward the southern tien shan and southward toward the northern pamir the pattern of seismicity across the region suggests that similar low angle thrust faults exist within the crystalline basement as well in order to reconstruct the present day stress strain state of the region we used data from over 15 000 earthquake focal mechanism solutions for small earthquakes m 1 0 gathered over the 27 year period 1963 1989 the method of reconstruction of the seismotectonic deformation std field involves dividing the data set into small spatial windows and summing the individual focal mechanism solutions to form an average earthquake mechanism tensor for each cell the std state of that cell can then be represented by the orientation of the principal axes of compression and tension the intensity or relative uniformity of the average mechanism and the lode nadai coefficient which defines the relation between the magnitudes of the principal strain components we observe throughout the study area a general predominance of subhorizontal compression manifested in a mixture of thrust and strike slip deformation normal fault deformation is observed in only two small portions of the study area the orientation of principal compression varies from nearly n s in the northern pamir and the southern tien shan to nw se in the peter the first range in general the std field has a clearly developed mosaic structure defined by spatial groupings of nearly uniform orientations of compression and tension axes the boundaries of these groups cannot in most cases be directly correlated with known geological contacts the std structure also shows some variation with depth with more or less uniform std orientation in the upper crust 0 14 km depth changing significantly at greater depths examination of various subsets of the focal mechanism catalog shows the spatial structure of the std field to be largely stable with respect to both time and magnitude the reliability of the reconstructed std field was verified using three approaches 1 comparison of individual focal mechanism determinations for a large subset of the data using both soviet and u s algorithms 2 comparison of std reconstruction results using the two independent focal mechanism catalogs and 3 examination of the effect of spatial sampling on the results the dominance of generally north oriented subhorizontal compression is interpreted to be primarily the result of convergence between the pamir and tien shan ranges in turn caused by the ongoing collision of india and eurasia

comment on tectonic control of yarlung tsangpo gorge revealed by a buried canyon in southern tibet wang et al reports 21 november 2014 p 978 describe a buried canyon upstream of the yarlung tsangpo gorge and argue that rapid erosion of the gorge was merely a passive response to rapid uplift at 2 5 million years ago ma we view these data as an expected consequence emerging from feedbacks between erosion and crustal rheology active well before 2 5 ma

discussion of subsurface characterization at ground failure sites in adapazari turkey by jonathan d bray rodolfo b sancio turan durgunoglu akin onalp t leslie youd jonathan p stewart raymond b seed onder k cetin ertan bol m b baturay c christensen and t karadayilar a discussion of an article with the aforementioned title published in this journal in july 2004 is presented the discussers question the authors reasoning concerning soil liquefaction without consideration of the bearing capacity failure of the foundations and the likelihood of liquefaction of the surface deposits encountered in adapazari during the 1999 earthquake while there were boils observed at several of the case sites in adapazari there is a concern that the samples might not be representative of the soil that actually liquefied it also appears that the peak ground accelerations exceeded the ultimate capacity of the foundations

least squares restoration of tertiary thrust sheets in map view tajik depression central asia the tajik depression located west of the pamirs and south of the tien shan is a compressional intermontane basin bounded by basement overthrusts and filled with mesozoic and cenozoic sediments the internal structure is typical of a thin skinned tbld and thrust belt kinematic data available in the literature suggest that indentation of the pamirs into asia durino the cenozoic collision of india and asia has been accommodated in various ways within the depression including westward extrusion thickening combined with wrenching along n s tblds and thrusts and counterclockwise rotations these various detbrmation processes can be analyzed and quantified by reconstruction of the predeformed state of the depression however the combina tion of thrusting wrenching and block rotations implies a nonplane deformation which cannot be restored properly using balanced cross sections alone we have therefore developed a numerical method for restoration of stratigraphic surfaces designed for regions of nonplane compressional tectonics the deformed region is represented in map view as a mosaic of fault bounded blocks overlapping each other along the faults blocks are separately unfolded and then numerically packed together by least squares minimization of overlaps yielding fields of finite horizontal translations and rotations about vertical axes to analyze the deformation postdating the collision of india and asia we have restored a stratigraphic surface at the base of the cenozoic first in order to test the numerical method we restored a map that had previously been restored by a purely manual method restoration of a second map drawn from newly available subsurface data leads to geometrical inconsistencies overlaps and gaps which cannot be reduced remain in the restored state after correction of these inconsistencies restoration yields a complex mode of deformation for the depression individual thrust slices have undergone counterclockwise rotations about verti cal axes the magnitudes increasing from west to east up to a maximum of 40 o near the pamirs horizontal shortening is 150 km 35 in the center of the depression and 240 km 85 in the northeastern part between the pamirs and the tien shan strike slip motions commonly not revealed by balancing cross sections are associated with thrusting on faults striking n s inde pendent paleomagnetic data and slip directions on small scale faults provide positive checks on the results of our restoration

liquefaction of silts and silt clay mixtures low plasticity silts and silty clays occur extensively in the central united states for evaluating their liquefaction potential during an earthquake no guidelines are available based on their density void ratio plasticity index standard penetration values or any other simple soil property their liquefaction behavior is not properly understood at present and is often confused with that of sand silt mixtures pore water pressures and liquefaction in silt and silt clay mixtures are discussed and the influences of plasticity index on their cyclic strength are reviewed critically it is concluded that considerable additional work is needed to fully understand the liquefaction behavior of these soils

the pamir hindu kush seismic zone as a strain marker for flow in the upper mantle we introduce a new hypothesis to explain the unusual pattern of intermediate depth earthquakes in the pamir hindu kush region of central asia in our model the seismicity of the zone is defined by a remnant piece of oceanic crust that became neutrally buoyant and now hangs in the mantle underneath the center of the active mountain belt we interpret an abrupt cutoff in seismicity shallower than 70 km under the pamir as evidence that the slab has become decoupled from the surface deformation and we suggest that the remnant slab has acted as a strain marker for flow in the upper mantle the contortion of the slab can be explained by superimposed vertical and lateral simple shear related to the western edge of the indian plate this model requires relatively low strain rates of the order of 10 15 s 1 consistent with strain rates estimated from earthquake moment release in benioff zones in contrast the double facing subduction zone model applied by a number of previous authors requires strain rates of the order of 10 13 s 1 which are much higher than inferred strain rates in subducting slabs the results are important for understanding mantle dynamics providing a unique way to measure strain in the upper mantle the implied flow field also has significant implications for the kinematics of the entire collisional plate boundary in tibet and the tien shan

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

landslides triggered by the 1949 khait earthquake tajikistan and associated loss of life abstract earthquake triggered landslides are a major geological hazard in central asia in july 1949 the m7 4 khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the tien shan mountains central tajikistan these landslides involved widespread rock slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region in the yasman valley hundreds of loess landslides coalesced to form a massive loess flow est vol 245 mm 3 that travelled up to 20 km on a slope of only 2 in an adjacent valley the khait landslide involved transformation of an earthquake triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement it travelled 7 41 km over a vertical distance of 1421 m with an estimated average velocity of 30 m s we estimate its volume as 75 mm 3 an order of magnitude less that previously published estimates the khait landslide was simulated using dan the number of casualties due to earthquake triggered landslides in the epicentral region was considerable approximately 4000 people were killed in the yasman valley loess flow as 20 villages kishlaks were overwhelmed in the khait landslide alone we estimate ca 800 people lost their lives when the villages of khait and khisorak were overrun by rapidly moving debris our data indicates that a total of approximately 7200 people were killed by earthquake triggered landslides in the epicentral region of the khait earthquake and that in terms of loss of life the 1949 yasman valley loess flow was one of the most destructive landslides in recent history

the giant shakhdara migmatitic gneiss dome pamir india asia collision zone 1 geometry and kinematics 1 cenozoic gneiss domes comprise one third of the surface exposure of the pamir and provide a window into the deep crustal processes of the india asia collision the largest of these are the doubly vergent composite shakhdara alichur domes of the southwestern pamir tajikistan and afghanistan they are separated by a low strain horst top to sse noncoaxial pervasive flow over the up to 4 km thick south pamir shear zone exhumed crust from 30 40 km depth in the 250 80 km shakhdara dome the top to nne alichur shear zone exposed upper crustal rocks in the 125 25 km alichur dome the gunt shear zone bounds the shakhdara dome in the north and records alternations of normal shear and dextral transpression it contributed little to bulk exhumation footwall exhumation along two low angle normal sense detachments resulted in up to 90 km syn orogenic n s extension extension in the southwestern pamir opposes shortening in a fold thrust belt north of the domes and in particular in the tajik depression where an evaporitic decollement facilitated upper crustal shortening gravitational collapse of the pamir plateau margin drove core complex formation in the southwestern pamir and shortening of the weak foreland adjacent to the plateau overall this geometry defines a vertical extrusion scenario comprising frontal and basal underthrusting and thickening and hanging gravitationally driven normal shear in contrast to the himalayan vertical extrusion scenario erosion in the pamir was minor preserving most of the extruded deep crust including the top of the south pamir shear zone at peak elevations throughout the dome

crustal and uppermost mantle velocity structure along a profile across the pamir and southern tien shan as derived from project tipage wide angle seismic data summary utilizing seismic refraction wide angle reflection data from 11 approximately in line earthquakes 2 d p and s velocity models and a poisson s ratio model of the crust and uppermost mantle beneath the southern tien shan and the pamir have been derived along the 400 km long main profile of the tipage tien shan pamir geodynamic program project these models show that the crustal thickness varies from about 65 5 km close to the southern end of the profile beneath the south pamir through about 73 6 km under lake karakul in the north pamir to about 57 7 km 50 km south of the northern end of the profile in the southern tien shan average crustal p velocities are low with respect to the global average varying from 6 26 to 6 30 km s 1 the average crustal s velocity varies from 3 54 to 3 70 km s 1 along the profile and thus average crustal poisson s ratio varies from 0 23 beneath the central pamir in the south central part of the profile to 0 265 towards the northern end of the profile beneath the southern tien shan the main layer of the upper crust extending from about 2 km below the earth s surface to 27 km depth below sea level b s l has average p velocities of about 6 05 6 1 km s 1 except beneath the south central part of the profile where they decrease to around 5 95 km s 1 this is in contrast to the s velocities which range from 3 4 to 3 6 km s 1 and exhibit the highest values of 3 55 3 6 km s 1 where the p velocity is lowest thus for the main layer of the upper crust is 0 26 beneath the profile except beneath the south central part of the profile where it decreases to 0 22 the low value of 0 22 for under the central pamir the along strike equivalent of the qiangtang terrane in tibet is similar to that within the corresponding layer beneath the northern lhasa and southern qiangtang terranes in central tibet and is indicative of felsic rocks rich in quartz in the state the lower crust below 27 km b s l has p velocities ranging from 6 1 km s 1 at the top to 7 1 km s 1 at the base further for this layer is 0 27 0 28 towards the northern end of the profile but is low at about 0 24 beneath the central and southern parts of the profile which is similar to the situation found in the northeast tibetan plateau the low values can be explained by felsic schists and gneisses in the upper part of the lower crust transitioning to granulite facies and possibly also eclogite facies metapelites in the lower part within the uppermost mantle the average p velocity is about 8 10 8 15 km s 1 and is about 0 26 assuming an isotropic situation then a relatively cool 700 800 c uppermost mantle beneath the profile is indicated this would in turn indicate an intact mantle lid beneath the profile an upper mantle reflector dipping from 104 km b s l 120 km from the southern end of the profile to 86 km b s l 155 km from the northern end of the profile has also been identified the preferred model presented here for the crustal and lithospheric mantle structure beneath the pamir calls for nearly horizontal underthrusting of relatively cool indian mantle lithosphere the leading edge of which is outlined by the pamir seismic zone this cool indian mantle lithosphere is overlain by significantly shortening warm asian crust the moho trough that is a feature seen beneath some other orogenic belts for example the alps and the urals beneath the northern pamir may mark the southern tip of the actively underthrusting tien shan crust along the main pamir thrust

feeding the aneurysm orogen parallel mass transport into nanga parbat and the western himalayan syntaxis the nanga parbat haramosh massif nphm western himalayan syntaxis requires an influx of mass exceeding that in the adjacent himalayan arc to sustain high topography and rapid erosional exhumation rates what supplies this mass flux and feeds this tectonic aneurysm we show using a simple 3 d model of oblique orogen convergence that velocity strain partitioning results in horizontal orogen parallel op crustal transport and the same behavior is inferred for the himalaya with op transport diverting converging crust toward the syntaxis model results also show that the op flow rate decreases in the syntaxis thereby thickening the crust and forming a structure like the nphm the additional crustal thickening over and above that elsewhere in the himalayan arc sustains the rapid exhumation of this aneurysm normally velocity strain partitioning would be minimal for the himalayan arc where the convergence obliquity is no greater than 40 however we show analytically that the himalayan system can act both as a critical wedge and exhibit strain partitioning if both the detachment beneath the wedge and the bounding rear shear zone which accommodates op transport are very weak corresponding numerical results confirm this requirement and demonstrate that a nanga parbat type shortening structure can develop spontaneously if the orogenic wedge and bounding rear shear zone can strain rate soften while active these results lead us to question whether the position of nphm aneurysm is localized by river incision as previously suggested or by a priori focused tectonic shortening of the crust in the syntaxis region as demonstrated by our models

late miocene pliocene deceleration of dextral slip between pamir and tarim implications for pamir orogenesis abstract the timing of the late cenozoic collision between the pamir salient and the tien shan as well as changes in the relative motion between the pamir and tarim are poorly constrained the northern margin of the pamir salient indented northward by 300 km during the late cenozoic accommodated by south dipping intracontinental subduction along the main pamir thrust mpt coupled to strike slip faults on the eastern flank of the orogen and both strike slip and thrust faults on the western margin the kashgar yecheng transfer system kyts is the main dextral slip shear zone separating tarim from the eastern pamir with an estimated cumulative offset of 280 km at an average late cenozoic dextral slip rate of 11 15 mm a cowgill 2010 in order to better constrain the slip history of the kyts we collected thermochronologic samples along the eastward flowing deeply incised antecedent tashkorgan yarkand river which crosses the fault system on the eastern flank of the orogen we present 29 new biotite 40 ar 39 ar ages apatite and zircon u th sm he ages and apatite fission track aft analysis combined with published muscovite and biotite 40 ar 39 ar and aft data to create a unique thermochronologic dataset in this poorly studied and remote region we constrain the timing of four major n trending faults the latter three are strands of the kyts the westernmost the kuke fault experienced significant dip slip west side up displacement between 12 and 6 ma to the east within the kyts our new thermochronologic data and geomorphic observations suggest that the kumtag and kusilaf dextral slip faults have been inactive since at least 3 5 ma long term incision rates across the aertashi dextral slip fault the easternmost strand of the kyts are compatible with slow horizontal slip rates of 1 7 5 3 mm a over the past 3 to 5 ma in summary these data show that the slip rate of the kyts decreased substantially during the late miocene or pliocene furthermore miocene present regional kinematic reconstructions suggest that this deceleration reflects the substantial increase of northward motion of tarim rather than a significant decrease of the northward velocity of the pamir

experimental study on the shearing behavior of saturated silty soils based on ring shear tests the shearing behavior of saturated silty soils has been examined extensively by performing undrained and partially drained the upper drainage valve of the shear box was open during shearing ring shear tests on mixtures of a sandy silt with different loess contents by performing tests at different initial void ratios the shear behavior of these silty soils at different initial void ratios is presented and discussed undrained shear test results showed that the liquefaction phenomena in ring shear tests were limited within the shear zone for a given void ratio or interfine void ratio both the peak and steady state shear strengths decreased with increase of loess content the partially drained shear tests revealed that a great reduction in the shear strength could result after the shear failure due to the buildup of excess pore water pressure within the shear zone the magnitude of reduction in shear strength after failure was affected by the initial void ratio the shear speed after failure as well as the loess content in the sample for a given void ratio or interfine void ratio with increase of loess content the drained peak shear strength became smaller while the brittleness index became greater it was also found that due to localized shearing the permeability of the soil within the shear box after drained shearing could be three orders of magnitude smaller than before shearing

a test of three dimensional radiative transfer simulation using the radiance signatures and contrasts at a high latitude coastal site 1 a three dimensional monte carlo radiation code is used to analyze surface observations of sky radiance at a high latitude coastal site observations were made at palmer station antarctica under uniform marine stratus clouds during both ice free and iced in ocean conditions the model results using actual snow ocean area coverage show good qualitative agreement with all sky images and high spectral resolution radiometer scans when viewing over the island toward the northeast observations and modeling indicate that sky radiance in the visible bands is up to a factor of two greater than for directions toward the southwest viewing out over open ocean owing to a decrease in snow reflectance at longer wavelengths modeled and observed radiance distributions in the near infrared tend to be much more symmetric results of the modeling study indicate that details of the snow brdf or island topography have a very small effect on model predictions in addition the model indicates that the angular distribution of sky radiance is fairly insensitive to cloud optical depth assumed homogeneous and is independent of cloud height as long as cloud layer thickness is not much larger than the cloud base height

liquefaction resistance of sands containing plastic fines with different plasticity abstractsoils in the field or at reclaimed sites commonly contain some amount of silt or clay rather than clean sand only the effect of a low fraction of plastic fines within sand matrix on liquefaction resistance is not clearly understood in this study clean sand was mixed with 10 plastic fines having different plasticity indexes pis and the effect on liquefaction resistance was evaluated in terms of cyclic stress ratio a series of undrained cyclic triaxial tests were carried out on loose medium and dense specimens that were reconstituted in the laboratory by the undercompaction method the results showed that liquefaction resistance tended to decrease as the pi of 10 fines in the specimens increased liquefaction resistance of loose specimens was marginally influenced by the plasticity of fines however in the case of dense specimens liquefaction resistance decreased up to 40 as the pi of 10 fines increased it was shown that even though a low fraction of plastic fines was included within

insight into the effects of clay mineralogy on the cyclic behavior of silt clay mixtures abstract results of a systematic testing program showed that the cyclic behavior of silt clay mixtures is greatly influenced by the dominant clay minerals in the mixture in particular it was demonstrated that given the same amount of clay clay mineral and or same value of plasticity index the montmorillonitic soils have the highest cyclic strength followed by the illitic soils and then by the kaolinitic soils moreover the rate of increase in cyclic strength with increasing clay mineral and pi is again the highest in the montmorillonitic soil lowest in the kaolinitic soil and intermediate in the illitic soil therefore without considering clay mineralogy the clay fraction clay mineral and plasticity index are unreliable indicators of the liquefaction susceptibility of fine grained soils the differing adhesive bond strength each clay mineral develops with the silt particles is deemed to largely explain the observed differences in the response of the three different soil mixtures to cyclic loading

late cenozoic tectonic development of the intramontane alai valley pamir tien shan region central asia an example of intracontinental deformation due to the indo eurasia collision 1 the pamir indentor of the northwestern himalayan syntaxis is a first order feature demonstrating partly the northward extent of deformation due to the cenozoic indo eurasia collision the alai valley of kyrgyzstan at the northern end of the indentor is a strategically positioned e w trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone to quantify the convergence accommodated across the alai valley during the late cenozoic we collected structural and stratigraphic field data reviewed existing soviet literature and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin our study suggests that the development progressive closure and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events 1 distributed north south contraction took place during the late oligocene early miocene accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface and 2 n s shortening resumed in the mid miocene and continues today during this second episode the thrust front migrated southward localized along the trans alai ranges and failed to reactivate earlier neogene structures horizontal shortening of about 35 across the alai valley implies relatively low strain rates and displacement rates of about 4 18 4 69 10 16 s 1 and 0 66 0 78 mm yr 1 respectively for the last 25 myr our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the asian continent as early as the late oligocene

seismic imaging of subducting continental lower crust beneath the pamir abstract exhumation of ultra high pressure metamorphic rocks testifies that the continental crust can subduct to significant depth into the mantle despite its buoyancy however direct observation of ongoing subduction of continental crust is rare the pamir is regarded as a possible place of active continental subduction because of the intermediate depth seismicity crustal xenoliths and estimates of crustal shortening versus convergence rates here we present for the first time receiver function images from a passive source seismic array traversing the tien shan and the pamir plateau showing southward subduction of eurasian continental crust in the eastern pamir we observe a southerly dipping 10 15 km thick low velocity zone lvz that extends from 50 km depth near the base of the crust to more than 150 km depth with a dip angle increasing to subvertical while the upper and mid crustal material seems to be shortened and incorporated into the pamir the lower eurasian crust detaches and subducts in its deeper part 80 km the lvz envelopes the intermediate depth earthquakes our observations imply that the complete arcuate intermediate depth seismic zone beneath the pamir traces a slab of subducting eurasian continental lower crust

assembly of the pamirs age and origin of magmatic belts from the southern tien shan to the southern pamirs and their relation to tibet 1 magmatic rocks and depositional setting of associated volcaniclastic strata along a north south traverse spanning the southern tien shan and eastern pamirs of kyrgyzstan and tajikistan constrain the tectonics of the pamirs and tibet the northern pamirs and northwestern tibet contain the north facing kunlun suture the south facing jinsha suture and the intervening carboniferous to triassic karakul mazar subduction accretion system the latter is correlated with the songpan garze hoh xi system of tibet the kunlun arc is a composite early paleozoic to late paleozoic triassic arc arc formation in the pamirs is characterized by 370 320 ma volcanism that probably continued until the triassic the cryptic tanymas suture of the southern northern pamirs is part of the jinsha suture a massive 227 ma batholith stitches the karakul mazar complex in the pamirs there are striking similarities between the qiangtang block in the pamirs and tibet like tibet the regional structure of the pamirs is an anticlinorium that includes the muskol and sares domes like tibet the metamorphic rocks in these domes are equivalents to the karakul mazar songpan garze system granitoids intruding the qiangtang block yield 200 230 ma ages in the pamirs and in central tibet the stratigraphy of the eastern pshart area in the pamirs is similar to the bangong nujiang suture zone in the amdo region of eastern central tibet but a triassic ocean basin sequence is preserved in the pamirs arc type granitoids that intruded into the eastern pshart oceanic basin arc sequence 190 160 ma and granitoids that cut the southern qiangtang block 170 160 ma constitute the rushan pshart arc cretaceous plutons that intruded the central and southern pamirs record a long lasting magmatic history their zircons and those from late miocene xenoliths show that the most distinct magmatic events were cambro ordovician 410 575 ma triassic 210 250 ma likely due to subduction along the jinsha suture middle jurassic 147 195 ma subduction along rushan pshart suture and mainly cretaceous middle and late cretaceous magmatism may reflect arc activity in asia prior to the accretion of the karakoram block and flat slab subduction along the shyok suture north of the kohistan ladakh arc respectively before india and asia collided the pamir region from the indus yarlung to the jinsha suture was an andean style plate margin our analysis suggests a relatively simple crustal structure for the pamirs and tibet from the kunlun arc in the north to the southern qiangtang block in the south the pamirs and tibet likely have a dominantly sedimentary crust characterized by karakul mazar songpan garze accretionary wedge rocks the crust south of the southern qiangtang block is likely of granodioritic composition reflecting long lived subduction arc formation and cretaceous cenozoic underthrusting