kinematics of active deformation in the sulaiman lobe and range pakistan the western margin of the indian plate is highly oblique to the direction of convergence between india and asia and represents an excellent example of large scale oblique continent continent collision determining the strain field in western pakistan and how it relates to the plate motion and plate margin geometry affords an exceptional opportunity for understanding oblique margin processes in general through the inversion of regional and teleseismic body waves we have determined the source parameters of 10 moderate sized earthquakes that occurred between 1964 and 1985 in and around the sulaiman range pakistan the earthquakes are dominantly thrust events with slip vectors that are approximately perpendicular to the lobate sulaiman mountain front slip vector orientations rotate 60 70 from a n s to a wnw ese direction of compression consistent with the geometries of the complex festoon shaped mountain belts of this margin we have estimated the spatial variation of the horizontal strain rate and velocity fields within sulaiman using vertically averaged models that accommodate plate motion constraints within a deforming layer the most important factors determining the style of strain rotation in the sulaiman lobe and range are the presence of pure strike slip motion along the chaman fault and the relatively rigid and undeformed katawaz basin that is therefore allowed to translate obliquely relative to india this same conclusion is obtained using either a three dimensional frictional analogue model with significant basal tractions or a thin sheet viscous numerical model without basal tractions thrusting in a predominantly nw se direction in the sulaiman range accommodates 5 14 mm yr of n s motion between india eurasia and 3 6 mm yr of e w shortening seismic moment release this century within the india eurasia plate boundary zone west of the western himalayan syntaxis constitutes roughly 40 of the expected total seismic moment release for this time period particularly significant moment rate deficits exist within the sulaiman range and along the chaman fault

migration of chlorinated hydrocarbon solvents through coventry sandstone rock columns the migration in the coventry sandstone aquifer system of aqueous solutions of various chlorinated hydrocarbon solvents chss 1 1 1 trichloroethane tca trichloroethylene tce and tetrachloroethylene tece was studied by means of percolation experiments with undisturbed rock cores the retardation factor rf was very low always less than 2 for tca less than 3 for tce and less than 5 for tece the rf varied slightly according to the nature of the solid sample but could not be related to the solid organic carbon content the solvent adsorption was always almost completely reversible and little affected by the percolation flow rate 0 08 0 56 m day 1 the chs breakthrough curves were typical of non equilibrium processes caused by sorption by the solids and possibly by diffusion between mobile and immobile water the rf values obtained experimentally were much lower than those calculated from batch adsorption studies showing that percolation experiments are necessary to evaluate the filtering properties of consolidated rocks these results indicate that in the coventry sandstone aquifer relatively high vertical and especially lateral hydraulic conductivities two carbon chs aqueous solutes should migrate readily with water with very little retardation

seismotectonics and focal mechanisms of earthquakes from pamir hindukush regions abstract the hindukush pamir and karakorum region lies to the north of the northern apex of the indian subcontinent approximately between latitude 34 5 40 n and longitude 68 80 e from the point of view of seismicity this region is one of the most active in the world the seismicity being attributed to the collision of the northward moving indian plate with eurasia in this region lie the junctions of several major mountains such as the himalayas karakorum pamirs hindukush and kun lun the northern part of this region is characterized by highly folded structures major faults in the region follow the trend of these structures while a number of faults has a strike slip nature several are thrusts or overthrusts the present paper discusses the seismicity of the hindukush pamir region its relationship to tectonics the nature of focal mechanism solutions and their significance in terms of plate tectonics seismicity maps have been prepared for 0 50 km 50 200 km depths in the northwestern part of the area the seismicity for shallow depths 0 50 km follows a convex trend from the hindukush mountains towards the north and northwest along the kunduz foredeep kuliab foredeep pamir alai zone and the pamir foredeep the badakshan massif is relatively less active while the southern kashmir zone in the southeast and gardez chaman fault zones in the southwest are quite active the seismicity is dispersed in the rest of the area for intermediate depths 50 200 km the seismicity has an east west trend in the northern part of the hindukush mountains and changes sharply to a nne direction following the trend of the badakshan massif and central pamirs a similar trend is observed in the pamir alai zone a number of seismic sections have been prepared through the pamir alai fracture zone the northern and central pamirs badakshan massif kunduz foredeep and the hindukush regions to show the nature of faults and of focal mechanisms occurring at different depths in most cases it is found that the fault fracture zones are steeply dipping and thrust as well as strike slip faulting is taking place up to considerable depths the present day seismic activity appears to be a result of stresses generated by the northward collision of the indian and eurasian plates and alpine orogenic movements which have possibly reactivated major faults of caledonian and hercynian age

postscript summary of the coventry groundwater investigation and implications for the future abstract the broader implications of the coventry groundwater investigation are discussed in this postscript the complex interbedded sandstone and mudstone sequence under coventry is seriously polluted by chlorinated hydrocarbon solvents investigations in such terrain will require much greater expenditure than was available for this project if they are to describe the distribution and movement of pollutants in enough detail to evaluate quantitatively options for aquifer clean up it is not realistic to consider clean up of coventry s groundwater at the present time because of the lack of detailed knowledge it is probable at least for the present that clean up is not feasible because of hydrogeological constraints arising from the extreme variability of permeability in the system and an absence of operational techniques for clean up stronger more pro active protection of groundwater is needed a major recommendation for future investigations is a procedure to avoid open boreholes which can allow pollution to penetrate deeper into the aquifer and may confuse the results of sampling

crustal structure and dynamics under himalaya and pamir ranges gravity profiles across the himalayas and the karakorum and pamir ranges are analysed using the information available from deep seismic sounding studies generalized inversion of a profile along with conventional modelling using multiple bodies has provided several details of the subsurface crustal structure the depth of the moho varies from 58 km under the himalayas to 71 km under the karakorum and rises to 55 km under the pamir and the trans alai beyond this a depression of the order of 10 12 km is depicted under the alai ranges about 14 15 km above the moho there is an interface which runs almost parallel to it through the entire section the material between this interface and the moho has a density which is higher 0 13 g cm3 than the density of a typical continental lower crust and appears to represent the material underthrust from the indian and the eurasian plates

propagation of crustal waveguide trapped pg and seismic velocity structure in the south indian shield short period vertical component digital recordings of the seismic wave field generated by mine tremors and explosions recorded at the gauribidanur array gba reveal relatively high frequency secondary energy with a group velocity of about 6 km sec accompanied by a long incoherent coda we interpret this part of the wave field including the coda as resulting from a crustal waveguide trapped pg and it is observable from a distance of about 150 km behind the first arrival pn phase these observations and extensive modeling results reveal the fine structure of the crust beneath the archaean eastern dharwar craton in the south indian shield a waveguide with random successions of high and low velocity layers in the upper crust possibly with considerable lateral extent beneath the closepet granite explains the main features of the waveguide pg such as coda length and group velocity reflectivity synthetic seismograms for 1d lamellae structures in the upper crust are found to reproduce the observed features of a record section assembled from gba seismograms extending to a distance of 240 km the preferred models of p and s velocity structure reveal lower than normal v p v s and poisson9s ratios respectively 1 63 1 65 and 0 20 0 21 in the upper crust including the lamellae structure and 1 70 and 0 235 in the lower crust a q p q s ratio nearly equal to or even slightly less than 1 in the upper crust is found to generate the synthetics consistent with the observed seismogram section f k spectral analysis of the observed p coda following the waveguide pg for travel paths mostly through the closepet granite convincingly reveals two dominant energy peaks at near on azimuth as well as relatively off the source azimuth both with an apparent velocity of 6 1 km sec appropriate to the upper crustal depths the inferred upper crustal structure modeled by alternating high and low velocity lamellae together with the derived physical properties and the f k analysis of the p coda suggests a scattering waveguide at 5 15 km depth in this region the scattering waveguide appears to be related to the large closepet granite intrusion which is believed to be a precambrian suture between the western and eastern dharwar cratons in the south indian shield possible lateral extent of the modeled lamellae structure receives added support from a recently proposed hypothesis of a late archaean mantle plume centered below the closepet granite the inferred crustal p velocity model for the eastern dharwar craton revealing a transitional moho at a shallow depth of 34 36 km is consistent with the models for other archaean cratons the observed pn velocity of 8 2 km sec and its gradient 0 013 sec 1 compare fairly well with similar values found for other shield regions v p v s and poisson9s ratios are found to increase respectively from 1 71 and 0 24 below the moho to 1 78 and 0 27 at about 60 km depth in the upper mantle

investigation of a solvent polluted industrial site on a deep sandstone mudstone sequence in the uk part 2 contaminant sources distributions transport and retardation abstract a single industrial site has been investigated in detail to gain information on sources and movement of chlorinated hydrocarbon solvent chs pollutants in groundwater under the industrialized city of conventry in the uk a soil gas survey identified the most polluted area of the site where two types of investigation borehole were drilled open boreholes lined with plain and slotted casing and a single dedicated borehole incorporating gas samplers and gas driven water samplers specially designed sampling techniques using pumps and packers were employed to determine vertical pollution profiles in the open boreholes core material was collected for sorption and diffusion experiments an assessment of field investigation procedures suggests that soil gas sampling is a useful method for reconnaissance surveying of pollution by volatile organic compounds but the results reflect only shallow pollution in the vertical profile open boreholes were found not to be satisfactory for accurate groundwater profile sampling and dedicated boreholes are recommended for such studies many uncertainties are involved in such a study of solvent pollution owing to the limited number of boreholes drilled and the complex spatial and temporal variations of pollutants despite the limitations of the investigation several useful conclusions are drawn concerning sources and movement of solvent pollution the main pollution source at the site is identified as the solvent storage tanks and pollution has resulted from poor use practices vertical pollution profiles indicate that the downward migration of 1 1 1 trichloroethane is following that of trichloroethene reflecting their history of use on the site the overall quality of groundwater abstracted in the system is set to deteriorate as high pollution loads presently at shallow levels in the system penetrate deeper little attenuated by sorption or degradation diffusion of pollutants between mobile fissure and immobile pore waters will result in poor quality groundwater under this site for the foreseeable future this trend is expected to be reflected throughout the urban area as a whole with most groundwaters falling below drinking water standards for chss

seismic data geometry evolution and shortening in the active sulaiman fold and thrust belt of pakistan southwest of the himalayas surface and subsurface data from the sulaiman fold and thrust belt are integrated to analyze the deep structure tectonic shortening and kinematics of the sulaiman fold and thrust belt at the western margin of the indian subcontinent seismic reflection data show that nearly all the 10 km thick sequence of dominantly platform 7 km and molasse strata is detached at the deformation front these strata thicken tectonically to about 20 km in the hinterland without significant thrust faults in the foreland a balanced structural cross section suggests that structural uplift in the sulaiman fold and thrust belt is a result of a thin skinned passive roof duplex style of deformation the duplex sequence consists of jurassic and older strata it is separated from the roof equence by a passive roof thrust in thick cretaceous shales that has a backthrust sense of displacement over foreland propagating duplexes the roof sequence with incipient out of sequence thrusting is intact for about 150 km northwards where it emerges along a passive backthrust sequential restoration of the balanced section reveals a series of structural and geometrical features including 1 development of low amplitude broad concentric detachment folds sui and loti at the tip of the decollement 2 increase in amplitude of a detachment fold to a critical level for development of ramp and duplex structures and 3 out of sequence thrusting to create required critical taper for an outward translation of the foreland fold and thrust belt a balanced structural cross section 349 km long from the sulaiman fold and thrust belt restores to an original length of 727 km suggesting a maximum of 378 km of shortening since 21 ma in the cover strata of the indian subcontinent calculation of displacement rates over the sulaiman fold and thrust belt 18 mm yr added to the resolved rate of the chaman fault vector for the component parallel to the plate convergence direction 15 mm yr are close to the current india asia plate convergence rate 37 mm yr

focal depths and fault plane solutions of earthquakes and active tectonics of the himalaya synthetic seismograms were compared with long period body waves for nine earthquakes with epicenters in the himalayan arc to determine depths of foci and to improve fault plane solutions focal depths are shallow 10 20 km inferred slip vectors are locally perpendicular to the mountain range they plunge very gently about 10 deg in the eastern sections of the range and more steeply about 25 deg in western sections assuming india to be a rigid plate the radially oriented slip vectors imply that southern tibet extends at about half the rate of underthrusting in the himalaya and therefore probably at about 5 10 mm yr the shallow depths and gentle dips of the fault planes at least for the events in the eastern half of the range are consistent with coherent underthrusting of the indian plate beneath at least the lesser himalaya the steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the greater himalaya

crustal shear velocity structure of the south indian shield 1 the south indian shield is a collage of precambrian terrains gathered around and in part derived from the archean age dharwar craton we operated seven broadband seismographs on the shield along a n s corridor from nanded nnd to bangalore bgl and used data from these to determine the seismic characteristics of this part of the shield surface wave dispersion and receiver function data from these sites and the geoscope station at hyderabad hyb give the shear wave velocity structure of the crust along this 600 km long transect inversion of rayleigh wave phase velocity measured along the profile shows that the crust has an average thickness of 35 km and consists of a 3 66 km s 1 12 km thick layer overlying a 3 81 km s 1 23 km thick lower crust at all sites the receiver functions are extremely simple indicating that the crust beneath each site is also simple with no significant intracrustal discontinuities joint inversion of the receiver function and surface wave phase velocity data shows the seismic characteristics of this part of the dharwar crust to be remarkably uniform throughout and that it varies within fairly narrow bounds crustal thickness 35 2 km average shear wave speed 3 79 0 09 km s 1 and vp vs ratio 1 746 0 014 there is no evidence for a high velocity basal layer in the receiver function crustal images of the central dharwar craton suggesting that there is no seismically distinct layer of mafic cumulates overlying the moho and implying that the base of the dharwar crust has remained fairly refractory since its cratonization index terms 7203 seismology body wave propagation 7205 seismology continental crust 1242 7255 seismology surface waves and free oscillations keywords continental crust archean crust receiver function indian shield

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

hydrogeology of the coventry region uk an urbanized multilayer dual porosity aquifer system abstract the coventry groundwater investigation has researched the sources and movement of chlorinated hydrocarbon solvents in the groundwater system underlying the coventry region the hydrogeological scene is set in this paper as a basis for the other aspects of the investigation which are reported in the other papers in this volume the deep intercalcated sandstones and mudstones of the permo carboniferous which underly the study area behave as a multilayer aquifer although individual aquifer units are not regionally extensive the sandstone units are fractured and behave as dual porosity aquifers with rapid tracer movement in fractures and diffusion into the low permeability but porous matrix the water balance of the groundwater system has changed from natural conditions because of man s influence although direct recharge has been reduced by the impermeable surfaces of roads and towns substantial extra recharge arises in the urban areas from leaking water mains

investigation of a solvent polluted industrial site on a deep sandstone mudstone sequence in the uk part 1 site description and groundwater flow abstract the sources and subsurface movement of chlorinated hydrocarbon solvents have been investigated at an industrial site as part of a wider study of groundwater pollution by these solvents in the area of coventry uk this paper presents a description of the site and groundwater flow as a prelude to a second paper describing the distribution transport and fate of pollutants both open boreholes and a single borehole incorporating a multilevel sampler were constructed and pumping and tracer tests performed the latter borehole was the most successful in defining hydraulic heads for individual aquifer units the cyclic pumping of the production borehole was analysed using a computer model to gain hydraulic data for aquifer and aquitard units the tracer test defined qualitatively the role played by matrix diffusion in solute transport within the dual porosity aquifer it is concluded that horizontal groundwater flow is dominant along fissured moderately permeable sandstone layers the low permeabilities of mudstone layers maintain high vertical hydraulic gradients sorption of contaminants on to the aquifer matrix is likely to be low owing to a low fraction of organic carbon however matrix diffusion will serve to attenuate peak concentrations of pollutants and stretch pollution pulses in time

evidence for a high velocity slab associated with the hindu kush seismic zone we used teleseismic travel time residuals to determine lateral velocity variations of the crust and upper mantle in the pamir hindu kush region in tadjikistan and afghanistan data from 29 analog seismic stations in tadjikistan and northern afghanistan were used to determine travel time residuals for 210 teleseismic events ranging in distance from 28 to 87 and covering a broad range of azimuths we inverted for velocity perturbations over a rectangular grid with a block size of 99 99 km the model extended to a depth of 350 km with a 50 km thick first layer and two 150 km thick deeper layers the results show a strong and well resolved zone of high velocities in the upper mantle at depths greater than 200 km coincident with the location of the hindu kush seismic zone no clear velocity perturbations are associated with the pamir seismic zone above 200 km little correlation is observed with the seismic zone but indications of thicker crust under the pamir and thinner crust under the tadjik depression are seen the high velocities are most likely caused by the presence of oceanic lithosphere at depth

thrusting of the hindu kush over the southeastern tadjik basin afghanistan evidence from two large earthquakes we infer from the mechanisms and depths of two large earthquakes that the hindu kush is actively thrusting northwest over the tadjik basin and that the basin is closing rather than being displaced to the west teleseismic body waves were used to determine focal mechanisms and depths for the two largest shallow earthquakes on the southern edge of the basin the two earthquakes on june 24 1972 mb 6 0 and december 16 1982 mb 6 2 have seismic moments of 2 1018 n m and 6 1018 n m respectively focal mechanisms of both events indicate almost pure thrust faulting with nodal planes striking northeast southwest the inferred fault planes dip southeast at 20 for the first event and 50 for the second the p axes for both events are oblique to the direction of relative motion between india and asia suggesting that the pamir is overthrusting the basin to the west depths for both earthquakes are between 20 and 25 km and place them well below the tadjik basin sediments the depths and steep fault planes suggest that these earthquakes represent a downdip extension within the basement of shallow folding and thrusting seen in the sediments northwest of the events thus convergence in afghanistan between india and eurasia is taken up along southeast dipping thrust faults north of the hindu kush as well as by northward subduction under the southern part of the range

seismic structure of iran from surface and body wave data summary an investigation of the lithospheric structure of the iranian plateau has been undertaken in order to find complementary information bearing on the tectonic evolution of the plateau the phase velocity dispersion of the fundamental mode rayleigh waves between the wwssn stations shiraz tabriz and mashad and between the sites of the iranian long period array and maio sro have been obtained from well dispersed wavetrains generated by eight great circle earthquakes the aftershocks of the destructive tabas earthquake in central iran which were accurately located by a field survey recorded clear p and s phases at maio providing supplementary travel time information for the interpretation of the phase velocity data the uppermost mantle p wave velocities beneath iran obtained in a previous study asudeh were also used in the analysis an alpine type crust was found for the iranian plateau while uppermost mantle velocities ranging from low velocity mantle in eastern iran to a high velocity shield like structure in the west of the country

receiver functions for the tien shan analog broadband network contrasts in the evolution of structures across the talasso fergana fault we determined the structure of the crust beneath the central and western tien shan by analyzing broadband 1 20 s analog seismograms of converted p sv phases generated by earthquakes at teleseismic distances and recorded by 14 seismograph stations the one dimensional structures that best explain the waveforms reveal pronounced differences in crustal velocities east and west of the talasso fergana fault specifically the transition zone between the crust and the mantle east of the fault is about 2 times broader than that west of the fault also velocities at depths between 10 and 35 km are about 10 lower in the east although the depth range of these lower velocities is not well resolved the talasso fergana fault is an important boundary for other observables in addition to the structural discontinuities observed at the surface the areas east of the talasso fergana fault are associated with abnormally low mantle velocities outcrops of basalt low q and short wavelength variations in anisotropy integrating these observations we interpret the broad mantle gradient as being due to vertical intrusions of mantle material into the lower crust likewise the low velocities in the midcrust could be thermally induced or due to the introduction of magmatically derived fluids the gross contrast in structure east and west of the talasso fergana fault could reflect a contrast in the dynamics of mountain building in these two regions we postulate that while crustal shortening is the dominant mechanism controlling topography west of the talasso fergana fault vertical uplift caused by a mass deficiency in the upper mantle may contribute significantly to the generation and maintenance of the high elevations east of the fault

p wave residuals at stations in nepal evidence for a high velocity region beneath the karakorum p wave residuals recorded at stations in nepal from events to the northwest and closer than about 20 deg are consistently earlier than those from other directions by about 2 5 sec these early arrivals are associated with paths confined to the upper 300 km of the earth and suggest that cold material occupies the uppermost mantle beneath the karakorum northwest himalaya and western kunlun thus these data suggest that convective downwelling occurs more vigorously in this region than beneath the rest of the himalaya tibet and their surroundings

constraints on plate motions in southern pakistan and the northern arabian sea from the focal mechanisms of small earthquakes the focal mechanism and depth were determined for nine small earthquakes m0 1025 dyn cm m 5 5 that occurred in southern pakistan and the northern arabian sea from an analysis of the vertical component of rayleigh waves in combination with limited first motion data focal parameters were determined from the rayleigh waves by using an event pair method of analysis for earthquakes that are located very close to each other 50 km the event pair method is able to remove a significant proportion of propagation effects at all periods in the range of interest 20 50 s for events separated by more than 100 km the propagation effects are reduced for only the longer periods 40 50 s the earthquakes that were studied provide evidence for a model of plate interactions in the vicinity of the southern pakistan triple junction the owen fracture zone is a transform fault that accommodates right lateral motion between the indian and arabian plates the plate boundary in the vicinity of the murray ridge is also partially made up of transform segments that strike subparallel to the owen fracture zone spreading centers may also exist in the vicinity of the murray ridge but were not documented by seismic or other evidence the slip azimuths for earthquakes along this boundary are significantly more northerly than those predicted by various regional and worldwide models of plate motion the arabian plate is being subducted beneath the eurasian plate along the southern coast of pakistan slip vectors for earthquakes along this boundary trend northnortheasterly in general agreement with predicted directions left lateral motion is documented along the boundary between the indian and eurasian plates in southern pakistan the predicted direction of relative motion between these plates is not significantly different from that observed two of the earthquakes studied appear to be intraplate in nature the depth and focal mechanism of one intraplate event which may have occurred within the accretionary prism along the makran coast however are based on limited data the other intraplate earthquake occurred within the sedimentary deposits along the western edge of the indian subcontinent near the indian eurasian plate boundary appendix is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b83 009 2 50 payment must accompany order

earthquake strain rates and instantaneous relative motions within central and eastern asia summary we use the spatial distribution of moment tensors of earthquakes in this century to estimate the velocity field in asia within a eurasian reference frame in a least squares inversion strain rates on the surface of the earth are matched with continuous spline functions in order to recover the velocity gradient tensor associated with the seismic moment release in asia earthquakes account for 40 60 per cent of the expected motion of india relative to eurasia with the missing component of strain rate equivalent to about 20 mm yr 1 of n s shortening between siberia and india in this solution south china rotates counterclockwise and moves eastwards relative to siberia using rigid plate constraints we next investigate the characteristics of the complete horizontal strain field in asia that accommodates plate motions our strain rate solutions are analogous to the response of a newtonian thin viscous sheet in which the rate of work done by the straining medium in accommodating the velocity boundary conditions is a minimum in these solutions the euler pole for india relative to eurasia is constrained nuvel 1a demets et al 1994 but in the process of fitting the vlbi velocity at shanghai china ward 1994 heki et al 1995 the euler pole for south china is determined in the inversion a solution that both fits the velocity at shanghai china and yields a strain rate field consistent with the earthquake mechanisms is one where the south china block has a motion relative to siberia described by the pole at 51 n 131 e 0 3 deg myr 1 comparison of the complete strain field that accommodates plate motion with the seismic strains indicates that earthquake moment release rates in this century within mongolia are about a factor of 4 larger than the long term rate within gansu ningxia the earthquake moment rates have been about a factor of 2 higher than the long term rate the strike slip faulting within mongolia gansu ningxia western sichuan and yunnan is possibly a direct result of velocity boundary conditions imposed on the south china block by forces unrelated to continental collision of india and eurasia such as forces associated with subduction along the margins of south eastern asia verification of this requires a better understanding of the role of pre existing zones of weakness within the asian continental lithosphere

rayleigh wave group velocity tomography of siberia china and the vicinity rayleigh waves are used in a tomographic inversion to obtain group velocity maps of east asia 40 e 160 e and 20 n 70 n the period range studied is 30 to 70 seconds seismograms used for this study were recorded at cdsn stations at a temporary broadband seismic array in tibet at several sro stations and kirnos equipped stations established in asia by the former soviet union in siberia in the sakhalin and in mongolia altogether more than 1200 paths were available in the tomographic inversion the study area includes the angara craton the geologically ancient core of asia and the subsequently accreted units the altaids a paleozoic collision complex the sino korean platform a chain of archaen terranes separated by belts of active structures the south china platform a collage of precambrian paleozoic and mesozoic metamorphic and igneous terranes as well as the tibetan plateau an active tectonic feature created in late cenozoic through collision of the indian subcontinent and the asian continent many of these main units are recognizable in the tomographic images as distinctive units tibet appears as a prominent low velocity about 15 from the average structure with western and central tibet often appearing as the areas with the lowest velocities the central asian fold belt and the angara craton are consistently high group velocity areas some lesser tectonic features are also recognizable for example lake baikal is seen as a high velocity feature at periods greater than 40 seconds however the high group velocity feature does not stop near the southern end of lake baikal it extends south southwestward across mongolia the north china plain a part of the platform where extensional tectonics dominate is an area of high velocities as a result of relatively thin crust the south china block the least tectonically active region of china is generally an area of high velocity for periods longer than 40 seconds a nne trending high group velocity gradient clearly exists in eastern china the velocities are noticeably higher in the east from the group velocity maps average dispersion curves at twelve locations were determined and inverted to obtain velocity structures main results of group velocity inversion include 1 a tibetan crust of around 60 km thick with low crustal and upper mantle shear velocities at 3 3 km s and 4 2 km s respectively 2 with the moho constrained at 40 43 km the angara craton and the central asian foldbelt have a v s in excess of 4 6 km s 3 relatively low shear velocities are obtained for tectonically active areas in many parts of the study area where precambrian basement is exposed the process in the crust and upper mantle due to recent tectonic activities have modified the crust and upper mantle velocity structures under the precambrian terranes they are no longer underlain by high velocity crust and mantle

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

three dimensional elastic wave velocity structure of the western and central tien shan arrival times of compressional p and shear s waves generated by earthquakes at local and teleseismic distances and recorded by seismographs located in the western and central tien shan are used to determine one and three dimensional elastic wave velocity structures of the crust and upper mantle beneath the mountain belt the best fit one dimensional structures suggest that the average depth of the mohorovicic discontinuity in this area is 50 km the three dimensional structure of the upper crust reveals thick sediments within each of the major depressions in the region a 7 km thick wedge of sediment beneath the chu depression is outlined at depth by a south dipping plane of seismic activity suggesting the presence of an active decollemont these low velocities extend continuously to the southeast toward issyk kul suggesting a structural relationship between the two however rather than being consumed it appears that issyk kul is overthrusting the surrounding ranges the low velocity sediments in the fergana basin reach depths of 10 km and are bounded on three sides by amorphous bands of seismicity velocities at midcrustal depths generally are lower beneath the central tien shan than beneath the western tien shan this pattern becomes more evident in the uppermost mantle with p velocity contrasts of as much as 10 across a boundary that corresponds roughly to the geographical position of the talasso fergana fault the low velocities beneath the central tien shan exceed 150 km depth but do not appear to be deeper than 300 km depth there is no evidence for a lithospheric root beneath this part of the range rather the low velocities imply the presence of a positive buoyancy force uplifting the mountains evidence that this low velocity region existed before the collision suggests that the tien shan may not owe its rejuvenation simply to its location at the northern edge of a strong tarim basin but rather to an anomalous upper mantle that was easier to deform than the surrounding lithosphere

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

gravity and tectonic model across the sulaiman fold belt and the chaman fault zone in western pakistan and eastern afghanistan abstract gravity data from the western boundary of the indian subcontinent have been analysed to infer the gross crustal structure across the indian afghan collision zone seismic reflection profiles reveal the gross structural duplex geometry of the sulaiman fold belt these data show that the wedge which is 10 km thick at the deformation front thickens northwestward to attain a tectonic thickness thickness due to deformation of about 20 km in the hinterland gravity modeling depicts the depth of the moho between 33 and 35 km at the deformation front of the sulaiman fold belt the moho depth shows an upward convexity along an e w profile it decreases northward with a gentle gradient of 1 1 20 m km below the sulaiman fold belt and then deepens abruptly with a gradient of about 7 8 136 m km across the chaman fault zone attaining a depth of about 57 km in eastern afghanistan the model suggests that the sulaiman fold belt is underlain by transitional crust 15 27 km thick in contrast to the continental crust 38 km thick underneath the fold belt of the himalayan collision zone in northern pakistan the about 57 km thick crystalline crust in eastern afghanistan may be due to 1 underplating by crust of the indian subcontinent and 2 structural thickening within the afghan block

the crustal structure of the southern caspian region the south caspian basin appears to behave as a relatively rigid aseismic block within the otherwise deforming alpine himalayan orogenic belt this anomalous character suggests that there is a fundamental compositional difference between the crust of the south caspian basin and that of the surrounding region five new estimates of crustal velocity structure beneath the southern caspian region are determined by the teleseismic receiver function method these models show that the crust in turkmenia along the trend of the apshceron balkhan sill kopet dag mountains is 50 km thick in the southwestern part of the caspian basin the crust is 33 km thick and consists of a 13 km thick sedimentary section lying on a high velocity vp 7 1 km s 1 lower crustal section in the southeastern part of the basin the crust is 30 km thick and consists of a 10 km thick sedimentary section overlying a 20 km thick low velocity vp 5 8 km s 1 crystalline crust the receiver function models are combined with velocity models from previous russian deep seismic sounding studies into a 1800 km long ese wnw trending crustal cross section across the kura depression the south caspian basin and the kopet dag mountains the most significant features of this crustal model are the 20 km variation in thickness of cenozoic sedimentary basin deposits the absence of a granitic vp 5 8 6 5 km s 1 crustal layer in the central part of the south caspian basin and 20 km of crustal thinning beneath the central part of the basin the moho beneath the south caspian basin has a broad arch like structure whose western boundary is a relatively narrow zone across which the crust thins rapidly 20 km thinning over a 100 km zone and whose eastern boundary has a more gradual change in crustal thickness 20 km thinning over a 400 km zone the velocity depth profiles derived from the receiver functions are compared to laboratory velocity estimates made at pressures and temperatures appropriate for the lower crust in turkmenia but the seismic p wave data alone do not permit differentiation between the various possible rock types the crustal model developed for the south caspian basin is consistent with the hypothesis that the crystalline crust of the basin is a section of oceanic crust that is being overthrust by the continental crust around much of its margins however we cannot rule out the possibility that the crystalline crust beneath the basin is a section of lower continental crust whose upper crustal section has been removed by erosion or faulting

crustal thickening under the palaeo meso proterozoic delhi fold belt in northwestern india evidence from deep reflection profiling summary the results of deep reflection profiling studies carried out across the palaeo meso proterozoic delhi fold belt dfb and the archaean bhilwara gneissic complex bgc in the northwest indian platform are discussed in this paper this region is a zone of proterozoic collision the collision appears to be responsible for listric faults in the upper crust which represent the boundaries of the delhi exposures in these blocks the lower crust appears to lie nw of the respective surface exposures and the reflectivity pattern does not correspond to the exposed blocks a fairly reflective lower crust northwest of the dfb exposures appears to be the downward continuation of the dfb upper crust the poorly reflective lower crust under the exposed dfb may be the westward extension of the bgc upper crust at depth thus the lower crust in this region can be divided into the fairly reflective marwar basin mb dfb crust and a poorly reflective bgc crust vertically oriented igneous intrusions may have disturbed the lamellar lower crustal structure of the bgc resulting in a dome shaped poorly reflective lower crust whose base not traceable in the reflection data may have a maximum depth of about 50 km as indicated by the gravity modelling the dfb appears to be a zone of thick 45 50 km crust where the lower crust has doubled in width this has resulted in three moho reflection bands two of which are dipping se from 12 5 to 15 0 s two way time twt and from 14 5 to 16 0 s twt another band of subhorizontal moho reflections at 12 5 s twt may have developed during the crustal perturbations related to a post delhi tectonic orogeny the signatures of the proterozoic collision in the form of strong se dipping reflections in the lower crust and moho have been preserved in the dfb indicating that the crust here has not undergone any significant ductile deformation since at least after the delhi rifting event

development and testing of a 3d velocity model for improved event location a case study for the india pakistan region 3d velocity models will play an important role in improving location accuracies of small events within the context of a comprehensive nuclear test monitoring treaty commonly such models are developed using tomographic methods that require the initial velocity model to be a reasonable approximation of the true earth structure in this article we present a method for the development of an a priori model for the crust and upper mantle in the india pakistan region and techniques for evaluating its suitability for use as an initial model in tomographic studies we developed the weston india pakistan 3d velocity model winpak3d by integrating the results of more than 60 previous studies related to crustal velocity structure in the region a well located event that occurred near nilore pakistan on 14 february 1977 provided a basis for testing the model via several different approaches evaluation of the 3d model included 1 cross validation analysis 2 comparison of model determined hypocenters with a known event location and 3 comparison of model based and empirically derived travel time correction surfaces generated for an event within 5 km of the seismic station at nilore the 3d model is demonstrated to improve the regional location of the 1977 event as compared to 1d models the epicenter mislocation using the first arrival phase at 23 regional stations determined by the 3d model was only 6 2 km compared to 13 1 km and 15 4 km for a regional 1d model and the iasp91 model respectively results of extensive testing demonstrate that winpak3d will be a particularly good initial model for tomographic studies as it improves regional location accuracy specifically for sparse networks these results demonstrate that 3d velocity models are essential for improving location accuracy in regions that have complicated crustal geology and structures such 3d models may be a prerequisite for achieving location accuracies as called for by the comprehensive nuclear test ban treaty particularly for small events that are not recorded teleseismically

changing mechanical response during continental collision active examples from the foreland thrust belts of pakistan abstract we have used data from teleseismic seismic reflection and field geologic studies along with both geomechanical and gravity modeling to contrast the tectonics of four active orogenic wedges in pakistan the kashmir himalaya the salt range potwar plateau foldbelt the sulaiman range and the makran accretionary wedge in makran oceanic crust is still being subducted and a thick pile of sediments is being accreted and underplated undercompaction and excess pore pressures can explain the narrow cross sectional taper and frontal aseismicity of this wedge beneath the sulaiman wedge continental crust is just starting to be underthrust indirect evidence suggests that fine grained carbonate rocks found in abundance deep in the stratigraphic section may be deforming ductilely at the base of the sulaiman wedge and provide a zone of ductile detachment the collision has proceeded to a much more mature stage in the salt range potwar plateau foldbelt and the kashmir himalaya isostatic response to underthrusting of continental crust has kept the sedimentary pile quite thin in both of these wedges so in that respect the two foldbelts are similar however thick eocambrian salt beneath the salt range and potwar plateau permits that foldbelt to be much wider in map view with a thinner cross sectional taper and a mixture of thrust vergence directions a major normal fault in basement causes the salt range to rise in front of the mildly deformed molasse basin of the southern potwar plateau much of the diversity among these mountain belts can be understood in terms of differences in the maturity of the collision process in each area the resulting thickness of the sedimentary pile encountered at the deformation front and the presence or absence of large contrasts in strength between the various layers of the stratigraphic section and basement relief

newly discovered paleogene deltaic sequence in katawaz basin pakistan and its tectonic implications in the katawaz basin pakistan the deltaic and turbidite facies of the khojak formation are the paleogene analogue of the modern indus river emptying into the arabian sea to form the indus delta fan system facies identified include upper continental slope to prodelta distal to proximal distributary mouth bar distributary channel interdistributary bay estuary fluvial channel natural levee and flood plains of lower and upper delta plains the proposed model is a fluvial dominated wave modified delta that axially fed khojak submarine fan turbidites exposed in the southwestern part of the basin these sediments were eroded from the early himalayan orogenic highlands and transported southwestward down the axis of the katawaz remnant ocean basin

regional waveform calibration in the pamir hindu kush region twelve moderate magnitude earthquakes m b 4 5 5 in the pamir hindu kush region are investigated to determine their focal mechanisms and to relocate them using their regional waveform records at two broadband arrays the kyrgyzstan regional network knet and the 1992 pakistan himalayas seismic experiment array pakh in northern pakistan we use the cut and paste source estimation technique to invert the whole broadband waveforms for mechanisms and depths assuming a one dimensional velocity model developed for the adjacent tibetan plateau for several large events the source mechanisms obtained agree with those available from the harvard centroid moment tensor cmt solutions an advantage of using regional broadband waveforms is that focal depths can be better constrained either from amplitude ratios of pnl to surface waves for crustal events or from time separation between the direct p and the shear coupled p wave spn spmp for mantle events all the crustal events are relocated at shallower depths compared with their international seismological centre bulletin or harvard cmt depths after the focal depths are established the events are then relocated horizontally using their first arrival times only minor offsets in epicentral location are found for all mantle events and the bigger crustal events while rather large offsets up to 30 km occur for the smaller crustal events we also tested the performance of waveform inversion using only two broadband stations one from the knet array in the north of the region and one from the pakh array in the south we found that this geometry is adequate for determining focal depths and mechanisms of moderate size earthquakes in the pamir hindu kush region

winds measured by the rover environmental monitoring station rems during the mars science laboratory msl rover s bagnold dunes campaign and comparison with numerical modeling using marswrf abstract a high density of rems wind measurements were collected in three science investigations during msl s bagnold dunes campaign which took place over 80 sols around southern winter solstice ls 90 and constituted the first in situ analysis of the environmental conditions morphology structure and composition of an active dune field on mars the wind characterization investigation was designed to fully characterize the near surface wind field just outside the dunes and confirmed the primarily upslope downslope flow expected from theory and modeling of the circulation on the slopes of aeolis mons in this season the basic pattern of winds is upslope from the northwest heading up aeolis mons during the daytime 09 00 17 00 or 18 00 and downslope from the southeast heading down aeolis mons at night 20 00 to some time before 08 00 between these times the wind rotates largely clockwise giving generally westerly winds mid morning and easterly winds in the early evening the timings of these direction changes are relatively consistent from sol to sol however the wind direction and speed at any given time shows considerable intersol variability this pattern and timing is similar to predictions from the marswrf numerical model run at a resolution of 490 m in this region although the model predicts the upslope winds to have a stronger component from the e than the w misses a wind speed peak at 09 00 and under predicts the strength of daytime wind speeds by 2 4 m s the namib dune lee investigation reveals blocking of northerly winds by the dune leaving primarily a westerly component to the daytime winds and also shows a broadening of the 1 hz wind speed distribution likely associated with lee turbulence the namib dune side investigation measured primarily daytime winds at the side of the same dune in support of aeolian change detection experiments designed to put limits on the saltation threshold and also appears to show the influence of the dune body on the local flow though less clearly than in the lee using a vertical grid with lower resolution near the surface reduces the relative strength of nighttime winds predicted by marswrf and produces a peak in wind speed at 09 00 improving the match to the observed diurnal variation of wind speed albeit with an offset in magnitude the annual wind field predicted using this grid also provides a far better match to observations of aeolian dune morphology and motion in the bagnold dunes however the lower overall wind speeds than observed and disagreement with the observed wind direction at 09 00 suggest that the problem has not been solved and that alternative boundary layer mixing schemes should be explored which may result in more mixing of momentum down to the near surface from higher layers these results demonstrate a strong need for in situ wind data to constrain the setup and assumptions used in numerical models so that they may be used with more confidence to predict the circulation at other times and locations on mars

separated earthquake location we present a practical method of locating earthquakes in laterally varying media the procedure has two distinct phases an estimation phase and an application phase in the estimation phase all existing arrival time residuals relative to some reference one dimensional velocity model for a region are used to estimate a set of path anomalies station corrections that vary as a function of source position this is done by sorting earthquakes into groups localized in space and applying a novel multiple event location algorithm this algorithm uses a pair of complementary projection operators to combine a priori information about the lateral structure that is indeterminate from the available data with the information that can be determined uniquely from the available data having estimated path anomalies as a function of source location we can generate a table of path anomalies that can be accessed and interpolated for future earthquake location this is the application phase of the method we have tested the method on synthetic data designed to study how well earthquakes can be located in the vicinity of the rupture zone of the 1984 morgan hill california earthquake we found precise absolute locations could be obtained provided the a priori information was specified appropriately distortion of relative locations occurred near large lateral velocity gradients and for groups of events spread over large areas because of the inadequacy of fitting a single set of path anomalies to the whole group

structural and thermal evolution of the karakoram crust prior to the eocene c 50 ma collision of the indian and asian plates the southern margin of asia along the karakoram plate was an andean type margin dominated by tonalitic granodioritic magmatism of jurassic lower cretaceous age hushe gneiss muztagh tower gneiss and k2 ortho gneiss and associated low pressure andalusite staurolite and garnet grade metamorphism m1 following india asia collision crustal shortening thickening and regional barrovian metamorphism m2 occurred between 50 37 ma thermobarometry of kyanite grade metapelites indicate burial to depths of around 30 35 km simultaneous solution of the garnet biotite geothermometer with the garnet muscovite biotite plagioclase and garnet ai 2 sio 5 quartz plagioclase geobarometers indicates peak m2 p t conditions of 696 20 c at 8 6 0 7kbar 860 mpa temperatures may have exceeded 700 c in sillimanite grade metapelites to produce in situ partial melting and leucogranitic melt pods peak m2 metamorphism occurred prior to 37 0 8 ma the crystallization age of the mango gusar two mica granite pluton which cross cuts syn metamorphic deformation fabrics post m2 thermal relaxation followed from 37 25 ma after which localized high heat concentrations at the base of the thickened crust caused widespread crustal melting and intrusion of the baltoro granite batholith at 25 21 ma a high temperature low pressure thermal aureole m3 along the northern contact is synchronous with the 21 0 5 ma zircon age of the baltoro granite andalusite hornfels along the northern contact of the batholith mitre thermal aureole indicates maximum pressures of 3 75 kbar 375 mpa a 75 c increase of temperature in kyanite sillimanite grade gneisses approaching the southern granite contact of the baltoro granite is interpreted as the thermal upwarping of pre 37 ma barrovian metamorphic m2 isograds around the 21 ma contact aureole m3 isotherms

mari bugti pop up zone in the central sulaiman fold belt pakistan abstract the sulaiman fold and thrust belt is an active tectonic feature of the himalayan mountain system in pakistan seismic reflection profiles borehole surface geology data and bouguer gravity modeling suggested a passive roof duplex geometry over a transitional crust related to the former passive margin of the indian subcontinent in the frontal part of the sulaiman fold belt a passive roof sequence of cretaceous and younger rocks is structurally uplifted at the surface the roof sequence displays a coherent stratigraphy over the underlying duplex sequence of jurassic and older strata the folds in the roof sequence reflect blind faults in the duplex sequence the duplex style of deformation persists throughout the central sulaiman fold belt however unlike the frontal sulaiman fold belt stratigraphy at the surface in the central sulaiman is disrupted by e w and ne trending faults with apparent map lengths of tens of kilometers these foreland and hinterland verging high angle faults juxtapose cretaceous rocks in the cores of tight symmetrical anticlines against eocene ghazij shale and kirthar limestone according to seismic reflection data they have only minor vertical offsets of 1 2 km and are mostly restricted to the roof sequence as a result cretaceous rocks bounded between reverse faults are exposed at the surface in the cores of tight anticlines as pop up structures this implies that 1 the exposed faults in the central sulaiman fold belt are not primary structures with major shortening and 2 recognition of these faults in the roof sequence may reflect an early stage of development of overstep back thrusts from the upper decollement passive roof thrust

large scale three dimensional seismic tomography of the zagros and pamir hindukush regions abstract the nature of the deep seismic structure of the zagros and pamir hindukush regions is inferred from the three dimensional p wave velocity images obtained using the aki christofferson and husebye ach inversion technique we use teleseismic 25 90 p wave arrival times recorded at 24 seismic stations during the period 1977 1986 a study of the azimuthal variation of residuals reveals that despite the crustal doubling the pamir hindukush region is characterized by faster arrivals 1 0 s of teleseismic p waves the iranian plateau on the other hand exhibits delayed arrivals 0 4 1 0 s from teleseisms the results of the ach inversion reveal contrasting p wave velocity characteristics in the upper mantle of these deformed zones in the depth interval 0 200 km the pamir hindukush region is characterized by 1 4 faster velocities relative to the iranian plateau accounting for the anomalous crustal thickening in the hindukush results in the subcrustal mantle up to 200 km exhibiting a significant higher velocity 2 comparable to that of the indian plate however in the depth interval 200 450 km the pamir hindukush region has 1 3 lower velocities relative to the indian plate while the upper mantle beneath the central iranian plateau is 2 4 slower relative to the surrounding region the high velocity upper mantle till a depth of 200 km beneath the hindukush region reflects the possible presence of both the oceanic lithosphere and the crust and uppermost mantle of the indian plate which subducted beneath eurasia the low velocity observed beneath central iran could be a reflection of the upper mantle thermal anomalies related to the pliocene quaternary volcanism in this region

oblique convergence and the lobate mountain belts of western pakistan the thin skinned structures of the pakistani convergent margin have formed as a consequence of the relative motion between india and eurasia most of the resultant motion is being accommodated along or near the current edge of the eurasian plate the southwest northeast striking chaman fault zone it has been observed at oblique margins that the total plate motion is resolved into a component parallel to the margin accommodated through strike slip faulting and a component normal to the margin taken up as contraction however the orientations of structures along the pakistani convergent margin in and around the sulaiman lobe and sulaiman range cannot be explained simply by resolving the plate motion vector into components normal and parallel to the plate boundary our modeling suggests that the complex juxtaposition of strike slip faults with thrust faults of various orientations can be explained by the presence of a block centered upon the katawaz basin that translates along the southwest northeast structural barrier of the chaman fault zone moving with respect to both eurasia and india as this relatively rigid block moves northeastward relative to asia it causes deformation of the sedimentary cover and is responsible for much of the structural complexity in the pakistani foreland our simple model explains several first order features of this oblique margin such as the eastward facing sulaiman range the strike slip kingri fault located between the sulaiman lobe and sulaiman range and the reentrant at sibi this leads us to conclude that very complex structural and geometric relationships at oblique convergent plate boundaries can result from the accommodation of strain with simple initial geometric constraints

crustal seismic velocity structure in the epicentral region of the latur earthquake september 29 1993 southern india inferences from modelling of the aftershock seismograms abstract we present 1 d models of crustal p and s wave velocity structure in the epicentral region of the devastating 1993 latur earthquake in southern india travel time and relative amplitude modelling of a seismogram section of well located aftershocks out to 80 km offset by reflectivity synthetic seismograms reveal alternating low velocity layers lvls for p and s waves in the upper crust at depths of 6 5 9 0 km and 12 3 14 5 km with about 7 velocity reduction a lower crustal lvl at 24 26 km depth is also inferred by modelling the seismic activity in the latur region is essentially confined to shallow upper crustal depths of less than 6 km above the lvls the upper crustal velocity models further reveal a relatively low vp vs ratio of 1 65 while synthetic seismogram models consistent with the upper crustal p wave reflection phases reveal a qp qs ratio certainly less than 1 a high conductivity zone at a shallow depth of 6 10 km brought out by broad band mt soundings in this region is found to be coincident with the upper crustal lvls these coincident anomalous properties of the upper crust suggest the presence of fluids probably in a partially or slightly under saturated state below the hypocentral region of the latur earthquake and its aftershocks

gravity anomalies and the structure of western tibet and the southern tarim basin gravity anomalies across the western part of the tarim basin and the kunlun mountain belt show that this area is not in local isostatic equilibrium these data can be explained if a strong plate underlying the tarim basin extends southwestward beneath the belt at least 80 km and supports part of the topography of northwest tibet this corroborates norin s inference that late tertiary crustal shortening has occurred in this area by southward underthrusting of the tarim basin beneath the kunlun this study places a lower bound on the amount of underthrusting

crustal thickness and upper mantle velocities in the tibetan plateau region from the inversion of regional pnl waveforms evidence for a thick upper mantle lid beneath southern tibet the crustal thickness and upper mantle velocity variation in tibet and surrounding regions was mapped through the inversion of 130 individual long period pnl waveforms the 130 paths crisscross the tibetan plateau hindu kush karakoram southwest china burma and northern india regions we regionalized these areas on the basis of topographic and geologic expression and determined the average upper mantle velocity and crustal thickness value for each block or region through a linear least squares inversion of the 130 parameter values crustal thicknesses in the tibetan plateau karakoram and hindu kush regions range from 63 to 72 km and pn velocities are 0 10 0 20 km s faster beneath these regions than those beneath northern india we observed impulsive first arrivals evidence for positive upper mantle gradients on seismograms recorded at distances between 1000 and 1400 km the paths of these waves crossed portions of tibet the hindu kush and east india regions simple modeling of the long period pn wave form and amplitude requires fairly high upper mantle gradients of 0 18 0 25 km s per 100 km beneath the pamir hindu kush region and requires an upper mantle lid in excess of 100 km thickness the southern half of tibet also requires a lid of about 100 km thickness a thinner upper mantle lid 50 km provided a poor match to the tibetan observations even with a very high gradient of 0 2 km s per 100 km the upper mantle structure of east india appears to be similar to the southern half of tibet 100 km thick positive gradient zone both the increase in pn velocity from india into tibet and the evidence for a thick upper mantle lid beneath tibet are consistent with the model in which indian lithosphere has underthrust southern tibet due to poor path coverage the structure beneath northern tibet cannot be resolved and thus underthrusting beyond central tibet cannot be constrained the rapid increase in upper mantle velocity from northern india into tibet can be explained by the pressure increase alone produced by the double thick crust and indicates that the indian lithosphere which underlies tibet is out of thermal equilibrium

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex