lithospheric structure of the central andes based on surface wave dispersion 1 shear wave velocity is very sensitive to temperature anomalies and partial melt and can provide important insights on the state of the lithosphere with that aim in mind phase velocities of rayleigh and love waves have been inverted for the regionalized shear wave velocity structure of the lithosphere across the central andes this inversion reveals strong lateral variations of vs both across the range and along strike in the altiplano crust in the upper crust the main features of our models are prominent low velocity anomalies probably related to partial melt below the los frailes ignimbrite complex and the southern altiplano at lower crustal level the altiplano is characterized by lower vs than the surrounding regions we find that the transition from the altiplano to the puna is associated with a 7 km thickening of the crust at mantle depths the nazca plate is found to be overlaid by a dipping low velocity zone with decreasing intensity with depth our results favor the idea of a cold mantle lid underlying the whole central andes

lithospheric structure beneath the south eastern zagros mountains iran recent slab break off integrated lithospheric modelling based on the combined interpretation of gravity geoid and topography data sets highlights a previously undocumented lithospheric thinning beneath the zagros collisional belt iran which we propose to relate to recent slab break off at the continent ocean transitional lithosphere recent published data on the distribution of seismicity at depth support this interpretation in agreement with other published models for the zagros mountains the overlying crust exhibits by contrast a noticeable thickening reaching a maximum of 52 km the consequent thermal uplift expected from slab break off is suggested to have modified the zagros wedge taper and triggered the recently documented switch from thin skinned to thick skinned deformation in the zagros fold thrust belt

deep crustal structure and flexure of the arabian plate beneath the zagros collisional mountain belt as inferred from gravity observations the zagros mountain belt region a neogene continental collisional zone between arabia and iran that is characterized by a suture a folded belt and a foreland basin is unusual among active mountain belts in that its 6 12 km thick sedimentary cover is shortening predominantly by folding while the basement is apparently thickening along numerous high angle reverse faults we have used over 9000 gravity measurements in the region in conjunction with limited seismological observations and geological cross sections of the uppermost 10 km of crust to infer the deeper crustal structure beneath the region crustal models constrained by the bouguer anomalies and other seismological and geological data are characterized by a moho that dips about 1 to the northeast beneath the folded belt and increases in dip to about 5 near the main zagros thrust mzt the moho depth increases from 40 km beneath the leading edge of the foreland basin the mesopotamian foredeep and persian gulf to as much as 65 km beneath the mzt alternative models that incorporate a subducted oceanic crust that is attached to the underthrusting arabian crust deviate little in their moho configurations from the above simpler models negative isostatic residual anomalies are interpreted to indicate local overcompensation beneath the foreland basin and near the folded belt and beneath the mzt we show that underthrust sedimentary rocks of the converging margins along the suture zone may account for the negative isostatic residual anomalies near the mzt however to explain the rest of the isostatic anomalies requires other forces to be acting on this collisional plate boundary for example elastic flexure models required a combination of topography and subsurface loads or downward force the origin of which is not clear to approximate the bouguer or isostatic residual anomalies associated with the foreland basin and the folded belt the topography load of the zagros mountain belt is insufficient to cause the required deflection of the underthrusting arabian plate a combination of isostatic elastic flexure and horizontal compression forces acting on the edge of the arabian craton and the transitional lithosphere of central iran appears to best model the crust of the zagros region we propose a model in which the lower crust of the converging arabian plate located beneath the zagros is being shortened and thickened plastically between the seismogenic rigid upper crust and a rigid uppermost mantle lid the mantle lid probably decoupled from the lowermost crust un der thrusts the iranian crustal blocks thus confined from below the horizontally compressed plastic lower crust hydraulically depresses the moho and raises the faulted and folded brittle upper crust in isostatic equilibrium

hydraulic impacts of glacier advance over a sediment bed a sedimentary sequence of till overlying a gravel aquifer was instrumented with water pressure transducers prior to a small anticipated surge of the margin of the glacier brei amerkurjokull in iceland the records of water pressure at each transducer site show a well defined temporal sequence of hydraulic regimes that reflect the changing recharge of surface derived meltwater the pressure drop along the drainage pathway and the pattern of ice loading the poroelastic and water pressure response of glacially overridden sediments to the recharge rate is determined in the frequency domain through an analytic solution this permits the in situ conductivity compressibility and consolidation states of subglacial sediments to be derived and reveals aquifer scale compressibility that produces an important water pressure wave associated with the advancing glacier the model is then used to explore how varying conductivity compressibility largely determined by granulometry can determine drainage states and instabilities that may have a large impact on glacier ice sheet dynamics and how the drainage time of surface water to the bed can determine the frequency response of subglacial groundwater regimes and their influence on subglacial sediment stability mismatches between model predictions and specific events in water pressure records are used to infer processes that are not incorporated in the model hydrofracturing that changes the hydraulic properties of subglacial sediments the impact on groundwater pressure of subglacial channel formation upwelling beyond the glacier margin and rapid variations in the state of consolidation the poroelastic model also suggests how seismic methods can be developed further to monitor hydraulic conditions at the base of an ice sheet or glacier

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

seismic imaging of the downwelling indian lithosphere beneath central tibet a tomographic image of the upper mantle beneath central tibet from indepth data has revealed a subvertical high velocity zone from 100 to 400 kilometers depth located approximately south of the bangong nujiang suture we interpret this zone to be downwelling indian mantle lithosphere this additional lithosphere would account for the total amount of shortening in the himalayas and tibet a consequence of this downwelling would be a deficit of asthenosphere which should be balanced by an upwelling counterflow and thus could explain the presence of warm mantle beneath north central tibet

off great circle propagation of intermediate period surface waves observed on a dense array in the french alps array analysis is performed on surface waves recorded in the french alps using a small aperture 25 km temporary array of six broad band stations the analysis shows that both rayleigh and love waves deviate relative to the great circle path the deviations are particularly strong up to 30 between 20 and 40 s period to interpret these observations we first study the effect of large scale structures using ray tracing in a smooth laterally heterogeneous model of the earth second we evaluate the local effect by considering a model for the french alps including strong lateral heterogeneities around the array that were not taken into account in the ray tracing by combining these two possible causes of the observed deviations we propose an explanation for the general trend in the observed deviations finally we show that by taking into account azimuthal deviations phase velocities measured at a regional scale can be significantly improved

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

on ach or how reliable is regional teleseismic delay time tomography abstract ach named after aki et al 1976 bull seismol soc am 66 501 524 aki et al 1977 j geophys res 82 277 296 is a standard widely used method for three dimensional seismic imaging of the earth the fundamental hypothesis which underlies the method is that the time residuals generated outside the given target volume from the seismic source to the bottom of the modelled zone are approximately constant across the seismic array the main purpose of this study is to check this assumption we computed travel times for a given station and event distribution using a three dimensional global earth model taken from seismic tomography we found that the relative residuals generated outside the target volume are not negligible and that the fundamental hypothesis underlying ach is thus not verified these deviations are generated in the lower and or upper mantle and the corresponding proportions are entirely dependent on the raypaths the bias in the inverted model is statistically similar to the input model outside the target volume we thus recommend caution in any interpretations involving ach generated models a secondary somewhat independent outcome of this study is that fermat s principle used to linearise the inverse problem in ray theory based tomography seems to be valid without any restrictions given our input model is representative for the true earth for rays with turning points in the lower mantle for rays with turning points in the upper mantle the constant raypath approximation is probably not true this applies to global tomography as well

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

a strong seismic velocity contrast in the shallow mantle across the zagros collision zone iran summary surface wave dispersion measurements are interpreted jointly with the inversion of teleseismic p wave traveltime residuals along a dense 620 km long temporary seismic profile across the zagros to investigate its upper mantle structure the s wave model determined from rayleigh wave dispersion in the zagros fold and thrust belt has high velocities from 4 5 0 2 km s 1 below the moho to 4 9 0 25 km s 1 at 200 km depth which are comparable to a shield like structure beneath the suture region from the main zagros thrust mzt to the urumiehdokhtar volcanic arc s wave velocities are lower than beneath the zagros in the top 50 km of the upper mantle with a minimum of 4 4 0 2 km s 1 at 80 km depth from 150 km and deeper s velocities are as high as beneath the zagros we suggest that part of the velocity difference at shallow depth is due to higher mantle temperatures and or higher fluid content beneath the northern half of the profile but that velocities are too high to support the hypothesis of mantle lid delamination under the suture zone teleseismic p traveltime relative residuals display a long wavelength variation along the transect with a difference of 1 1 s between negative residuals in the zagros simple folded belt and positive residuals in central iran this difference backprojects into a 6 7 per cent lateral variation of p wave velocity in the shallow upper mantle with higher vp beneath zagros and lower vp beneath central iran the main short wavelength variation of the residual is located in the suture region with late p arrivals in the region of the mzt and early arrivals in the sanandaj sirjan zone ssz using synthetic models of vp perturbations we show that the high velocities of the arabian platform have to extend laterally at least to the ssz to fit the observed p delays this model also predicts rayleigh wave phase velocities which are within the error bars of the observed dispersion it supports the model of crustal scale overthrusting at the mzt

tomographic imaging of lg and sn propagation in the middle east observations based on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation lg and sn is very complex in the middle east accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations we have compiled a large data set of regional and local seismograms recorded in the middle east this data set comprises approximately four years of data from national short period networks in turkey and syria data from temporary broadband arrays in saudi arabia and the caspian sea region and data from gsn mednet and geofon stations in the middle east we have used this data set to decipher the character and pattern of regional seismic wave propagation we have mapped zones of blockage as well as inefficient and efficient propagation for lg pg and sn throughout the middle east two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the middle east we observe evidence of major increase in lg attenuation relative to pg across the bitlis suture and the zagros fold and thrust belt corresponding to the boundary between the arabian and eurasian plates we also observe a zone of inefficient sn propagation along the dead sea fault system which coincides with low pn velocities along most of the dead sea fault system and with previous observations of poor sn propagation in western jordan our observations indicate that in the northern portion of the arabian plate south of the bitlis suture there is also a zone of inefficient sn propagation that would not have been predicted from prior measurements of relatively low pn velocities mapped high attenuation of sn correlates well with regions of cenozoic and holocene basaltic volcanism these regions of uppermost mantle shear wave attenuation most probably have anomously hot and possibly thin lithosphere

eurasian fundamental mode surface wave phase velocities and their relationship with tectonic structures we automatically analyzed 32 000 fundamental mode love and rayleigh wave signals with earthquake station paths traversing eurasia and indonesia and obtained robust average phase velocity measurements between 20 s and 170 s periods along 4389 love and 4020 rayleigh paths these were inverted to give phase velocity maps at 14 fixed periods resolution tests suggest that features with diameter 750 km and 500 km are resolved over most of eurasia and central se asia respectively low period love waves image areas with thick sedimentary cover as low velocity zones and almost all periods image mountainous regions since these have thick crust and hence low average lithospheric shear velocity at long periods both love and rayleigh waves define high phase velocity zones across shield and cratonic areas reflecting their deep lithospheric roots we observe significant along strike heterogeneity in the zagros fold belt and tien shan altai system taking sections across eurasian phase velocity space allows us to make approximate interpretations in terms of shear velocity structure directly for example the red river and east vietnam boundary faults are traced on their eastern side by low velocities which extend at depth into indonesia we relate this to mantle upwelling associated with early eocene rotation of indochina and reversal of the sense of shear across the red river fault post 20 ma we observe dipping subduction of the mediterranean beneath the aegean of the philippine sea beneath indonesia and of the indian shield beneath tibet we also image a fossil subducted plate beneath ne borneo which we associate with subduction of the proto south china sea between 50 ma and 15 ma

pn tomographic imaging of mantle lid velocity and anisotropy at the junction of the arabian eurasian and african plates an edited version of this paper was published by blackwell publishing in geophysical journal international copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02355 x http atlas geo cornell edu middleeastnorthafrica publications al lazki2004 htm

high resolution teleseismic body wave tomography beneath se romania i implications for three dimensional versus one dimensional crustal correction strategies with a new crustal velocity model summary the calixto carpathian arc lithosphere x tomography experiment offers a dense high quality data set to study the lithospheric asthenospheric system underneath se romania an earthquake prone region in se europe to increase the image resolution of structures in the uppermost mantle the application of crustal traveltime corrections by a priori information before the teleseismic traveltime inversion has become a well accepted procedure for such a correction we present a regional 3 d crustal seismic velocity model that serves as the basis for a high resolution teleseismic tomography forthcoming paper by martin et al our 3 d crustal model is based on recent research in the region we collect new results from two long range seismic refraction lines 3 d refraction tomography and teleseismic ps conversions adding previously published models of the sediment distribution conrad and moho depths as well as crustal seismic p wave velocities we compile a 3 d crustal model for se romania this 3 d model does not contain shallow small scale heterogeneities 10 km but it reflects the large scale structures such as variations in sediment thickness average seismic velocities and 3 d moho depth it is well suited for the correction of teleseismic traveltime residuals a prerequisite for a high resolution teleseismic tomography study for example traveltime delays of up to 1 3 s are caused by the almost 20 km thick layer of sediments in the focsani basin such delays are comparable to or larger in size than the expected upper mantle traveltime residuals we study the significance of 3 d crustal traveltime corrections relative to 1 d station corrections and show that the complex basin structures in se romania require a 3 d approach to reduce the smearing of crustal anomalies into the mantle by modelling synthetic mantle structures with a slab as it is expected for se romania we also investigate how to adapt the inversion strategy if crustal corrections are applied significant improvements are found by including the already corrected crustal layers in the inversion procedure thereby enabling the inversion algorithm to project still remaining uncertainties in the less resolved upper crustal layers however the fixing of the upper layers during the inversion due to the a priori knowledge of the crustal velocity anomalies clearly leads to smearing of uncorrected anomalies that are possibly located close to the crust mantle boundary

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

upper mantle structure beneath the alpine orogen from high resolution teleseismic tomography 1 to understand the evolution of the alpine orogen knowledge of the actual structure of the lithosphere asthenosphere system is important we perform high resolution teleseismic tomography with manually picked p wave arrival times from seismograms recorded in the greater alpine region the resulting data set consists of 4199 relative p wave arrivals and 499 absolute p wave arrivals from 76 teleseismic events corrected for the contribution of the alpine crust to the travel times the three dimensional 3 d crustal model established from controlled source seismology data for that purpose represents the large scale alpine crustal structure absolute p wave arrival times are used to compute an initial reference model for the inversion tests with synthetic data document that the combination of nonlinear inversion high quality teleseismic data and usage of an a priori 3 d crustal model allows a reliable resolution of cells at 50 km 50 km 30 km hence structures as small as two cells can be resolved in the upper mantle our tomographic images illuminate the structure of the uppermost mantle to depth of 400 km along strike of the alps the inversion reveals a high velocity structure that dips toward the se beneath the adriatic microplate in the western and central alps in the eastern alps we observe a northeastward dipping feature subducting beneath the european plate we interpret this feature in the western and central alps as subducted mainly continental european lower lithosphere for the east we propose that parts of the vardar oceanic basin were subducted toward the ne forcing continental adriatic lower lithosphere to subduct northeastward beneath the european plate

synoptic flow and density observations near an arctic shelf break analyses of data from three shipborne surveys describe the quasi synoptic density and velocity fields near barrow canyon alaska the canyon parallels the northwestern coast of alaska and contains three different water masses these are 1 warm and fresh alaskan coastal waters that originate from the bering strait 2 cold and moderately salty waters that originate from the chukchi shelf and 3 warm and salty waters that originate from the atlantic layer of the arctic ocean a halocline separates the chukchi shelf and atlantic layer waters the halocline slopes upward into the canyon where it is then twisted to slope across the wide canyon an intensification of the beaufort gyre near the shelf break just seaward of barrow canyon raises the halocline more than 100 m toward the surface locally upwelling favorable winds raise the arctic halocline which thus is ventilated within barrow canyon adjacent to the coast in the absence of winds the halocline slopes acrosscanyon in the thermal wind sense due to a northward flowing coastal current velocity measurements from a towed acoustic doppler current profiler reveal a northward flowing jet that transports about 0 3 sv sv 106 kg m23 of bering sea summer water into the arctic ocean at speeds that exceed 0 7 m s21 total northward transports through the canyon exceed 1 0 sv the warm waters of this coastal current supply more than 100 w m22 of heat to the atmosphere the jet separates both from the bottom and from the coast hence a laterally and vertically sheared jet forms which breaks into three branches at about 71 88n latitude

surface wave velocities across arabia the group velocity distribution beneath the arabian plate is investigated using love and rayleigh waves we obtained a balanced path coverage using seismograms generated by earthquakes located along the plate boundaries we measured love and rayleigh wave group velocity dispersion using multiple filter analysis and then performed a tomographic inversion using these observations to estimate lateral group velocity variations in the period range of 5 60 s the love and rayleigh wave results are consistent and show that the average group velocity across arabia increases with increasing period the tomographic results also delineate first order regional structure heterogeneity as well as the sharp transition between the arabian shield and the arabian platform systematic differences are observed in the distribution of the short period group velocities across the two provinces which are consistent with surface geology the slower velocities in the platform reveal the imprint of its thick sedimentary section while faster velocities correlate well with the exposed volcanic flows in the shield shear wave velocity models for the two regions obtained from the inversion of the group velocities confirm results from previous studies of higher s wave velocity in the upper crust beneath the shield this may be due to the present remnants of the oceanic crust ophiolite belts associated with the island arcs evolutionary model of the arabian shield