the deep structure of the north anatolian fault zone abstract multi scale full waveform inversion of complete continental and regional scale seismograms reveals the crustal and upper mantle signature of the north anatolian fault zone which shapes the neotectonics of turkey and the eastern mediterranean within the crust the fault zone is mostly bounded by several high velocity blocks suggesting that it developed along the edges of continental fragments with high rigidity below the crust the surface expression of the eastern and central parts of the north anatolian fault zone correlate with a pronounced low velocity band that extends laterally over 600 km around 100 km depth the low velocity band merges into the shallow anatolian asthenosphere thereby providing a link to the kirka afyon isparta volcanic field and the central anatolian volcanics we interpret the low velocity band beneath the north anatolian fault zone as the upper mantle expression of the tethyan sutures that formed 60 15 ma ago as a result of africa eurasian convergence the structurally weak suture facilitated the formation of the younger less than 10 ma crustal fault zone in this sense the north anatolian fault zone is not only a crustal feature but a narrow zone of weakness that extends into the upper mantle

on crustal corrections in surface wave tomography summary mantle models from surface waves rely on good crustal corrections we investigated how far ray theoretical and finite frequency approximations can predict crustal corrections for fundamental mode surface waves using a spectral element method we calculated synthetic seismograms in transversely isotropic prem and in the 3 d crustal model crust2 0 on top of prem and measured the corresponding time shifts as a function of period we then applied phase corrections to the prem seismograms using ray theory and finite frequency theory with exact local phase velocity perturbations from crust2 0 and looked at the residual time shifts after crustal corrections residuals fall within the uncertainty of measured phase velocities for periods longer than 60 and 80 s for rayleigh and love waves respectively rayleigh and love waves are affected in a highly non linear way by the crustal type oceanic crust affects love waves stronger while rayleigh waves change most in continental crust as a consequence we find that the imperfect crustal corrections could have a large impact on our inferences of radial anisotropy if we want to map anisotropy correctly we should invert simultaneously for mantle and crust the latter can only be achieved by using perturbation theory from a good 3 d starting model or implementing full non linearity from a 1 d starting model

global adjoint tomography first generation model we present the first generation global tomographic model constructed based on adjoint tomography an iterative full waveform inversion technique synthetic seismograms were calculated using gpu accelerated spectral element simulations of global seismic wave propagation accommodating effects due to 3d anelastic crust mantle structure topography bathymetry the ocean load ellipticity rotation and self gravitation frechet derivatives were calculated in 3d anelastic models based on an adjoint state method the simulations were performed on the cray xk7 named titan a computer with 18 688 gpu accelerators housed at oak ridge national laboratory the transversely isotropic global model is the result of 15 tomographic iterations which systematically reduced differences between observed and simulated three component seismograms our starting model combined 3d mantle model s362ani kustowski et al 2008 with 3d crustal model crust2 0 bassin et al 2000 we simultaneously inverted for structure in the crust and mantle thereby eliminating the need for widely used crustal corrections we used data from 253 earthquakes in the magnitude range 5 8 mw 7 0 for the first 12 iterations we combined 30 s body wave data with 60 s surface wave data the shortest period of the surface waves was gradually decreased and in the last three iterations we combined 17 s body waves with 45 s surface waves we started using 180 min long seismograms after the 12th iteration and assimilated minor and major arc body and surface waves the 15th iteration model features enhancements of well known slabs an enhanced image of the samoa tahiti plume as well as various other plumes and hotspots such as caroline galapagos yellowstone and erebus furthermore we see clear improvements in slab resolution along the hellenic and japan arcs as well as subduction along the east of scotia plate which does not exist in the starting model point spread function tests demonstrate that we are approaching the resolution of continental scale studies in some areas for example underneath yellowstone this is a consequence of our multi scale smoothing strategy in which we define our smoothing operator as a function of the approximate hessian kernel thereby smoothing gradients less wherever we have good ray coverage such as underneath north america

long period seismic source inversions using global tomographic models summary we investigate the effect of laterally varying earth structure on centroid moment tensor inversions using fundamental mode mantle waves theoretical seismograms are calculated using a full formulation of surface wave ray theory calculations are made using a variety of global tomographic earth models results are compared with those obtained using the so called great circle approximation which assumes that phase corrections are given in terms of mean phase slowness along the great circle and which neglects amplitude effects of heterogeneity synthetic tests suggest that even source parameters which fit the data very well may have large errors due to incomplete knowledge of lateral heterogeneity the method is applied to 31 shallow large earthquakes for a given earthquake the focal mechanisms calculated using different earth models and different forward modelling techniques can significantly vary we provide a range of selected solutions based on the fit to the data rather than one single solution difficulties in constraining the dip slip components of the seismic moment tensor often produce overestimates of seismic moment leading to near vertical dip slip mechanisms this happens more commonly for earth models not fitting the data well confirming that more accurate modelling of lateral heterogeneity can help to constrain the dip slip components of the seismic moment tensor

separating intrinsic and apparent anisotropy abstract seismic anisotropy plays a key role in studies of the earth s rheology and deformation because of its relation to flow induced lattice preferred orientation lpo of intrinsically anisotropic minerals in addition to lpo small scale heterogeneity produces apparent anisotropy that need not be related to deformation in the same way as intrinsic anisotropy quantitative interpretations of observed anisotropy therefore require the separation of its intrinsic and apparent components we analyse the possibility to separate intrinsic and apparent anisotropy in media with hexagonal symmetry typically used in surface wave tomography and sks splitting studies our analysis is on the level of the wave equation which makes it general and independent of specific data types or tomographic techniques we find that observed anisotropy can be explained by isotropic heterogeneity when elastic parameters take specific combinations of values in practice the uncertainties of inferred anisotropy are large enough to ensure that such a combination is always within the error bars it follows that commonly observed anisotropy can always be explained completely by a purely isotropic laminated medium unless all anisotropic parameters are known with unrealistic accuracy most importantly minute changes in the poorly constrained p wave anisotropy and the parameter can switch between the possible or impossible existence of an isotropic equivalent important implications of our study include 1 intrinsic anisotropy over tomographically resolved length scales is never strictly required when reasonable error bars for anisotropic parameters are taken into account 2 currently available seismic observables provide weak constraints on the relative contributions of intrinsic and apparent anisotropy 3 therefore seismic observables alone are not sufficient to constrain the magnitude of mantle flow 4 quantitative interpretations of anisotropy in terms of mantle flow require combined seismic geodynamic inversions as well as the incorporation of additional data such as topography gravity and scattered waves

full waveform tomography for radially anisotropic structure new insights into present and past states of the australasian upper mantle article i nfo we combine spectral element simulations and adjoint techniques in a non linear full seismic waveform tomography for the radially anisotropic structure of the australasian upper mantle our method allows us to explain 30 s waveforms in detail and it yields tomographic images with locally 2 lateral resolution in the course of 19 conjugate gradient iterations the total number of exploitable waveforms increased from 2200 to nearly 3000 the final model amsan 19 thus explains data that were not initially included in the inversion this is strong evidence for the effectiveness of the inversion scheme and the physical consistency of the tomographic model amsan 19 confirms long wavelength heterogeneities found in previous studies and it allows us to draw the following inferences concerning the past and present states of the australian upper mantle and the formation of seismic anisotropy 1 small scale neutral to low velocity patches beneath central australia are likely to be related to localised paleozoic intraplate deformation 2 increasing seismic velocities between the moho and 150 km depth are found beneath parts of proterozoic australia suggesting thermochemical variations related to the formation and fragmentation of a centralian superbasin 3 radial anisotropy above 150 km depth reveals a clear ocean continent dichotomy we find strong vshnvsv beneath the coral and tasman seas the anisotropy is strongest at the top of the inferred asthenospheric flow channel where strain is expected to be largest radial anisotropy beneath the continent is weaker but more variable localised patches with vshbvsv appear in accord with small scale intraplate deformation 4 the ocean continent dichotomy disappears gradually between 150 and 250 km depth where the continental lithospheric mantle and the oceanic asthenosphere pass into the underlying convecting mantle 5 significant anisotropy exists below 250 km depth its character can be explained by sublithospheric small scale convection and a change in the dominant glide system of olivine

a simple method for improving crustal corrections in waveform tomography summary accurate accounting for the effects of crustal structure on long period seismic surface waves and overtones is difficult but indispensable for determining elastic structure in the mantle while standard linear crustal corrections slc have been shown to be inadequate on the global scale newer non linear correction nlc techniques are computationally expensive when applied to waveforms containing higher frequencies and or overtones we devise implement and verify a modified slc approach that mimics the non linear effects of the crust without substantially increasing the computational costs while theoretically less accurate than the nlc approach in practice the reduced computational costs allow this modified linear correction mlc technique to be applied at higher frequencies and using more detailed crustal regionalizations than is possible with nlc in order to validate the mlc technique we use the spectral element method to carry out a series of synthetic tests these tests demonstrate that mlc nearly eliminates the contamination of mantle isotropic structure by unmodelled crustal effects which can be substantial in the uppermost 150 km when using slc furthermore we show that mlc significantly reduces contamination of anisotropic structure compared to slc the inaccuracies of which are significant in the upper 250 km and can even obliterate the mantle anisotropic signature at depths shallower than 100 km finally we apply the mlc technique to a real long period waveform data set and demonstrate the benefit of improved crustal corrections on the retrieved model

global mantle shear velocity model developed using nonlinear asymptotic coupling theory we present a three dimensional shear velocity model of the whole mantle developed using s h waveform data the model is expressed horizontally in terms of spherical harmonics up to degree 12 and vertically in terms of legendre polynomials up to degrees 5 and 7 in the upper and lower mantle respectively what distinguishes this model from other tomographic models published to date is 1 the theoretical normal mode based wave propagation approach where we include across branch mode coupling terms in order to model the body wave sensitivity to structure along the path more accurately 2 the wave packet weighting scheme which allows to balance contributions from high amplitude and low amplitude phases increasing the resolution in some parts of the mantle we also relax the constraints on the moho depth which is allowed to vary in the inversion thus absorbing some uncertainties in crustal structure the resulting model is generally in good agreement with other recent global mantle s velocity models and with some regional models the rms profile with depth has more power than other models in the upper mantle lower mantle transition region and the zone of increased power and low degree structure near the base of the mantle is confined to the last 500 km in depth this model provides a particularly good fit to the non hydrostatic geoid through harmonic degree 12 79 variance reduction as well as good fits to observed splitting functions of s velocity sensitive mantle modes indicating that both large scale and small scale features are really well constrained

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

quantifying seismic anisotropy induced by small scale chemical heterogeneities observations of seismic anisotropy are usually used as a proxy for lattice preferred orientation lpo of anisotropic minerals in the earth s mantle in this way seismic anisotropy observed in tomographic models provides important constraints on the geometry of mantle deformation associated with thermal convection and plate tectonics however in addition to lpo smallscale heterogeneities that cannot be resolved by long period seismic waves may also produce anisotropy the observed i e apparent anisotropy is then a combination of an intrinsic and an extrinsic component assuming the earth s mantle exhibits petrological inhomogeneities at all scales tomographic models built from long period seismic waves may thus display extrinsic anisotropy in this paper we investigate the relation between the amplitude of seismic heterogeneities and the level of induced s wave radial anisotropy as seen by long period seismic waves we generate some simple 1 d and 2 d isotropic models that exhibit a power spectrum of heterogeneities as what is expected for the earth s mantle that is varying as 1 k with k the wavenumber of these heterogeneities the 1 d toymodels correspond to simple layeredmedia in the 2 d case our models depict marble cake patterns in which an anomaly in shear wave velocity has been advected within convective cells the long wavelength equivalents of these models are computed using upscaling relations that link properties of a rapidly varying elastic medium to properties of the effective that is apparent medium as seen by long period waves the resulting homogenized media exhibit extrinsic anisotropy and represent what would be observed in tomography in the 1 d case we analytically show that the level of anisotropy increases with the square of the amplitude of heterogeneities this relation is numerically verified for both 1 d and 2 d media in addition we predict that 10 per cent of chemical heterogeneities in 2 d marble cake models can induce more than 3 9 per cent of extrinsic radial s wave anisotropy we thus predict that a non negligible part of the observed anisotropy in tomographic models may be the result of unmapped small scale heterogeneities in the mantle mainly in the form of fine layering and that caution should be taken when interpreting observed anisotropy in terms of lpo and mantle deformation this effect may be particularly strong in the lithosphere where chemical heterogeneities are assumed to be the strongest the authors 2017

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

fully nonlinear inversion of fundamental mode surface waves for a global crustal model 1 we use neural networks to find 1 dimensional marginal probability density functions pdfs of global crustal parameters the information content of the full posterior and prior pdfs can quantify the extent to which a parameter is constrained by the data we inverted fundamental mode love and rayleigh wave phase and group velocity maps for pdfs of crustal thickness and independently of vertically averaged crustal shear wave velocity using surface wave data with periods t 35 s for phase velocities and t 18 s for group velocities moho depth and vertically averaged shear wave velocity of continental crust are well constrained but vertically averaged shear wave velocity of oceanic crust is not resolvable the latter is a priori constrained by crust2 0 we show that the resulting model allows to compute global crustal corrections for surface wave tomography for periods t 50 s for phase velocities and t 60 s for group velocities

assessment of global phase velocity models summary we construct new love and rayleigh wave phase velocity models based on measurements made from an aspherical starting model and strict data quality control derived from cluster analyses these new models are in good agreement with previous ones and the question arises whether the slight changes show an improved capacity to explain the data to this effect we propose an objective method to compare different phase velocity models published in recent literature the method is based on comparing calculated synthetics to raw seismograms we find a reassuring convergence between all the models we tested at the longest periods and more scatter at the shorter periods at 40 s the different models show gains of up to 3 5 cycles over prem generally the higher the gain over prem the smaller the period considered which confirms that the earth s heterogeneity is strongest in the uppermost parts of the earth apart from assessing different models against each other our method gives an estimate comparable to cluster analyses of the underlying data errors that went into the construction of the models themselves moreover ray coverage is still far from perfect for constructing phase velocity models as a result we find that without precaution degree zero is biased through spectral leakage by 0 1 to 0 2 per cent with respect to prem the earliest information concerning the earth s 3 d structure came from surface waves when tams 1921 noticed clear velocity differences for waves propagating along continental versus oceanic paths gutenberg 1924 attempted an explanation of such differences in terms of regional variations in crustal structure when he noticed that short period surface waves are more sensitive to crustal structure than long period ones this led the way to intensive studies both theoretical and observational to link dispersive properties of surface waves to the internal structure of the earth the first regional models of the earth s dispersive properties of crust and upper mantle are summarized in papers by brune 1969 and dorman 1969 respectively with the start of digital recording of seismograms in the late

probability of radial anisotropy in the deep mantle article i nfo it is well established that the earth s uppermost mantle is anisotropic but observations of anisotropy in the deeper mantle have been more ambiguous radial anisotropy the discrepancy between love and rayleigh waves was included in the top 220 km of prem but there is no consensus whether anisotropy is present below that depth fundamental mode surface waves for commonly used periods up to 200 s are sensitive to structure in the first few hundred kilometers and therefore do not provide information on anisotropy below higher mode surface waves however have sensitivities that extend to and below the transition zone and should thus give insight about anisotropy at greater depths but they are very difficult to measure we previously developed a new technique to measure higher mode surface wave phase velocities with consistent uncertainties these data are used here to construct probability density functions of a radially anisotropic earth model down to approximately 1500 km in the uppermost mantle we obtain a high probability of faster horizontally polarized shear wave speed likely to be related to plate motion in the asthenosphere and transition zone however we find a high probability of faster vertically polarized shear wave speed to a depth of 1500 km in the lower mantle we see no significant shear wave anisotropy this is consistent with results from laboratory measurements which show that lower mantle minerals are anisotropic but lpo is unlikely to develop in the pressure temperature conditions present in the mid mantle 2008 elsevier b v all rights reserved

non linear crustal corrections in high resolution regional waveform seismic tomography summary we compare 3 d upper mantle anisotropic structures beneath the north american continent obtained using standard and improved crustal corrections in the framework of non linear asymptotic coupling theory nact applied to long period three component fundamental and higher mode surface waveform data our improved approach to correct for crustal structure in high resolution regional waveform tomographic models goes beyond the linear perturbation approximation and is therefore more accurate in accounting for large variations in moho topography within short distances as observed for instance at ocean continent margins this improved methodology decomposes the shallow layer correction into a linear and non linear part and makes use of 1 d sensitivity kernels defined according to local tectonic structure both for the forward computation and for the computation of sensitivity kernels for inversion the comparison of the 3 d upper mantle anisotropic structures derived using the standard and improved crustal correction approaches shows that the model norm is not strongly affected however significant variations are observed in the retrieved 3 d perturbations the largest differences in the velocity models are present below 250 km depth and not in the uppermost mantle as would be expected we suggest that inaccurate crustal corrections preferentially map into the least constrained part of the model and therefore accurate corrections for shallow layer structure are essential to improve our knowledge of parts of the upper mantle where our data have the smallest sensitivity

epcrust a reference crustal model for the european plate summary we present a new crustal model for the european plate derived from collection and critical integration of information selected from the literature the model covers the whole european plate from north africa to the north pole 20 n 90 n and from the mid atlantic ridge to the urals 40 w 70 e the chosen parametrization represents the crust in three layers sediments upper crust and lower crust and describes the 3 d geometry of the interfaces and seismologically relevant parameters isotropic p and s wave velocity plus density with a resolution of 0 5 0 5 on a geographical latitude longitude grid we selected global and local models derived from geological assumptions active seismic experiments surface wave studies noise correlation receiver functions model epcrust presents significant advantages with respect to previous models it covers the whole european plate it is a complete and internally consistent model with all the parameters provided also for the sedimentary layer it is reproducible it is easy to update in the future by adding new contributions and it is available in a convenient digital format epcrust could be used to account for crustal structure in seismic wave propagation modelling at continental scale or to compute linearized crustal corrections in continental scale seismic tomography gravity studies dynamic topography and other applications that require a reliable crustal structure because of its resolution our model is not suited for local scale studies such as the computation of earthquake scenarios where more detailed knowledge of the structure is required we plan to update the model as new data will become available and possibly improve its resolution for selected areas in the future

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

trace element partitioning during high p partial melting and melt rock interaction an example from northern fiordland new zealand pods of granulite facies dioritic gneiss in the pembroke valley milford sound new zealand preserve peritectic garnet surrounded by trondhjemitic leucosome and vein networks that are evidence of high p partial melting garnet bearing trondhjemitic veins extend into host gabbroic gneiss where they are spatially linked with the recrystallization of comparatively low p two pyroxene hornblende granulite to fine grained high p garnet granulite assemblages in garnet reaction zones new data acquired using a laser ablation inductively coupled plasma mass spectrometer la icpms for minerals in various textural settings indicate differences in the partitioning of trace elements in the transition of the two rock types to garnet granulite mostly due to the presence or absence of clinozoisite garnet in the garnet reaction zone gabbroic gneiss has a distinct trace element pattern inherited from reactant gabbroic gneiss hornblende peritectic garnet in the dioritic gneiss and garnet in trondhjemitic veins from the pembroke granulite have trace element patterns inherited from the melt producing reaction in the dioritic gneiss the distinct trace element patterns of garnet link the trondhjemitic veins geochemically to sites of partial melting in the dioritic gneiss

assessment of tomographic mantle models using spectral element seismograms summary we investigated the agreement between real seismograms and those predicted by long wavelength mantle models by looking at phase and amplitude differences we computed full synthetic seismograms using a spectral element method together with 3 d mantle models and the appropriate crustal model on top we selected differently damped mantle models to see the effect of regularization on the computed seismograms to check the phase agreement we measured time shifts between the real and synthetic surface waves and body wave phases such as p s and ss using a cross correlation technique we also compared the amplitudes of the real and synthetic seismograms to understand how well the models explain not only the phases but the whole waveforms 3 d mantle models improve the phase agreement of surface waves in particular the remaining misfit however is still so large that we cannot distinguish between different tomographic models we suggest that this is mainly due to an imperfect modelling of the crust and or source location if body waves are included which have to be addressed in future inversions amplitude mismatches are large regardless which 3 d mantle model is used we observe that 3 d scattering or focusing defocusing effects can only explain half of the surface wave amplitudes whereas body wave amplitudes are dominated by scattering effects 1 d q models particularly in the crust and upper mantle strongly affect surface wave amplitudes and have to be modelled properly

finite frequency effects in global surface wave tomography summary we compare traditional ray theoretical surface wave tomography with finite frequency tomography using 3 d born sensitivity kernels for long period fundamental mode dispersion measurements the 3 d kernels preserve sidelobes beyond the first fresnel zone and fully account for the directional dependence of surface wave scattering and the effects of timedomain tapering and seismic source radiation tomographic inversions of love and rayleigh phase delay measurements and synthetic checkerboard tests show that 1 small scale s wave velocity anomalies are better resolved using finite frequency sensitivity kernels especially in the lowermost upper mantle 2 the resulting upper mantle heterogeneities are generally stronger in amplitude than those recovered using ray theory and 3 finite frequency tomographic models fit long period dispersion data better than ray theoretical models of comparable roughness we also examine the reliability of 2 d phase velocity sensitivity kernels in global surface wave tomography and show that phase velocity kernels based upon a forwardscattering approximation or previously adopted geometrical simplifications do not reliably account for finite frequency wave propagation effects 3 d sensitivity kernels with full consideration of directional dependent seismic scattering are the preferred method of inverting long period dispersion data finally we derive 2 d boundary sensitivity kernels for lateral variations in crustal thickness and show that finite frequency crustal effects are not negligible in long period surface wave dispersion studies especially for paths along continent ocean boundaries unfortunately we also show that in global studies linear perturbation theory is not sufficiently accurate to make reliable crustal corrections due to the large difference in thickness between oceanic and continental crust

thermo rheological structure of the northern margin of the south china sea structural and geodynamic implications abstract rheological properties of continental lithosphere are key controls on the behavior of continental deformation using thermal structure constrained by surface heat flow data and measured thermal properties of rocks the present study calculates different thermo rheological structure scenarios for the ocean continent transition oct at the northern margin of the south china sea using two different models a conventional model taking into account frictional sliding and power law creep and a model that additionally includes a high pressure brittle fracture mechanism two compositions of the lower part of the lithosphere are considered a soft case with felsic granulite lower crust and wet peridotite lithospheric mantle and a hard case with mafic granulite lower crust and dry peridotite lithospheric mantle the former scenario shows a major rheological change from a jelly sandwich to a christmas tree type of rheology from north to south along the margin this complex rheological structure explains lateral changes in earthquake distribution and geometries of extensional faults of the oct at the northern margin of the south china sea further our analyses indicate that the initial lithospheric rheology profile probably has only one ductile layer in the lower part of upper crust such an initial lithospheric rheology model predicts focused extension to form asymmetric margins which is the case for the scs

seismic and electrical signatures of the lithosphere asthenosphere system of the normal oceanic mantle although plate tectonics started as a theory of the ocean basins nearly 50 years ago the mechanical details of how it works are still poorly known our understanding of these details has been hampered partly by our inability to characterize the physical nature of the lithosphere asthenosphere system las beneath the ocean we review the existing observational constraints on the seismic and electrical properties of the las particularly for normal oceanic regions away from mid oceanic ridges hot spots and subduction zones where plate tectonics is expected to present its simplest form whereas a growing volume of seismic data on land has provided remarkable advances in large scale pictures seafloor observations have been shedding new light on essential details by combing through these observational constraints researchers are unveiling the nature of the enigmatic las future directions for large scale seafloor observations are also discussed

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

nonlinear crustal corrections for normal mode seismograms we present an efficient and accurate method for calculating local nonlinear crustal effects on the eigenfrequency of free oscillations of the earth we implement the method in the calculation of synthetic normal mode seismograms and demonstrate that neglecting the nonlinear crustal effects in the tomographic waveform inversion leads to velocity models that appreciably overestimate fast velocity anomalies beneath orogenic belts and cratons at 250 400 km depth online material color versions of figures

ubiquitous lower mantle anisotropy beneath subduction zones seismic anisotropy provides key information to map the trajectories of mantle flow and understand the evolution of our planet while the presence of anisotropy in the uppermost mantle is well established the existence and nature of anisotropy in the transition zone and uppermost lower mantle are still debated here we use three dimensional global seismic tomography images based on a large dataset that is sensitive to this region to show the ubiquitous presence of anisotropy in the lower mantle beneath subduction zones whereas above the 660 km seismic discontinuity slabs are associated with fast sv anomalies up to about 3 in the lower mantle fast sh anomalies of about 2 persist near slabs down to about 1 000 1 200 km these observations are consistent with 3d numerical models of deformation from subducting slabs and the associated lattice preferred orientation of bridgmanite produced in the dislocation creep regime in areas subjected to high stresses this study provides evidence that dislocation creep may be active in the earth s lower mantle providing new constraints on the debated nature of deformation in this key but inaccessible component of the deep earth lower mantle anisotropy is present beneath all subduction zones indicating that dislocation creep is active in the lower mantle according to analysis of 3d global seismic tomography images

new images of the earth s upper mantle from measurements of surface wave phase velocity anomalies 1 the sensitivity of a surface wave to the lateral structure of the earth s mantle depends on the local structure and thickness of the crust particularly at short periods the strong lateral heterogeneity of the crust has a significant nonlinear effect on the surface wave sensitivity functions thus far this effect has not been quantified and tomographic studies of the upper mantle based on surface wave observations have not taken it into account on the basis of a jeffreys wentzel kramers brillouin jwkb description of surface wave propagation we find and discuss the lateral variations of the sensitivity of love and rayleigh waves to mantle seismic anomalies associated with a realistic model of the crust mooney et al 1998 we then use the resulting laterally varying sensitivity kernels to determine a new tomographic image of horizontally and vertically polarized shear velocity in the upper mantle from love and rayleigh wave phase velocity measurements periods from 35 to 300 s in terms of large scale patterns of high and low velocity our model is similar to previously published ones confirming among other features the anomalous anisotropy underlying the central pacific ekstrom and dziewonski 1998 we find however that the lateral dependence of the surface wave sensitivity kernels has a significant effect on the absolute amplitude of the anomalies which should not be neglected as we attempt to obtain higher resolution images of the upper mantle