an automated time window selection algorithm for seismic tomography we present flexwin an open source algorithm for the automated selection of time windows on pairs of observed and synthetic seismograms the algorithm was designed specifically to accommodate synthetic seismograms produced from 3 d wavefield simulations which capture complex phases that do not necessarily exist in 1 d simulations or traditional traveltime curves relying on signal processing tools and several user tuned parameters the algorithm is able to include these new phases and to maximize the number of measurements made on each seismic record while avoiding seismic noise our motivation is to use the algorithm for iterative tomographic inversions in which the synthetic seismograms change from one iteration to the next hence automation is needed to handle the volume of measurements and to allow for an increasing number of windows at each model iteration the algorithm is sufficiently flexible to be adapted to many tomographic applications and seismological scenarios including those based on synthetics generated from 1 d models we illustrate the algorithm using data sets from three distinct regions the entire globe the japan subduction zone and southern california

a geodynamic model of mantle density heterogeneity using cenozoic and mesozoic plate motion reconstructions we derive a model of present day mantle density heterogeneity under the assumption that subducted slabs sink vertically into the mantle the thermal buoyancy of these slabs is estimated from the observed thermal subsidence cooling of oceanic lithosphere slab velocities in the upper mantle are computed from the local convergence rate we assume that slabs cross the upper lower mantle interface and continue sinking into the lower mantle with a reduced velocity for a velocity reduction factor between 2 and 5 our slab heterogeneity model is as correlated with current tomographic models as these models are correlated with each other we have also computed a synthetic geoid from our density model for a viscosity increase of about a factor of 40 from the upper to lower mantle our model predicts the first 8 spherical harmonic degrees of the geoid with statistical confidence larger than 95 and explains 84 of the observed geoid assuming that the model c21 and s21 terms are absent due to a long relaxation time for earth s rotational bulge otherwise 73 of the geoid variance is explained the viscosity increase is consistent with our velocity reduction factor for slabs entering the lower mantle since downwelling velocities are expected to scale roughly as the logarithm of viscosity loge 40 3 7 these results show that the history of plate tectonics can explain the main features of the present day structure of the mantle the dynamic topography induced by this heterogeneity structure consists mainly of about 1 km amplitude lows concentrated along the active continental margins of the pacific basin our model can also be used to predict the time variation of mantle heterogeneity and the gravity field we find that the age of the geoid defined as the time in the past before which the geoid becomes uncorrelated with the present geoid is about 50 m y our model for the history of the degree 2 geoid which is equivalent to the history of the inertia tensor should give us a tool to study the variations in earth s rotation pole indicated in paleomagiietic studies

radial thermo chemical structure beneath western and northern pacific from seismic waveform inversion abstract the earth s deep mantle seismic structure is dominated by two large low shear wave velocity provinces llsvps located beneath africa and the pacific while the existence of these structures has been attested by many studies and data sets their detailed nature purely thermal or thermo chemical is still a matter of debate discriminating between these hypotheses requires constraints independent from seismic velocity structure seismic shear wave attenuation measured by the quality factor q s strongly depends on temperature but not or weakly on composition it may bring key information on temperature resolving in turn the trade off between temperature and composition here we invert seismic waveform data for radial models of shear wave velocity anomalies dln v s and q s at two different locations in the pacific and from a depth of 2000 km down to the core mantle boundary cmb we show that western pacific wp models sampling the western tip of the pacific llsvp and the caroline plume cannot be explained by thermal anomalies alone but require excess in iron of 4 0 from the cmb up to 2600 km by contrast northern pacific models np if unaffected by seismic anisotropy may have a purely thermal origin based on these observations we build radial thermo chemical models at wp and np

constraints on the correlation of p and s wave velocity heterogeneity in the mantle from p pp ppp and pkpab traveltimes we investigate the correlation of large scale p and s velocity heterogeneity in the mantle by determining how well 106 000 compressional p pp ppp and pkpab traveltimes can be explained by s wave velocity model s20rts scaled using a depth dependent factor and by a model in which the lateral p velocity variations are different we first assess the assumption that p wave traveltimes can be explained by a model in which lateral p velocity variations p are identical to s velocity variations s in model s20rts for a given depth we project s from s20rts into model s2p using a depth dependent scaling factor r defined as s r z x p we find by grid search that the highest reduction of data variance is obtained when r increases linearly from 1 25 at the surface to 3 0 at the core mantle boundary a comparison of s wave ss and p wave pp traveltimes for identical source receiver pairs also indicates that r increases with depth significantly higher variance reduction is not obtained when r is parametrized with an additional degree of freedom therefore the precise shape of r cannot be constrained by our data p and pp wave traveltime anomalies with respect to the scaled model s2p yield coherent geographic variations this indicates that there are large scale lateral p velocity variations in the mantle that are different from those in model s2p we estimate these variations by inverting p wave traveltime anomalies with respect to model s2p for a degree 12 model of p velocity heterogeneity this model p 12 s 2 p indicates where in the well sampled mantle regions we need to modify model s2p to further improve the fit to the traveltime data anomalies in p12 s 2 p exist throughout the mantle it is therefore not obvious that compositional heterogeneity is prominent in the lower 1000 km of the mantle only as suggested previously low p wave velocities in the upper mantle beneath oceans are the strongest anomalies in p12 s 2 p and explain better the delayed traveltimes of pp wave phases with oceanic surface refection points lower mantle anomalies include high and low p velocity structures beneath eastern asia and north america respectively the high p velocity anomaly in the lower mantle beneath the central pacific is consistent with the assertion made by other researchers that large scale lower mantle upwellings are not purely thermal in origin

complex anisotropy in d beneath the eastern pacific from sks skks splitting discrepancies article i nfo although observations of seismic anisotropy in the lowermost mantle are abundant the mechanism which generates anisotropy in the d layer is not well understood most observational constraints on d anisotropy come from the splitting of shear waves that propagate nearly horizontally through the lowermost mantle however anisotropy in the d layer can also give rise to discrepancies in shear wave splitting for sks and skks phases for the same event station pair as these phases sample different regions of the lowermost mantle here i report observations of strongly discrepant sks skks splitting observed at broadband stations in western mexico and california in particular strong skks splitting with fast polarization directions near 60 and delay times up to 3 s is observed for a group of raypaths that sample a region of the d layer beneath the eastern pacific ocean a comparison of skks splitting with sks splitting observed from the same events as well as with sks splitting observed at a variety of backazimuths at each station suggests that the anomalous anisotropic structure is in the lowermost mantle my preferred model for the unusual anisotropic geometry in this region is large shear deformation in d at the edge of a region where slab material impinges upon the core mantle boundary resulting in lattice preferred orientation of lower mantle minerals

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

the stability and structure of primordial reservoirs in the lower mantle insights from models of thermochemical convection in three dimensional spherical geometry large scale chemical lateral heterogeneities are inferred in the earth s lowermost mantle by seismological studies we explore the model space of thermochemical convection that can maintain reservoirs of dense material for a long period of time by using similar analysis in 3 d spherical geometry in this study we focus on the parameters thought to be important in controlling the stability and structure of primordial dense reservoirs in the lower mantle including the chemical density contrast between the primordial dense material and the regular mantle material buoyancy ratio thermal and chemical viscosity contrasts volume fraction of primordial dense material and the clapeyron slope of the phase transition at 660 km depth we find that most of the findings from the 3 d cartesian study still apply to 3 d spherical cases after slight modifications varying buoyancy ratio leads to different flow patterns from rapid upwelling to stable layering and large thermal viscosity contrasts are required to generate long wavelength chemical structures in the lower mantle chemical viscosity contrasts in a reasonable range have a second order role in modifying the stability of the dense anomalies the volume fraction of the initial primordial dense material does not effect the results with large thermal viscosity contrasts but has significant effects on calculations with intermediate and small thermal viscosity contrasts the volume fraction of dense material at which the flow pattern changes from unstable to stable depends on buoyancy ratio and thermal viscosity contrast an endothermic phase transition at 660 km depth acts as a filter allowing cold slabs to penetrate while blocking most of the dense material from penetrating to the upper mantle

geographic boundary of the pacific anomaly and its geometry and transitional structure in the north 1 we determine the geographical boundary and average shear velocity structure of the pacific anomaly at the base of the mantle based on travel time analysis of scsh sh and scs2 scsscs ss phases and waveform modeling results we further constrain the detailed geometry of the northern anomaly around 20 n 170 e and its transition to the surrounding high velocity region along three perpendicular cross sections on the basis of forward waveform modeling of the observed direct s and scs phases the observed differential travel time residuals and waveform modeling results allow the whole geographic boundary of the anomaly to be delineated and the area of the base of the anomaly is estimated to be 1 9 107 km2 the maximum shear velocity perturbation inside the anomaly reaches 5 in the lowermost 500 km of the mantle waveform analysis suggests that the northern anomaly reaches 450 km above the cmb with both steeply and shallowly dipping edges and its basal layer extends beneath the surrounding mantle with the degree of extension changing rapidly across a small distance the inferred characteristics of the anomaly support the previous suggestion that the pacific anomaly represents a chemical anomaly however unlike the inferred features of the african anomaly pointing to an ancient compositionally distinct and geologically stable anomaly the existence of several separated piles extending into the mid lower mantle the complex morphology of the piles with both steeply and shallowly dipping edges and the presence of many ultra low velocity zones at its base suggest that the pacific anomaly likely possesses varying intrinsic compositions and exhibits complex interaction with the surrounding mantle

seismic evidence for earth s crusty deep mantle abstract seismic tomography resolves anomalies interpreted as oceanic lithosphere subducted deep into earth s lower mantle however the fate of the compositionally distinct oceanic crust that is part of the lithosphere is poorly constrained but provides important constraints on mixing processes and the recycling process in the deep earth we present high resolution seismic array analyses of anomalous p waves sampling the deep mantle and deterministically locate heterogeneities in the lowermost 300 km of the mantle spectral analysis indicates that the dominant scale length of the heterogeneity is 4 to 7 km the heterogeneity distribution varies laterally and radially and heterogeneities are more abundant near the margins of the lowermost mantle large low velocity provinces llvps consistent with mantle convection simulations that show elevated accumulations of deeply advected crustal material near the boundaries of thermo chemical piles the size and distribution of the observed heterogeneities is consistent with that expected for subducted oceanic crust these results thus suggest the deep mantle contains an imprint of continued subduction of oceanic crust stirred by mantle convection and modulated by long lasting thermo chemical structures the preferred location of the heterogeneity in the lowermost mantle is consistent with a thermo chemical origin of the llvps our observations relate to the mixing behaviour of small length scale heterogeneity in the deep earth and indicate that compositional heterogeneities from the subduction process can survive for extended times in the lowermost mantle

low seismic resolution cannot explain s p decorrelation in the lower mantle 1 inverted models of the deep mantle show a decorrelation between maps of shear vs and compressional vp wave velocities an anti correlation between the bulk sound velocity v and vs and a much larger variability of vs with respect to vp expressed by large values of the ratio of their relative lateral variations we carried out synthetic tests to verify if these features could be artifacts explained by limits in tomographic resolution synthetic data are calculated for an input model and linearly inverted as in tomography to find an output model comparing the values of the aforementioned parameters for two different chemically homogeneous input models with the associated reconstructed output ones we found that artifacts caused by realistic data noise and the nonuniform distribution of seismic sources and stations over the globe are not sufficient to introduce the features previously described we confirm that compositional effects are required to explain them

sp12rts a degree 12 model of shear and compressional wave velocity for earth s mantle we present the new model sp12rts of isotropic shear wave vs and compressional wave vp velocity variations in the earth s mantle sp12rts is derived using the same methods as employed in the construction of the shear wave velocity models s20rts and s40rts and the same data types sp12rts includes additional traveltime measurements of p waves and new splitting measurements 33 normal modes with sensitivity to the compressional wave velocity and 9 stoneley modes with sensitivity primarily to the lowermost mantle contrary to s20rts and s40rts variations in vs and vp are determined without invoking scaling relationships lateral velocity variations in sp12rts are parametrised using spherical harmonics up to degree 12 to focus on long wavelength features of vs and vp and their ratio r largelow velocity provinces llvps are observed for both vs and vp sp12rts also features an increase of r up to 2500 km depth followed by a decrease towards the core mantle boundary a negative correlation between the shear wave and bulk sound velocity variations is observed for both the llvps and the surrounding mantle these characteristics can be explained by the presence of post perovskite or large scale chemical heterogeneity in the lower mantle

on the temporal evolution of long wavelength mantle structure of the earth since the early paleozoic the seismic structure of the earth s lower mantle is characterized by a dominantly degree 2 pattern with the african and pacific large low shear velocity provinces i e llsvp that are separated by circum pacific seismically fast anomalies it is important to understand the origin of such a degree 2 mantle structure and its temporal evolution in this study we investigated the effects of plate motion history and mantle viscosity on the temporal evolution of the lower mantle structure since the early paleozoic by formulating 3 d spherical shell models of thermochemical convection for convection models with realistic mantle viscosity and no initial structure it takes about 50 myr to develop dominantly degree 2 lower mantle structure using the published plate motion models for the last either 120 ma or 250 ma however it takes longer time to develop the mantle structure for more viscous mantle while the circum pangea subduction in plate motion history models promotes the formation of degree 2 mantle structure the published pre pangea plate motions before 330 ma produce relatively cold lower mantle in the african hemisphere and significant degree 1 structure in the early pangea 300 ma or later times even if the lower mantle has an initially degree 2 structure and a viscosity as high as 1023 pas this suggests that the african llsvp may not be stationary since the early paleozoic with the published plate motion models and lower mantle viscosity of 1022 pas our mantle convection models suggest that the present day degree 2 mantle structure may have largely been formed by 200 ma

lower mantle structure from scs s differential travel times knowledge of the spectrum of structure in the lower mantle is crucial to our understanding of the dynamical evolution of the earth and in principle can be inferred from the analysis of global seismic data sets the long wavelength compressional velocity structure has usually been constrained through tomographic inver sion of the isc catalogue of p wave travel times1 3 whereas shear velocity has been inferred from waveform modelling of long period shear waves4 6 the models that have been produced are similar in only the largest scale features7 and explain little of the variance of the raw data used in their construction thus there is a legitimate concern that the current generation of global scale models give only a crude approximation to the largest scale structure and that there may be significant aliasing of short wavelength heterogeneity here we use scs s differential travel times to demonstrate that the three dimensional structure of the lower mantle is indeed dominated by continental scale features particularly convincing is the fact that the features are apparent in the raw data and are not the product of a complicated modelling procedure

seismic rays and traveltime tomography of strongly heterogeneous mantle structure application to the central mediterranean summary the structure of the earth s upper mantle near convergent plate margins such as along the nubia eurasia collision zone in the mediterranean involves strong seismic wave speed contrasts associated with subducting lithospheric slabs and opening backarc basins in this environment seismic wave propagation is strongly influenced by heterogeneity and requires appropriate modelling practice although accurate numerical methods are often used to model seismic traveltimes in the crust only approximate techniques have been used for the mantle on the assumption that speed contrasts are weaker we devise optimize and test a method aimed at recovering strongly heterogeneous mantle structures using a finite difference scheme to calculate first arrival traveltimes and trace seismic rays with high accuracy even in the presence of strong gradients we adapt this forward scheme successfully used in local scale tomography to spherical geometry through source specific earth flattening approximations and we split calculations in meshes with different step size to model optimally the crust with a 2 km step and the mantle 6 km step we then use an iterative non linear inversion approach starting from a simple 1 d prior model we test the ability of this procedure to reconstruct sample structures devised to be illustrative for the mediterranean region using synthetic data calculated on the real distribution of sources and stations reported by the bulletins of the international seismological centre isc besides regular checkerboard patterns we also reconstruct a more representative model different strategies are used and compared in linear and non linear inversion we find that a linear approach by which rays are only traced once in the background model may result in an illusory fit to data realistic upper mantle structures strongly deflect seismic rays and correct paths can only be found after a few iterations although linear inversion seems able to identify the main features quite well we verify how non linear inversion and 3 d ray tracing significantly improve the results especially when we attempt to reconstruct a realistic structure we also apply the finite difference non linear traveltime tomography to data from the isc to retrieve upper mantle structure in the central mediterranean we verify that the non linear inversion is able to reveal sharpened velocity contrasts and thinner bodies than linear inversion clear differentiation found in the nonlinear result between signatures of northern and southern dinarides showing lithosphere subducting only beneath the southern sector is more coherent with the regional geodynamic framework such improvements due to non linear mantle tomography may contribute to the general picture of slab detachment and small scale mantle convection in the mediterranean region and therefore significantly impact on geodynamic implications of resulting models

c3 c4 vegetation evolution over the last 7 0 myr in the chinese loess plateau evidence from pedogenic carbonate δ13c the stable carbon and oxygen isotopic compositions of soil carbonate were measured on an eolian loess and red clay sequence at lingtai the chinese loess plateau this sequence is composed of 130 m of tertiary red clay deposits with a basal age of 7 05 ma overlain by 175 m of pleistocene loess in the field we identified ca 110 carbonate nodule horizons in the red clay and 27 nodule horizons in the loess these carbonate nodule horizons are formed by leaching and re precipitation of carbonate from the eolian material the d13c record of soil carbonate indicates a major expansion of c 4 plants at ca 4 0 myr in the loess plateau this event is comparable in timing with the expansion of c 4 plants in northern north america cerling et al 1997 nature 389 153 158 but is ca 3 million years later than the c 4 biomass expansion in pakistan quade et al 1989 nature 342 163 166 the pedogenic characteristics of the soils and the d18o record in the red clay suggest that the c 4 plant expansion in the loess plateau was not driven by local climatic changes which may support cerling et al s 1997 assertion that the decline of atmospheric co 2 levels in the neogene is responsible for this global vegetation change our record also implies that the tibetan plateau could have been uplifted to a critical height in the late miocene thus resulting in the formation of the atmospheric great east asia trough 2000 elsevier science b v all rights reserved

long period body wave traveltimes through the crust implication for crustal corrections and seismic tomography summary the traveltimes of p and sh waves through the crust depend strongly on wave period at periods longer than 10 15 s where traveltime measurements for indirect e g surface reflected and core reflected waves are typically made the traveltimes are shorter than predicted by ray theory crustal corrections often used in global mantle tomography to isolate the effects of the crust on teleseismic traveltimes may have a complex frequency dependence and influence finite frequency inversions crustal corrections for profiles of crust2 0 and the prem reference model for the mantle may be several seconds larger or smaller than ray theoretical values depending on crustal thickness crustal velocities and wave period this variability is observed in the difference times between the seismic phases ss and s and between pp and p it is therefore important to incorporate the effects of the crust on traveltimes in finite frequency tomography in order to take full advantage of the variable mantle sensitivity of body waves at different periods

anisotropy and vp vs in the uppermost mantle beneath the western united states from joint analysis of pn and sn phases pn and sn phases are valuable for resolving velocity structure in the mantle lid as they propagate horizontally right below the moho relatively few sn tomography attempts have been made compared to pn because sn is often highly attenuated or buried in p wave coda usarray has greatly increased data coverage for regional phases and both pn and sn are routinely picked by network analysts here we jointly invert pn and sn arrival time residuals with a modified time term analysis and a regularized tomography method and present new maps of crustal thickness uppermost mantle p velocity perturbations vp vs ratios and azimuthal anisotropy strength and orientation beneath the western united states the results indicate partially molten mantle below the snake river plain and the colorado plateau the seismic structure of the top 40 km of the mantle below the colorado plateau differs from that seen at greater depths in other studies such as surface wave or teleseismic body wave tomography whereas the snake river plain anomaly just below the moho is comparable to structures seen at about 200 km depth pn fast axes provide complementary information to sks shear wave splitting observations and our analysis indicates that in several regions in the western united states the orientation of azimuthal anisotropy changes with depth in the upper mantle however we have so far been unable to resolve shear wave splitting directly in sn waveforms which seem to be dominated by sn sv energy

multiple branching rupture of the 2009 tonga samoa earthquake several source models have been proposed to explain the enigmatic 2009 tonga samoa earthquake the long period data require a composite source model and can be fit with a normal faulting subevent followed by one or more reverse faulting subevents the short period data in contrast indicate a more compact rupture pattern around the epicenter the lack of a unified source model reflects the complexity of the event we analyze the spatiotemporal evolution of this earthquake with p wave back projection from globally distributed stations in different frequency bands low frequency 0 05 0 2 hz high frequency 0 2 2 hz and a multiple moment tensor inversion the rupture propagation revealed by back projection exhibits frequency dependent behavior with two branches of high frequency enriched bilateral rupture around the epicenter and a high frequency deficient rupture branch at the subduction interface a composite source model with one mw 8 0 normal faulting earthquake east of the trench axis seaward followed by one mw 8 1 reverse faulting earthquake along the subduction interface west of the trench axis landward can explain the very long period data 200 500 s combined with high resolution swath bathymetry data the back projection images show that the azimuth of rupture branches east of the trench axis were controlled by the geometry of bending related faults on the pacific plate and that the rupture branch west of the trench axis may correlate with the along strike fore arc segmentation the rupture along the subduction interface was triggered by the seaward rupture and a partially subducted normal fault may have played a key role in facilitating the triggering the apparent normal reverse faulting interactions pose a higher seismic risk to this region than their individual strands at the northernmost corner of the tonga subduction zone

determination and analysis of long wavelength transition zone structure using ss precursors summary global mapping of 410 and 660 km discontinuity topography and transition zone thickness has proven to be a powerful tool for constraining mantle chemistry dynamics and mineralogy numerous seismic and mineral physics studies suggest that the 410 km discontinuity results from the phase change of olivine to wadsleyite and the 660 km discontinuity results from the phase change of ringwoodite to perovskite and magnesiowustite underside reflections of the 410 and 660 km discontinuities arrive as precursors to ss with the recent development of a semi automated method of determining ss arrivals we have more than tripled the flanagan and shearer 1998a data set of handpicked ss waveforms we are able to increase resolution by stacking waveforms in 5 rather than 10 radius bins as well as increasing data coverage significantly in the southern hemisphere the resulting ss s410s and ss s660s times are heavily influenced by upper mantle velocity structure we perform a joint inversion for discontinuity topography and velocity heterogeneity as well as performing a simple velocity correction to the precursor differential times and find little difference between the two methods the 660 km discontinuity topography and transition zone thickness are correlated with velocities in the transition zone whereas the 410 km discontinuity topography is not in addition the 410 km discontinuity topography is not correlated with the 660 km discontinuity topography rather anticorrelated as expected due to the opposite signs of the clapeyron slopes of their respective phase changes these results suggest that whereas the topography of 660 km discontinuity could be dominated by thermal effects the topography of the 410 km discontinuity is likely dominated by compositional effects in addition unlike previous studies which find less topography on the 410 km discontinuity than on the 660 km discontinuity our 410 and 660 km topography have similar amplitudes

elasticity of single crystal periclase at high pressure and temperature the effect of iron on the elasticity and seismic parameters of ferropericlase in the lower mantle

brachiopod taxa and shell portions reliably recording past ocean environments toward establishing a robust paleoceanographic proxy 1 fossils of rhynchonelliform brachiopods marine invertebrates constitute 70 of the samples used for delineating a well known phanerozoic trend in oxygen isotope composition 18o of low mg calcite shells the trend represents secular variations in temperature and or 18o of ancient seawater however the use of brachiopods as a paleoceanographic proxy is based on the presupposition that the shell calcite is precipitated in isotopic equilibrium with ambient seawater here we show that high resolution time series of the shell 18o values along the maximum growth axes of two long lived cool water brachiopods are identical to greater than or less than those of calcite precipitated in isotopic equilibrium with ambient seawater depending on the difference in shell growth rates coupled with 18o data from subtropical and warm temperate brachiopod species examined in our previous studies we provide a sound framework illustrating which taxa and shell portions reliably recorded past ocean environments

shear and compressional velocity models of the mantle from cluster analysis of long period waveforms summary we present a new technique for the efficient measurement of the traveltimes of long period body wave phases the technique is based on the fact that all arrivals of a particular seismic phase are remarkably similar in shape for a single event this allows the application of cross correlation techniques that are usually used in a regional context to measure precise global differential times the analysis is enhanced by the inclusion of a clustering algorithm that automatically clusters waveforms by their degree of similarity this allows the algorithm to discriminate against unusual or distorted waveforms and makes for an extremely efficient measurement technique this technique can be applied to any seismic phase that is observed over a reasonably large distance range here we present the results of applying the algorithm to the long period channels of all data archived at the iris dmc from 1976 to 2005 for the seismic phases s and p from 23 to 100 and ss and pp from 50 to 170 the resulting large data sets are inverted along with existing surface wave and updated differential traveltime measurements for new mantle models of s and p velocity the resolution of the new model is enhanced particularly in the mid mantle where ss and pp turn we find that slow anomalies in the central pacific and africa extend from the core mantle boundary to the upper mantle but their direct connection to surface hotspots is beyond our resolution furthermore we find that fast anomalies that are likely associated with subducting slabs disappear between 1700 and 2500 km and thus are not continuous features from the upper to lower mantle despite our extensive coverage and high resolution of the mid mantle

simultaneous inversion for 3 d variations in shear and bulk velocity in the mantle until recently most of the seismic tomographic modeling has been addressing the question of lateral heterogeneity either in p or s wave velocities the s wave velocity variations are larger and hence provide stronger signal on long period waveforms the direct p travel times being the first arrivals on the other hand are most frequently reported in the international seismological centre isc bulletins in mineral physics experiments the variation in bulk velocity is more often measured to better understand the differences between vp and vp patterns and better link the results from mineral physics to those of seismic tomography we formulate the inverse problem in terms of relative perturbations in the shear velocity vs 12 and bulk sound velocity v k 12 we use a large data set which consists of waveforms waveform derived travel times and travel times from the isc bulletins the earthquakes are relocated using corrections for lateral heterogeneity the events which cannot be reliably determined are discarded the model is defined as spherical harmonics to degree 12 horizontally and as chebyshev polynomials to order 13 radially for both shear and bulk sound velocity the inversion is performed under smoothness constraint the resolution tests and bootstrapping analysis indicate that the model is well recovered particularly at long wavelength the results indicate a much larger variability of shear than bulk sound velocity the model explains observations well the most intriguing result obtained in this study is that the variations in shear velocity and bulk sound velocity are negatively correlated in the lowermost mantle the explanation is not very clear from the mineral physics point of view it is not unlikely that this could be explained in terms of thermal variation even though we are unwilling to rule out the possibility of large wavelength compositional variations

high resolution 3 d s velocity structure in the d region at the western margin of the pacific llsvp evidence for small scale plumes and paleoslabs abstract although previous tomographic studies found a large low s velocity province llsvp in the lowermost mantle beneath the pacific due to a lack of resolution it remains unclear whether the llsvp consists of clusters of small scale low velocity anomalies or large scale anomalies we recently deployed a seismic array in thailand which provides a dataset with wide azimuthal coverage at the western pacific llsvp we analyze the new dataset using waveform inversion and find high velocity anomalies extending vertically to a height of 400 km above the core mantle boundary cmb beneath the philippine sea and small scale low velocity patches with a diameter of 300 km at the cmb beneath new guinea the locations of the high velocity anomalies are consistent with the past izanagi plate subduction boundary and the low velocity anomalies can be interpreted as a small scale plume cluster hence we conclude that vertical flow upwelling plumes and downwelling of slabs is dominant in the lowermost mantle beneath the western pacific region

global upper mantle structure from long period differential travel times we have made over ten thousand measurements of pp p and ss s differential travel times from long period global digital seismograph network recordings of all events with mb 5 5 which occurred during the years 1976 to 1986 we have obtained reasonable global coverage with very good sampling of several regions of the world the residuals range from 5 to 5 s for pp p and 12 to 12 s for ss s and reveal a large scale pattern of heterogeneity when plotted at the reflected phase s bounce point our experiments indicate that lower mantle structure and source receiver structure can each contribute approximately 0 5 s to our measured pp p residuals so there is considerable signal to be explained the pattern observed in the pp p measurements is similar to the pattern observed in the ss s measurements with the ss s residuals 2 to 4 times larger in magnitude comparisons of our measured residuals to those predicted by the upper mantle models of woodhouse and dziewonski show that the overall patterns are quite similar but the amplitude of the model residuals is roughly a factor of 2 too small comparisons with the predictions of a whole mantle model of tanimoto again shows that the predicted pattern of residuals is reasonably consistent with the observations but now the predicted residuals are too large by about a factor of 2 this variation in predicted amplitudes is probably mainly due to differences in the near surface structure of the models we have also binned our measurements according to the tectonic regionalization gtr1 of jordan and find a qualitative correlation of average residual with tectonic region in particular precambrian shields show a strong anomaly and there is a correlation of residual size with the age of oceanic crust at the bounce point for all tectonic regions the ratio of ss s to pp p residuals is approximately 2 this ratio is consistent with a thermal origin for the observed signal finally our measurements show no compelling evidence for azimuthal anisotropy which might be related to fossil spreading direction or the direction of absolute plate motion such a signal is probably overwhelmed by the large signal from three dimensional structure

detection of ridge like structures in the pacific large low shear velocity province abstract waveform tomography is conducted for sh velocity structures of the entire mantle using approximately 3 5 times the data used for obtaining the previous model sh18ce the resultant new model sh18cex exhibits a cluster of ridge like low velocity anomalies in the western part of the pacific large low shear velocity province llsvp the location of the ridge like anomalies is in good agreement with the location of the abrupt change in the topography of the d discontinuity these results suggest that the llsvp is associated with a cluster of ridge like piles rather than a single large pile spread over the entire region the piles probably consist of intrinsically dense material however either their volume or density contrast may not be sufficiently large to develop large scale domes

global mantle tomography progress status in the past 10 years abstract we review the present status of global mantle tomography and discuss two main classes of models that have been developed in the past 10 years p velocity models based on large datasets of travel times from the international seismological centre bulletins often referred to as high resolution models and s velocity models based on a combination of surface wave and hand picked body wave travel times or waveforms referred to as long wavelength models we discuss their respective strengths and weaknesses as well as progress in the resolution of other physical parameters such as anisotropy anelasticity density and bulk sound velocity using tomographic approaches we present the view that future improvements in global seismic tomography require the utilization of the rich information contained in complete broadband seismic waveforms this is presently within our reach owing to theoretical progress as well as the increase in computational power in recent years

rapid south atlantic spreading changes and coeval vertical motion in surrounding continents evidence for temporal changes of pressure driven upper mantle flow the south atlantic region displays 1 a topographic gradient across the basin with africa elevated relative to south america 2 a bimodal spreading history with fast spreading rates in late cretaceous and eo oligocene and 3 episodic regional uplift events in the adjacent continents concentrated in late cretaceous and oligocene here we show that these observations can be linked by dynamic processes within earth s mantle through temporal changes in asthenosphere flow beneath the region the topographic gradient implies westward pressure driven mantle flow beneath the basin while the rapid spreading rate changes on order 10 million years require significant decoupling of regional plate motion from the large scale mantle buoyancy distribution through a mechanically weak asthenosphere andean topographic growth in late miocene can explain the most recent south atlantic spreading velocity reduction arising from increased plate boundary forcing associated with the newly elevated topography but this mechanism is unlikely to explain the late cretaceous tertiary spreading variations as changes in andean paleoelevation at the time are small we propose an unsteady pressure driven flow component in the asthenosphere beneath the south atlantic region to explain the late cretaceous tertiary spreading rate variations temporal changes in mantle flow due to temporal changes in regional mantle pressure gradients imply a correlation of horizontal and vertical motions we find that this prediction from our models agrees with geologic and geophysical observations of the south atlantic region including episodes of passive margin uplift regional basin reactivation and magmatic activity

imaging mantle transition zone thickness with sds ss finite frequency sensitivity kernels summary we invert differential sds ss traveltime residuals measured from stacked waveforms and finitefrequency sensitivity kernels for topography on the 410 and 660 km discontinuities this approach yields higher resolution images of transition zone thickness than previous stacking methods which simply average smooth over topographic features apparent structure measured using simple stacking is highly dependent upon the bin size of each stack by inverting for discontinuity topography with a variety of bin sizes we can more accurately calculate the true structure the inverted transition zone model is similar to simple stack models with an average thickness of 242 km but the lateral variations in thickness are larger in amplitude and smaller in scale fast seismic velocities in 3 d mantle models such as sb4l18 correlate with areas of thicker transition zone the elongated curvilinear regions of thickened transition zone that occur near subduction zones are narrow and high amplitude which suggests relatively little lateral spreading and warming of subducted lithosphere within the transition zone the anomalously thin transition zone regions are laterally narrow and not broadly continuous if these variations in transition zone thickness are interpreted as thermal in nature then this model suggests significant temperature variations on small lateral scales

lowermost mantle anisotropy beneath the northwestern pacific evidence from pcs scs sks and skks phases 1 in this study we utilize data from broadband seismic stations of the japanese f net network to investigate anisotropic structure in the lowermost mantle beneath the northwestern pacific the comparison of shear wave splitting from phases that have similar paths in the upper mantle but different paths in the lowermost mantle such as pcs scs or sks skks can yield constraints on anisotropy in the d region we measured splitting for sks skks pcs and scs phases at f net stations and compared the measured splitting parameters to previously published estimates of upper mantle anisotropy beneath the region we observed many examples of discrepant sks skks splitting and splitting of scs pcs sks and skks phases that does not agree well with the known upper mantle anisotropy beneath individual stations the most likely explanation for these discrepancies is a contribution to splitting from anisotropy in the lowermost mantle in particular for sks skks phases that sample the lowermost mantle just to the south and east of the kamchatka peninsula we observed generally n s fast directions with delay times between 0 5 and 1 5 s these data suggest the presence of a fairly large coherent region of deformation in the lowermost mantle beneath the northwestern pacific our preferred model for these observations is that solid state flow at the base of the mantle induces a lattice preferred orientation of lowermost mantle minerals generating a seismically anisotropic fabric

tethyan subducted slabs under india abstract tomographic imaging of the mantle under tibet india and the adjacent indian ocean reveals several zones of relatively high p wave velocities at various depths under the hindu kush region in northeastern afghanistan and southern tajikistan a regional northward dipping slab is seen in the entire upper 600 km of the mantle and is apparently still attached to the lithosphere of the indian plate under northern pakistan this same slab shows a roll over structure with the deeper portion overturned and dipping southward as can also be seen in the distribution of earthquake hypocenters farther east southeast e g in the vicinity of nepal a well resolved anomaly below 450 km depth is connected to the slab under the hindu kush but seems to be separated from the lithosphere above 350 km these upper mantle anomalies are interpreted as the remnants of delaminated sub continental lithosphere that went down when greater india continued to converge northward with asia after 45 ma the deeper high velocity anomalies under the indian sub continent appear clearly separated from the shallower ones as well as from each other and are inferred to represent remnants of oceanic lithospheric slabs that have sunk into the lower mantle and were subsequently overridden by the indian plate they occur at depths between 1000 and 2300 km and occasionally descend down to the core mantle boundary the anomalies form three parallel wnw ese striking zones we interpret the two southern zones as remnants of oceanic lithosphere that was subducted when the neo tethys ocean closed between india and tibet in the cretaceous and earliest tertiary the northern deep mantle zone under northern afghanistan the himalayas and the lhasa block in southern tibet may represent the last subducted remnant of the paleo tethys ocean which is thought to have closed before the hauterivian stage of the early cretaceous the middle zone continues southeastward as a rather straight high velocity zone towards sumatra where it becomes convex southward and parallel to the subduction zone under the sunda arc comparison of this straight middle zone near india with the shallower upper 600 1000 km northern zone which displays a cusp like shape near the yunnan sw china syntaxis of the eastern himalayas supports the notion that the shallow northern zone represents later subduction than the deeper middle zone the suggestion of a counterclockwise rotation 20 of the indian plate during tertiary indentation of asia is supported by these features the present day latitudes of 5 35 n of the deep slabs under india and adjacent areas correspond to the approximate paleolatitudes of the cretaceous subduction zones the slab remnants in the middle mantle occur therefore near the ancient locations where they started their downward journey which implies that lateral movements in the deeper mantle were not large

complex and diverse rupture processes of the 2018 mw 8 2 and mw 7 9 tonga fiji deep earthquakes author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 46 5 2019 2434 2448 doi 10 1029 2018gl080997

array analyses of smks waves and the stratification of earth s outermost core abstract we perform array analyses of smks waves in order to investigate the vp structure of the earth s outermost core for earthquakes recorded by broadband seismometer networks in the world we measure differential travel times between s3ks and s2ks between s4ks and s3ks and between s5ks and s3ks by array techniques the differential times are well fit by a vp model of the earth s outermost core khomc kaneshima and helffrich 2013 differential slownesses of s4ks and s2ks relative to s2ks are also measured for the highest quality data the measured slownesses with unique sensitivity to the outer core 200 400 km below the cmb are matched by khomc these observations consolidate the evidence for the presence at the top of the outer core of a layer that has a distinctively steeper vp gradient than the bulk of the outer core we invert new smks differential time data set by a tau p method and attempt to refine the vp profile of khomc the essential features of khomc are preserved after the model refinement however the newly estimated layer thickness is nearly 450 km which is thicker than that of khomc the vp anomalies relative to prem for the depths 400 800 km below the cmb are less than 0 03 km s consistent with the degree of agreement between different vp models for the depth range

tomographic imaging of the lowermost mantle with differential times of refracted and diffracted core phases pkp pdiff the mapping of variations in p wave speed in the deep mantle is restricted by the uneven sampling of p waves in particular beneath the southern hemisphere to enhance data coverage we augmented the 1 6 million summary rays of p pp and pwp that we used in previous studies with differential travel times of diffracted and refracted core phases for the core refracted differential travel time residuals pkpab pkpdf and pkpab pkpbc we used 1383 cross correlated digital waveforms as well as 27 000 routinely processed bulletin data we used the waveform data to define quality criteria for the selection and reduction of the bulletin pkp data for pkpdf pdiff we only considered 543 records derived from waveform cross correlation no pcp data were used in this study we used optical ray theory to calculate the ray paths associated with the p pp pwp and pkp data which are measured at 1 hz however to account for the large fresnel zones of the low frequency 50 mhz pkpdf pdiff data we estimated the three dimensional shape of the frechet sensitivity kernels from kernels calculated by normal mode summation the use of these kernels allows us to properly distribute the sensitivity for a given seismic phase over a large mantle volume while allowing the high frequency data to constrain small scale structure the differential times are relatively insensitive to source mislocation and to structure in the shallow mantle beneath source and receivers and they have previously been interpreted exclusively in terms of lateral structure directly above the core mantle boundary cmb however images thus obtained can be contaminated by effects of small scale structure elsewhere in the mantle here we do not make a priori assumptions about the mantle source of anomalous time differentials from test inversions we conclude that both upper and lower mantle structures that are poorly resolved by p data can be mapped into the core along pkp paths but that the effect of outer core structures if any on the mantle model is small compared to the inversion of the p pp and pwp alone the inclusion of the pkpab pkpdf and pkpab pkpbc and pkpdf pdiff data improves the resolution of structure beneath 2200 km depth in particular the joint inversion puts better constraints on the long wavelength variations in the very deep mantle and yields an increase in the amplitude of velocity perturbations near the cmb that is in agreement with but still smaller than inferences from shear wave studies resolution tests indicate that in some regions the enhanced definition of structure is significant but in most regions the improvements are subtle and structure remains poorly resolved in large regions of the mantle

illuminating the near sonic rupture velocities of the intracontinental kokoxili mw 7 8 and denali fault mw 7 9 strike slip earthquakes with global p wave back projection imaging 1 the denali and kokoxili strike slip earthquakes are two of the longest recent intracontinental ruptures previous studies report a range of rupture velocities here we image these earthquakes by reverse time migration of the intermediate frequency p wave train recorded by global broadband seismometers this technique permits a relatively direct measure of rupture velocity speed and direction as constrained by the radiated seismic energy free from restrictive assumptions or rupture speed bounds placed on the solution we compare our results with published seismic gps displacement and surface slip inversion results both ruptures were initially subshear and transitioned over a distance no longer than 40 km to supershear speeds close to the p wave speed of 5 6 km s we investigate the accuracy of our results with synthetic data and experiment with using different imaging parameters and seismic subnetworks these tests allow us to rule out the possibility of subshear speeds along the supershear segments although we cannot exclude supershear speeds of 4 5 6 5 km s our most reliable rupture velocities of 5 6 km s are close to the local p wave speeds we hypothesize that these intracontinental faults have weak shear strengths or high breakdown slips or crustal rigidities and experience at least moderate slip or slip rate weakening our observations and previous published results lead us to speculate that very long surface extending faults with general homogeneity in prestress and fault strength together with smaller adjacent fault segments to provide triggering may be necessary ingredients for the sub rayleigh to supershear rupture speed transition in strike slip earthquakes

radial 1 d seismic structures in the deep mantle in mantle convection simulations with self consistently calculated mineralogy 1 numerical thermo chemical mantle convection simulations in a spherical annulus geometry with self consistently calculated mineralogy and mineral physics are used to predict detailed deep mantle seismic structures particularly local radial profiles of shear wave velocity vs and bulk sound velocity vb the predicted structures are compared to seismological observations and used to guide the interpretation of seismic observations and to test the model the mantle composition is described as a mixture of morb mid oceanic ridge basalt and harzburgitic end members in the na2o cao feo mgo al2o3 sio2system to assess the influence of chemical variability four different sets of end member compositions are evaluated results confirm that the post perovskite ppv phase causes anti correlated s wave and bulk sound velocities in the deep mantle due to ppv being fast in vs but slow in bulk sound velocity local 1 d seismic profiles display great lateral variability and often have multiple discontinuities in the deep mantle due to morb layers in folded slabs with a positive vs anomaly and negative bulk sound anomaly or the perovskite ppv phase transition the ppv transition is not visible inside piles of segregated morb because of the high temperature and small velocity contrast of ppv in morb piles of segregated morb are seismically slow in both vs and bulk sound despite being expected to be fast in vs because they are hotter than the surrounding material anelasticity has a significant influence on profiles of vs only in the lower thermal boundary layer which corresponds to below 2600 to 2800 km depth depending on region where temperatures are higher than the extrapolated adiabat these results indicate the importance of using a joint geodynamical mineralogical approach to predict and aid in the interpretation of deep mantle seismic structure because interpretations based on seismology and mineral physics alone may be misleading and do not capture the strong lateral variability in 1 d structure obtained here for example multiple reflections arising from folded slabs and the precise balance between thermal and compositional influences on seismic structure

anomalously low amplitude of s waves produced by the 3d structures in the lower mantle abstract direct s and sdiff phases with anomalously low amplitudes are recorded for the earthquakes in papua new guinea by seismographs in northern america according to the prediction by a standard 1d model the amplitudes are the lowest at stations in southern california at a distance and azimuth of around 95 and 55 respectively from the earthquake the amplitude anomaly is more prominent at frequencies higher than 0 03 hz we checked and ruled out the possibility of the anomalies appearing because of the errors in the focal mechanism used in the reference synthetic waveform calculations the observed anomaly distribution changes drastically with a relatively small shift in the location of the earthquake the observations indicate that the amplitude reduction is likely due to the 3d shear velocity vs structure which deflects the wave energy away from the original ray paths moreover some previous studies suggested that some of the s and sdiff phases in our dataset are followed by a prominent postcursor and show a large travel time delay which was explained by placing a large ultra low velocity zone ulvz located on the core mantle boundary southwest of hawaii in this study we evaluated the extent of amplitude anomalies that can be explained by the lower mantle structures in the existing models including the previously proposed ulvz in addition we modified and tested some models and searched for the possible causes of low amplitudes full 3d synthetic waveforms were calculated and compared with the observations our results show that while the existing models explain the trends of the observed amplitude anomalies the size of such anomalies remain under predicted especially at large distances adding a low velocity zone which is spatially larger and has less vs reduction than ulvz on the southwest side of ulvz contributes to explain the low amplitudes observed at distances larger than 100 from the earthquake the newly proposed low velocity zone mostly overlaps with the northern part of the pacific large low shear velocity province llsvp revealed in tomographic models although the very low amplitudes observed at a distance of about 95 remain unexplained our results indicate that the boundary of the pacific llsvp is sharp and the amplitude of s waves at these large distances is lowered by strong vertical and or lateral deflection at the boundary toward the interior of the low velocity province

global scale p wave tomography optimized for prediction of teleseismic and regional travel times for middle east events 1 data set development 1 we extend the bayesloc seismic multiple event location algorithm for application to global arrival time data sets bayesloc is a formulation of the joint probability distribution spanning multiple event location parameters including hypocenters travel time corrections pick precision and phase labels stochastic priors may be used to constrain any of the bayesloc parameters markov chain monte carlo sampling is used to draw samples from the joint probability distribution and the posteriori samples are summarized to infer conventional location parameters such as the hypocenter the first application of the broad area bayesloc algorithm is to a data set consisting of all well recorded events in the middle east and the most well recorded events with 5 spatial sampling globally this sampling strategy is designed to provide the ray coverage needed to determine lithospheric scale p wave velocity structure in the middle east using the complementary ray geometry provided by regional subhorizontal and teleseismic subvertical raypaths and to determine a consistent albeit lower resolution image of global mantle structure the data set consists of 5401 events and 878 535 p pn pp sp and pcp arrivals recorded at 4606 stations relocated epicenters are an average of 16 km from bulletin locations the data set included events that are known to an accuracy of 1 km a k a gt1 based on nonseismic information the average distance between gt1 epicenters and our relocated epicenters is 5 6 km for arrivals labeled p pn and pcp 92 90 and 96 are properly labeled with probability 0 9 respectively incorrect phase labels are found to be erroneous at rates of 0 6 0 2 1 6 and 2 5 for p pn pcp and depth phases pp and sp respectively labels found to be incorrect but not erroneous were reassigned to another phase label p and pn residual standard deviation with respect to ak135 travel times are dramatically reduced from 3 45 s to 1 01 s the differences between travel time residuals for nearly reciprocal raypaths are significantly reduced from the input event locations suggesting that bayesloc relocation improves data set consistency the reciprocity tests suggest that the dominant contribution to travel time residuals calculated from information provided in global bulletins is location and picks errors not travel time prediction errors due to 3 d structure modeling the whole multiple event system results in accurate locations and an internally consistent data set that is ideal for tomography and other travel time calibration studies simmons et al 2011 companion paper use the bayesloc processed data set to develop a 3 d tomographic image which further reduces residual standard deviation to 0 50 s

j362d28 a new joint model of compressional and shear velocity in the earth s mantle summary the discrimination between chemical and thermal heterogeneity in the earth s mantle remains one of the most important and challenging questions to be answered by observational and theoretical geophysics to answer this question requires a thorough knowledge of the ratio between compressional and shear velocity anomalies we describe results of a joint inversion for compressional and shear velocity in the mantle using a large and diverse data set consisting of traveltimes complete waveforms and surface wave dispersion measurements a horizontal tessellation consisting of 362 spherical splines is used to parametrize the model which is approximately equivalent to a spherical harmonic of degree 18 in resolution the model contains peak variations from prem of up to 7 per cent in s velocity and 2 5 per cent in p velocity in the upper mantle these variations decrease to 1 5 and 0 6 per cent respectively at 1000 km depth and reach 2 5 and 1 0 per cent respectively in the d region the rms ratio of s to p velocity perturbations is fairly constant between 2 0 and 2 5 in the lower mantle but a local minimum in this ratio occurs at a depth of approximately 1700 km resolution tests show that the recovery of p and s velocity is not geographically uniform but also show that this amplitude ratio is well resolved between 670 and 2700 km depth we also observe a persistent negative correlation between bulk sound and shear velocity throughout the same region of the mantle in addition the model contains a minimum correlation between p and s velocity between 670 and 1100 km this feature is supported by both the favourable outcome of resolution experiments and the poor fit provided by the starting model from the inversion in which the p and s velocities are perfectly correlated to our data set of p wave traveltimes the power spectra of both p and s velocity heterogeneity are similar although we note a slightly larger dominance of degree two in the spectra for p velocity in the mid mantle where resolution is highest

comparing p and s wave heterogeneity in the mantle from the reprocessed data set of engdahl and co workers we have carefully selected matching p and s data for tomographic imaging we assess data and model error and conclude that our s model uncertainty is twice that of the p model we account for this in our comparison of the perturbations in p and s wavespeed in accord with previous studies we find that p and s perturbations are positively correlated at all depths however in the deep mantle systematic differences occur between regions that have undergone subduction in the last 120 million years and those that have not in particular below 1500 km depth ln vs ln vp is significantly larger in mantle regions away from subduction than in mantle beneath convergent margins this inference is substantiated by wavespeed analyses with random realizations of the slab non slab distribution through much of the mantle there is no significant correlation between bulk sound and s wave perturbations but they appear to be negatively correlated between 1700 and 2100 km depth which is also where the largest differences in ln vs ln vp occur this finding supports convection models with compositional heterogeneity in the lowermost mantle

coherent seismic arrivals in the p wave coda of the 2012 m w 7 2 sumatra earthquake water reverberations or an early aftershock

intermittent layered convection in a model mantle with an endothermic phase change at 670 km it is not yet known whether convection in the earth s mantle occurs in cells that extend throughout the entire depth of the mantle or if the upper and lower mantle convect in independent layers both possibilities seem to be consistent with geochemical and seismologi cal observations1 4 it is generally accepted however that the seismologically observed boundary between the upper and lower mantle at 670 km depth arises from the endothermic phase change spinel perovskite mgo here we investigate the results of including this phase change in a model of mantle convection for realism and to eliminate scaling problems our calculations use commonly accepted values of geophysical parameters for a clapeyron slope y 2 106 a value close to experimental results and theoretical expectations we observe local intermittent mixing between the upper and lower mantle such behaviour may offer a way to reconcile the existence of geophysical evidence for both whole mantle and layered convection

slabs in the lower mantle and their modulation of plume formation numerical mantle convection models indicate that subducting slabs can reach the core mantle boundary cmb for a wide range of assumed material properties and plate tectonic histories an increase in lower mantle viscosity a phase transition at 660 km depth depth dependent thermal expansivity and depth dependent thermal diffusivity do not preclude model slabs from reaching the cmb we find that ancient slabs could be associated with lateral temperature anomalies 500 c cooler than ambient mantle plausible increases of thermal conductivity with depth will not cause slabs to diffuse away regional spherical models with actual plate evolutionary models show that slabs are unlikely to be continuous from the upper mantle to the cmb even for radially simple mantle structures the observation from tomography showing only a few continuous slab like features from the surface to the cmb may be a result of complex plate kinematics not mantle layering there are important consequences of deeply penetrating slabs our models show that plumes preferentially develop on the edge of slabs in areas on the cmb free of slabs plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin however in areas beneath slabs the basal thermal boundary layer would be thicker and plume formation infrequent beneath slabs a substantial amount of hot mantle can be trapped over long periods of time leading to mega plume formation we predict that patches of low seismic velocity may be found beneath large scale high seismic velocity structures at the core mantle boundary we find that the location buoyancy and geochemistry of mega plumes will differ from those plumes forming at the edge of slabs various geophysical and geochemical implications of this finding are 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

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