metastable olivine wedge and deep dry cold slab beneath southwest japan abstract oceanic plates subducted at trenches penetrate into the deep mantle and encounter a structural boundary at a depth of 410 km where olivine the dominant element of mantle rocks transforms into a higher density form wadsleyite this transformation may be delayed within the coldest core of subducting plates slabs due to kinetic effects and it has been suggested that metastable olivine may persist deeper than 410 km using high density seismic array data in japan we show the direct image of the structure corresponding to this metastable olivine wedge mow beneath southwest japan numerical simulation of a subducting slab including the kinetic effect of water h 2 o on the olivine wadsleyite transformation indicates that the presence of the imaged mow requires an insignificant amount of water less than 100 wt ppm be present in the slab mantle thus a deep dry cold slab we infer that the transportation of water into the deep mantle occurs along the top surface of the subducting slab but no significant amount within the slab itself we also demonstrate that a numerical simulation including the kinetics of 660 km phase transformation can reconcile the observed deep depression of the 660 km discontinuity with a gentle clapeyron slope

two dimensional three dimensional waveform modeling of subducting slab and transition zone beneath northeast asia subduction plays a fundamental role in dynamics of the mantle convection and in material circulations of the earth s interior slabs have been imaged to subduct near horizontally in the transition zone tz beneath the northeast asia in seismic tomography triplication waveform modeling is an effective tool to study the detailed seismic structure in the tz however tz triplication modeling has traditionally relied on 1 d models in this study we use the spectral element method to explore influences of 2 d 3 d slab structure on tz triplication waveforms and to model for the first time the slab and tz structures beneath the northeast asia synthetic tests suggest that for a subduction zone earthquake slab structure can have important influences on tz triplication waveforms and that even in a narrow azimuth range the effects from 2 d 3 d slab structure on the wave propagation can lead to erroneous conclusions with 1 d modeling our data are high quality triplicated sh waveforms at distances of 10 32 from a deep event below 410 km discontinuity in the pacific subducting slab our 2 d 3 d waveform modeling results suggest that a simple model of the subducting slab 5 high velocity anomaly and 100 km thick down to 560 km but normal below 560 km can match most of the observed waveforms remarkably well the bottom of the tz of the sampling region north of the yellow sea contains a patch of very slow anomaly the results indicate that subhorizontal slab above the 660 discontinuity is not everywhere beneath northeast asia and the subducting slab is not everywhere continuous to the bottom of the tz compared with the traditional 1 d modeling our new 2 d 3 d approach provides better fits to the data and allows us to constrain the slab geometry and to separate tz structure from slab structure

strain induced phase changes within cold basal ice from taylor glacier antarctica indicated by textural and gas analyses this paper reports detailed textural and gas measurements conducted in cold basal ice 178c from the margin of taylor glacier an outlet glacier of the east antarctic ice sheet the analyzed samples were retrieved from a basal ice sequence excavated at the end of a subglacial tunnel dug near the glacier snout the basal sequence exhibits two contrasting ice facies defined as the englacial and stratified facies on the one hand analysis of ice crystal textures from the basal ice sequence provides evidence for localized ductile deformation especially within the stratified facies where significant dynamic recrystallization was detected on the other hand high resolution gas analyses reveal that strong changes in gas composition occurred at the structural interfaces of the stratified facies these gas composition changes are typical of melting refreezing processes but are not associated with any significant loss of gas volume given the specific subglacial thermal conditions at the margin of taylor glacier we interpret this phenomenon as resulting from microscopic phase changes involving selective gas redistribution through the pre melt phase it is argued that such processes may play an important role in the post genetic geochemical evolution of cold debris laden ice and may be enhanced through intense strain conditions

seismic and mineralogical structures of the lower mantle from probabilistic tomography 1 one of the most powerful approaches for understanding the 3 d thermo chemical structure of the lower mantle is to link tomographic models with mineral physics data this is not straightforward because of strong trade offs between thermal and chemical structures and their influence on seismic structures they can be reduced by mapping simultaneously perturbations of wave speeds and density anomalies and by the quantitative assessment of the accuracy and uniqueness of seismic and mineralogical data here we present new tomographic maps of low order even degree seismic structures which are an improvement on earlier models they satisfy constraints from body wave surface wave and normal mode data simultaneously thereby enhancing the spatial resolution furthermore the seismic structure at a given location is represented by a probability density function pdf which takes into account the uncertainty and non uniqueness of the solution due to modeling and data restrictions following a robust statistical procedure we fit heterogeneity of wave speeds and density from hypothetical thermo chemical models to those of our tomographic maps we thereby constrain lateral variations of temperature as well as iron silica and post perovskite concentration in terms of pdfs our work shows that large scale chemical variations are likely everywhere in the lower mantle in most of the d region post perovskite is most abundant in the circum pacific belt but near the core its lateral variation is more complex furthermore post perovskite concentration trades off with the amplitudes of temperature and silicate variations but not with their lateral distribution this might be the reason why temperature and silicate variations appear not constrained by our data in the lowermost few hundred km of the mantle

seismological evidence for a slab detachment in the tonga subduction zone abstract the tonga wadati benioff zone is characterized by a large seismicity gap beneath the lau basin that raises the question of the slab continuity between the shallow to intermediate part 60 300 km and the deep part 400 700 km to address this problem we investigated the wadati benioff zone geometry and stress regime through a detailed analysis of the spatial distribution of moment tensors and variation of the stress tensor using the global seismicity engdahl e van der hilst r buland r 1998 global teleseismic earthquake relocation with improved travel times and procedures for depth determination bull seism soc am 88 722 743 and the centroid moment tensor solutions cmt catalogs dziewonski a m chou t woodhouse j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 the stress tensors were computed using the gephart s program gephart j w forsyth d 1984 an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence j geophys res 89 9305 9320 the stress inversion results indicate that between 21 s and 27 s and depths down to 700 km the slab is under homogeneous down dip compressional stress regime while north of 21 s we found strong variations of the stress orientations between the intermediate and deep portions of the slab we also show that between 14 and 19 s the stresses at intermediate depth 60 300 km can be resolved into two slab parallel domains a thin upper part of the slab that is under downdip compression and the lower part that is under downdip extension this pattern of two zones with opposite mechanical behavior is characteristic of a subducted plate with a free lower limit that does not interact with the 670 km depth boundary these results together with the large seismicity gap within the slab argue for a slab detachment

phase transition in mgsio 3 perovskite in the earth s lower mantle a new polymorph of mgsio3 more stable than the pbnm perovskite phase has been identified by first principles computations it has the cairo3 structure with cmcm symmetry and consists of sio3 layers intercalated by eightfoldcoordinated mg ions high temperature calculations within the quasiharmonic approximation give a volume change of f1 5 and a clapeyron slope of f7 5f0 3 mpa k at f2750 k and f125 gpa these pressure temperature p t conditions are close to those in which a phase transition in mgsio3 perovskite has been observed by in situ angle dispersive x ray diffraction measurements this transition appears to be associated with the du discontinuity d 2004 elsevier b v all rights reserved

direct observation of basal sliding and deformation of basal drift at sub freezing temperatures in a tunnel at the base of sub polar urumqi glacier no 1 china three new mechanisms of glacier flow at sub freezing temperatures have been observed taken individually or in combination these modes of flow can account for nearly all 60 80 of the overall glacier motion and yet they act only within the lowermost 1 2 of the effective glacier thickness these mechanisms are 1 enhanced deformation of the frozen and ice laden subglacial drift 2 motion across discrete shear planes or shear bands within the frozen drift or at the ice drift interface and 3 basal sliding at an ice rock interface at a temperature of nearly 5 c the ice laden drift has an effective viscosity of more than one hundred times less than that measured in the overlying ice thus allowing very rapid shear deformation the observed rate or basal sliding at the ice rock interface agrees favorably with that predicted by the recent work of shreve 1984 if proper account is taken of the measured surface roughness and reduced ice viscosity

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

seismic thermal and compositional structures of the stagnant slab in the mantle transition zone beneath southeastern china abstract the structure of earth s mantle transition zone mtz contains important information about how oceanic plates are recycled into the mantle however morphologies of stagnant slab in the mtz inferred from seismic studies remain controversial here we conduct combined geodynamic mineral physical and seismologic modeling to infer fine features of the stagnant slab in the mtz beneath southeastern china this method applies mineral physics modeling in combination with geodynamically consistent thermal anomalies to predict seismic velocity structures in the mtz that are used in triplication waveform modeling the synthetic waveforms are systematically compared with observed data using a grid search optimization our best fit model reveals a stagnant slab lying at the bottom of the mtz with a peak temperature reduction of 350 80 k and a thickness of 85 20 km indicating that it underwent little deformation by joint modeling of the mineral physics and thermal history of the slab our approach improves estimates of both the thickness and temperature of the stagnant slab and provides a better understanding of the paleo subduction system beneath southeastern china

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

s to p heterogeneity ratio in the lower mantle and thermo chemical implications we evaluate the thermo chemical state of the lower mantle by analysing the differences in the pattern of heterogeneity between shear and compressional velocity variations and the s to p heterogeneity ratio rs p lnvs lnvp as mapped in our model spani and in alternative joint models robust structural differences between vp and vs evidence the presence of compositional heterogeneity within the two large low shear velocity provinces llsvps we find also an increasing decorrelation with depth that can be associated with compositional layering of the llsvps in addition our model shows heterogeneity in the transition zone and mid mantle by complex morphology of subducting slabs and further differences between vp and vs that point to an unexpected heterogeneous lower mantle precise estimates of compositional heterogeneities are not yet affordable because of the difficulty to provide quantitative measure of rs p making it difficult to use this ratio to evaluate chemical heterogeneity for instance rs p global median value drops from 2 8 to 1 9 at 2500 km depth when the vp component of spani is replaced by a vp model resulting from a differently regularized inversion and obtaining an equally good data fit an increase of 20 of the spani vp anomalies also drastically reduces without significantly degrading the data fit noise in model parameters also leads to overestimate rs p in the two llsvps as we show with synthetic tests additional mineral physics uncertainties for compositional effects on rs p and for the conversion of lnvs and lnvp into density further complicates a precise chemical interpretation

chemical versus thermal heterogeneity in the lower mantle the most likely role of anelasticity a widely held belief is that anelasticity can contribute significantly to seismic wave speed variations in the lower mantle in particular it has been argued that anelasticity can strongly increase the sensitivity of vs to temperature and that anelasticity may also increase vs relative to vp as measured by the parameter rs p dlnvs dlnvp if true this could significantly reduce or in some cases eliminate the need to explain seismic signals in the mantle with chemical heterogeneity and that most of the variation in seismic velocities in the lower mantle could be attributed to temperature alone we re visit this view and find that a strong anelastic effect is unlikely in the earth s lower mantle given the present knowledge of the properties of perovskite under lower mantle conditions we find it unlikely that anelasticity can affect dlnvs dt by more than about 30 and it is most likely less than 20 we also find that the probable upper bound on dlnvs dlnvp due to thermal variations is about 1 8 in the shallow lower mantle and about 2 1 in the deeper lower mantle we conclude therefore that anelasticity cannot be invoked to significantly reduce or remove interpretations of lower mantle chemical heterogeneity based on large scale seismic wave speed variations 2007 elsevier b v all rights reserved

sensitivities of seismic velocities to temperature pressure and composition in the lower mantle we calculated temperature pressure and compositional sensitivities of seismic velocities in the lower mantle using latest mineral physics data the compositional variable refers to the volume proportion of perovskite in a simplified perovskite magnesiowustite mantle assemblage the novelty of our approach is the exploration of a reasonable range of input parameters which enter the lower mantle extrapolations this leads to realistic error bars on the sensitivities temperature variations can be inferred throughout the lower mantle within a good degree of precision contrary to the uppermost mantle modest compositional changes in the lower mantle can be detected by seismic tomography with a larger uncertainty though a likely trade off between temperature and composition will be largely determined by uncertainties in tomography itself given current sources of uncertainties on recent data anelastic contributions to the temperature sensitivities calculated using karato s approach appear less significant than previously thought recent seismological determinations of the ratio of relative s to p velocity heterogeneity can be entirely explain by thermal effects although isolated spots beneath africa and the central pacific in the lowermost mantle may ask for a compositional origin 2001 elsevier science b v all rights reserved

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

upper mantle and mantle transition zone thermal and water content anomalies beneath ne asia constraints from receiver function imaging of the 410 and 660 km discontinuities abstract the 410 and 660 km discontinuities d410 and d660 bordering the mantle transition zone mtz beneath ne asia including ne china eastern mongolia and southern siberia are imaged in successive circular bins with a radius of 1 degree by stacking a total of 274 413 p to s radial receiver functions recorded by 799 broadband seismic stations after moveout correction based on the 1 d iasp91 earth model the resulting apparent depths of the discontinuities exhibit significant and spatially systematic variations three approximately n s elongated narrow zones with significantly thickened mtz are observed which may be associated with the thermal effect and dehydration of subducted slabs the major volcanoes in ne china are underlain by a d660 that is apparently depressed by 19 km which can be interpreted by the presence of an anomalously high water concentration in the lower mtz released from the stagnated slabs low wavespeed anomalies above the d410 west of the datong volcanic fields are underlain by an mtz with normal thickness and are attributable by dehydration of the leading portion of the stagnant pacific slab in the mtz that is revealed in an n s oriented narrow zone east of this area the lateral shift of the upper mantle low wavespeed zone and the area with thickened mtz may suggest a westward drift of the upper mantle relative to the subducted slab an abnormally thin mtz is observed beneath the hangay dome in central mongolia suggesting the possible existence of thermal upwelling from the lower mantle through the mtz

a three dimensional radially anisotropic model of shear velocity in the whole mantle summary we present a 3 d radially anisotropic s velocity model of the whole mantle saw642an obtained using a large three component surface and body waveform data set and an iterative inversion for structure and source parameters based on non linear asymptotic coupling theory nact the model is parametrized in level 4 spherical splines which have a spacing of 8 the model shows a link between mantle flow and anisotropy in a variety of depth ranges in the uppermost mantle we confirm observations of regions with vsh vsv starting at 80 km under oceanic regions and 200 km under stable continental lithosphere suggesting horizontal flow beneath the lithosphere we also observe a vsv vsh signature at 150 300 km depth beneath major ridge systems with amplitude correlated with spreading rate for fast spreading segments in the transition zone 400 700 km depth regions of subducted slab material are associated with vsv vsh while the ridge signal decreases whilethemid mantlehasloweramplitudeanisotropy vsv in the lowermost 300 km which appears to be a robust conclusion despite an error in our previous paper which has been corrected here the 3 d deviations from this signature are associated with the large scale low velocity superplumes underthecentralpacificandafrica suggestingthatvsh vsv isgeneratedinthepredominant horizontal flow of a mechanical boundary layer with a change in signature related to transition to upwelling at the superplumes

oceanic plateau of the hawaiian mantle plume head subducted to the uppermost lower mantle the hawaiian emperor seamount chain that includes the hawaiian volcanoes was created by the hawaiian mantle plume although the mantle plume hypothesis predicts an oceanic plateau produced by massive decompression melting during the initiation stage of the hawaiian hot spot the fate of this plateau is unclear we discovered a megameter scale portion of thickened oceanic crust in the uppermost lower mantle west of the sea of okhotsk by stacking seismic waveforms of ss precursors we propose that this thick crust represents a major part of the oceanic plateau that was created by the hawaiian plume head 100 million years ago and subducted 20 million to 30 million years ago our discovery provides temporal and spatial clues of the early history of the hawaiian plume for future plate reconstructions

waveform modeling of the slab beneath japan 1 the tomographic p wave model for the japan subduction zone derived by zhao et al 1994 has two very striking features a slab about 90 km thick with p wave velocities 3 6 higher than the surrounding mantle and a mantle wedge with 6 low velocity anomalies we study three component seismograms from more than 600 hi net stations produced by two earthquakes which occurred in the downgoing pacific plate at depths greater than 400 km we simulate body wave propagation in the three dimensional 3 d p wave model using 2 d finite difference fdm and 3 d spectral element sem methods as measured by cross correlation between synthetics and data the p wave model typically explains about half of the traveltime anomaly and some of the waveform complexity but fails to predict the extended sh wave train in this study we take advantage of the densely distributed hi net stations and use 2 d fdm modeling to simulate the p sv and sh waveforms our 2 d model suggests that a thin elongated low velocity zone exists atop the slab extending down to a depth of 300 km with an s wave velocity reduction of 14 if a thickness of 20 km is assumed further 3 d sem simulations confirm that this model explains a strong secondary arrival which cannot easily be imaged with standard tomographic techniques the low velocity layer could explain the relatively weak coupling associated with most subduction zones at shallow depths 50 km generally involving abundant volcanic activity and silent earthquakes and it may also help to further our understanding of the water related phase transition of ultramafic rocks and the nature of seismicity at intermediate depths 70 300 km

gypsum a joint tomographic model of mantle density and seismic wave speeds 1 gypsum is a 3 d model of mantle shear wave s speeds compressional wave p speeds and density the model is developed through simultaneous inversion of seismic body wave travel times p and s and geodynamic observations while using realistic mineral physics parameters linking wave speeds and density geodynamic observations include the global free air gravity field divergence of the tectonic plates dynamic topography of the free surface and the flow induced excess ellipticity of the core mantle boundary gypsum is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution models of the density field from earth s free oscillations have provided great insight into the density configuration of the mantle but are limited to very long wavelength solutions alternatively scaling higher resolution seismic images to obtain density anomalies generates density fields that do not satisfy geodynamic observations the current study provides a 3 d density model for the mantle that directly satisfies geodynamic and seismic observations through a joint seismic geodynamic inversion process notable density field observations include high density piles at the base of superplume structures supporting the general results of past normal mode studies however we find that these features are more localized and have lower amplitude than past studies would suggest when we consider both fast and slow seismic anomalies in gypsum we find that p and s wave speeds are strongly correlated throughout the mantle however we find a low correlation of fast s wave zones in the deep mantle 1500 km depth with the corresponding p wave anomalies suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies the cratonic lithosphere and d regions are shown to have strong compositional signatures however we argue that temperature variations are the primary cause of p wave speed s wave speed and density anomalies throughout most of the mantle

normal mode and free air gravity constraints on lateral variations in velocity and density of earth s mantle with the use of a large collection of free oscillation data and additional constraints imposed by the free air gravity anomaly lateral variations in shear velocity compressional velocity and density within the mantle dynamic topography on the free surface and topography on the 660 km discontinuity and the core mantle boundary were determined the velocity models are consistent with existing models based on travel time and waveform inversions in the lowermost mantle near the core mantle boundary denser than average material is found beneath regions of upwellings centered on the pacific ocean and africa that are characterized by slow shear velocities these anomalies suggest the existence of compositional heterogeneity near the core mantle boundary

seismic structure of the deep kurile subduction zone three dimensional modeling of p wave travel time residuals was performed to investigate the deep slab related velocity structure within the kurile subduction zone travel times of p waves from earthquakes at all depths within the kurile subduction zone to world wide standard seismograph network and canadian stations were measured instead of analyzing the travel time residuals of a single event relative travel time residuals of p waves to common stations have been analyzed and used in this study to isolate near source contributions from the total travel time residuals the effect of uncertainties in long wavelength heterogeneity far from the source in the lower mantle and the effect of uncertainties in the reference earth model have been significantly reduced by analyzing relative travel time residuals the effect of uncertainties in station corrections are eliminated by relative travel time residuals our measured p wave travel time data clearly indicate that high velocity anomalies exist in the lower mantle beneath the kurile subduction zone but they do not appear to be caused by simple slab continuation into the lower mantle the travel time modeling was accomplished using a fully three dimensional finite difference technique for wave propagation within the source region the modeling results show that high velocity anomalies extend several hundred kilometers into the lower mantle but they appear to be very complicated a large number of models consisting of simple slab continuation into the lower mantle were tested and the results show that none ofthese models was able to produce synthetics which match the observed p wave travel time data the slab related velocity anomalies in the upper mantle of the kurile subduction zone are generally consistent with the seismicity the high velocity anomalies in the lower mantle below the kurile subduction zone are broad and geometrically change from the southern to the northern kuriles below the southern kuriles the high velocity anomalies appear to be subhorizontal however beneath the central kuriles there are broad about 600 km wide high velocity anomalies on the continental side of the slab which extend several hundred kilometers into the lower mantle the high velocity anomalies found below the northern kuriles are broad and on both the continental and the ocean side of the slab and extend several hundred kilometers into the lower mantle

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

grain growth in polar ice i theory many observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood here we develop the theory of grain growth in ice that is not deforming rapidly and in the succeeding paper we use this theory to explain observations from glacial ice in the absence of significant strain energy the driving force for grain growth arises from grain boundary curvature grain growth is slowed by the interaction of grain boundaries with extrinsic materials microparticles bubbles and dissolved impurities if the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material then the grain boundary velocity is determined by the velocity characteristic of the extrinsic material low velocity regime if the driving force is large enough to cause separation then boundaries migrate more rapidly than the extrinsic material high velocity regime but the net driving force is reduced through transient pinning by the extrinsic material polar ice is typically in the low velocity regime relative to dissolved impurities and the high velocity regime relative to microparticles and bubbles cross sectional area of grains is predicted to increase linearly with time under most but not all circumstances

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

mineralogical effects on the detectability of the postperovskite boundary the discovery of a phase transition in mg silicate perovskite pv to postperovskite ppv at lowermost mantle pressure temperature p t conditions may provide an explanation for the discontinuous increase in shear wave velocity found in some regions at a depth range of 200 to 400 km above the core mantle boundary hereafter the d discontinuity however recent studies on binary and ternary systems showed that reasonable contents of fe2 and al for pyrolite increase the thickness width of the mixed phase region of the pv ppv boundary 400 600 km to much larger than the d discontinuity 70 km these results challenge the assignment of the d discontinuity to the pv ppv boundary in pyrolite homogenized mantle composition furthermore the mineralogy and composition of rocks that can host a detectable pv ppv boundary are still unknown here we report in situ measurements of the depths and thicknesses of the pv ppv transition in multiphase systems san carlos olivine pyrolitic and midocean ridge basaltic compositions at the p t conditions of the lowermost mantle searching for candidate rocks with a sharp pv ppv discontinuity whereas the pyrolitic mantle may not have a seismologically detectable pv ppv transition due to the effect of al harzburgitic compositions have detectable transitions due to low al content in contrast al rich basaltic compositions may have a detectable pv ppv boundary due to their distinct mineralogy therefore the observation of the d discontinuity may be related to the pv ppv transition in the differentiated oceanic lithosphere materials transported to the lowermost mantle by subducting slabs

ice dynamics and thermal regime of taylor glacier south victoria land antarctica les donnees glaciologiques recueillies sur le taylor glacier ont servi a reconstituer les principaux traits de la dynamique et du regime thermique du glacier les etudes du bilan de masse montrent que le glacier est proche de l equilibre les conditions thermiques de la glace basale sur une grande partie de la zone d ablation ont ete calculees a partir d estimation du flux de chaleur geothermique et de mesures des temperatures de la glace pres de la surface des vitesses et de l epaisseur de la glace on a trouve que jusqu a 50 de la zone d ablation la glace basale pouvait etre fondante

a perovskitic lower mantle inferred from high pressure high temperature sound velocity data determination of the shear wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle indicates that perovskite constitutes much more of the lower mantle than predicted by the conventional mantle model and is consistent with the chondritic earth model earth s upper mantle is apparently depleted of silicon when compared with meteorites which are thought to represent the material from which the earth formed this missing silicon problem has provoked intense debate it suggests that the deficit might be balanced by silicon in the core or that the upper mantle is not representative of the entire mantle and that the lower mantle is enriched in silicon murakami et al provide evidence to support the latter case they made laboratory measurements of sound wave transmission through silicate perovskite and ferropericlase minerals at pressures and temperatures matching those of the lower mantle and compared the resulting shear wave values with seismic data that sample the lower mantle they conclude that the mineralogical model that provides the best fit is one in which perovskite constitutes greater than 93 of the lower mantle this suggests that the lower mantle is enriched in silicon in comparison with the upper mantle consistent with the chondritic earth model and that there is limited mass transport between the upper and lower mantle the determination of the chemical composition of earth s lower mantle is a long standing challenge in earth science accurate knowledge of sound velocities in the lower mantle minerals under relevant high pressure high temperature conditions is essential in constraining the mineralogy and chemical composition using seismological observations1 but previous acoustic measurements were limited to a range of low pressures and temperatures here we determine the shear wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle using brillouin scattering spectroscopy2 the mineralogical model that provides the best fit to a global seismic velocity profile1 indicates that perovskite constitutes more than 93 per cent by volume of the lower mantle which is a much higher proportion than that predicted by the conventional peridotitic mantle model it suggests that the lower mantle is enriched in silicon relative to the upper mantle which is consistent with the chondritic earth model such chemical stratification implies layered mantle convection with limited mass transport between the upper and the lower mantle

when slabs collide a tectonic assessment of deep earthquakes in the tonga vanuatu region an unusual group of more than 100 earthquakes is located 600 km beneath the north fiji basin in the southwest pacific ocean these earthquakes are attributed to seismicity within detached segments of the subducted australian plate one of these detached slab segments has collided with and now impinges on the subducted pacific plate at a depth of 500 km the region in the mantle where the two slab segments meet is also characterized by an unparalleled abundance of large magnitude mw 7 0 earthquakes for this depth the folded shape of the pacific slab beneath fiji as well as the abundance of earthquakes is interpreted to result from deformation and deformation enhanced phase transformations as the two slabs collide and settle on the 660 km discontinuity detachment of the slab segments is interpreted to have occurred at ca 5 ma but collision between the eastern segment and the west dipping pacific slab is interpreted to have occurred at ca 4 ma coincident with initial opening of the overriding lau basin

the dynamics of plate tectonics and mantle flow from local to global scales plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries but observationally constrained high resolution models of global mantle flow remain a computational challenge we capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions with individual plate margins resolved down to a scale of 1 kilometer back arc extension and slab rollback are emergent consequences of slab descent in the upper mantle cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high viscosity slabs altering the velocity of oceanic plates viscous dissipation within the bending lithosphere at trenches amounts to 5 to 20 of the total dissipation through the entire lithosphere and mantle

modeling the dynamics of subducting slabs cold dense subducting lithosphere provides the primary force driving tectonic plates at earth s surface the force available to drive the plates depends on a balance between the buoyancy forces driving subduction and the mechanical and buoyancy forces resisting subduction because both the buoyancy and rheology of the slab and mantle depend on temperature composition grain size water content and melt fraction unraveling which of these processes exert a first order control on slab dynamics and under what circumstances other processes become first order effects can be challenging laboratory and numerical models of slab dynamics provide a powerful method for testing the combined effects of buoyancy and strength changes that accompany the slab evolution in the upper mantle transition zone and lower mantle recent studies have focused on understanding how rheologic variations newtonian versus non newtonian viscosity or water content geometry 2d versus 3d and plate motions trench roll back or advance influence the evolution of slabs in the upper mantle and how they sink into the lower mantle these models suggest that spatial and temporal variations in slab strength and the history of subduction determine whether slabs sink directly into the lower mantle or are trapped in the transition zone

imaging subducted slab structure beneath the sea of okhotsk with teleseismic waveforms the structure of subducted slabs is not well imaged in most global tomographic models with anomalies typically less than 1 synthetic waveforms for such models are not noticeably different from their 1d reference models in contrast we find that observed teleseismic waveforms sampling slabs in the down dip direction display multipathing features indicative of substantial structure such waveform complexity patterns appear distinctly different for various source locations with outer rise events generally displaying relatively simple waveforms here we model these waveform patterns for a portion of the kuril subduction zone the best fitting slab models have relatively fast cores 5 with smooth edges compatible with thermal modeling in shape complete seismograms for these 2d models indicate that multibounce p and s waves are slab sensitive and can be used in refining models

elasticity of ferropericlase and seismic heterogeneity in the earth s lower mantle deciphering the origin of seismic heterogeneity has been one of the major challenges in understanding the geochemistry and geodynamics of the deep mantle fully anisotropic elastic properties of constituent minerals at relevant pressure temperature conditions of the lower mantle can be used to calculate seismic heterogeneity parameters in order to better understand chemically and thermally induced seismic heterogeneities in this study the single crystal elastic properties of ferropericlase mg0 94fe0 06 o were measured using brillouin spectroscopy and x ray diffraction at conditions up to 50 gpa and 900 k the velocity density results were modeled using third order finite strain theory and thermoelastic equations along a representative geotherm to investigate high pressure temperature and compositional effects on the seismic heterogeneity parameters our results demonstrate that from 660 to 2000 km compressional wave anisotropy of ferropericlase increased from 4 to 9 7 while shear wave anisotropy increased from 9 to as high as 22 5 the thermally induced lateral heterogeneity ratio rs p lnvs lnvp of ferropericlase was calculated to be 1 48 at ambient pressure but decreased to 1 43 at 40 gpa along a representative geotherm the rs p of a simplified pyrolite model consisting of 80 bridgmanite and 20 ferropericlase was approximately 1 5 consistent with seismic models at depths from 670 to 1500 km but showed an increased mismatch at lower mantle depths below 1500 km this discrepancy below mid lower mantle could be due to either a contribution from chemically induced heterogeneity or the effects of the fe spin transition in the deeper parts of the earth s lower mantle

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

earthquakes and strain in subhorizontal slabs 1 using an extensive database of fault plane solutions and precise locations of hypocenters we show that the classic patterns of downdip extension dde or downdip compression ddc in subduction zones deteriorate when the dip of the slab is less than about 20 this result is depth independent demonstrated by both intermediate focus depths from 70 to 300 km and deep focus depths greater than 300 km earthquakes the absence of pattern in seismic strain in subhorizontal slabs also occurs locally over scales of about 10 km as evident from a detailed analysis of a large mw 7 1 earthquake sequence beneath fiji following the paradigm that a uniform strain of dde ddc results from sinking of the cold dense slab as it encounters resistance from the highly viscous mantle at depth breakdown of dde ddc in subhorizontal slabs reflects waning negative buoyancy slab pull in the downdip direction our results place a constraint on the magnitude of slab pull that is required to dominate over localized sources of stress and to align seismic strain release in dipping slabs under the condition of a vanishing slab pull eliminating the only obvious source of regional stress the abundance of earthquakes in subhorizontal slabs indicates that a locally variable source of stress is both necessary and sufficient to sustain the accumulation of elastic strain required to generate intermediate and deep focus seismicity evidence is growing that the process of seismogenesis under high pressures including localized sources of stress is tied to the presence of petrologic anomalies

using probabilistic seismic tomography to test mantle velocity density relationships we use a neighborhood algorithm to explore the fit to long period seismic data of a wide variety of long wavelength mantle models this approach to the global tomographic inverse problem yields probability distributions for seismic velocities density and related properties as functions of depth such distributions can be robust even when individual models are not and allow us to test several assumptions about the earth that have long been enforced a priori in inversions in particular we are able to test the paradigm ofdeep mantle heterogeneity that is dominantly thermal in origin producing velocity and density perturbations that are well correlated and have relative amplitudes given by nlnb nlnvs 6 0 5 our distributions show that such relationships are unlikely and even though the results are consistent with recent best fitting models from damped seismic inversions they demonstrate that many specific properties ofsuch models are not robust the data clearly f density perturbations that are poorly or negatively correlated with velocity heterogeneity and have amplitudes several times larger yielding nlnb nlnvs s 1 0 than damped inversions allow these characteristics are most pronounced in the upper mantle transition zone and the base ofthe lower mantle suggesting layered convection the negative density velocity correlations f at these depths imply dominantly chemical heterogeneity while the likelihood ofrelatively high amplitude density variations suggests that variable iron content is an important component ofthis heterogeneity these results which we show to be consistent with independent gravity constraints represent a profound change in the interpretation of seismic constraints in addition the distributions show that even though best fitting density models from recent inversions or our sampling are consistent with the data most specific properties of such models are not robust this implies that it is more appropriate to use seismic model distributions rather than individual models to make geodynamic and geochemical inferences

can we resolve 3d density heterogeneity in the lower mantle we reexamine the possibility of resolving 3d density structure in the mantle by performing test inversions using a dataset of well constrained degree 2 splitting coefficients we show that degree 2 in vs and vp can be resolved and confirm that dlnvs dlnvp 2 5 at depths 2000km indicating a chemical component to large scale heterogeneity models with positively correlated with vs in the deepest mantle fit the data at least as well as those in which density and velocities are anti correlated however some rough bounds on dln dlnvs can be inferred models obtained from geodynamic considerations are acceptable in contrast to models with large negative 0 6 dln dlnvs throughout the lower mantle the most robust feature is a marked increase in dln dlnvs at the top of the lower mantle reaching a maximum around 1500 km

waveform effects of a high velocity subducted slab creager and jordan 1986 propose that penetration of subducting slabs under the kurile islands and other subduction zones to depths of at least 1000 km is necessary to explain travel time anomalies of deep earthquakes such penetration would also be expected to affect the amplitudes and waveforms of the body waves from earthquakes synthetic seismograms appropriate for a record section in a plane perpendicular to the strike of the slab are presented using a coupled finite difference and kirchhoff method our shear wave version of the compressional wave velocity structure of creager and jordan 1986 produces an amplitude decrease up to a factor of four and waveform broadening up to 20 seconds for sh arrivals with a take off angle pointing straight down the slab slabs that extend only 300 km below the earthquake but are half as thick and twice as anomalously fast as creager and jordan s 1986 velocity model will roughly preserve the travel time variation pattern and show less waveform broadening but produce first arrivals that are emergent slabs that become thicker with depth show less waveform broadening reconciliation of the amplitude waveform distortion and timing of body waves from deep events is necessary to understand the geometry of slabs in the upper mantle and near and below the 650 km discontinuity

mgsio3 postperovskite at d conditions the postperovskite transition in mgsio3 at conditions similar to those expected at the d discontinuity of earth s lower mantle offers a paradigm for interpreting the properties of this region despite consistent experimental and theoretical predictions of this phase transformation the complexity of the d region raises questions about its geophysical significance here we report the thermoelastic properties of cmcm postperovskite at appropriate conditions and evidences of its presence in the lowermost mantle these are i the jumps in shear and longitudinal velocities similar to those observed in certain places of the d discontinuity and ii the anticorrelation between shear and bulk velocity anomalies as detected within the d region in addition the increase in shear modulus across the phase transition provides a possible explanation for the reported discrepancy between the calculated shear modulus of postperovskite free aggregates and the seismological counterpart in the lowermost mantle

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

efficacy of the post perovskite phase as an explanation for lowermost mantle seismic properties constraining the chemical rheological and electromagnetic properties of the lowermost mantle d is important to understand the formation and dynamics of the earth s mantle and core to explain the origin of the variety of characteristics of this layer observed with seismology a number of theories have been proposed including core mantle interaction the presence of remnants of subducted material and that d is the site of a mineral phase transformation this final possibility has been rejuvenated by recent evidence for a phase change in mgsio3 perovskite thought to be the most prevalent phase in the lower mantle at near core mantle boundary temperature and pressure conditions here we explore the efficacy of this post perovskite phase to explain the seismic properties of the lowermost mantle through coupled ab initio and seismic modelling of perovskite and post perovskite polymorphs of mgsio3 performed at lowermost mantle temperatures and pressures we show that a post perovskite model can explain the topography and location of the d discontinuity apparent differences in compressional and shear wave models and the observation of a deeper weaker discontinuity furthermore our calculations show that the regional variations in lower mantle shear wave anisotropy are consistent with the proposed phase change in mgsio3 perovskite

geodynamic evidence for a chemically depleted continental tectosphere the tectosphere namely the portions of earth s mantle lying below cratons has a thermochemical structure that differs from average suboceanic mantle the tectosphere is thought to be depleted in its basaltic components and to have an intrinsic buoyancy that balances the mass increase associated with its colder temperature relative to suboceanic mantle inversions of a large set of geodynamic data related to mantle convection using tomography based mantle flow models indicate that the tectosphere is chemically depleted and relatively cold to 250 kilometers depth below earth s surface the approximate equilibrium between thermal and chemical buoyancy contributes to cratonic stability over geological time

investigation of deep slab structure using long period s waves travel times and amplitudes of long period sh scsh ssh and sscsh phases from several deep focus earthquakes in the northwest pacific are analyzed for evidence of lithospheric slab penetration into the lower mantle inclusion of amplitude observations in the analysis provides constraints on lateral velocity gradients present in the deep slabs which are not resolvable using travel times alone travel time and amplitude residual spheres are presented for two deep focus events with good azimuthal coverage but while interesting patterns are present quantitative analysis is precluded by the lack of accurate methods for calculating synthetic long period seismograms for three dimensional slab models therefore we focus our analysis on a two dimensional approximation to the downdip geometry of the kurile and japan slabs which allows comparison of a much larger data set with accurate two dimensional synthetics as well as the use of ss and sscs travel time and amplitude patterns as empirical corrections for deep mantle structure while the limited azimuth range required for this approximation reduces the diagnostic capability of the data it also increases our confidence that the corrected data are most sensitive to the near source region the ss and sscs observations indicate that the downdip shear wave travel time pattern previously attributed to a deep slab extension is primarily caused by broad scale lower mantle heterogeneity once corrected for this structure the s wave observations do not support a simple undeformed slab steepening in dip and penetrating deep into the lower mantle beneath the kurile and japan islands as proposed by jordan 1977 and creager and jordan 1984 1986 rather the observations support shorter and or broader slab models man those previously hypothesized models which can probably be reconciled with p wave data further analysis of the complete three dimensional patterns will be required for more precise resolution of the penetration depths of these slabs if indeed any deep slab heterogeneity is actually seismically detectable

anomalies of temperature and iron in the uppermost mantle inferred from gravity data and tomographic models we propose a method to interpret seismic tomography in terms of thermal and compositional anomalies in addition to the tomographic model we use gravity data which provide information on the density expressed as a relative density to shear wave velocity scaling factor ln ln vs the inferred values of are not consistent with the presence of thermal anomalies alone however simultaneous anomalies of temperature and composition explain the observations compositional anomalies can have several origins but we find the most relevant parameter to be the global volumic fraction of iron xfe fe fe mg we invert the tomographic model s16rlbm woodhouse and trampert 1995 and the density anomalies correlated to vs anomalies 0 vs v0 for anomalies of temperature t and iron fe the partial derivatives are provided by a numerical method that reconstructs density and seismic velocity for given temperatures and petrologic models vacher et al 1998 down to z 300 km depth the distribution of temperature and iron anomalies strongly depends on the surface tectonics the continental mantle below old cratons and stable platforms is colder than average and depleted in iron whereas the oceanic mantle is mostly homogeneous due to uncertainties on the reference state of the mantle error bars on t and fe reach 10 of the inverted values finally we apply these results to the stability of continental roots and test the hypothesis that the negative buoyancy induced by lower than average temperatures is balanced by the positive buoyancy induced by the depletion in iron we find that continental roots are stable only if the viscosity of the mantle is strongly temperature dependent however some uncertainties remain on the real effects and importance of rheology 2002 elsevier science b v all rights reserved

on the anelastic contribution to the temperature dependence of lower mantle seismic velocities abstract there is little agreement regarding the importance of anelastic contributions to the temperature dependence of seismic wave velocities some studies consider the anelastic contribution to be negligible whereas others argue that it may be as important as the purely elastic contribution in order to evaluate these claims we review physically plausible models for mantle relaxation processes and construct a model of activation enthalpy based on solid state physics as well as on recent experimental results we then deduce self consistent 1 d q profiles and evaluate the anelastic contribution to the temperature dependence of v s and v p physically plausible values of activation enthalpies yield anelastic contributions that increase with depth and account for at least 20 of the velocity temperature derivatives at 2600 km we show that anelasticity may significantly moderate temperature variations in hot slow velocity zones this suggests that inferred lateral changes in temperature as well as arguments regarding the presence of chemical heterogeneity and or temperature induced phase transformations are likely to be significantly affected by anelastic effects in the mantle we also compute values of the dimensionless parameters r s p r s and r s we find that anelasticity can either increase or decrease r s p but the magnitude of the correction of the order of 15 is smaller than the uncertainty in the elastic value anelasticity cannot change the sign of r s and r s but it can decrease their values by as much as 50 however given current uncertainties in seismic and mineral data the effects of anelasticity on the dimensionless parameters do not bring any quantitative constraints on lateral variations of temperature chemical composition and or mineral phase

finite frequency whole mantle p wave tomography improvement of subducted slab images received 23 july 2013 revised 14 october 2013 accepted 17 october 2013 1 we present a new whole mantle p wave tomographic model gap p4 we used two data groups short period data of more than 10 million picked up onset times and long period data of more than 20 thousand differential travel times measured by waveform cross correlation finite frequency kernels were calculated at the corresponding frequency bands for both long and short period data with respect to an earlier model gap p2 we find important improvements especially in the transition zone and uppermost lower mantle beneath the south china sea and the southern philippine sea owing to broadband ocean bottom seismometers bbobss deployed in the western pacific ocean where station coverage is poor this new model is different from a model in which the full data set is interpreted with classical ray theory bbobs observations should be more useful to sharpen images of subducted slabs than expected from simple raypath coverage arguments citation obayashi m j yoshimitsu g nolet y fukao h shiobara h sugioka h miyamachi and y gao 2013 finite frequency whole mantle p wave tomography improvement of subducted slab images geophys res lett 40 doi 10 1002 2013gl057401

a generalized equilibrium model for predicting daily to interannual shoreline response coastal zone management requires the ability to predict coastline response to storms and longer term seasonal to interannual variability in regional wave climate shoreline models typically rely on extensive historical observations to derive site specific calibration to circumvent the challenge that suitable data sets are rarely available this contribution utilizes twelve 5 year shoreline data sets from around the world to develop a generalized model for shoreline response the shared dependency of model coefficients on local wave and sediment characteristics is investigated enabling the model to be recast in terms of these more readily measurable quantities study sites range from microtidal to macrotidal coastlines spanning moderate to high energy beaches the equilibrium model adopted here includes time varying terms describing both the magnitude and direction of shoreline response as a result of onshore offshore sediment transport between the surf zone and the beach face the model contains two coefficients linked to wave driven processes 1 the response factor that describes the memory of a beach to antecedent conditions and 2 the rate parameter c that describes the efficiency with which sand is transported between the beach face and surf zone across all study sites these coefficients are shown to depend in a predictable manner on the dimensionless fall velocity that in turn is a simple function of local wave conditions and sediment grain size when tested on an unseen data set the new equilibrium model with generalized forms of and c exhibited high skill brier skills score bss 0 85

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