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

deformation and texture development in cairo3 post perovskite phase up to 6 gpa and 1300 k at near ambient conditions cairo3 is isostructural with the high pressure polymorph mgsio3 post perovskite ppv mgsio3 ppv is thought to be a major phase in the earth s lowermost mantle cairo3 can thus serve as an analog for studying deformation of the ppv phase under conditions achievable with a multi anvil deformation apparatus here we study the rheologic behavior of cairo3 ppv at a variety of pressure and temperature conditions from 2 gpa to 6 gpa and 300 k to 1300 k and various strain rates sintered polycrystalline cairo3 ppv cylindrical in shape was deformed in the d dia multi anvil press in several shortening cycles up to 20 axial strain at each temperature and pressure shortening cycles were followed by lengthening back to 0 strain quantitative texture information was obtained using in situ synchrotron x ray diffraction and the rietveld method to analyze images in all cases we find that 010 lattice planes align perpendicular to the compression direction upon shortening and that there is little change in texture with temperature or pressure this texture pattern is consistent with slip on 010 100 the texture observed here is different from that produced in room temperature diamond anvil cell dac experiments on mggeo3 and mgsio3 ppv which both display textures of 100 and 110 lattice planes at high angles to the compression direction this implies that cairo3 ppv may not be a good analog for the plastic behavior of mgsio3 ppv 2008 elsevier b v all rights reserved

petrological constraints on seismic anisotropy the purpose of this paper is to investigate the correlations between anisotropic parameters for different orientations and mineralogies for realistic mineralogical and petrological models of the upper mantle such correlations make it possible to reduce the number of independent parameters required in seismic modelling of the upper mantle the variation with depth and with degree of random orientation is also investigated it is shown that the anisotropic combinations involved in an equivalent transversely isotropic medium azumithally averaged velocities with a vertical symmetry axis are strongly correlated but the combinations involved in azimuthal anisotropy are more weakly correlated comparison with available seismic data does not yet allow discrimination based on anisotropy between different petrological models it is shown that even if a proportion of random orientation is introduced it should be possible to achieve petrological discrimination from seismic data for some orientation configurations if the inverse problem is well posed i e takes account of the correlations between anisotropic parameters these correlations are incorporated in an inversion process to show that it is possible to explain the dataset used to derive the prem by alternative anisotropic models for the uppermost 220 km

the limits of ray theory when measuring shear wave splitting in the lowermost mantle with scs waves observations of shear wave splitting provide unambiguous evidence of the presence of anisotropy in the earth s lowermost mantle a region known as d much recent work has attempted to use these observations to place constraints on strain above the core mantle boundary cmb as this may help map flow throughout the mantle previously this interpretation has relied on the assumption that waves can be modelled as infinite frequency rays or that the earth is radially symmetric due to computational constraints it has not been possible to test these approximations until now we use fully three dimensional generally anisotropic simulations of scs waves at the frequencies of the observations to show that ray methods are sometimes inadequate to interpret the signals seen we test simple uniform models and for a d layer as thin as 50 km significant splitting may be produced and we find that recovered fast orientations usually reflect the imposed fast orientation above the cmb ray theory in these cases provides useful results though there are occasional notable differences between forward methods isotropic models do not generate apparent splitting we also test more complex models including ones based on our current understanding of mineral plasticity and elasticity in d the results show that variations of anisotropy over even several hundred kilometres cause the ray theoretical and finite frequency calculations to differ greatly importantly models with extreme mineral alignment in d yield splitting times not dissimilar to observations t 3 s suggesting that anisotropy in the lowermost mantle is probably much stronger than previously thought potentially 10 shear wave anisotropy or more we show that if the base of the mantle is as complicated as we believe future studies of lowermost mantle anisotropy will have to incorporate finite frequency effects to fully interpret observations of shear wave splitting

the postperovskite transition the discovery of the postperovskite ppv transition has profound impact on our understanding of the core mantle boundary cmb region unlike perovskite pv the ppv phase has a layered structure of the sio6 octahedra which may lead to a large contrast in some properties with pv recent studies have proposed unusual properties of ppv such as a large positive clapeyron slope a large sensitivity of the transition depth to iron a decrease in bulk sound speed at the transition and a development of significant lattice preferred orientation many of the proposed properties can provide explanations for the intriguing seismic observations at the cmb region yet significant discrepancies still exist however rapid developments in mineral physics will continue to improve our knowledge on the changes across the ppv transition

using moma broadband array scs s data to image smaller scale structures at the base of the mantle scs s residuals obtained at stations of the missouri to massachusetts moma temporary broadband seismic array are used to delineate variations in seismic velocity structure above the core mantle boundary cmb at scales smaller than observable with tomographic models south american earthquakes recorded at moma reveal a slow velocity anomaly that is at least as small as the limit of the resolution of scs waves about 300 km across this is modeled as being within a region of fast velocities in whole mantle models the slow scs s residuals correlate well with a peak in scs s relative amplitudes the small region of slow shear velocity at the cmb could be a pocket of lower mantle rock trapped beneath the descending farallon slab or evidence of chemical boundary layer variations

lowermost mantle anisotropy beneath the north pacific from differential s scs splitting summary seismic anisotropy is an important tool for studying the nature origin and dynamics of the lowermost mantle d we introduce differential s scs splitting as a tool for removing the effect of near source and near receiver anisotropy to estimate splitting accrued in the d region this is applicable to events recorded at epicentral distances between 60 and 85 near source anisotropy has often been ignored in previous studies of lowermost mantle anisotropy we apply differential s scs splitting to records from canadian national seismic network stations of western pacific earthquakes these sample the lowermost mantle beneath the north pacific the residual splitting in scs which we attribute to d shows lag times between 1 0 and 3 9 s given the near horizontal ray path of scs in d we interpret the recovered fast directions as the orientation of the fast shear wave in the plane defined by the vertical and transverse directions and observe a clearly non vti transverse isotropy with a vertical axis of symmetry style of anisotropy the largest population of results shows an approximately southeasterly dipping symmetry axis which we speculate might be explained by descending palaeoslab material being swept horizontally across the core mantle boundary towards an upwelling region beneath the central pacific non vti symmetry and the many possible contributions to d anisotropy from lower mantle minerals melt and subducted materials suggest that our understanding of the lowermost mantle could be greatly improved by trying to resolve a more general style of anisotropy

in situ measurement of texture development rate in cairo3 post perovskite the rate of crystallographic preferred orientation cpo development during deformation of post perovskite is crucial in interpreting seismic anisotropy in the lowermost mantle but the stability field of mgsio3 post perovskite prevents high strain deformation experiments being performed on it therefore to constrain the rate of cpo development in post perovskite we deformed cairo3 a low pressure analogue of mgsio3 post perovskite in simple shear at 3 2 gpa and 400 c to a shear strain of 0 81 from x ray diffraction patterns acquired during deformation we invert for cpo as a function of strain by comparing the cpo that develops with visco plastic self consistent vpsc models we constrain the critical resolved shear stresses crss of the non primary slip systems in cairo3 to be of order 6 times stronger than the primary 100 010 slip system this value is significantly less than has been assumed by previous studies and if applicable to mgsio3 implies that seismic anisotropy in the d layer develops slower than has previously been assumed

the occurrence of alpine permafrost in the front range of colorado abstract permafrost distribution or ground that remains frozen for at least 2 years has been modeled using a combination of geographic information system gis techniques digital elevation model dem variables and land cover in alpine regions of the world in the front range however no such empirical models have been developed and field data are restricted in spatial extent but rock glaciers are in abundance here i present a probabilistic logistic regression model that is based on topoclimatic information elevation and aspect for rock glaciers derived from u s geological survey usgs 10 m dems classes of land cover obtained from an enhanced thematic mapper plus etm image classification were assigned weights and were then multiplied by the regression results to refine estimates the effectiveness of the model was evaluated by comparing mean probability scores with rock glacier activity categories mean annual air temperature maat from climatic stations on niwot ridge and bottom temperature of winter snow bts measurements while a monte carlo simulation was used to detect uncertainty associated with the original dem permafrost scores 50 covered about 8 9 242 km 2 of the study area 2722 km 2 with the highest scores clustered around longs and rowe peaks permafrost locations showed a strong correlation with rock glacier activity classes the 1 0 c maat isotherm and bts measurements less than 3 0 c the uncertainty analysis revealed that slight global differences exist between the original and error prone dem however local variations in aspect caused the most uncertainty these results indicate that the model accurately represents regional distribution of permafrost therefore topoclimatic information from rock glaciers and land cover when combined with an uncertainty analysis can effectively be used to map the occurrence of front range permafrost providing an imperative tool for cartographers planners and geocryologists

mechanisms of al3 incorporation in mgsio3 post perovskite at high pressures abstract aluminum is the fifth most abundant element in the earth s mantle yet its effect on the physical properties of the newly found mgsio3 post perovskite ppv the major mineral of the earth s d layer is not fully known in this paper large scale ab initio simulations based on density functional theory dft within the generalized gradient approximation gga have been carried out in order to investigate the substitution mechanism of al3 into ppv at high pressures we have examined three types of al substitution in ppv 6 25 mol al substitution via a charge coupled mechanism ccm 6 25 mol al substitution via oxygen vacancy mechanism ovm and an oxygen vacancy si free end member mg2al2o5 for both the ccm and ovm five models where the al atoms were put in different positions were simulated at various pressures in the range 10 150 gpa our calculations show that the most favorable mechanism is a charge coupled substitution where al3 replaces the next nearest neighbor cation pairs in the ppv structure the calculated zero pressure bulk modulus of al bearing ppv is 3 15 lower than that of the al free ppv in agreement with previous works we find that the incorporation of al2o3 slightly increases the post perovskite phase transition pressure with the al partition coefficient k 2 67 at 120 gpa and 3000 k

three dimensional variations in love and rayleigh wave azimuthal anisotropy for the upper 800 km of the mantle we present a new mantle model yb14shani of azimuthal anisotropy for horizontally polarized shear waves sh in parallel with our previously published vertically polarized shear wave sv anisotropy model yb13svani yb14shani was obtained from higher mode love wave phase velocity maps with sensitivity to anisotropy down to 1200 km depth sh anisotropy is present down to the mantle transition zone mtz with an average amplitude of 2 in the upper 250 km and 1 in the mtz consistent with yb13svani changes in sv and sh anisotropy were found at the top of the mtz where olivine transforms into wadsleyite which might indicate that mtz anisotropy is due to the lattice preferred orientation of anisotropic material beneath oceanic plates sv fast axes become subparallel to the absolute plate motion apm at a depth that marks the location of a thermally controlled lithosphere asthenosphere boundary lab in contrast sh anisotropy does not systematically depend on ocean age moreover while upper mantle sv anisotropy is anomalously high in the middle of the pacific as seen in radial anisotropy models sh anisotropy amplitude remains close to the average for other oceans based on the depth at which sv fast axes and the apm direction begin to align we also found that the average thickness of cratonic roots is 250 km consistent with yuan and romanowicz 2010 for north america here we add new constraints on the nature of the cratonic lab and show that it is characterized by changes in both sv and sh anisotropy 2014 american geophysical union all rights reserved

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

observational evidence for diffracted sv in the shadow of the earth s core on the basis of observational evidence it has been assumed for a long time in the seismological literature that the diffracted s wave in the deep shadow of the earth s core is polarized as sh in good agreement with models that do not contain a well pronounced low velocity zone at the base of the mantle while this seems often to be the case broad band horizontal records from the geoscope network show that for some wavepaths the diffracted sv is strong enough to be clearly observed at distances between 107 and 117 moreover in some cases the diffracted sv is shifted with respect to sh by approximately a quarter period such observations should put additional constraints on the structure near the core mantle boundary among other possibilities lateral variations of the gradient at the base of the mantle allowing for regions with negative gradient and possibly azimuthal anisotropy in d should be considered in order to explain these data

small scale lateral shear velocity and anisotropy heterogeneity near the core mantle boundary beneath the central pacific imaged using broadband scs waves core reflected scs waves from 49 large m 5 1 deep tonga fiji events recorded in western north america are used to study a localized region of the core mantle boundary cmb under the central pacific ocean a total of 248 observations from the berkeley digital seismic network bdsn caltech united states geological survey usgs terrascope and the incorporated research institutions for seismology iris broadband arrays span epicentral distances of 73 85 scs reflection points sample a cmb patch southeast of the hawaiian islands at latitude 4 to 16 n and longitude 156 to 144 w near the proposed source location of the hawaiian plume highly variable scs travel times amplitudes waveforms and shearwave splitting indicate that the lowermost mantle in this region is heterogeneous both laterally and radially scsh sh differential travel times are on average 4 s larger than predicted by the preliminary reference earth model prem this is due to delayed scs arrivals and is largely accounted for by a model with a strong velocity decrease in d the scsh sh residuals also show a spatial trend not accounted for by a radial model indicating a lateral decrease in lower mantle shear velocity to the northeast this lateral velocity gradient appears to cause focusing of scs energy scsh sh amplitude ratios are larger than predicted by prem or by a model with a strong negative gradient with depth in d which enhances scs scs splitting corrected for lithospheric anisotropy beneath the receivers indicates spatial variations in d anisotropy with a systematic change in the orientation of the fast polarization direction from transverse to the ray path fast scsh to parallel to the ray path fast scsv along a northeast traverse these spatial trends suggest lateral gradients in the boundary layer shear flow on scale lengths of a few hundred kilometers which may be related to dynamical flow near the near the root of the large hawaiian plume

the lowermost mantle beneath northern asia ii evidence for lower mantle anisotropy summary we have analysed prediffracted s waves with turning points beneath northern siberia in a study of anisotropy in the lowermost mantle deep focus earthquakes beneath the marianas izu bonin and the sea of japan recorded at stations in western europe are used a correction for upper mantle anisotropy is applied to the data comparisons of the data with synthetic data for models with and without a high velocity d layer suggest that there is a velocity discontinuity at the top of the d region and that the style of anisotropy is transversely isotropic in this region time separations between s waves on the radial and transverse component show a weak trend where the separation increases with epicentral distance a normalization of this separation with the travel distance within d 300 km thick in this region suggests that the anisotropy is uniformly distributed within this layer and has an average value of 0 5 per cent a combination of different studies which investigate the structure of the lowermost mantle beneath europe and northern siberia reveals a complicated picture tomographic models from this area and evidence of d anisotropy lower mantle scatterers reflections from a d discontinuity and ultralow velocity zones suggest two distinct regions one exhibits high velocities d anisotropy a d discontinuity and no evidence of scatterers or ultra low velocity zones these features are likely associated with the palaeosubduction of the izanagi plate well into the lowermost mantle the other region has a lower overall velocity and shows evidence of scatterers and ultra lowvelocity zones perhaps suggesting the presence of partial melt these results suggest dramatic lateral variations in the nature of the lowermost mantle beneath northern asia over a length scale of roughly 30 degrees

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

application of an edge detection method to satellite images for distinguishing sea surface temperature fronts near the japanese coast abstract this study applies an edge detection method to satellite sea surface temperature sst images in order to distinguish sst fronts frequently occurring near the japanese coast first we develop a new set of edge detection algorithms the method is based on an entropic approach using jensen shannon divergence which is certified as a robust technique for detecting edge pixel candidates additionally we incorporate ridge line extraction morphological filter to obtain edge pixels which is suited to delineate intricate frontal features the methodology allows us to detect reasonable amount of possible fronts to the fullest extent according to the original image resolution therefore it enables us to analyze finer scale fronts near the coast as well as larger scale fronts associated with major currents then we present four case study examples of sst fronts near the japanese coast by applying the method to advanced very high resolution radiometer avhrr sst images with a grid size of 0 01 we describe the configuration and seasonal variability of the sst frontal systems from the viewpoint of occurrence probability sst gradient magnitude and orientation to the local bathymetry as compared with the previous observational studies consequently it is demonstrated that application of the method can derive new views of finer scale and highly variable sst fronts moreover this study first verifies the capability of comprehensive and statistical description of sst front configurations and variations near the japanese coast by applying edge detection method to sequences of satellite sst images

upper mantle low velocity zone structure beneath the kaapvaal craton from s wave receiver functions summary the southern african plateau is marked by anomalously high elevations reaching 1 2 km above sea level and there is much debate as to whether this topography is compensated by a lower mantle source or by elevated temperatures in the upper mantle in this study we use s wave receiver functions srfs to estimate the lithospheric thickness and sublithospheric mantle velocity structure beneath the kaapvaal craton which forms the core of the plateau to fit the srf data a low velocity zone lvz is required below a 160 km thick lithospheric lid but the lvz is no thicker than 90 km although the lid thickness obtained is thinner than that reported in previous srf studies neither the lid thickness nor the shear velocity decrease 4 5 associated with the lvz is anomalous compared to other cratonic environments therefore we conclude that elevated temperatures in the sublithospheric upper mantle contribute little support to the high elevations in this region of southern africa

inferences on flow at the base of earth s mantle based on seismic anisotropy we applied global waveform tomography to model radial anisotropy in the whole mantle we found that in the last few hundred kilometers near the core mantle boundary horizontally polarized s wave velocities vsh are on average faster by 1 than vertically polarized s wave velocities vsv suggesting a large scale predominance of horizontal shear this confirms that the d region at the base of the mantle is also a mechanical boundary layer for mantle convection a notable exception to this average signature can be found at the base of the two broad low velocity regions under the pacific ocean and under africa often referred to as superplumes where the anisotropic pattern indicates the onset of vertical flow

lowermost mantle anisotropy beneath the pacific imaging the source of the hawaiian plume we utilized recordings of seismic shear phases provided by several north american broadband seismometer arrays to provide unique constraints on shear wave anisotropy beneath the northern and central pacific ocean using a new analysis method that reduces measurement errors and enables the analysis of a larger number of available waveforms we examined relative travel times of teleseismic s and sdiff that sample a large area of lowermost mantle structure the results of this study provide evidence for small scale lateral and depth variations in shear wave anisotropy for a broad region of the lowermost mantle beneath the pacific ocean in particular we image a localized zone of anomalously strong anisotropy whose strength increases toward the top of dq beneath hawaii our results combined with a previous study of vp vsh ratios indicate that ancient subducted slab material may be responsible for observations beneath the northern pacific while lenses or layers of core mantle boundary reaction products or partial melt oriented by horizontal inflow of mantle material to the hawaiian plume source can explain observations beneath the central pacific fl 2001 elsevier science b v all rights reserved

constraints from seismic anisotropy on the nature of the lowermost mantle the d layer lies at the bottom of the earth s rocky mantle and separates it from the liquid metal alloy core this region extending from the core mantle boundary to a few hundred kilometres above fig 1 is geodynamically analogous to the more easily studied lithosphere at the top of the mantle the structure of d may reflect the style of lower mantle convection the nature of core mantle interaction and perhaps even the fate of subducting lithosphere1 observations of lithospheric seismic anisotropy have provided valuable insight into the nature of the upper mantle boundary layer but discussion of lower mantle seismic anisotropy has been somewhat contentious2 5 here we present evidence from seismic waves that have traversed the lowermost mantle beneath the caribbean region for a zone of seismic anisotropy below the d discontinuity which in this region lies 250 km above the core mantle boundary the anisotropy is most probably due to horizontal layering or aligned inclusions of a material with differing shear wave velocity if d is a graveyard for subducted lithosphere a plausible explanation of the anisotropy may be the contrast between cold lithospheric mantle and material that formerly constituted the oceanic crust which may have lower shear wave velocity owing to the presence of melt