effects of a perovskite post perovskite phase change near core mantle boundary in compressible mantle convection 1 numerical simulations of compressible isochemical mantle convection are used to investigate the effect of the perovskite to post perovskite phase transition at around 2700 km depth which has recently been discovered by high pressure experiments and ab initio calculations on the convective planform temperature and heat transport characteristics of the mantle the usual phase transitions at 410 km olivine spinel and 660 km spinel perovskite are also included the exothermic post perovskite phase change at 2700 km depth destabilizes the lower thermal boundary layer increasing the heat flow increasing interior mantle temperature and increasing the number and time dependence of upwelling plumes the resulting weak highly time dependent upwellings also have a smaller horizontal spacing than the plumes that occur in the absence of the phase transition while the influence of post perovskite phase change may be smaller than that of some other complexities such as compositional stratification it appears to have an important enough effect that it should not be ignored in dynamical studies of mantle convection

influence of water insoluble content on the short term strength of bedded rock salt from three locations in china unlike the presence of thick domes and thick layers of rock salt deposits in europe and the usa rock salt in china is mainly composed of thin layers 80 300 m characterized by a high content of water insoluble impurities thus the influence of these impurities on the strength of rock salt is barely known and has become an important topic for basic research in the construction of underground salt caverns for energy storage in china in this paper the influence of water insoluble content on the short term strength of bedded rock salt based on a series of combined laboratory tests including solubility uniaxial and triaxial compression tests on bedded rock salt samples from three locations in china namely the huai an ha site in jiangsu province the pingdingshan pds site in henan province and the anning an site in yunnan province is presented samples in which the water insoluble content was less than 50 were defined as rock salt and the remainder as impure rocks with salt analysis of the experimental results for rock salt samples leads to the conclusion that the uniaxial strength including the error in its measurement increases with increase in the water insoluble content in the sample meanwhile the triaxial strength of rock salt will hardly vary with changes in the water insoluble content it can also be concluded that application of confining pressure will suppress the impact of the water insoluble content on the short term strength of rock salt i e the inhibition will increase with increasing confining pressure application of hou s strength model to bedded rock salt from the three regions yields comparable results with the measured data nevertheless with a bearable small degree of uncertainty the modified hou s strength model has been proved to be more suitable for the determination of strength of bedded rock salt from the three study locations in china

seismic detection of folded subducted lithosphere at the core mantle boundary seismic tomography of the d region beneath the caribbean reveals a 100 km vertical step in an otherwise flat d shear velocity discontinuity and localized low velocities at the edge of the slab material which may involve upwellings caused by the slab laterally displacing a thin hot thermal boundary layer seismic tomography has been used to infer that some descending slabs of oceanic lithosphere plunge deep into the earth s lower mantle1 2 the fate of these slabs has remained unresolved but it has been postulated that their ultimate destination is the lowermost few hundred kilometres of the mantle known as the d region relatively cold slab material may account for high seismic velocities imaged in d beneath areas of long lived plate subduction and for reflections from a seismic velocity discontinuity just above the anomalously high wave speed regions3 4 the d discontinuity itself is probably the result of a phase change in relatively low temperature magnesium silicate perovskite5 6 here we present images of the d region beneath the cocos plate using kirchhoff migration of horizontally polarized shear waves and find a 100 km vertical step occurring over less than 100 km laterally in an otherwise flat d shear velocity discontinuity folding and piling of a cold slab that has reached the core mantle boundary as observed in numerical and experimental models can account for the step by a 100 km elevation of the post perovskite phase boundary due to a 700 c lateral temperature reduction in the folded slab we detect localized low velocities at the edge of the slab material which may result from upwellings caused by the slab laterally displacing a thin hot thermal boundary layer

unsolved problems in the lowermost mantle 1 many characteristics of d layer may be attributed to the recently discovered mgsio3 post perovskite phase without chemical heterogeneities they include a sharp discontinuity at the top of d regional variation in seismic anisotropy and a steep clapeyron slope however some features remain unexplained the seismically inferred velocity jump is too large in comparison to first principles calculations and the sharpness of the discontinuity may require a chemical boundary chemical heterogeneity may play an important role in addition to the phase transformation from perovskite to post perovskite phase transformation and chemical heterogeneity and the attendant changes in physical properties such as rheology and thermal conductivity are likely to play competing roles in defining the dynamical stability of the d layer revealing the relative roles between phase transition and chemical anomalies is an outstanding challenge in the study of the role of d in thermal chemical evolution of the earth

in situ x ray observations of phase assemblages in peridotite and basalt compositions at lower mantle conditions implications for density of subducted oceanic plate 1 phase relationships in klb 1 peridotite normal type mid oceanic ridge basalt nmorb and k rich basalt compositions were investigated experimentally from 28 to 143 gpa and 2050 to 3000 k a laser heated diamond anvil cell with the synchrotron x ray diffraction was developed to perform in situ observations of samples at simultaneous high pressures and temperatures we confirmed that the peridotite composition crystallized into an assemblage of mg perovskite ca perovskite magnesiowustite at pressures below 97 gpa and that nmorb and k rich basalt compositions both crystallized as mg perovskite ca perovskite stishovite an aluminous phase with a cafe2o4 type structure at pressures below 68 gpa the orthorhombic mg perovskite is stable in natural rock compositions at pressures less than 97 gpa corresponding to about 2200 km depth phase transition of silica phase from stishovite to cacl2 type phase was observed at 78 gpa in nmorb composition moreover we observed that nmorb crystallized in to an assemblage of cairo3 type mg fe sio3 ca perovskite pbo2 type silica an aluminous phase with a calcium cati2o4 type structure at 143 gpa corresponding to the core mantle boundary depth we measured the unit cell volumes of minerals in the nmorb composition at high p t and thereby estimated the density of subducted morb to a depth of 1800 km in the lower mantle in this depth regime morb is denser than model mantle densities e g prem and ak135 the estimated density of morb may contribute to an understanding of dynamics of the subducted slab in the deep lower mantle

the influence of post perovskite strength on the earth s mantle thermal and chemical evolution abstract we have investigated the influence of post perovskite ppv viscosity on mantle convective dynamics and stirring efficiency using numerical modeling and simple analytical theory our results show that the strength of ppv has a dramatic influence on convective dynamics the presence of a weak ppv enhances heat transfer across the bottom thermal boundary layer resulting in higher temperatures lower mantle viscosities and considerably larger convective velocities this leads to a significant increase in stirring efficiencies with decreasing the ppv strength by at least one order of magnitude in addition using a simple parameterized convection evolution that includes the influence of ppv coupled to a mixing model we show that during the long term history of the earth s mantle the presence of ppv yields systematically hotter thermal evolution and more efficient convective stirring such a strong effect of ppv strength on mantle stirring efficiency suggests that the influence of ppv phase must be considered when interpreting both geochemical and geophysical observations

stability metastability and elastic properties of a dense silica polymorph seifertite 1 dense silica polymorphs with sixfold coordinated si have been found in snc and lunar meteorites and may be important minerals for silica rich components in the lower mantle however the stable crystal structure in the lower mantle and properties of dense silica remain controversial under stable heating and quasi hydrostatic stress conditions we found that the cacl2 type undergoes a phase transition to the pbo2type seifertite at 130 140 gpa and 2500 k our data suggest that this phase transition occurs at a greater depth than the perovskite postperovskite transition in the lowermost mantle the molar volume measured at 1 bar is the smallest among the reported silica polymorphs therefore having the highest calculated density and in excellent agreement with recent first principles calculations the greater molar volume of seifertite found in the shergottite meteorite and previous experiments supports a metastable synthesis of the phase outside its stability field our data combined with the hugoniots of silica polymorphs also rule out the possibility of the formation of seifertite in the meteorite within its stability field we found very little change in bulk sound speed across the cacl2 type seifertite transition if shear wave velocity decreases at the transition to seifertite as suggested by some computational studies this silica transition may provide an alternative explanation for the discontinuities with a shear wave velocity decrease found at depths greater than the d discontinuity

lateral variation of the d discontinuity beneath the cocos plate 1 broadband shear wave signals from 15 deep south american earthquakes reveal small scale variations of the d shear velocity discontinuity beneath the cocos plate deconvolution by average event source wavelets allows multiple event and california station combinations to be double array stacked in 4 geographically separate reflection point bins with lateral dimensions of about 200 km reflections from the top of d are apparent in all 4 bins with significant variations in timing and strength relative to scs the data are compatible with a discontinuous shear velocity increase 264 km above the core mantle boundary that varies laterally in strength from 0 9 to 2 6 with corresponding lateral velocity variations within d

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

constraints on the presence of post perovskite in earth s lowermost mantle from tomographic geodynamic model comparisons abstract lower mantle tomography models consistently feature an increase in the ratio of shear wave velocity v s to compressional wave velocity v p variations and a negative correlation between shear wave and bulk sound velocity v c variations these seismic characteristics also observed in the recent sp12rts model have been interpreted to be indicative of large scale chemical variations other explanations such as the lower mantle post perovskite ppv phase which would not require chemical heterogeneity have been explored less constraining the origin of these seismic features is important as geodynamic simulations predict a fundamentally different style of mantle convection under both scenarios here we investigate to what extent the presence of ppv explains the observed high v s v p ratios and negative v s v c correlation globally we compare the statistical properties of sp12rts with the statistics of synthetic tomography models derived from both thermal and thermochemical models of 3 d global mantle convection we convert the temperature fields of these models into seismic velocity structures using mineral physics lookup tables with and without ppv we account for the limited tomographic resolution of sp12rts using its resolution operator for both v s and v p structures this allows for direct comparisons of the resulting velocity ratios and correlations although the tomographic filtering significantly affects the synthetic tomography images we demonstrate that the effect of ppv remains evident in the ratios and correlations of seismic velocities we find that lateral variations in the presence of ppv have a dominant influence on the v s v p ratio and v s v c correlation which are thus unsuitable measures to constrain the presence of large scale chemical variations in the lowermost mantle to explain the decrease in the v s v p ratio of sp12rts close to the cmb our results favour a ppv bearing cmb region which has implications for the stability field of ppv in the earth s mantle

the effect of temperature on the seismic anisotropy of the perovskite and post perovskite polymorphs of mgsio3 using elastic constants determined by ab initio molecular dynamics over a range of temperatures we show that the seismic anisotropy of mgsio3 perovskite is significantly temperature dependent at 90 gpa the direction of greatest shear wave splitting changes from 001 at 0 k to 010 at 3500 k in addition there is no shear wave splitting in the 100 direction at 0 k but a significant amount of splitting is exhibited at 3500 k we have also calculated the first set of high temperature elastic constants of the new post perovskite phase by ab initio molecular dynamics methods we find that in contrast to mgsio3 perovskite temperature has little effect on the acoustic anisotropy of this phase we determine ln vs ln vp for the post perovskite phase and find it to be very low about 0 9 this may be an important parameter for mapping out the post perovskite phase in the lowermost mantle

a doubling of the post perovskite phase boundary and structure of the earth s lowermost mantle a new model of the deep earth allows geophysicists to measure variations in earth s temperature near the boundary between the rocky mantle and core using a recently discovered phase change in the lowest part of the earth s mantle where atoms rearrange themselves in crystals under extreme pressure and temperature the model also explains odd features of this part of the mantle such as patchy regions that reflect seismic waves generated by large earthquakes and inferences of dense partial melting combined with observations the results imply very large variations in temperature providing further evidence for circulation of material throughout the earth s mantle the thermal structure of the earth s lowermost mantle the d layer spanning depths of 2 600 2 900 kilometres1 is key to understanding the dynamical state and history of our planet earth s temperature profile the geotherm is mostly constrained by phase transitions such as freezing at the inner core boundary or changes in crystal structure within the solid mantle that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory a recently discovered phase transition at pressures of the d layer2 3 4 is ideally situated to reveal the thermal structure of the lowermost mantle where no phase transitions were previously known to exist here we show that a pair of seismic discontinuities observed in some regions of d can be explained by the same phase transition as the result of a double crossing of the phase boundary by the geotherm at two different depths this simple model can also explain why a seismic discontinuity is not observed in some other regions and provides new constraints for the magnitude of temperature variations within d

a computational study of ionic vacancies and diffusion in mgsio3 perovskite and post perovskite we have performed first principles simulations within density functional theory to investigate the effects of pressure on the formation of defects ionic vacancies and ionic diffusion in the perovskite pv and post perovskite ppv phases of mgsio3 our results show that the predicted formation enthalpies of three schottky mgo sio2 and mgsio3 defects are similar between the two phases at high pressures 100 to 150 gpa with mgo schottky defect being the most favorable however the calculated activation enthalpies and activation volumes of diffusion are shown to differ substantially between them in particular the activation enthalpies for mg and si diffusion in ppv are smaller than the corresponding values for pv for example by factors of 2 2 and 3 4 respectively at 120 gpa whereas the o migration enthalpy of ppv is only slightly larger than that of pv the easy migration paths of the cations in ppv are shown to take place along the 100 direction in which si o octahedra share the edges visualization of the simulation data reveals that the vacancy defects and migrating ions induce substantial distortions in the atomic and electronic structures around them it is suggested that diffusion is equally easy for all three species in ppv and is likely to occur through extrinsic processes near the bottom of the lower mantle published by elsevier b v

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

using seismic waves to image earth s internal structure seismic waves generated in earth s interior provide images that help us to better understand the pattern of mantle convection that drives plate motions

phase transitions in pyrolite and morb at lowermost mantle conditions implications for a morb rich pile above the core mantle boundary abstract subduction of mid oceanic ridge basalt morb gives rise to strong chemical heterogeneities in the earth s mantle possibly extending down to the core mantle boundary phase relations in both pyrolite and morb compositions are precisely determined at high pressures and temperatures corresponding to lowermost mantle conditions the results demonstrate that the post perovskite phase transition occurs in pyrolite between 116 and 121 gpa at 2500 k while post perovskite and sio2 phase transitions occur in morb at 4 gpa lower pressure at the same temperature theory predicts that these phase changes in pyrolite and morb cause shear wave velocity increase and decrease respectively near the northern margin of the large low shear velocity province in the lowermost mantle beneath the pacific reflections from a negative shear velocity jump near 2520 km depth are followed by reflections from a positive velocity jump 135 to 155 km deeper these negative and positive velocity changes are consistent with the expected phase transitions in a dense pile containing a mixture of morb and pyrolitic material this may be a direct demonstration of the presence of accumulations of subducted morb crust in the deep mantle

high pressure elastic anisotropy of mgsio3 perovskite and geophysical implications using plane wave pseudopotential method within the local density approximation lda we calculate single crystal elastic constants cij of orthorhombic mgsio3 perovskite generally accepted to be the major component of the lower mantle as a function of pressure up to 150 gpa our results are in excellent agreement with experimental data at zero pressure and compare favorably with other pseudopotential predictions over the pressure regime studied here we use our elastic constants to calculate anisotropy of seismic wave velocities as a function of pressure depth mgsio3 perovskite is shown to be highly anisotropic in all portions of the lower mantle and the nature of anisotropy changes significantly with depth the absence of significant seismic anisotropy in most of the lower mantle suggests that mgsio3 perovskite assumes nearly random orientation in most of this region anisotropy at the topmost lower mantle suggested by some studies can be attributed to the preferred orientation of perovskite however anisotropy in the d layer is difficult to be attributed to preferred orientation of perovskite some other mechanisms including the presence of the aligned melt pockets and or lattice preferred orientation of magnesiowustite are needed

mineral chemistry and density of subducted basaltic crust at lower mantle pressures subducted slabs are less dense than the surrounding mantle near the base of the transition zone 660 km depth because of the survival of garnet in former basaltic crust by this depth mantle peridotite has transformed to denser perovskitite1 2 the buoyancy of the former basaltic crust may contribute to the observed accu mulation or horizontal displacement of many slabs at the base of the transition zone3 here we report experimental confirmation of the widely held belief that the basaltic crust of slabs eventually transforms to a dense perovskititic lithology stable in the lower mantle synthetic mid ocean ridge basalt more glass subjected to pressures of 45 80 and 100 gpa in a laser heated diamond anvil cell transforms to an assemblage of aluminous mg fe silicate perovskite non quenchable casio3 perovskite stishovite and a sodic aluminous phase with the ca ferrite structure fig 1 per ovskititic more is about 0 06 g cm 3 more dense than a model lower mantle prem derived from seismological data thus even thermally equilibrated perovskititic slabs should encounter no sig nificant hindrance to subduction and convection in the lower mantle

normal mode sensitivity to earth s d layer and topography on the core mantle boundary what we can and cannot see the core mantle boundary cmb is earth s most profound internal boundary separating the liquid iron outer core and the solid silicate mantle the detailed structure near the cmb has a major influence on mantle convection and the evolution of the core seismic observations such as topography on the cmb thin ultra low velocity zones ulvzs seismic anisotropy and the anticorrelation between shear wave and bulk sound velocity heterogeneities have mainly been made using body waves and are still poorly constrained we investigate the sensitivity of earth s free oscillations to these features and specifically show how large individual anomalies must be for them to be observable in addition we discuss the possible trade offs between these different lowermost mantle structures although modes have strong sensitivity to all the structures inserted the results illustrate the limits of what normal modes can resolve our tests show that i even small scale features such as ulvzs with a thickness larger than 19 km can be observed as long as their distribution contains a long wavelength component ii the peak to peak amplitude of cmb topography has a larger influence than its pattern and has to be smaller than 5 km to fit the data iii the effect of scaling between shear wave velocity and density anomalies is less constrained but a laterally varying pattern is implied by a simple test suggesting the presence of chemical variations iv a strong trade off exists between anisotropy in compressional wave velocity and incidence angle whereas shear wave anisotropy is less observable these findings provide valuable information for future normal mode studies on structures in earth s lowermost mantle and their trade offs

study of the relationship between surface subsidence and internal pressure in salt caverns because of the ultra low permeability and favorable rheological properties of rock salt salt caverns are globally considered to be an ideal medium for energy storage the prediction and control of surface subsidence above storage caverns are the key problems that require steady attention to ensure their long term safety and stable operation for salt caverns already in existence factors such as depth shape and geological conditions cannot be changed therefore the operating condition i e internal pressure becomes a key factor in influencing surface subsidence however cyclic pressure change during the operation phase has not been seriously considered by analytical investigation yet in this paper theoretical models for the volume convergence rates in spherical and cylindrical caverns have been derived thereby developing a new concept equivalent internal pressure that of rock salt is considered

lower mantle seismic discontinuities and the thermal morphology of subducted slabs abstract the nature of the lowermost few 100 km of the mantle holds insights into the scale of convection of the earth s mantle here we investigate the fine structure of this region using seismic migration of shear waves reflecting from velocity discontinuities near the core mantle boundary cmb recorded by a dense network of european seismic stations two main features are found one structure exhibits large scale topography and can be explained by a sharp increase in seismic velocity 206 316 km above the cmb the second structure lies 55 85 km above the cmb and marks a sharp reduction in velocity to explain the origin of these discontinuities we appeal to numerical simulations of three dimensional 3d mantle convection incorporating rigidly moving plates the plates organize the convective flow to allow for the development of large convection cells and cool sheet like downwellings at a convergent plate boundary the results suggest that in places observed seismic complexity in d discontinuity structure may be due to the thermal gradients resulting from the accumulation of cool subducted plate material at the cmb

evidence for a ubiquitous seismic discontinuity at the base of the mantle a sharp discontinuity at the base of earth s mantle has been suggested from seismic waveform studies the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first order discontinuity superimposed on global seismic velocity structure derived from tomography the observations can be modeled by a solid solid phase transition that has a 200 kilometer elevation above the core mantle boundary under adiabatic temperatures and a clapeyron slope of about 6 megapascal per kelvin

the importance of radiative heat transfer on superplumes in the lower mantle with the new post perovskite phase change abstract a new post perovskite phase has been identified recently from both x ray observations and first principles calculations this novel phase change occurs at a depth about 200 km above the core mantle boundary for temperatures of around 2800 k using a two dimensional extended boussinesq model we have studied the dynamical consequences of this deep mantle phase transition on mantle convection with particular emphasis on the effects on lower mantle plume structures we have employed a depth dependent viscosity with a viscosity maximum in the mid lower mantle and two phase transitions one at 670 km depth and the other at a depth of 2650 km the phase transition at 670 km is endothermic while we have examined both exothermic and endothermic possibilities for the new phase transition our results show the following situations favorable for the development of superplumes 1 endothermic phase transition for both constant and radiative thermal conductivities and 2 exothermic phase transition and radiative thermal conductivity smaller unstable plumes are found for exothermic phase transition and constant thermal conductivity extremely high lateral temperature increases exceeding 1500 degrees are found inside the lower mantle plume for constant thermal conductivity this lateral temperature contrast is mitigated by the presence of radiative thermal conductivity in order for superplumes to prevail in the lower mantle with a deep exothermic phase change we must invoke some form of radiative thermal conductivity for stabilizing and promoting large upwellings with a width exceeding at least 500 km strong lateral heterogeneities in both the seismic velocity and density fields can be produced in the plumes and the surrounding mantle for this new phase transition with a large clapeyron slope close to 10 mpa k

in situ observations of phase transition between perovskite and cairo 3 type phase in mgsio 3 and pyrolitic mantle composition abstract in situ observations of the perovskite cairo3 phase transition in mgsio3 and in pyrolitic compositions were carried out using a laser heated diamond anvil cell interfaced with a synchrotron radiation source for pure mgsio3 the phase boundary between the orthorhombic mg perovskite and cairo3 type phases in the temperature range of 1300 3100 k was determined to be p gpa 130 3 0 0070 0 0030 t 2500 k using platinum as a pressure calibrant we confirmed that the cairo3 type phase remained stable up to pressures of at least 156 gpa and temperatures of 2600 k the consistency of our results with previous theoretical calculations leads us to conclude that the 2700 km seismic discontinuity at the bottom of the lower mantle can be attributed to a phase transition to the cairo3 type phase the phase change from an orthorhombic mg perovskite to a cairo3 type bearing assemblage in a pyrolitic mantle composition was also observed at p 125 gpa which corresponds to the same mantle depth as the seismic discontinuity the phase boundary between the orthorhombic mg perovskite and cairo3 type bearing assemblage was determined to be p gpa 124 4 0 008 0 005 t 2500 k using gold as a pressure calibrant this transition boundary indicates that the temperature at a depth of 2700 km is about 2600 k and the adiabatic temperature gradient in the lower mantle is estimated to be 0 31 k km the partition coefficients and the effect of some elements on the phase equilibrium between the orthorhombic mgsio3 perovskite and cairo3 type mgsio3 were estimated from ab initio calculations our experimental and theoretical results indicate that the d layer consists of a cairo3 type bearing assemblage which is likely to have significant effect on the chemical and thermal evolution of the earth s mantle

d beneath the arctic from inversion of shear waveforms 1 the structure of the d region beneath the arctic has not previously been studied in detail using waveform inversion we find that the average s wave velocity in d beneath the arctic is about 0 04 km s higher than prem which is consistent with the existence of post perovskite ppv in d it is difficult to strongly constrain the fine structure of s velocity within d due to the small number of stations at epicentral distances 90 but by weighting those stations heavily in the inversion we show that the data suggest the existence of high s velocity in the upper half of d and low s velocity in the lower half consistent with the possibility of a double crossing ppv pv reverse phase transition within d we conduct a computational experiment to show that resolution of the velocity structure within d could be significantly improved by temporary installation of a portable array of seismographs in northern canada which would greatly increase the number of stations in the range 70 90

fabric development in mg fe o during large strain shear deformation implications for seismic anisotropy in earth s lower mantle abstract large strain shear deformation experiments were performed on mg 1 x fe x o x 0 25 1 0 one of the important minerals in earth s lower mantle deformation experiments were made on coarse grained 15 20 m grain size hot pressed aggregates at conditions of t t m 0 46 0 65 t temperature t m melting temperature and 0 4 10 3 to 0 9 10 3 differential stress shear modulus up to the shear strain of 7 8 under these conditions deformation occurs by dislocation creep the microstructural development in mg fe o is found to be sluggish and the complete dynamic recrystallization and nearly steady state fabric lattice preferred orientation are achieved only after shear strains of 4 at nearly steady state mg fe o shows strong fabrics characterized by the 1 1 0 axes being parallel to the shear direction and the poles of the 1 0 0 planes and to a lesser extent the poles of the 1 1 1 planes normal to the shear plane the seismic anisotropy corresponding to the deformation fabrics in mg fe o was calculated the nature of anisotropy corresponding to a given flow geometry changes significantly with strain as a result of fabric evolution anisotropy changes also with depth pressure due to the large variation of elastic anisotropy of mg fe o with depth seismic anisotropy caused by the deformation fabric of mg fe o is very weak in the shallow lower mantle v sh v sv anisotropy assuming that mg fe o occupies 20 volume fraction of the lower mantle and little shear wave splitting of vertically travelling waves a result that is consistent with the seismological observations in the d layer of the circum pacific regions thus the deformation fabric of mg fe o is a vital candidate of the cause of seismic anisotropy in these regions anisotropy caused by the lattice preferred orientation of mg fe o has a distinct azimuthal anisotropy with a strong 4 term azimuth the direction of propagation of the fastest slowest sh or p wave is parallel perpendicular to the flow direction and the slowest fastest sh or p wave is at 45 from these two directions

element partitioning between magnesium silicate perovskite and ferropericlase new insights into bulk lower mantle geochemistry n this study we investigated iron magnesium exchange and transition metal trace element partitioning between magnesium silicate perovskite mg fe sio3 and ferropericlase mg fe o synthetised under lower mantle conditions up to 115 gpa and 2200 k in a laser heated diamond anvil cell recovered samples were thinned to electron transparency by focused ion beam and characterized by analytical transmission electron microscopy atem and nanometer scale secondary ion mass spectroscopy nanosims iron concentrations in both phases were obtained from x ray energy dispersive spectroscopy measurements and nanosims our results are the first to show that recently reported spin state and phase transitions in the lower mantle directly affect the evolution of fe mg exchange between both phases mg perovskite becomes increasingly iron depleted above 70 80 gpa possibly due to the high spin low spin transition of iron in ferropericlase conversely the perovskite to post perovskite transition is accompanied by a strong iron enrichment of the silicate phase ferropericlase remaining in the fe rich phase though nanoparticles of metallic iron were observed in the perovskite bearing runs suggesting the disproportionation of ferrous iron oxide but were not observed when the post perovskite phase was present implications on the oxidation state of the earth and core segregation will be discussed transition trace element ni mn concentrations determined with the nanosims show similar trends and could thus be used to trace the origin of diamonds generated at depth this study provides new results likely to improve the geochemical and geophysical models of the earth s deep interiors

subducted banded iron formations as a source of ultralow velocity zones at the core mantle boundary ultralow velocity zones ulvzs are regions of the earth s core mantle boundary about 1 10 kilometres thick exhibiting seismic velocities that are lower than radial earth reference models by about 10 20 per cent for compressional waves and 10 30 per cent for shear waves it is also thought that such regions have an increased density of about 0 20 per cent ref 1 a number of origins for ulvzs have been proposed such as ponding of dense silicate melt2 core mantle reaction zones3 or underside sedimentation from the core4 here we suggest that ulvzs might instead be relics of banded iron formations subducted to the core mantle boundary between 2 8 and 1 8 billion years ago consisting mainly of interbedded iron oxides and silica such banded iron formations were deposited in the world s oceans during the late archaean and early proterozoic eras we argue that these layers as part of the ocean floor would be recycled into the earth s interior by subduction5 sink to the bottom of the mantle and may explain all of the observed features of ulvzs

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

a speculation on the structure of the d layer the growth of anti crust at the core mantle boundary through the subduction history of the earth abstract the growth curve of the continental crust shows that large amounts of continental crust formed in the early part of the earth history are missing in order to test a hypothesis that the former crust was subducted to the deep mantle we performed phase assemblage analysis in the systems of mid oceanic ridge basalt morb anorthosite and tonalite trondhjemite granite ttg down to the core mantle boundary cmb conditions results show that all these materials can be subducted to the cmb leading to the development of a compositional layering in the d layer we speculate that there could be five layers of feo enriched melt from partial melting of morb morb crust anorthosite ttg and slab or mantle peridotite in ascending order although the polymorphic transformation of perovskite to post perovskite in mg fe sio3 may explain the seismic discontinuity at the top of the d layer d discontinuity the effects of solid solution on the sharpness of the transformation suggest that the compositional layering is more plausible for the origin of the d discontinuity the d layer can be an anti crust made up mostly of ttg anorthosite derived from the former continental crust tectonic style of the anti crust at the cmb is similar to that at the surface at both places chemically distinct layers are density stratified and are also characterized by the processes of accretion magmatism and metasomatism

high pressure high temperature equation of state for fe2sio4 ringwoodite and implications for the earth s transition zone 1 we measured the density of iron ringwoodite and its pressure and temperature dependence at conditions of the mantle transition zone using the laser heated diamond anvil cell in conjunction with x ray diffraction our new data combined with previous measurements constrain the thermoelastic properties of ringwoodite as a function of pressure and temperature throughout the transition zone our best fit mie gruneisen debye equation of state parameters for fe end member ringwoodite are v0 42 03 cm3 mol k0 202 4 gpa k 4 0 1 08 6 q 2 and d 685 k this new equation of state revises calculated densities of the fe end member at transition zone conditions upwards by 0 6 compared with previous formulations we combine our data with equation of state parameters across the mg fe compositional range to quantify the effect of iron and temperature on the density and bulk sound velocity of ringwoodite at pressure and temperature conditions of the earth s transition zone the results show that variations in iron content and temperature have opposing effects on density and bulk sound velocity suggesting that compositional iron content and temperature variations in the transition zone may be distinguished using seismic observables

seismic imaging of the d and constraints on the core heat flux abstract recent seismic imaging of the deep mantle has revealed lens shaped layers near the bottom of the mantle the morphology of this layering has been attributed to the crossing of the post perovskite phase boundary by the local geotherm we have developed a technique for quantifying the relationships between the depths of the double crossings of the post perovskite transition developed in 3d spherical mantle convection as a means for testing the viability for using the clapeyron slope of the phase transition to put bounds on the heat flux from the core we have argued from the probability distribution of the local heat flow at the core mantle boundary that there are intrinsic problems in using error function from half space cooling curves for constraining the core heat flux because of the non gaussian shape of the probability distribution of the core heat flow in realistic 3d convection models in order to constrain better the core heat flux with the above arguments we need to know much better the mantle viscosity stratification and the pressure dependence of thermal conductivity in the deep mantle only then can we put together enough constraints to discuss with greater certainty about the core heat flux

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

lower mantle dynamics with the post perovskite phase change radiative thermal conductivity temperature and depth dependent viscosity the new post perovskite phase near the core mantle boundary has important ramifications on lower mantle dynamics we have investigated the dynamical impact arising from the interaction of temperature and depth dependent viscosity with radiative thermal conductivity up to a lateral viscosity contrast of 10 4 on both the ascending and descending flows in the presence of both the endothermic phase change at 670 km depth and an exothermic post perovskite transition at 2650 km depth the phase boundaries are approximated as localized zones we have employed a two dimensional cartesian model using a box with an aspect ratio of 10 within the framework of the extended boussinesq approximation our results for temperature and depth dependent viscosity corroborate the previous results for depth dependent viscosity in that a sufficiently strong radiative thermal conductivity plays an important role for sustaining superplumes in the lower mantle once the post perovskite phase change is brought into play this aspect is especially emphasized when the radiative thermal conductivity is restricted only to the post perovskite phase these results revealed a greater degree of asymmetry is produced in the vertical flow structures of the mantle by the phase transitions mass and heat transfer between the upper and lower mantle will deviate substantially from the traditional whole mantle convection model streamlines revealed that an overall complete communication between the top and lower mantle is difficult to be achieved 2005 elsevier b v all rights reserved

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

a lower mantle s wave triplication and the shear velocity structure of d summary a lower mantle s wave triplication detected with short and longperiod wwssn and csn recordings indicates a substantial shear velocity discontinuity near 280 km above the core mantle boundary the triplication can be observed in rotated sh seismograms from intermediate and deep focus events throughout the distance range from 70 to 95 three distinct source region receiver array combinations that have been investigated in detail demonstrate consistent travel time and relative amplitude behaviour of the triplication with slight systematic shifts in the triplication indicating up to 40km variations in the depth of the discontinuity modelling of the observations with synthetic seismograms produced with the cagniard de hoop and reflectivity methods constrains the shear velocity increase to be 2 75 k 0 25 per cent comparable to upper mantle discontinuities short period observations indicate that the velocity increase may be a sharp first order discontinuity or may extend over a transition zone no more than 50 km thick the shear velocity gradient below the discontinuity within the d layer is not well constrained by the sh data but slightly positive or near zero velocity gradients are consistent with the long period amplitude ratios of scsh sh

dipping low velocity layer in the mid lower mantle evidence for geochemical heterogeneity data from western united states short period seismic networks reveal a conversion from an s to a p wave within a low seismic velocity layer greater than or equal to the 4 percent velocity difference compared to the surrounding mantle in the mid lower mantle 1400 to 1600 kilometers deep east of the mariana and izu bonin subduction zones the low velocity layer about 8 kilometers thick dips 30 to 40 southward and is at least 500 kilometers by 300 kilometers its steep dip large velocity contrast and sharpness imply a chemical rather than a thermal origin ancient oceanic crust subducted into the lower mantle is a plausible candidate for the low velocity layer because of its broad thin extent

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

the p wavespeed structure in the lowermost 700 km of the mantle below the central part of the indian ocean abstract earthquakes from the indonesian region recorded at distances between 78 and 104 from broad band stations of the kaapvaal network were used to investigate the p wavespeed structure of the lowermost 700 km of the mantle below the central part of the indian ocean analysis of arrival times indicates a maximum in slowness gradients at a distance of 88 and wavespeeds in the lowermost 700 km of the mantle that are lower than in the reference model iasp91 these results suggest that the lowermost mantle is relatively hot measurements of p wave amplitudes also show a pronounced maximum at a distance close to 88 phase weighted stacking of waveforms from three deep focus earthquakes do not show any later arrivals that might identify a triplication in travel times associated with the presence of a discontinuity at the top of d however synthetic seismograms produced by both the wkbj and reflectivity methods for models having a small discontinuity at the top of d show the presence of an amplitude maximum due to constructive interference between the closely spaced signals near the cross over point of a triplication whose branches are not clearly resolvable visually the observed amplitude maximum however is too large to be explained by the smooth model midind01 fitted to the travel times stacking of synthetic seismograms constructed from models with small discontinuities at the top of d gives similar results to those for the real seismograms the observed amplitudes travel times results of phase weighted stacking and synthetic seismograms together suggest the presence of a small p wave discontinuity of 0 4 0 6 that defines the top of d 210 20 km above the core mantle boundary

estimates of heat flow in the deep mantle based on the power requirements for the geodynamo 1 regeneration of the magnetic field by convection in the core places demands on heat flow into the base of the mantle if the heat flow is too low thermal convection is shut off and the rate of generation of compositional buoyancy by the solidification of the core becomes too low to sustain the geodynamo conversely a large heat flow causes rapid growth of the inner core so that convection prior to the appearance of the inner core must be sustained by thermal buoyancy alone the attendant requirements on primordial heat become more severe as the age of the inner core decreases we show that estimates of the present day heat flow satisfy the power requirements for the geodynamo however the resulting thermal history is incompatible with estimates of mantle temperatures prior to 3 ga this discrepancy can be resolved by accumulating radioactive isotopes in d or adding heat sources to the core

geophysically consistent values of the perovskite to post perovskite transition clapeyron slope the double crossing hypothesis posits that post perovskite bearing rock in earth s d layer exists as a layer above the core mantle boundary bounded above and below by intersections between a curved thermal boundary layer geotherm and a relatively steep phase boundary increasing seismic evidence for the existence of pairs of discontinuities predicted to occur at the top and bottom of this layer motivates an examination of the consistency of this model with mineral physics constraints for the clapeyron slope of this phase transition using independent constraints for a lower bound on temperature in earth s deep mantle and the temperature of earth s inner core boundary we show that a post perovskite double crossing is inconsistent with plausible core temperatures for a clapeyron slope less than about 7 mpa k with the higher range of experimental values yielding better agreement with recent estimates of the melting temperature of earth s core

rolling hills on the core mantle boundary recent results suggest that an iron rich oxide may have fractionally crystallized from a primordial magma ocean and settled on the core mantle boundary cmb based on experimental results the presence of only a few percent of fe rich oxide could slow seismic waves down by several percent this heavy layer can become highly undulating as predicted from dynamic modeling but can remain as a distinct structure with uniform velocity reductions here we use the large usarray seismic network to search for such structures strong constraints on d 00 are provided by the core phase sks where it bifurcates containing a short segment of p wave diffractions pd when crossing the cmb called sksd synthetics from models with moderate velocity drops less than 10 involving a layer with variable thickness perhaps a composite of sharp small structures with strong variation in thickness can explain both the observed sksd waveforms and large scatter in differential times between skks and sks a smooth 3d image is obtained from inverting sksd waveforms displaying rolling hills with elongated dome like structures sitting on the cmb the most prominent one has an 80 km height 81 length and 41 width thus adding still more structural complexity to the lower mantle we suggest that these results can be explained by a dynamically stabilized material containing small amounts 5 ironrich mg fe o providing a self consistent physical interpretation

effects of the postperovskite phase change on the observed geoid in the lowermost mantle seismic velocity variations beneath pacific margins have been related to the perovskite to postperovskite ppv phase transition we investigate the influence of this phase transformation on the geoid using 3 d spherical mantle circulation models based on a seismic tomography model and strong lateral viscosity variations in the lower mantle we demonstrate that the geoid anomalies are strongly affected by the presence of ppv because of phase dependent viscosity changes relative to the surrounding mantle whereas geoid heights above subduction zones are increased for high viscosity ppv the presence of weak ppv reduces them thereby improving the fit to the observed geoid an investigation using two different tomography models different ppv density contrasts and the presence or absence of a global thermal boundary layer and of lateral viscosity variations in the lower mantle demonstrates the various effects of weak ppv on the geoid

mid mantle heterogeneities and iron spin transition in the lower mantle implications for mid mantle slab stagnation abstract recent high pressure experimental results reveal that the elastic and transport properties of mantle materials are impacted by the electronic spin transition in iron under lower mantle pressure and temperature conditions the electronic transition in ferropericlase fp the second major constituent mineral of the lower mantle material is associated with a smooth increase in density starting from the mid mantle depth to the core mantle boundary cmb the transition also yields softening in the elastic moduli and an increase in the thermal expansivity over the transition zone in the lower mantle although there is not yet robust experimental evidence for spin transition induced density change in the perovskite pv phase the major constituent mineral in the lower mantle the spin transition in the octahedral b site in al free perovskite causes a bulk modulus hardening increase in the bulk modulus in the mineral we have incorporated these physical processes into high resolution 3d spherical control volume models for mantle convection a series of numerical experiments explore how the electronic spin transition in iron modifies the mantle flow and in particular the fate of sinking cold slabs such mid mantle stagnations are prevalent globally in seismic tomographic inversions but previous explanations for their existence are not satisfactory employing density anomalies from the iron spin transition in ferropericlase and density anomaly models for perovskite we study the influence of the spin transition in the minerals of the lower mantle on mantle flow our model results reveal that while the spin transition induced property variations in ferropericlase enhance mixing in the lower depths of the mantle the density anomaly arising from the hardening in the bulk modulus of al free perovskite can be effective in slowing the descent of slabs and may cause stagnation at mid mantle levels a viscosity hill in the lower mantle may further enhance the stagnation effect cold descending slabs can stall in the mid mantle for tens of million years or even longer before penetrating to the lower mantle

influences of filling abandoned salt caverns with alkali wastes on surface subsidence abandoned salt caverns particularly those that allow free draining of brine are serious potential causes of subsidence above salt mines filling such caverns with alkali wastes may eliminate these troubles based on the filling project in jingshen salt mine of china the influences of filling abandoned free draining salt caverns with alkali wastes on surface subsidence are discussed the deposition characteristics of alkali waste slurry were studied by laboratory simulation tests it is found that alkali waste slurry has good flowability during injection into a cavern based on the results of compression tests under drained conditions a distribution model of void ratio of sediment is established a method for determining the ultimate subsidence value is presented based on the distribution model the relationship of average effective stress and void ratio of the sediment is also established further a method for predicting development process of surface subsidence is presented finally the specific application procedure of the prediction methods is discussed according to the research results filling free draining salt caverns with alkali wastes can restrain surface subsidence successfully the reasons can be summed up as volume convergence of salt caverns slows down after the caverns are filled owing to the supporting effect of alkali wastes on the rock surrounding caverns and then subsidence slows down and decreases and finally subsidence stops when the fill material is compacted to its compressed limit

phase transition and density of subducted morb crust in the lower mantle abstract phase relations mineral chemistry and density of a natural mid oceanic ridge basalt morb composition were investigated up to 134 gpa and 2300 k by a combination of in situ x ray diffraction measurements and chemical analyses using transmission electron microscope tem results demonstrate that the morb composition consists of mgsio 3 rich perovskite stishovite casio 3 perovskite and cafe 2 o 4 type al phase in the upper part of the lower mantle the most abundant mineral of mgsio 3 rich perovskite undergoes phase transition to a cairo 3 type post perovskite phase above 110 gpa and 2500 k post perovskite phase is similar in composition to perovskite except considerably high na 2 o content stishovite transforms to cacl 2 type sio 2 phase above 62 gpa and 2000 k and further to pbo 2 type phase above 110 gpa pbo 2 type sio 2 phase includes large amount of al 2 o 3 which significantly expands its stability relative to cacl 2 type phase phase transition of casio 3 perovskite from tetragonal to cubic was also observed with increasing temperature cafe 2 o 4 type al phase is stable to the bottom of the mantle the density of morb crust was calculated using volume data combining with measured chemical compositions and calculated mineral proportions the former morb crust is denser than the average lower mantle at all depths greater than 720 km contrary to earlier predictions the subducted basaltic crust may have accumulated at the base of the mantle

evidence for a shear velocity discontinuity in the lower mantle beneath india and the indian ocean abstract sh and ssh seismograms are modeled to determine the shear velocity structure in the d region beneath india and the indian ocean the signals show waveform complexities similar to those observed in data sampling the d region beneath alaska the caribbean and eurasia lay and helmberger which have been attributed to a 2 7 shear velocity discontinuity 280 km above the core mantle boundary the new data set consists of long period tangential component recordings at wwssn stations in africa the middle east and europe for 11 intermediate and deep focus indonesian earthquakes in the distance range 70 82 the waveforms show an arrival between sh and scsh with systematic moveout from 89 to 94 there is a strong distortion of the sh waveforms indicating the arrival of several phases closely spaced in time the relative time shifts of similar complexity in the corresponding ssh phases requires a deep mantle origin the depth dependence and moveout of the interference effects are well predicted for both sh and ssh phases by a model with a lower mantle discontinuity alternative explanations of the interference as resulting from receiver reverberations sks contamination multiple source complexity or near source multipathing are ruled out by systematic tests while it is apparent that lateral variations in the lower mantle velocity structure prevent any single model from fitting all of the data synthetic waveform modeling using generalized ray theory and reflectivity shows that the data can be well fit by a model with a discontinuity similar in size and depth to that proposed for the previously investigated regions lay and helmberger but with a negative velocity gradient within the d layer

complexity of d in the presence of slab debris and phase changes 1 a lower mantle s wave triplication with a scd branch is easily observed beneath central american and its lateral variations has been studied extensively attempts to model scd depth variations with a phase boundary based on tomography predict smooth variations e g sidorin et al 1999a recently hutko et al 2005 presents evidence of a sharper feature with a vertical step like jump of over 50 km for paths sampling the western edge of a fast lower mantle structure beneath the cocos plate we present a similar type of very anomalous scd waveforms sampling the edge further to the east we are able to model these waveforms by adopting the phase boundary model but enhancing the existing tomographic anomaly just above the velocity jump which appears to be a folded slab

melting temperature of the earth s mantle and core earth s thermal structure abstract although the temperature at the top of the lower mantle is well constrained by phase equilibrium data for the transformation of transition zone minerals to the denser perovskite polymorphs the temperature distribution in the lower mantle is poorly known models depend strongly on the assumptions of the amount of internal heating and the viscosity profile new melting data on iron to pressures of the outer core 2 mbar and the observed strong decrease of eutectic melting depression in the fe feo fes system with increasing pressure however tightly constrain the temperature at the inner core boundary to slightly less than 5000 k this estimate can be reconciled with all recent static melting measurements on iron and lays within the uncertainty of shock temperature measurements the resulting temperature at the core mantle boundary of about 4000 k then requires a large temperature gradient at the bottom of the lower mantle of about 1500 k recent findings of the very high melting temperatures o

high resolution imaging of lowermost mantle structure under the cocos plate 1 broadband seismic shear waves are analyzed to investigate the fine velocity structure in the lowermost mantle beneath the cocos plate a region where previous studies have indicated the presence of a shear velocity increase about 200 300 km above the core mantle boundary data from 14 south american earthquakes recorded at california broadband networks provide dense ray path sampling of the lowermost mantle in an approximately 700 km long north south corridor roughly 150 km wide application of a simplified seismic migration method that uses a homogeneous background velocity model suggests topography of the previously imaged positive impedance jump varying in depth from north to south by as much as 150 km with a weakly reflecting transition zone in between the migration approach enables examination of small scale spatial variations and out of plane scattering effects topography of the discontinuity may account for observed variations in the amplitude of reflected arrivals or there may be lateral variations in the velocity contrast across the boundary lateral variations of the shear velocity structure within the d layer may produce some apparent topography in the discontinuity image but any such volumetric structure is not yet well enough determined to incorporate in the migration a localized negative impedance contrast reflector or scatterer is imaged at depths about 100 km below the positive reflector in the northern portion of the study area several scenarios can explain these results including 1 a slab that reaches the lowermost mantle 2 the birth of an upwelling beneath a recumbent slab or 3 chemical layering in this region

postperovskite phase transition and its geophysical implications 1 the stability of mg fe sio3 perovskite in the deep lower mantle has long been uncertain recently a phase transition from perovskite to postperovskite was discovered through a significant change in the x ray diffraction pattern at high pressure and high temperature conditions corresponding to the core mantle boundary region this phase transition was also confirmed by first principles calculations these suggest that mg fe sio3 postperovskite is the predominant mineral in the lowermost mantle called the d layer and phase transition from perovskite to postperovskite has significant geophysical implications for its nature and dynamics the postperovskite phase may account for the large seismic anomalies observed in the d region such as the d discontinuity s wave anisotropy and anticorrelation between the anomalies in s wave and bulk sound velocities in addition this phase transition is a strongly exothermic reaction it destabilizes the thermal boundary layer at the base of the mantle and should promote the formation of high temperature upwelling plumes

salt cavern gas storage in an ultra deep formation in hubei china abstract the target formation of jianghan salt district qianjiang city hubei province china for underground gas storage ugs construction has a depth of more than 1800 m the cavern will be the deepest salt cavern ugs in asia a 3d geomechanical model of the proposed salt cavern ugs is built based on the geologic characteristics and mechanical parameters of the target formation a new indexes system composed of displacement volume shrinkage plastic zone dilatancy safety factor and equivalent strain is proposed to quantitatively evaluate the safety of jianghan salt cavern ugs the thresholds of each indicator are proposed based on the characteristics of rock salt in china by using the proposed indexes system the cavern shape dimensions operating parameters and pillar width are optimized calculating results show that the optimized cavern has a slender cylindrical shape with a domed roof and an inverted cone bottom its diameter ranges from 80 to 90 m its height is about 210 m and its free volume accessible to gas is about 50 65 104 m3 the maximum operating gas pressure is about 34 mpa and the minimum gas pressure is no less than 17 mpa the width of the pillar between adjacent caverns is about 2 5 3 times the cavern diameter the gas storage capacity of a single cavern is about 1 1 109 m3 and the working gas is about 0 7 109 m3 which is about three times that of a single cavern in jintan salt cavern ugs jiangsu province china the results indicate that jianghan salt cavern ugs has a good feasibility for large scale gas storage

the anisotropic signal of topotaxy during phase transitions in d abstract while observations and modelling of seismic anisotropy in the lowermost mantle offers the possibility of imaging mantle flow close to the core mantle boundary current models do not explain all observations here we seek to explain a long wavelength pattern of shear wave anisotropy observed in anisotropic tomography where vertically polarised shear waves travel faster than horizontally polarised shear waves in the central pacific and under africa but this pattern is reversed elsewhere in particular we test an explanation derived from experiments on analogues which suggest that texture may be inherited during phase transitions between bridgmanite perovskite structured mgsio3 and post perovskite and that such texture inheritance may yield the long wavelength pattern of anisotropy we find that models that include this effect correlate better with tomographic models than those that assume deformation due to a single phase in the lowermost mantle supporting the idea that texture inheritance is an important factor in understanding lowermost mantle anisotropy it is possible that anisotropy could be used to map the post perovskite stability field in the lowermost mantle and thus place constraints on the temperature structure above the core mantle boundary

study on nonlinear damage creep constitutive model for high stress soft rock rock engineering especially deep rock engineering undergoing long term effects of external loading and gravity all or most may gradually damage deformation or creep deformation accumulation leading rock structures to damage crack such as severe plastic deformation or even progressive failure in this paper based on the nonlinear damage creep characteristics of rock and damage variable a new nonlinear damage creep constitutive model of high stress soft rock is defined in series with the improved burgers model hooke model and st venant model this new nonlinear damage creep constitutive model can work out fairly reasonably explanations for the soft rock creep deformation a series of uniaxial compression creep tests were performed to study the creep damage characteristics of typical soft rock in jinchuan no 2 mine in the northwest of china using the increment step loading and single step loading the results of creep experiments and nonlinear damage creep constitutive model results are very consistent in this study the new model not only can reflect the whole course of creep deformation but also can reasonably describe the soft rock under different initial creep stage steady state creep stage and accelerated creep stage therefore the new nonlinear creep damage model is a reasonable reference model for the research of soft rock creep

the trouble with seeing double 1 the recently discovered phase transition for mg fe sio3 from perovskite to post perovskite structure for pressure temperature conditions in the lowermost mantle provides a plausible mechanism to explain a several percent shear velocity increase detected at the top of the d region in many regions the phase transition has a large positive clapeyron slope and given the likely presence of a strong temperature increase just above the core mantle boundary d conditions may reintersect the phase boundary resulting in a thin layer of perovskite below a lens of post perovskite separated by a few percent velocity decrease detection of such a velocity decrease is shown to be much harder than detection of the shallower velocity increase due to fundamental properties of seismic waves purported observations in support of a double discontinuity are re evaluated based on waveform modeling waveform stacking procedures are required for reliable detection of the lower half of any double crossing of the phase boundary

erratum to magnesium sulphate salts on monuments in saxony germany regional geological and environmental causes a record of mortar and salt analyses from the last 20 years on various monuments in saxony demonstrates the close relation between the occurrence of magnesium sulphate salts and the use of dolomitic lime mortars in a regional frame the regional distribution scheme of dolomitic lime in historic mortars depends on the geological setting of the territory i e the natural occurrence of dolomite deposits sulphation of these mortars with the formation of magnesium sulphate and gypsum is mainly due to environmental pollution as can be shown by sulphur stable isotope analyses exposure of the sulphated mortar surfaces to rain leads to the preferential dissolution and advective transport of the novel formed magnesium sulphate salts which effloresce or subfloresce on the mortar surface or can be accumulated in the structure of adjoining porous building materials like natural stones these processes may cause severe damages in mortars by the weakening of the binder and in porous stones by salt crystallisation of phases like epsomite and hexahydrite

modeling layered structure in deep pacific circulation the layered structure of the deep pacific circulation is investigated using a multilevel numerical model with idealized geometry the circulation is driven by sea surface heating and newtonian body cooling at the southwest corner of the basin the latter forcing is intended to incorporate thermohaline forcing in the southern ocean a layered structure forms in the zonally averaged meridional circulation when the reference density for the body cooling varies vertically the density balance between vertical advection and vertical diffusion holds in the zonally averaged field as well as in the interior this balance combined with the reference density for the body cooling determines the zonally averaged vertical velocity and hence the zonally averaged meridional circulation from the zonally averaged continuity equation this two dimensional mechanism for describing the layered structure for this three dimensional rotating fluid model is identical to that for a two dimensional nonrotating fluid model the increased vertical structure is accompanied by the enhancement of some higher vertical modes which brings about various changes in the three dimensional structure such as the formation of a broad diffusive deep western boundary current

dynamical consequences in the lower mantle with the post perovskite phase change and strongly depth dependent thermodynamic and transport properties article i nfo we have carried out numerical simulations of large aspect ratio 2 d mantle convection with the deep phase change from perovskite pv to post perovskite ppv using the extended boussinesq approximation for a fluid with temperature and pressure dependent viscosity we have investigated the effects of various ppv phase parameters on the convective planform heat transport and mean temperature and viscosity profiles since ppv is expected to have a relatively weak rheology with respect to pv and a large thermal conductivity we have assumed that the transition from pv to ppv is accompanied by both a reduction in viscosity by 1 to 2 orders of magnitude and by an increase in thermal conductivity by a factor of 2 furthermore we have analyzed the combined effects of a strongly decreasing thermal expansivity in pv and steeply increasing thermal conductivity according to recent evidence from high pressure experiments and first principle calculations as long as the thermal expansivity and conductivity are constant ppv exerts a small but noticeable effect on mantle convection it destabilizes the d layer causes focusing of the heat flux peaks and an increase of the average mantle temperature and of the temporal and spatial frequency of upwellings when the latest depth dependent thermal expansivity and conductivity models are introduced the effects of ppv are dramatic on the one hand without ppv we obtain a very sluggish convective regime characterized by a relatively cool mantle dominated by large downwellings that tend to stagnate beneath the transition zone with ppv on the other hand we observe an extremely significant increase of the average mantle temperature due to the formation of large sized and vigorous upwellings that in some cases tend to cluster thus forming superplumes if a very large thermal conductivity at the core mantle boundary is assumed k 20 wk 1 m 1 we obtain a quasi steady state regime characterized by large and stable plumes with long lifetimes the combination of strongly depth dependent expansivity and conductivity is a viable mechanism for the formation of long wavelength long lived thermal anomalies in the deep mantle even if a low viscosity ppv atop the core mantle boundary is included

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

lower mantle tomography and phase change mapping a lower mantle s wave triplication scd has been recognized for many years and appears to be explained by the recently discovered perovskite pv to postperovskite ppv phase change seismic observations of scd display 1 rapid changes in strength and timing relative to s and scs and 2 early arrivals beneath fast lower mantle regions while the latter feature can be explained by a clapeyron slope of 6 mpa k and a velocity jump of 1 5 when corrected by tomographic predictions it does not explain the first feature here we expand on this mapping approach by attempting a new parameterization that requires a sample of d near the scs bounce point vs where the phase height hph and velocity jump are functions of vs these parameters are determined by modeling dense record sections collected from usarray and passcal data where grand s tomographic model is the most detailed in d structure beneath central america we also address the range of to generate new global models of the phase boundary and associated temperature variation we conclude that a near 9 mpa k is most satisfactory but requires to be nonuniform with a range from about 1 0 to 4 0 with some slow region samples requiring the largest values moreover the edges of the supposed buckled slabs delimitated by both p and s waves display very rapid changes in phase boundary heights producing scd multipathing these features can explain the unstable nature of the scd phase with easy detection to no detection commonly observed the fine structure at the base of the mantle beneath these edges contains particularly strong reflections indicative of local ultralow velocity zones which are predicted in some dynamic models

structure constraints and instability leading to the post perovskite phase transition of mgsio3 abstract recent experience with rietveld refinement of structural analogues and literature surveys suggests anion anion repulsion limits the stability of the perovskite phase including in the mgsio3 perovskite to post perovskite transition assuming rigid octahedral coordination still to be tested experimentally the critical point where intra and inter octahedral anion anion distances are equal provides a useful metric for predicting the pressure of the perovskite post perovskite transition and the clapeyron slope of the phase boundary once pressure and temperature derivatives of relevant structure parameters are known the inter octahedral anion anion distances and the polyhedral volume ratio are rigorously formulated as a function of octahedral rotation in this work assuming the orthorhombic pbnm perovskite structure where regular octahedra share each corner and conform to the in and anti phase rotation schemes designated by space group symmetry these mathematical expressions are consistent with structure data from 70 perovskite structured materials surveyed in the literature at ambient as well as extreme conditions and define structure constraints such as the minimum polyhedral volume ratio which must be reached before the phase transition to the post perovskite structure type can proceed the formalism we present is general for perovskite pbnm and dependent on the accuracy with which structures can be determined from sometimes compromised high pressure diffraction data

stability evaluation of the underground gas storage in rock salts based on new partitions of the surrounding rock based on uniaxial and triaxial compression experiments the yield dilatancy and failure behaviors of the jianghan rock salts were investigated accurate description of the yield and failure behaviors is helpful to reduce the space between storage caverns and offer more storage in a salt mine of limited extent the experimental results showed that the yield function is a straight line and thus the tresca yield criterion can be used to describe the yield behavior of the tested rock salt the second invariant of the plastic strain was used as the hardening parameter to analyze the hardening behavior of the rock salt the result shows that the rock salt is an isotropic hardening material from the perspective of yielding the rock salt acts like metals while from the perspective of failure it acts like rocks the dilatancy boundary was estimated in each experiment by determining the volume turnover point from compression to dilatation it is found that the dilatancy boundary for the jianghan rock salt is different from the results in the previous studies especially under high stresses shear and splitting failures were observed in the compression tests splitting failure was analyzed based on the elastic theory for thick cylinders the results indicate that failure depends on confining pressure when the confining pressure is equal or greater than 5 mpa the rock salt never breaks even when the axial strain reaches 20 a no broken condition was imported into the mohr coulomb criterion based on the yield dilatancy failure model the rock surrounding an underground gas storage ugs is divided into four zones elastic plastic permeability and failure zone a new stability criterion based on the partitions is proposed the constitutive model was modified and the state parameters were self defined in flac3d a geologic model for the jianghan ugs was constructed to provide an example of the stability evaluation based on the partitions of the surrounding rock the minimum internal pressure in emergency was also discussed for the jianghan ugs

phase transition and thermal equations of state of fe al bridgmanite and post perovskite implication for the chemical heterogeneity at the lowermost mantle abstract in this study we have determined the phase boundary between mg0 735fe0 21al0 07si0 965o3 bm and ppv and the thermal equations of state of both phases up to 202 gpa and 2600 k using synchrotron x ray diffraction in laser heated diamond anvil cells our experimental results have shown that the combined effect of fe and al produces a wide two phase coexistence region with a thickness of 26 gpa 410 km at 2200 k and addition of fe lowers the onset transition pressure to 98 gpa at 2000 k consistent with previous experimental results furthermore addition of fe was noted to reduce the density and bulk sound velocity v contrasts across the bm ppv phase transition which is in contrast to the effect of al using the obtained phase diagram and thermal equations of state of bm and ppv we have also examined the effect of composition variations on the and v profiles of the lowermost mantle our modeling results have shown that the pyrolitic lowermost mantle should be highly heterogeneous in composition and temperature laterally to match the observed variations in the depth and seismic signatures of the d discontinuity normal mantle in a pyrolitic composition with 10 fe and al in bm and ppv will lack clear seismic signature of the d discontinuity because the broad phase boundary could smooth the velocity contrast between bm and ppv on the other hand fe enriched regions close to the cold slabs may show a seismic signature with a change in the velocity slope of the d discontinuity consistent with recent seismic observations beneath the eastern alaska only regions depleted in fe and al near the cold slabs would show a sharp change in velocity fe in such regions could be removed to the outer core by strong core mantle interactions or partitions together with al to the high pressure phases in the subduction mid ocean ridge basalts our results thus have profound implication for the composition of the lowermost mantle

sound velocity measurements of casio 3 perovskite to 133 gpa and implications for lowermost mantle seismic anomalies abstract we report the measurements of aggregate shear velocity v s of casio 3 perovskite capv at high pressure p between 32 and 133 gpa and room temperature t on the basis of brillouin spectroscopy the sample had a tetragonal perovskite structure throughout the experiments the measured p v s data show the shear modulus and its pressure derivative at ambient condition to be g 0 115 8 gpa and g 1 20 respectively the zero pressure shear velocity is determined to be v s0 5 23 km s in good agreement with the previous estimate inferred from the ultrasonic measurements on ca si ti o 3 perovskite at 1 bar our experimental results are broadly consistent with the earlier calculations on tetragonal capv but exhibit lower velocity at equivalent pressure such tetragonal capv is present in cold subducting slabs and possibly in wide areas of the lowermost mantle while primitive mantle includes certain amount of capv a depleted peridotite former harzburgite layer in subducted oceanic lithosphere is deficient in capv and enriched in ferropericlase in the lower mantle such harzburgite exhibits 0 9 faster v s and 0 7 slower bulk sound velocity v at the lowermost mantle p t conditions if capv is present in the tetragonal form in the surrounding mantle the observed fast v s and slow v anomalies in the d layer underneath the circum pacific region might be attributed in large part in the presence of subducted harzburgitic materials

pressure generation and investigation of the post perovskite transformation in mggeo3 by squeezing the kawai cell equipped with sintered diamond anvils article i nfo high pressure generation has been tried by using the kawai cell equipped with sintered diamond cubes and the synchrotron radiation at spring 8 the maximum attainable pressure reached 90 4 gpa at 300 k based on the anderson et al 1989 au scale simultaneously we investigated the perovskite pv postperovskite ppv transformation in mggeo3 up to ca 74 gpa and 2200 k by means of in situ x ray diffraction method transformation from pv to ppv was observed at pressures and temperatures higher than 63 gpa and 1300 k both the forward and the reverse reactions were found to be fairly sluggish over the examined temperature range we determined the phase boundary by passing through the conditions at which either pv or ppv phase grew and that of coexistence of both the phases which is expressed by the equation t k 177 p gpa 9677 our dp dt slope of 5 6 mpa k for mggeo3 is close to the minimum estimate for mgsio3 and accordingly suggests relatively deeper d discontinuity and a high heat flux from the core we emphasize that the phase boundary completely relies on the pressure scale adopted

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

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

sharpness of the d discontinuity beneath the cocos plate implications for the perovskite to post perovskite phase transition 1 the depth extent or sharpness of the d seismic velocity discontinuity is determined by modeling distance dependence of reflected s wave signals sampling the lowermost mantle beneath the cocos plate the data spanning distances from 64 to 83 and grouped in two small turning point bins from 5 to 10 n and 10 to 15 n are compatible with a sharp 1 to 2 shear velocity increase near 300 km above the core mantle boundary but not with reflection from a transition zone extending more than 30 km in depth interpretation of the velocity structure as the result of magnesium silicate perovskite undergoing a phase transition to post perovskite requires limited presence of al and fe which will broaden the phase transition current experiments indicate that the phase transition may occur over 5 gpa 90 km in pyrolitic material requiring either distinct chemistry or dynamical mechanisms to sharpen the phase transition for this high velocity sub circum pacific region

seismic imaging the d region beneath the central atlantic abstract the lowermost mantle beneath the central atlantic is bounded by the western edge of african large low shear wave province llsvp and a high velocity region beneath the eastern americas which is attributed to the accumulated subducted slab material at the core mantle boundary cmb data recorded at broadband seismic arrays in western europe and morocco allow us to investigate the detailed structure beneath the central atlantic which provides an important constraint on how remnant slab material and llsvp interact and reshape the d layer here we exploit lower mantle triplicated s waveform data from deep earthquakes beneath south america our modelling results show that the d discontinuity is constantly observed from north to south beneath the central atlantic but at varied depths and with varied shear velocities in the lowermost mantle beneath east of caribbean our results indicate a sharp 2 1 shear velocity increase at 340 km above the cmb representing a possible bridgmanite dominant normal mantle d layer whereas the models of northern and southern portions of central atlantic indicate a gradual velocity increase of 4 2 across 200 km starting from 360 km above the cmb downwards we also find a distinct low velocity zone on top of the velocity jump which can be interpreted as an upwelling produced by the dynamic response of ancient slab material reaching the cmb

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

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

the interaction between the post perovskite phase change and a thermo chemical boundary layer near the core mantle boundary numerical simulations of thermo chemical mantle convection with the newly discovered post perovskite ppv phase change are used to characterize its dynamical consequences for the dq region which has frequently been interpreted as being thermo chemical in origin a strong lateral variation in the appearance of the ppv region is observed with high cmb temperatures leading to bdouble crossingq of the phase boundary in average or cold regions or no crossing in hot regions lower cmb temperatures result in a single crossing everywhere but with highly variable depth the strongly exothermic nature of the post perovskite phase change induces an anti correlation between regions containing a thick ppv layer and piles of chemically dense material formed by the segregation of the crustal component from subducted slabs the ppv phase change destabilizes chemically dense material allowing subducted slabs to easily penetrate into a dense layer forming isolated patches of the post perovskite phase whereas the lateral spectrum of thermal anomalies in the deep mantle is dominated by long wavelengths the lateral spectrum of composition is relatively flat and is the dominant contributor to seismic velocity variations at all wavelengths except the very longest ones d 2005 elsevier b v all rights reserved

horizontal natural gas caverns in thin bedded rock salt formations natural gas storage caverns are usually built either in a rock salt dome or in a bedded rock salt formation in china the rock salt stratum has the following characteristics thin inter layered bedded and highly impure the height of a cavern in bedded rock salt deposit in china depends largely on the thickness of the salt formation 80 300 m and is much smaller than in thick domes and thick layers of rock salt deposits in europe and the usa where a storage cavern is typically cylindrically shaped this renders the diameter of a bedded salt cavern in china to be greater than its height to obtain sufficient storage volume the stability of horizontal salt caverns with different diameters and varied minimal internal pressures during its long term operation was numerically analyzed in this paper regarding convergence damage stress to peak or dilatancy strength ratio and effective strain the hou lux constitutive model including some relevant parameters from previous laboratory investigations were used for the numerical simulations the simulation results show that a horizontal cavern height length for underground gas storage is more efficient profitable and suitable because of its few times larger storage capacity than the most used vertical cavern height diameter or a prolate cavern height or diameter under the chinese special geological condition of thin bedded rock salt deposits provided with appropriate construction and operation parameters

thermodynamic properties and phase relations in mantle minerals investigated by first principles quasiharmonic theory this research has been motivated by geophysics and materials physics the objective of this research has been to advance materials theory and computations for high pressure and high temperature applications to the point that it can make a difference in our understanding of the earth understanding of the mineralogy composition and thermal structure of the earth evolves by close interaction of three fields seismology geodynamics and mineral physics earth s structure is imaged by seismology which obtains body wave velocities and density throughout the earth s interior fig 1 interpretation of this data relies on knowledge of aggregate properties of earth forming materials either measured in laboratory or calculated in many cases by both however the conditions of the earth s interior especially at the core may be challenging for important experiments and materials computations have emerged to contribute decisively to this field earth s evolution is simulated by geodynamics but these simulations need as input information about rheological and thermodynamic properties of minerals including phase transformation properties such as clapeyron slopes our research has concentrated on the phases of the earth s mantle particularly the deep mantle whose conditions are more challenging for experiments the mantle accounts for 83 of the earth s volume in this article we will review the essential first principles approach used to investigate solids at high temperatures and pressures summarize their performance for mantle minerals fig 2 and point to critical results that have stirred us in the current research path the success is remarkable but some limitations point the way to future developments in this field figure 1 a velocities and density profiles kennett et al 1995 b earth s cross section and c composition and mineralogy of earth s layers figure 2 phases proportions versus depth and or pressure ol mg fe 2sio4 olivine also known as phase mg fe

seismic velocity structures and detailed features of the d discontinuity near the core mantle boundary beneath eastern eurasia abstract shear and compressional velocity structures and features of the d discontinuity near the core mantle boundary cmb beneath eastern eurasia are studied based on forward waveform modeling and differential travel time analysis of scsh sh sscs ss pcp p and ppcp pp phases high quality differential travel time analysis reveals two high velocity patches spanning a width of 3000 km and separated by a 300 km wide normal velocity gap the maximum shear and compressional velocity perturbations reach 3 8 and 2 7 respectively seismic data indicate that the d discontinuity emerges in the high velocity patches and disappears in the normal velocity gap furthermore the features of the d discontinuity although constrained by rather sparse seismic data vary from diffusive discontinuities in the eastern patch to sharp discontinuities in the western patch the d discontinuities occur at about 270 km above the cmb in the eastern patch with a shear velocity jump of 3 0 5 0 and a transitional depth of at least 100 km and at 250 km above the cmb in the western patch with an abrupt shear velocity jump of 5 0 a diffusive p wave discontinuity is also observed in the eastern patch with the similar features of the s wave discontinuity the inferred features of the d discontinuity can be explained by the post perovskite transformation in the lower mantle the observations that the d discontinuities occur only in the high velocity patches may be due to the effect of the positive clapeyron slope of the post perovskite transition and the varying transitional depths of the d discontinuity in the high velocity regions may be caused by the compositional effects on the post perovskite transition in the presence of strong variations of composition within the high velocity anomalies the high velocity patches geographically correlate with the subduction of the pacific and indian plates in the past 30 60 ma and the normal velocity gap falls into the subduction gap between the pacific and indian plates these geographical correlations raise the possibility that the existence of the d discontinuity is intimately related to the presence of the past subduction material at the cmb and varying features of the discontinuity further suggest existence of strong variations of composition within the subduction materials at the cmb