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

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

hydrological changes in shuangchi lake hainan island tropical china during the little ice age abstract hydrological changes in east asia during the last millennium have been addressed by numerous earlier studies but spatial characteristics and dynamics in precipitation variations during the little ice age lia remain unclear perhaps especially due to the sparse coverage of high resolution hydrological records from tropical and sub tropical regions in east asia in this study a sediment core was obtained from shuangchi lake in northern hainan island tropical china of which geochemical proxies including the ratios of rb sr rb k zr rb and si ti were analyzed using an x ray fluorescence xrf core scanner meanwhile the grain size distribution of sediments was also determined the results show that the rb sr and rb k ratios decreased significantly during the lia whilst the zr rb and si ti ratios increased along with higher median grain size the changes of these proxies likely suggest that precipitation was enhanced during the lia in this region and this was consistent with other hydrological records from tropical southern china the synthesis of hydrological records from east asia and the tropical pacific suggest that the co existence of a contracted intertropical convergence zone itcz and strengthened pacific walker circulation pwc could contribute synchronously to the increased precipitation in the tropical region of southern china during the lia

a new catalogue of normal mode splitting function measurements up to 10 mhz the splitting of the earth s free oscillation spectra places important constraints on the wave speed and density structure of the earth s mantle and core we present a new set of 164 self coupled and 32 cross coupled splitting functions they are derived from modal spectra up to 10 mhz for 91 events with mw 7 4 from the last 34 yr 1976 2010 our data include the 2001 june 23 peru event mw 8 4 the sumatra events of 2004 mw 9 0 and 2005 mw 8 6 the 2008 wenchuan china event mw 7 9 and the 2010 chile event mw 8 8 the new events provide significant improvement of data coverage particularly in continental areas almost half of the splitting functions have never been measured before in particular we measured 33 new modes sensitive to mantle compressional wave velocity 10 new inner core sensitive modes and 22 new cross coupled splitting functions these provide new constraints on the large scale compressional structure of the mantle and the odd degree structure of the mantle and inner core and can be used in future inversions of heterogeneous earth structure our new splitting function coefficient data set will be available online

reliable mantle density error bars an application of the neighbourhood algorithm to normal mode and surface wave data summary we demonstrate the feasibility and reliability of a new approach to seismic modelling of long wavelength mantle structure in doing so we present new estimates of mantle model uncertainties that successfully explain apparent discrepancies in earlier 3d seismic density models and justify a new generation of model building the characteristics of good models and of modelling error are described by model space maps that display the data fit of a representative set of potential models the neighbourhood algorithm na recently developed by malcolm sambridge allows efficient production of such maps for the long wavelength model parametrizations used in imaging the mantle density using normal mode data we observe that when na is applied to our global modelling problem the results are not only self consistent and consistent with independent resolution tests but also explain discrepancies in the results of damped inversions synthetic mapping experiments using the sensitivity kernels and measurement errors of several data catalogues allow us to determine the resolution of these data sets such resolution tests let us know which model parametrizations and data sets if any can yield meaningful results in inversions of real data the new resolution tests reveal that recent density models from damped inversions of normal mode data are not robust however we also show that the addition of the most recent long wavelength data will for the first time reduce model covariances enough to achieve robust constraints on the depth and size of long wavelength density heterogeneity throughout the mantle

calculation of normal mode spectra in laterally heterogeneous earth models using an iterative direct solution method summary normal mode observations play an important role in studying broad scale lateral variations in the earth such studies require the calculation of accurate synthetic spectra in realistic earth models and this remains a computationally challenging problem here we describe a new implementation of the direct solution method for calculating normal mode spectra in laterally heterogeneous earth models in this iterative direct solution method the modecoupling equations are solved in the frequency domain using the preconditioned biconjugate gradientalgorithm andthetime domainsolutionisrecoveredusinganumericalinversefourier transform a number of example calculations are presented to demonstrate the accuracy and efficiency of the method for performing large full coupling calculations as compared to methods based on matrix diagonalization and the traditional direct solution method

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

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

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

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

compressible thermochemical convection and application to lower mantle structures a new finite element code for compressible thermochemical convection is developed to study the stability of a chemical layer at the base of the mantle using composition dependent compressibility and a density difference between compositions at a reference pressure a composition dependent density profile is derived together with depth dependent thermal expansion this combination of parameters yields a wide range of dynamic evolutions for the chemical layer the chemical structures are classified into five major categories classical plumes mushroom shaped plume domes ridges and continuous layers and a few abnormal cases such as hourglass shaped plumes and columnar plumes several models have a chemical structure morphologically similar to the african low v s structure in the lower mantle at least at a single time guided by our models several dynamic scenarios are proposed for the dynamic nature of the lower mantle low velocity structures a k a superplumes including plumes at an early stage plume clusters ridges passive piles sluggish domes and high bulk modulus domes we predict seismic velocity anomalies from these dynamic models the thermoelastic parameters used in the conversion are additional constraints we compare the density structure with normal mode inversion the predicted seismic signature observations and the required thermoelastic parameters with mineral physics data among the proposed scenarios only the scenario of high bulk modulus domes satisfies all constraints simultaneously the implication on the geochemistry and mineralogy of lower mantle chemical structures is discussed

short scale heterogeneity in the lowermost mantle insights from pcp p and scs s data we compare lateral variations at the base of the mantle as inferred from a global dataset of pcp p travel time residuals measured on broadband records and existing p and s tomographic velocity models as well as scs s travel time data in some selected regions in many regions the pcp p dataset implies short scale lateral variations that are not resolved by global tomographic models except under eastern eurasia where data and models describe a broad region of fast velocity anomalies across which variations appear to be of thermal origin in other regions such as central america and southeastern africa correlated short scale lateral variations several hundred kilometers are observed in pcp and scs implying large but not excessive values for the ratio r d ln vs d ln vp v2 5 on the other hand in at least two instances in the heart of the african plume and on the edge of the pacific plume variations in p and s velocities appear to be incompatible implying strong lateral gradients across compositionally different domains possibly also involving topography on the core mantle boundary one should be cautious in estimating r at the base of the mantle from global datasets as different smoothing and sampling of p and s datasets may result in strong biases and meaningless results 7 2002 elsevier science b v all rights reserved

prospecting for water in the transition zone d ln vs d ln vp abstract we report the values of r d ln vs d ln vp due to water as a function of pressure for mg 2 sio 4 olivine wadsleyite ringwoodite the results show that ringwoodite has significantly lower r than olivine and wadsleyite due to the reason that bulk modulus of ringwoodite is more sensitive to water than shear modulus r of ringwoodite decreases with pressure while r of olivine and wadsleyite increases with pressure r reported here was calculated using theoretical method derived equation of states r due to temperature is also reported as a comparison of r due to water the local value of r in the upper mantle and transition zone can discriminate between lateral variations of water content and temperature as the origin of lateral seismic variations

on the resolution of density anomalies in the earth s mantle using spectral fitting of normal mode data summary the resolution of the 3 d density structure in the earth s deep interior has long eluded geoscientists high quality data from digital seismic instruments emplaced this decade have renewed interest in the measurement of low frequency earth normal modes with the goal of extracting heterogeneous density structure here we perform a series of synthetic experiments aimed at investigating the resolution of lateral variations in the mantle from normal mode spectral data contamination effects between seismic velocities and density are examined in two ways 1 by using resolution matrices computed from data kernels and 2 by inverting synthetic spectra computed from realistic input earth models the first type of experiment assumes that the non linearity of the inverse problem is weak no such assumptions are necessary in the second type of tests which nevertheless concur in their results with the former these synthetic tests indicate that density structure retrieved from presently available normal mode data is not reliable contamination of seismic velocity structure into the density model space produces patterns that resemble those obtained from inversions of real data the resulting density models appear to be dependent on a combination of the starting velocity models and the model parametrization

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

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

splitting function measurements for earth s longest period normal modes using recent large earthquakes recent megathrust earthquakes such as the 23 june 2001 peru event the sumatra events of 2004 and 2005 and the 27 february 2010 chile event have given us the opportunity to measure splitting of the longest period normal modes we use wave spectra to make robust measurements for modes 0s2 0s3 0s4 2s1 and 1s2 singlet frequencies of these modes have been measured previously using gravimeters but here we use seismic records to observe splitting functions for 0s2 and 2s1 for the first time cross coupling with nearby modes is included to account for ellipticity and rotation of the earth and results in significantly improved splitting function measurements for 0s3 0s4 and 1s2 compared with previous studies the new splitting function measurements can easily be implemented in future tomographic modelling of aspherical velocity and particularly density structure

toroidal splitting observations from the great 1994 bolivia and kuril islands earthquakes the june 9 1994 bolivia earthquake and the october 4 1994 kuril islands earthquake provide a unique opportunity for a splitting analysis of the earth s long period toroidal free oscillations we present toroidal splitting observations for the 6 fundamental modes 0t4 0t5 0t6 0t7 0t8 and 0t9 and for the 5 first overtones 1t1 1t2 1t3 1t4 and 1t6 the first identification of mode 1t1 is made possible by simultaneously fitting the multiplets 1t1 and 0t7 the observed splitting is reasonably well explained by current shear velocity models of the mantle our analysis yields new estimates of the center frequencies and quality factors of these 11 toroidal modes

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept

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