distribution and chronological framework for iberian variscite mining and consumption at pico centeno encinasola spain abstract ams radiocarbon and osl dating and profiling were used to directly delimit periods of variscite production at pico centeno mine 2 these results were integrated with analysis of other well dated periods of variscite production to establish an iberian wide chronological framework variscite production at pico centeno mine 2 began at 5200 bc coincident with alpine jade production or casa montero iberian flint production variscite was only used occasionally together with other greenstones during the 5th and 6th millennia bc during the 4th millennium bc variscite use began to increase to its apogee in the first half of 3rd millennium bc when it appeared in nearly every iberian burial site this increase in variscite production and use coincided with decline in the popularity of alpine jade by the end of the 3rd millennium bc new resources began to be valued such as asian and african ivory baltic and sicilian amber and copper based metal products the variscite cycle thus started with the decline of jade in the 5th 4th millennium bc and ended with the appearance of copper ivory and extra peninsular amber by the end of the 3rd millennium bc

core mantle boundary shape constraints inferred from the pressure torque acting between the core and the mantle summary in the last few years models of the flow at the top of the earth s core and of the related pressure field have been calculated from the secular variation of the geomagnetic field and core mantle topographies have been computed by seismologists a pressure torque results from the action of the pressure field on the core topography which can theoretically be computed from models of both the pressure field and the core mantle interface small scale features of the flow and of the topography are shown to be capable of contributing strongly to the pressure torque it is thus impossible to calculate the exact value of the torque from the knowledge of only the long wavelength components of the models but the interaction between the large scale components generates by itself torques two orders of magnitude larger than the torques inferred from the irregularities of the length of the day it is nevertheless possible to reconcile the topographic coupling mechanism with the length of the day observations keeping the amplitude of the core topography proposed by seismologists if an orthogonality relation between the geometry of the fluid upwellings and downwellings at the top of the core and the topography is satisfied it is shown how to compute such a topography for a given flow and close to an original topography provided by seismic tomography some consequences of the so inferred link between the fluid flow at the top of the core and the core mantle boundary topography are discussed

travel times of s and sks implications for three dimensional lower mantle structure beneath the central pacific the travel times of s and sks phases from deep focus fiji tonga events recorded in north america by canadian station network and world wide seismographic station network stations exhibit a strong azimuthal dependence the differential times of s sks exhibit relatively little scatter and are used to investigate three dimensional mantle models for the central pacific region s sks times are corrected for earth s ellipticity and residuals are computed with respect to the iasp91 reference model anomalously large s sks times ranging up to 9 s larger than iasp91 predictions for 100 suggest a slow lower mantle beneath the central pacific these results are compared to the predictions of three tomographic models mdlsh of tanimoto 1990 model sh12 wm13 of su et al 1992 and model sh 10c 17 of masters et al 1992 the three dimensional whole mantle models have been parameterized into 11 spherical shells qualitative agreement between the tomographic model predictions and observations is encouraging varying from fair to good however inconsistencies are present and suggest anomalies in the lower mantle of scale length smaller than the present 2000 km scale resolution of tomographic models laterally varying outer core structure is not necessary to explain the anomalies in this data set although such a scenario cannot be resolved with this data

waveform inversions and the significance of surface wave mode coupling summary if body wave phases in laterally heterogeneous media are modelled by surface wave mode summation mode coupling is required to bring out the ray character of the body wave phases however it is frequently assumed that in laterally heterogeneous media surface wave modes propagate without interacting with other modes the effects of neglecting surface wave mode coupling on the results from waveform inversions including body wave arrivals have been studied by performing inversions with and without taking surface wave mode coupling into account the two inversion schemes are similar to the partitioned waveform inversion nolet 1990 but differ in the approximations used to compute the synthetics wkbj which neglects mode coupling or sea marquering snieder 1995 which does take mode coupling into account synthetic inversion experiments show that neglecting mode coupling can lead to biases in the deeper part of the model their most striking feature is that for real shallow lateral heterogeneities artificial anomalies with an opposite sign may show up in the deeper part of the model when mode coupling is taken into account as in the sea inversion scheme these biases do not occur we have also studied possible bias effects as the result of using wkbj in the eur s91 model of zielhuis nolet 1994 which is characterized by strong velocity anomalies extending as deep as the transition zone one of the most striking features in this model is the region of low velocities at larger depths beneath the fast russian platform on the eastern side of the tornquist teisseyre zone ttz nolet zielhuis 1994 suggested that these low velocities are an indication for injection of water in the mantle by an earlier subduction our results show that the neglect of mode coupling indeed does bias the model towards a larger reversal of velocities with depth and heterogeneities show up even where the s ray does not sample the mantle however low velocities deep below the eastern part of the ttz persist even when mode coupling is taken into account

anomalous difference traveltimes and amplitude ratios of sks and skks from tonga fiji events difference traveltimes skks sks for 12 tonga fiji events observed from 96 117 at north and south american wwssn and csn stations exceed the difference times of standard earth model prem by 2 3 s also the amplitude ratios sks skks at american stations from 96 107 are lower than the prem ratios no such anomalies occur in directions from tonga fiji towards eurasia and africa and for a sea of japan event and paths to north america and africa the regional variations in the data point to pronounced lateral variations in earth structure the anomalous difference times imply either an advance of sks or a delay of skks relative to prem the interpretation of the anomalies is not unique our preferred explanation involves s velocity anomalies in the lower mantle on the source side east of tonga fiji

coupling of the core dynamo and mantle thermal or topographic static features in the earth s magnetic field and fixed sources of secular variation suggest the dynamo is anchored to the lowermost mantle via either thermal or topographic coupling here we show a correspondence with dynamic core topography which is related to mantle temperature and suggest further effects due to topography associated with subducting slabs the two coupling mechanisms may occur on different time scales providing a potential means for discriminating between them

a study of the outermost liquid core using differential travel times of the sks skks and s3ks phases abstract differential travel times of sks skks and s3ks seismic phases are analysed to specify the structure of the outermost liquid core which is poorly sampled by the pkp waves currently used for core tomography the data are mainly broadband records at epicentral distances of 83 140 they have been selected to obtain a good global earth coverage skks sks and s3ks skks travel time residuals have been computed with respect to the mean earth model preliminary reference earth model prem and corrected for ellipticity the skks sks residuals plotted as a function of epicentral distance exhibit a general positive slope for distances greater than 105 with mean positive values of approximately 2 s at 120 130 c these features may be accounted for by slight perturbations in prem involving a 2 5 s velocity increase in the d layer at the base of the mantle and a small decrease in the p velocity in the upper 800 km of the liquid core the structure in the uppermost 100 km of the core is mainly constrained by the s3ks data a high velocity gradient followed by a low gradient is obtained immediately beneath the core mantle boundary this may suggest the existence of a thin low velocity layer at the top of the liquid core as a result of a possible accumulation of light elements beneath the core mantle boundary the skks sks residuals exhibit strong coherent regional variations whereas the s3ks skks residual variations remain small this indicates that the lateral heterogeneitics at the core side of the core mantle boundary if any are very small the simultaneous analysis of s3ks sks and skks sks residuals suggests a prevailing contribution of long wavelength heterogeneities in d

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

the stably stratified outermost core revisited the p wave velocity structure of the outermost 200 km of the outer core the e region is analyzed using a suite of differential travel times for sks skks and s waves bottoming below within and above this depth range core penetrating phases with paths beneath alaska exhibit similar sks skks differential travel time patterns to phases sampling the core beneath the central pacific but very different sks s differential travel times these patterns can be explained by a core velocity model in which the outermost 50 to 100 km has 1 2 slower p wave velocities than standard earth models perhaps due to a stably stratified chemical boundary layer combined with 3 lateral variations in s wave velocity in the lowermost mantle

new perspectives on the li isotopic composition of the upper continental crust and its weathering signature abstract lithium isotopes are increasingly used to trace both present day and past weathering processes at the surface of the earth and could potentially be used to evaluate the average degree of past weathering recorded by the upper continental crust ucc yet the previous estimate of average 7li of the ucc has a rather large uncertainty hindering the use of li isotopes for this purpose new 7li for desert and periglacial loess deposits windblown dust from several parts of the world europe argentina china and tajikistan demonstrate that the former are more homogeneous than the latter and may therefore serve as excellent proxies of the average composition of large tracts of the ucc the li isotopic compositions and concentrations of desert loess samples are controlled by eolian sorting that can be quantified by a binary mixing between a weathered fine grained end member dominated by phyllosilicates and having low 7li and an unweathered coarse grained end member that is a mixture of quartz and plagioclase having higher 7li we use correlations between insoluble elements ree nd hf and fe2o3 sio2 li concentrations henceforth referred as li and 7li to estimate a new more precise average li isotopic composition and concentration for the ucc li 30 5 3 6 2 ppm and li 7 0 6 0 6 2 the 7li for desert loess deposits is anti correlated with the chemical index of alteration cia using this relationship along with our average 7li we infer that 1 the present day cia of the average ucc is 61 2 4 2 higher than the common reference value of 53 and 2 the average proportion of chemically weathered components is as high as 37 10 17 2 at the surface of the earth

on the scale of mantle heterogeneity abstract a data set comprising 3313 residuals measured from digital records of 429 earthquakes is analyzed for the heterogeneity of the earth s mantle the smoothed ss residuals reveal a large pattern of heterogeneity and agree well with the major tectonic features on the earth s surface and the residual patterns predicted by upper mantle and whole mantle models the spectrum of ss residuals indicates that the heterogeneity in the earth s mantle which probably reflects the patterns of mantle convection is dominated by long wavelength features our analysis of the power of ss residuals as a function of harmonic degree shows a distinct difference in the rate of decrease of the power below and above degree 8 the rate is first slower than l 1 and then it exceeds l 2 this is also true for ss residuals predicted for model sh 425 2 and love wave phase velocities at 100 s measured by other researchers this indicates that there is a preference for features with dimensions larger than 2500 3500 km we find that the power spectrum of the velocity anomalies associated with the subducted slabs is two orders of magnitude lower for 1 l 8 than that of velocity anomalies obtained by inversion of waveform data for the ocean basins correlation of the ss residuals with the square root of age of the oceanic lithosphere is highly significant however the age correlation predicts only 10 of the variance this means that the thermal signature of the spreading center represents only a small fraction of the thermal anomalies introduced into the upper mantle by convection

upper mantle structure from long period differential traveltimes and free oscillation data summary we have performed an inversion to model upper mantle structure using ss s differential traveltime residuals in conjunction with previously reported structure coefficient estimates obtained from free oscillation frequency and attenuation measurements the model we obtain is consistent with both the differential traveltime and structure coefficient data sets and provides nearly the same level of fit as independent inversions of these data sets we find that a relatively simple model parametrization appears to be adequate for the data used upper mantle velocity perturbations and lateral variations in the radii of boundaries at 400 and 670 km depth are parametrized with spherical harmonic expansions up to degree and order 8 the expansions are fixed at specific depth knots separated by roughly 200 km spanning the range 20 670 km radial variations in velocity are obtained by linear interpolation between these depth knots smoothness constraints were applied as part of the inversion procedure as well as corrections for the thickness and velocity variations of the crust the smoothness constraints were adjusted to require a smoother structure in the bottom portion 400 to 670 km depth of the model where the structure coefficients have the greatest sensitivity the upper part of the model is primarily constrained by the differential traveltime data the resulting misfit of the final model shows that on average the individual structure coefficients and ss s measurements are fit to within approximately 1 5 standard deviations we suggest that some of the misfit is due to lower mantle structure which is not included in the modelling the power as a function of harmonic degree for the top portion of the model 20 to 220 km depth does not fall off significantly at the higher harmonic degrees suggesting that the differential traveltime data may require models which include structure for degrees greater than 8 boundary perturbations at depths of 400 and 670 km trade off strongly with the velocity variations allowing variations of the order of f10 km in the radii of the discontinuities at 400 and 670 km provides a slight improvement to the data fit comparisons of several depths of our upper mantle velocity model to the geoid show the strongest correlation at degree 2 for structure near 670 km depth the distribution of slab structures is highly correlated to the degree 2 components of the model for depths of 200 to 670 km examination of the model in the vicinity of hotspots shows no consistent hotspot related signal

lateral variations near the core mantle boundary differential travel times between s and sks ts sks and skks and sks tskks sks along with amplitude behavior have been used to study lateral variations at the core mantle boundary the data were recorded by the world wide seismographic station network wwssn and the canadian seismograph network csn from source regions in south america and the fiji tonga area a core mantle boundary region traversed by sks and s beneath the mid pacific from the fiji tonga area to north american stations shows the most anomalous behavior in ts sks sks and s are anomalously separated by up to 8 seconds in addition to ts sks anomalies sks and skks are anomalously separated by 2 to 3 seconds a model fitting ts sks for this anomalous region requires one or more of the following 1 up to 5 increase in the top 300 km of outer core velocity 2 a large scale high vs region 2 increase in the lower mantle ne of tonga 3 lateral variations in d shear wave velocities of up to 3 however 1 above predicts a decrease in tskks sks contradicting the observations this suggests that 2 and 3 are more likely explanations in modeling this data set

whole mantle p wave travel time tomography abstract a method of tomographic inversion to obtain three dimensional velocity perturbations in the earth s whole mantle has been developed and applied to more than two million p wave arrival time data reported by international seismology center isc the model is parameterized with 32 768 blocks the divisions in latitude longitude and radius are 32 64 and 16 respectively horizontal cell size is 5 6 5 6 the layer thicknesses vary with depth 29 km just below the surface and 334 km just above the core mantle boundary starting from a spherically symmetric earth model we obtained a three dimensional model using the following iterative procedures first we relocated all the events second we backprojected the residual into the whole mantle third we refined the spherically symmetric earth model the solutions have been converged in five iterations we adopted the following techniques in the backprojection procedure the first order smoothness was introduced as a damping which makes the solution independent of the starting model and its apparent fluctuation minimal the basic equations for delay times and smoothness are solved using the conjugate gradient method an iterative method which guarantees the convergence of solution into the exact least squares solution the weight on the smoothness i e the damping factor was objectively determined by a simplified cross validation technique the final solution was obtained as an average of the ten solutions each of which was derived from one tenth of the total data set the reliability of the solution is examined in two ways 1 mapping the resolution given by the reconstruction of checkerboard patterns and 2 mapping the variance given from the gaussian noise input this is the first result which delineates the whole mantle structure with its reliability mapping the longest wavelength anomalies of the lower mantle are similar to those of previous studies by dziewonski 1984 and hager and clayton 1989 however the shorter wavelength patterns have many discrepancies the fast anomalies of the uppermost mantle beneath the shield and the slow anomalies beneath the active tectonic regions are clearly seen we also revealed the l 2 pattern at the transition zone reported by the previous surface wave and free oscillation studies the most striking feature is that of the fast anomalies lying along the extension of the large subducting plate up to depths of about 1000 km or more the resolving powers in these regions are generally good

tomographic inversions for mantle p wave velocity structure based on the minimization of l 2 and l 1 norms of international seismological centre travel time residuals we use international seismological centre isc p arrival data 1964 1987 and iterative algorithms which minimize the l1 and l2 residual norms to solve simultaneously for three dimensional p velocity variations in earth s mantle source mislocations and station corrections we find that the maximum velocity perturbations produced by the l1 minimization approximately 4 in our final model are relatively insensitive to smoothing and damping constraints therefore using an l1 norm criterion allows us to keep the bias introduced to the inversion to a minimum among the well resolved features contained in both the l1 and the l2 velocity models are a fast anomaly in the lower mantle beneath the tonga new hebrides subduction zone to a depth of 1670 km and another fast anomaly beneath the japanese island arc and eastern asia continuity between these anomalies and shallower fast anomalies is not clear a fast anomaly extending from 670 km to 2070 km depth appears beneath eastern north america the caribbean and north central south america a broad fast anomaly appears beneath eastern asia just above the core mantle boundary as well as several slow anomalies under the pacific basin of comparable size both models contain a circum pacific ring of 2 lower velocities in the depth range 0 200 km associated with back arc basins high velocities over 2 associated with the continental shields tend to disappear below 400 km though a significant region of high velocity remains beneath the siberian platform in the 400 to 670 km depth interval

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

the 3 d shear wave structure in the mantle by overtone waveform inversion ii inversion of x waves r waves and g waves summary the 3 d upper mantle structure from the surface of the earth to a depth of about 1000 km is obtained by inverting waveforms of fundamental and higher mode surface waves minor and major arc waves of r waves g waves and x waves higher mode wave packets are used as basic data two features of the solution seem fairly robust one is the shallow structure in the upper few hundred kilometres which is strongly correlated with the age of the crust the second feature is the deep fast velocity anomaly near the western pacific indonesia philippines and mariana region and its antipodal region of south america both of which are subduction zones which forms a strong l 2 pattern simple slab models with 100 km thicknesses of 10 per cent faster velocity material do not explain such large scale fast velocity anomalies this may indicate large scale deformation of the 670 km discontinuity piling up of slabs in the upper mantle or thickening lithosphere in the lower mantle or large horizontal motions of subducted material these results are stable whether an earth model 1066a or prem is used as a starting model

predominance of long wavelength heterogeneity in the mantle analysis of travel time anomalies of long period shear waves recorded by the global digital seismographic network indicates that mantle heterogeneities which probably reflect patterns of mantle convection occur most prominently on length scales greater than about 6 000 km when projected onto a two dimensional map at the earth s surface models of mantle convection will need to be able to produce a similar power spectrum

high pressure metallization of feo and implications for the earth s core the phase diagram of feo has been experimentally determined to pressures of 155 gpa and temperatures of 4000 k using shock wave and diamond cell techniques we have discovered a metallic phase of feo at pressures greater than 70 gpa and temperatures exceeding 1000 k the metallization of feo at high pressures implies that oxygen can be present as the light alloying element of the earth s outer core in accord with the geochemical predictions of ringwood the high pressures necessary for this metallization suggest that the core has acquired its composition well after the initial stages of the earth s accretion direct experimental observations at elevated pressures and temperatures indicate that core forming alloy can react chemically with oxides such as those forming the mantle the core and mantle may never have reached complete chemical equilibrium however if this is the case the core mantle boundary is likely to be a zone of active chemical reactions

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

one layer global inversion for outermost core velocity the most direct method for constraining physical properties of the outermost core involves analysis of snks waveforms where n is an integer however the physical nature of this region remains ambiguous in spite of its significance in geodynamic geomagnetic and seismic models of the earth s deep interior global inversion for p wave velocity in the outermost 200 km of the core from sks and skks waveforms is examined here the inversion process consists of constructing synthetic seismograms using normal mode theory and solving for first order perturbations to p wave velocity spheroidal modes with periods between 33 and 100 s are chosen to model the waveforms and p wave velocity perturbation is solved along individual raypaths assuming a laterally homogeneous initial model the dataset includes about 800 digital long period radial seismograms from earthquakes which have occurred globally seismograms were chosen for source receiver distances of 110 130 in which sks and skks are best isolated in time from nearby phases we have attempted to remove the effects of mantle heterogeneity by incorporating the mantle velocity model mdlsh figures of p wave velocity results plotted at the midpoint between source and receiver show large scale patterns of positive and negative lateral velocity variation there are also regions of inconsistencies not simply explained by core mantle boundary cmb topography or crisscrossing raypaths there is no clear dependence of residuals on latitude incorporation of a modified version of mdlsh does not significantly change our solutions suggesting that the resolution length scales of global mantle models are too large to remove important smaller wavelength less than 1000 km mantle heterogeneity effects furthermore raypaths of sks and skks independently go through laterally different structure relative to normal mode wavelengths starting well above the cmb these results suggest that simultaneous waveform inversion for p and s wave velocities is a more reliable way of constructing a model of outermost core structure

a latitudinal pattern in the structure of the outermost liquid core revealed by the travel times of skks sks seismic phases differential travel times of sks and skks seismic phases are analysed in order to specify the properties of the outermost liquid core the data have been selected in order to obtain a good sampling of the earth they are mainly intermediate period gdsn and broadband geoscope and nars records of events at epicentral distances 83 130 the skks sks travel times are referred to the mean earth model prem dziewonski and anderson 1981 and are corrected for ellipticity a general baseline shift and slope with respect to prem is also removed from the data the skks sks residuals indicate a departure from spherically symmetric structure in the liquid core in particular they exhibit a clear latitude dependence with lower values at the poles and higher values at the equator indicating that heterogeneities with cylindrical symmetry are present in the most external liquid core this latitudinal pattern exhibits some similarities with that of the zonal flow in the outermost liquid core deduced from the secular variations of the magnetic field this suggests that the distribution of the seismic velocities in the outermost liquid core may be influenced by the circulation of the fluid beneath the core mantle boundary or that both are similarly influenced by the earth rotation

three dimensional velocity structure and resolution of the core mantle boundary region from whole mantle inversions of body waves the nature of the core mantle boundary cmb has important implications for deep earth processes particularly those which have their origin in the lower mantle or outer core the possibility of the existence of lateral p wave velocity variations in the outermost core is explored here by obtaining models of three dimensional cmb region velocity structure using an inversion of waveform data the numerical inversions involve determination of the three dimensional structure of the earth s outermost core and lower mantle using over 5000 long period seismic waveforms collected from global digital seismic networks spheroidal modes with periods between 33 and 100 s were selected to model the body wave portion of seismograms recorded from global earthquakes first order perturbations in s wave velocities in 11 mantle layers 200 350 km thick and p wave velocities in one outermost core layer comprise the least squares solutions to the inverse problem although the statistical f test supports the additional layer in the inversions this layer is not required by the f ratio to occur in the outermost core pattern retrieval resolution tests in which synthetic data constructed from an initial synthetic earth model are inverted for model parameters are used to compare parameters for one region to those of another in which some coefficient power smearing is suspected depth resolution tests indicate that the best radial resolution at the cmb is 500 km thus this method does not produce the resolution required for outermost core lateral velocity variation analysis an examination of the limitations of this approach demonstrates the need for waveform inversion techniques which more accurately predict raypaths in the deep mantle improvements in radial resolution are needed before whole mantle velocity models can begin to distinguish whether significant heterogeneity related to core mantle interactions occurs in the cmb region

lateral temperature variations at the core mantle boundary deduced from the magnetic field recent studies of the secular variation of the earth s magnetic field over periods of a few centuries have suggested that the pattern of fluid motion near the surface of earth s outer core may be strongly influenced by lateral temperature variations in the lowermost mantle in this paper we introduce a self consistent method for finding the temperature variations near the core surface by assuming that the dynamical balance there is geostrophic and that lateral density variations there are thermal in origin the calculation is accomplished by using the radial and horizontal components of the magnetic field at the core mantle boundary to calculate the fluid flow and its radial derivative near the core surface which are related to the pattern of lateral temperature variations by the thermal wind equation as expected these lateral temperature variations are very small we find some agreement between this pattern and the pattern of topography of the core mantle boundary but are unable to answer conclusively to what extent core surface motions are controlled by the mantle rather than being determined by processes in the core

a 2 d synthetic study of global traveltime tomography a 2 d synthetic test study of global traveltime inversion for deep seated earth structure has been undertaken this was done by generating traveltime residual data using reasonable models for earth structure the data were then inverted by similar methods to those applied in global studies of earth structure our results indicate that models of the aspherical structure in the lower mantle based on traveltime data are only partially successful and only at the largest scales harmonic degree 3 and that maps of the core mantle boundary based on traveltimes are unsuccessful

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

thermal core mantle interactions maps of the magnetic field at the core mantle boundary for 1715 1980 reveal static features in the field and an absence of westward drift from much of the core mantle boundary the static features suggest that flow in the core is coupled to the mantle we examine different coupling mechanisms and predict lateral inhomogeneity at the core mantle boundary comparison with models of the lower mantle and core mantle boundary derived seismically and from the geoid is encouraging though their resolution is currently inadequate for a full comparison to be made with the much better resolved magnetic field