new transfer functions for nutations of a nonrigid earth there are differences between the observed values of nutation and the computed ones based on the international astronomical union iau 1980 adopted nutation series these differences can be expressed in the frequency domain where they may reach several milliarc seconds a level that is too large for practical use this paper aims to resolve part of these differences by computing a new theoretical model accounting for additional geophysical effects a new transfer function is computed based on an earth initially in a nonhydrostatic equilibrium corresponding to the steady state associated with the present mantle convection the mantle mass anomalies are deduced from seismic tomography data and the flow induced boundary deformations are computed from internal loading for an earth made up of a viscous inner core a liquid outer core a viscous mantle and a solid lithosphere in this way a new core mantle boundary cmb flattening is obtained which gives the observed free core nutation fcn period furthermore the global earth dynamical flattening induced by the mass anomalies in the mantle associated with tomography and by the mass anomalies due to the computed boundary deformations is in agreement with the j2 form factor or the observed precession constant in addition to this nonhydrostatic initial state the rheology of the mantle is considered as inelastic the transfer function for nutation is then obtained by numerical integration of motion equations from the earth s center up to the surface to provide a model which is completely self consistent in order to validate our model the transfer function is convolved with new rigid earth nutations ocean corrections are applied and the final results are then compared with the observed nutations or with the international earth rotation service iers nutation series the residuals between our model and the observation are about 3 times smaller than those between the iau 1980 adopted model and the observation however our model still presents residuals above the observational error this is particularly true for the out of phase part of the residuals while the in phase part gives very small residuals improvement of about 1 order of magnitude a further step in this study is a refinement of the modeling of geophysical fluids core ocean and atmosphere

joint inversions of seismic and geodynamic data for models of three dimensional mantle heterogeneity the seismic models of three dimensional 3 d mantle heterogeneity may be interpreted in terms of the density perturbations which drive mantle flow and thus provide important predictions of flow related observables such as the nonhydrostatic geoid the current models of global scale shear velocity heterogeneity provide reasonably good fits to the long wavelength nonhydrostatic geoid data 60 70 variance reductions but rather poor fits to the corresponding free air gravity anomalies 30 40 variance reductions this major difference is due to two factors 1 the very different amplitude spectrum of the gravity anomalies which is nearly flat for degrees l 3 the largest mismatch between the pattern of predicted and observed gravity anomalies is in the southern hemisphere this observation suggests that one reason for the poor overall match between the two fields may be that the global seismic data are not resolving sufficiently well the heterogeneity in the southern hemisphere portion of the deep mantle in contrast the gravity data provide accurate and geographically uniform constraints on the vertically integrated heterogeneity in the mantle we therefore perform a series of experiments in which we simultaneously invert a large set of seismic data which includes long period waveforms ss s and scs s differential travel times and normal mode structure coefficients and the long wavelength gravity anomaly data we thus determine whether it is possible to derive new 3 d heterogeneity models which satisfy both data sets the gravity anomaly data are interpreted in the context of spherically symmetric viscous flow models of the mantle in these inversion experiments we test several radial viscosity and ln ln profiles and thereby assess their plausibility the joint seismic geodynamic inversions reveal that it is indeed possible to greatly improve the fit to the free air gravity anomalies with variance reductions of 80 90 readily accessible while preserving the fit to the seismic data this improvement is achieved with some adjustment to the heterogeneity in the depth range 1500 2500 km where the seismic data constraints appear to be weakest the joint inversions also reveal new structures in the southern hemisphere portion of the lower mantle which apparently are not resolved by the seismic data alone

long period variations in gravity field caused by mantle anelasticity a numerical perturbation approach is used to assess the effect of mantle anelasticity on the earth s zonal response coefficient the zonal geopotential coefficient j2 and the orbital node of geodetic satellites the theoretical predictions are used to compare solutions of elastic ocean tide models and tides observed by geodetic satellites for mr m m ssa and s a the discrepancies between the satellite observed tides and the solution from schwiderski and recent altimetric ocean tide models can be partly explained by the predicted effect of mantle anelasti city at mf and m m frequencies approximately 80 of the observed semiannual variation in 2 by geodetic satellites can be attributed to the tidal deformation from anelasticity and from the classical equilibrium ocean the predicted for the 18 6 year tide was computed for an earth with an anelastic mantle and a nonequilibrium ocean the range of the lower and upper bounds of for the 18 6 year tide is from 0 345 to 0 377 in amplitude and from 6 o to 3 o in phase with preferred amplitude of 0 365 and phase of 0 o8

accuracy assessment of recent ocean tide models over 20 global ocean tide models have been developed since 1994 primarily as a consequence of analysis of the precise altimetric measurements from topex poseidon and as a result of parallel developments in numerical tidal modeling and data assimilation this paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy oceanography and geophysics a variety of tests indicate that all these tide models agree within 2 3 cm in the deep ocean and they represent a significant improvement over the classical schwiderski 1980 model by approximately 5 cm rms as a result two tide models were selected for the reprocessing of topex poseidon geophysical data records in late 1995 current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry other significant contributions include theft applications in an improved orbit computation for topex poseidon and other geodetic satellites to yield accurate predictions of earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins the largest differences between these tide models occur in shallow waters indicating that the current models are still problematic in these areas future improvement of global tide models is anticipated with additional high quality altimeter data and with advances in numerical techniques to assimilate data into high resolution hydrodynamic models

on the nutations of a more realistic earth model summary the last adopted nutation series corresponds to an elliptical uniformly rotating earth it is now well known that when comparing the theory with very long baseline interferometry vlbi lunar laser ranging llr or astronomical observations relatively large residuals appear this paper reviews and evaluates different possibilities to explain these differences i new rigid nutations are used in the convolution for computing nutations series the elastic nutation amplitudes are computed at each frequency by multiplying the ratios with rigid earth results ii the mantle inelasticity is introduced in the earth model iii the core flattening and thus the free core nutation fcn is changed among these effects the only very significant one is the effect of a change in the core flattening it explains the discrepancy between recent data and the amplitude adopted by the international astronomical union iau for the annual component these are still some differences to be explained for the semi annual and the fortnightly components

internal loading of an inhomogeneous compressible earth with phase boundaries summary we use an approach described by dehant wahr 1991 to estimate the geoid and boundary topography caused by mass loads inside the earth we show how the estimates are affected by compressibility and a radially varying density distribution and by the presence of phase boundaries with density discontinuities we compare results for earth models that have a chemical boundary at 670 km depth with those that have a phase boundary at that depth we find that the 670 km topographies predicted for models with a chemical boundary are several times larger than for models with a phase boundary depending principally on the value of the clapeyron slope in the phase case the geoid predicted in the chemical boundary case is about 30 40 per cent smaller than that predicted in the phase case the effects of compressibility and radially varying density are likely to be small we estimate the laterally varying structure inside the fluid core by computing the topography on constant potential surfaces within the core we conclude that this structure is not likely to be a complicating factor when using nutation and earth tide observations to estimate the flattening of the core mantle boundary finally we compute the inner core outer core icb topography for loading inside the mantle and for loading inside the inner core we show that in the first case the icb topography is small and dominated by long wavelengths in the second case we conclude that if the density heterogeneities inside the inner core are two orders of magnitude smaller than in the mantle the icb topography can be about 100 m peak to peak

a numerical simulation of the evolution of temperature and co2 stratification in lake nyos since the 1986 disaster a one dimensional numerical model has been applied to simulate the evolution of the temperature and co2 stratification in lake nyos since the 1986 disaster it incorporates a second moment turbulence closure scheme for mixing and heating and cooling in the upper layers of the lake the effects of inflowing stream water and input of the co2 heat and dissolved solids at the bottom of the lake are taken into account the model is initialized by conditions observed immediately after the disastrous outgassing event in 1986 and integrated forward for 10 years forced by seasonally modulated diurnal heating and nocturnal cooling and heavy summer time precipitation at the surface four possible conditions are investigated the first simulation considers the normal seasonal heating cooling cycle and steady input of heat dissolved solids and co2 at the bottom it shows that the upper layers of the lake are quite stable under normal seasonal forcing but the bottom layers reach high co2 concentrations in less than a decade the second simulation considers a brief introduction at the bottom of the lake of cooler waters that contain less co2 and temporarily destabilize the bottom layers the third and fourth simulations consider anomalous surface forcing conditions that can produce anomalous mixed layer deepening during the cooling seasons capable of releasing the co2 stored immediately below the normal mixed layer these results suggest that a destabilization of the bottom layers is more likely to lead to massive and catastrophic degassing the results also demonstrate the utility of a numerical model in investigations of caldera crater lakes such as lake nyos

tides for a convective earth in this paper we give values of the tidal gravimetric factor as well as of the love numbers for the tidal surface displacement and for the tidal mass redistribution potential that are consistent with the presently adopted definitions we present analytical expressions for these quantities and compute numerical values for two rotating nonspherical earth models in the first model the earth is everywhere in hydrostatic equilibrium and the inner core and mantle are both elastic in the second model the earth is ellipsoidal with an inelastic mantle and with a nonhydrostatic initial state for which the effects of mantle convection and its associated boundary deformations are considered this latter model is constrained to reproduce the observed free core nutation period and global earth dynamical flattening

regional seismic observations of the 9 october 2006 underground nuclear explosion in north korea and the influence of crustal structure on regional phases 1 the crustally guided shear wave lg is typically the most prominent phase of a nuclear explosion at regional distance this lg phase is analyzed often to discriminate a nuclear explosion from a natural earthquake in addition the lg phase allows us to determine the size of the detonation a nuclear explosion test in north korea was conducted on 9 october 2006 the epicenter was located close to the eastern shore of the korean peninsula resulting in raypaths that vary significantly according to the azimuths in particular rays radiated in the southern direction experience lateral variation of crustal structures at the continental margin we examine the influence of raypaths on regional seismic phases by comparing the spectra and waveforms from different raypaths three natural earthquakes in north korea are also examined to determine the raypath effect we find that the lg from the nuclear explosion dissipated significantly as result of energy leakage into the mantle resulting from variations in crustal thickness along the portion of the raypath traversing the western tip of the sea of japan east sea some of the leaked energy develops into mantle lid waves sn causing a large energy increase to sn a similar feature is observed in the records of natural earthquakes this feature is confirmed by seismic waveform modeling the raypath effect also causes underestimation of magnitude the lg body wave magnitude mb lg is estimated to be 3 8 4 2 for records from pure continental paths and 2 6 3 4 for records from paths crossing continental margins this result illustrates the need to consider raypath effects for the correct estimation of magnitudes of regional events including a nuclear explosion

magma flow and thermal contraction fabric in tabular intrusions inferred from ams analysis a case study in a late variscan folded sill of the albarracin massif southeastern iberian chain spain abstract the effects of different petrological processes on the rock fabric of a folded sill from the albarracin massif southeastern iberian chain spain were studied by means of the anisotropy of magnetic susceptibility ams technique the most outstanding feature of the sill at outcrop scale is a network of joints linked to thermal contraction which define polygonal columns the analysis of the magnetic fabric taking the orientation of sill walls and column axes as a reference and using the restored directional data corresponding to the whole of k3 susceptibility axes has revealed magnetic fabrics related to two processes a magma flow with a sw trending flow vector characterized by a curved geometry of the magma foliations and b thermal contraction coeval to lava cooling early magnetite crystals grown in a relatively high viscosity calc alkaline magma are the main carriers involved in the ams fabric passive rotation of the early magnetic mineralogy within a medium viscosity magma explains the magnetic fabric linked to both magma flow and near solidus thermal contraction of the magma late variscan folding of the sill produced the rigid body reorientation of the magnetic fabric

stacking gravity tide observations in central europe for the retrieval of the complex eigenfrequency of the nearly diurnal free wobble summary we have used tidal gravity measurements from six stations in central europe to investigate the resonance in the diurnal tidal band caused by inertial coupling between the mantle and outer core of the earth by the use of stacking it was possible to determine the eigenfrequency and quality factor of this eigenmode commonly called the nearly diurnal free wobble we assessed the effect of systematic errors from the ocean correction to the tidal measurements employing a monte carlo method the observed eigenfrequency is 1 1 434 f 7 cycles per sidereal day and is significantly higher than predicted by theories the observed quality factor is 2 8 0 5 x 10

inference of core mantle boundary topography from isc pcp and pkp traveltimes we invert isc pcp and pkp absolute and differential traveltimes in an attempt to infer the long wavelength topography of the core mantle boundary cmb the data selection and processing methods are described and evaluated these travel time data are very noisy and the geographic distribution of the data is highly non uniform inhibiting reliable inference of cmb topography spatial averaging enhances the coherent component of the residual variance related to heterogeneity however the random component of the variance is much larger than the coherent component we show that for pcp data the coherent signal due to mantle heterogeneity overshadows that arising from the cmb and that the effects of mantle heterogeneity are mapped into our inferred cmb solutions the pcp data are not correlated across the spatial averaging bins and seem to have a strong bias due to small scale structure and or noise the non uniform geographic sampling of the data plays a role in the mapping of mantle heterogeneity onto the cmb spatial patterns of cmb models inferred from different phases do not agree amplitudes of seismically inferred cmb undulations vary greatly the sensitivity of inferred cmb models to the processing spatial averaging procedure and inversion techniques are investigated topographic amplitudes increase strongly with increasing input residual variance the power spectrum of inferred topography indicates that there are unmodelled heterogeneities that must be described with spherical harmonics of degree 6 and higher based on this work we conclude that reliable inference of long wavelength cmb topography is not likely with the current isc data set or with a spherical harmonic expansion truncated to degree and order 6

onset of thermal chemical convection with crystallization and its geological implications 1 buoyancy forces derived from either thermal or compositional origins or both are the main driving mechanisms for dynamic instabilities within natural fluid systems crystallization can contribute to the compositional buoyancy due to density differences between the original bulk fluid and the residual fluid of crystallization depending on the density contrast the compositionally induced buoyancy force may enhance or decrease the thermal buoyancy force established by the prevailing temperature gradient of the environment the purpose of this paper is to examine the complex interactions between the compositional and the thermal buoyancy forces within a thermal chemical system incorporating the effects of crystallization like a thermal chemical system without crystallization also known as an ordinary double diffusive system our results identify a dynamic and an oscillatory instability boundary in a traditional stability diagram a dynamic instability boundary separates the stability diagram into two regimes on one side of the boundary fluid dynamic perturbations will grow indefinitely leading to rigorous convection eventually on the other side perturbations decay in time and the system will ultimately return to a static condition in the absence of crystallization the oscillatory instability boundary defines a regime where perturbations lead to oscillatory motions in the presence of crystallization however other investigators have observed the formation of convective layering despite these similarities our results show significant differences in flow characteristic when crystallization is present when crystallization is taken into consideration the slope of a dynamic instability boundary is no longer governed by the diffusion coefficient ratio between heat and composition alone the release of latent heat and the location of crystallization also play some roles in addition convective layering i e the oscillatory instability regime is no longer confined within a domain where fluid composition is stably stratified it can extend into the compositionally unstable domain as well applications of our results to the solidification of magmatic bodies the formation of columnar joints and the cooling of the outer liquid core are examined the existence of oscillatory instability within the compositionally unstable domain is significant because it suggests that the possible existence of convective layering within a cooling tholeiitic magma body cannot be ruled out in contrast to a conclusion derived from double diffusion studies in the absence of crystallization our analysis also suggests a possible criterion to test if columnar jointing has a double diffusive origin if columnar joints were thermal cracks formed along a preexisting double diffusive fingering pattern as speculated they should occur only in calc alkaline basaltic lava and they are not expected to appear in tholeiitic basalts iron nickel precipitation above the inner outer core boundary operates in a compositionally unstable domain because the residual liquid is expected to be less dense since the condition is unstable both thermally and compositionally at this boundary solidification should lead to rigorous convection above the inner core however the existence of convective layering remains a possibility if the latent heat release is sufficient to cause the solidification process to operate within the newly determined oscillatory instability regime although the averaged temperature beneath the core mantle boundary is believed to exceed the melting temperature of iron and nickel local solidification is possible resulting in the production of stabilizing convective layering that can inhibit large scale convection near the top of the liquid outer core

the effect of ocean tides on the earth s rotation as predicted by the results of an ocean tide model the published ocean tidal angular momentum results of seiler 1991 are used to predict the effects of the most important semidiurnal m2 s2 n2 diurnal k1 o1 p1 and long period mf mf mm and ssa ocean tides on the earth s rotation the separate as well as combined effects of ocean tidal currents and sea level height changes on the length of day ut1 and polar motion are computed the predicted polar motion results reported here account for the presence of the free core nutation and are given in terms of the motion within the rotating body fixed terrestrial reference frame of the celestial ephemeris pole so that they can be compared directly to the results of observations outside the retrograde diurnal tidal band the summed effect of the semidiurnal and diurnal ocean tides studied here predict peak to peak polar motion amplitudes as large as 2 mas within the retrograde diurnal tidal band the resonant enhancement caused by the free core nutation leads to predicted polar motion or equivalently nutation amplitudes as large as 9 mas at the unobservable retrograde k1 tidal frequency

constraints on magnetic energy and mantle conductivity from the forced nutations of the earth observations of the earth s nutations are used to explore the possible presence of a conducting layer at the base of the mantle the existence of such a layer is suggested by recent experiments on iron and silicate mixtures at high pressures and temperatures knittle and jeanloz 1986 1989 which indicate that iron may react with silicate minerals to produce metallic compounds nutations provide an ideal tool for investigating the existence of such a layer because they are sensitive to the electrical properties within a thin magnetic boundary layer along the core mantle boundary cmb evidence in favor of a conducting layer is found in the effects of ohmic dissipation which cause the amplitude of the earth s nutation to be out of phase with tidal forcings although out of phase components in the earth s nutations are conventionally attributed to the dissipative influences of ocean tides and mantle anelasticity these effects appear incapable of explaining nutation amplitudes determined from very long baseline interferometry vlbi observations the additional effects of ohmic dissipation enhanced by the presence of a thin conducting layer at the cmb are sufficient to reconcile theory and observation the largest mismatch between observations and theory taking account of ocean tides and mantle anelasticity is a discrepancy of 0 39 0 04 milliarcseconds in the out of phase component of the retrograde annual nutation this discrepancy can be eliminated if the lowermost 200 m of the mantle has a conductivity of 5 105s m 1 and the magnetic energy in the spherical harmonic components of the field at the cmb in degrees l 12 is approximately 4 times greater than the energy inferred in degrees l 12 from surface observations unfortunately the vlbi observations do not uniquely resolve the mantle conductivity and magnetic energy so that trade offs exist between these two parameters nevertheless a high mantle conductivity is favored on the grounds that the alternative involving high levels of magnetic energy yields an excessive amount of ohmic heating other interpretations of the vlbi discrepancy are also discussed one such alternative involves viscous dissipation at the cmb requiring a kinematic viscosity of 0 1m2s 1

influence of mantle compressibility and ocean warping on dynamical models of the geoid summary the influence of mantle compressibility and warping of the ocean surface on dynamical models of the geoid has been investigated topography and geoid kernels show that compressibility modifies the mantle flow pattern and hence the geoid whereas the deflection of the oceanic surface amplifies the geoid signal without affecting the global flow the combined influence of these two effects is significant and depends on the viscosity profile in the mantle comparisons with incompressible dynamical geoids show that including the effects of compressibility and ocean warping improves the fit to the observed geoid thus these effects must not be neglected in dynamical computations of the geoid

analysis of tidal signals in surface displacement measured by a dense continuous gps array abstract we analyze the tidal displacement signals for the eight major diurnal and semidiurnal tides from global positioning system gps measurements made at the western united states over the past 16 years with 1075 independent stations by careful examinations among inland versus coastal gps data we are able to demonstrate that estimated precisions down to the level of 0 1 mm horizontal and 0 3 mm vertical have been reached for the tidal signals and that at such precisions coherent spatial patterns are revealed in the residual tidal amplitudes and phases after the removal of a priori modeled effects of body tides and ocean tidal loading otl we demonstrate the facility of modern precise gps data in not only constraining the ocean tide models but more significantly in providing source data in terms of regional complex love numbers for geophysical inference of the heterogeneities of elastic and inelastic structures in the solid earth s deep interior on tidal timescales

characteristics of lg attenuation in the tibetan plateau 1 lg a regional seismic wave comprised of multiple shear wave reverberations trapped in the crustal waveguide is important for magnitude estimation and source discrimination for monitoring nuclear testing treaties in stable continental regions lg propagates with a group velocity of about 3 5 km s and can often be observed at distances up to 4000 km to better understand the absence of high frequency lg arrivals for paths traversing the northern boundary of the tibetan plateau we investigate spatial variations of broadband 0 15 5 0 hz energy in the lg group velocity window 3 6 3 0 km s using regional waveforms recorded at the chinese digital seismic network station wmq vertical component seismograms are analyzed for 90 events with magnitudes of 4 4 mb 6 4 that occurred between 1987 and 1999 in the tibetan plateau and around its margins the lg amplitude spectra for events located near the northern margin of the plateau have apparent corner frequencies of 1 2 hz nearly identical to those for comparable size events at similar distances outside the plateau high frequency 1 hz lg energy recorded at wmq decreases rapidly as a function of source distance into the plateau a path length of 300 400 km within the northern plateau suffices to eliminate 2 5 hz lg energy for events in southern tibet with paths crossing the central portion of the tibetan plateau almost total lg extinction occurs even for energy in the low frequency band of 0 2 1 hz corresponding apparent corner frequencies of the lg amplitude spectra range between 0 2 and 0 4 hz the corner frequency shift is found to vary systematically with path length across the plateau linear regressions demonstrate that the shift in apparent corner frequency of lg amplitude spectra is negatively correlated with features of the tibetan plateau such as mean elevation along the paths or travel distance within the plateau above specified elevation thresholds the systematic variations in the amplitude and frequency content of energy in the lg window as a function of path length within the plateau indicate that strong crustal attenuation plays an important role in lg extinction for paths traversing central and northern tibet superimposed on any structural blockage effects associated with abrupt thinning of the crust near the northern boundary of the plateau spectral ratios of many event pairs along great circle paths give estimates of frequency dependent lg attenuation for paths crossing western central and eastern sectors of tibet the region of strong sn attenuation in northern central tibet also has strong lg attenuation with qlg for 1 hz on the order of qo 80 90 while in southern central tibet qo increases to about 316 and in eastern and western tibet qo is on the order of 120 200 for paths traversing the entire plateau the strong lg attenuation in northern central tibet is responsible for the so called lg blockage and may be associated with partial melting in the crustal low velocity layer in northern tibet our qlg values for tibet are significantly lower than most earlier estimates primarily as a result of not excluding blocked observations along with allowing for lateral variations within tibet index terms 7203 seismology body wave propagation 7255 seismology surface waves and free oscillations 7205 seismology continental crust 1242 keywords lg tibetan plateau nuclear event discrimination crustal attenuation lg blockage crustal partial melting

starch columns analog model for basalt columns desiccation of starch water mixtures produces tensile crack patterns which appear to be interesting but largely unknown study objects for fracture mechanics structural geology and volcanology this paper concentrates on columnar jointing and on columns in starch starch columns have polygonal cross sections and are very similar to basalt columns they are produced by lamp drying starch specimens with dimensions of several centimeters and have diameters in the millimeter range the columns develop behind a crack front which propagates from the surface into the interior the experiments supported by x ray tomograms show that polygonal regularity of the crack pattern is not present at the surface but develops during penetration this transition is steered by a minimum fracture energy principle the analogy between basalt cooling and starch desiccation is far reaching water concentration in starch is analogous to temperature in basalt both quantities obey diffusion equations water loss is equivalent to heat loss the resulting contraction stresses have similar dependences on depth and time and in both cases the material strength is exceeded the starch experiments show that column diameters are controlled by the depth gradient of water concentration at the crack front high low gradients are connected with thin thick columns by analogy a similar relation with the temperature gradient exists for basalt columns the normalized starch gradients are about 3 orders of magnitude larger than the normalized gradients in basalt this explains why starch columns are much thinner than basalt columns the gradients are so different because the crack front speeds differ by a factor of about 10 after 3 days the speed is about 10 mm d in starch but about 100 mm d in basalt peck 1978 the speed difference in turn results from the difference of the diffusion constants the hydraulic diffusivity of starch is 2 orders of magnitude lower than the thermal diffusivity of basalt

diurnal semidiurnal polar motion excited by oceanic tidal angular momentum the axial component of the oceanic tidal angular momentum otam has been demonstrated to be responsible for most of the diurnal and semidiurnal variations in earth s rotational rate in this paper we study the equatorial components of otam and their corresponding effects on the orientation of earth s rotational axis or polar motion three ocean tide models derived from topex poseidon satellite altimetry are employed to predict the polar motion excited by eight major diurnal semidiurnal tides q1 o1 p1 k1 n2 m2 s2 k2 the predictions are compared with geodetic measurements of polar motion from both long term observations and during the intensive campaign cont94 the prograde diurnal and prograde and retrograde semidiurnal periods are treated whereas the retrograde diurnal polar motion is not treated because it cannot be observed directly and uniquely the comparison shows generally good agreement with discrepancies typically within 10 30 micro arc seconds for the largest tides the eight tides collectively explain nearly 60 of the total variance in subdaily polar motion during cont94 this establishes the dominant role of otam in exciting the diurnal semidiurnal polar motion and paves the way for detailed studies of short period nontidal polar motion the present accuracy however is inadequate to shed light on the prograde diurnal polar libration

the period and q of the chandler wobble summary we have extended our calculation of the theoretical period of the chandler wobble to account for the non hydrostatic portion of the earth s equatorial bulge and the effect of the fluid core upon the lengthening of the period due to the pole tide we find the theoretical period of a realistic perfectly elastic earth with an equilibrium pole tide to be 426 7 sidereal days which is 8 5 day shorter than the observed period of 435 2 day using rayleigh s principle for a rotating earth we exploit this discrepancy together with the observed chandler q to place constraints on the frequency dependence of mantle anelasticity if q in the mantle varies with frequency u as u between 30 s and 14 months and if q in the lower mantle is of order 225 at 30 s we find that 0 04 5 a 5 0 1 1 if instead q in the lower mantle is of order 350 near 200 s we find that 0 11 5 a 0 19 in all cases these limits arise from exceeding the 68 per cent confidence limits of 2 6 day in the observed period since slight departures from an equilibrium pole tide affect the q much more strongly than the period we believe these limits to be robust

attenuation of 1 6 s lg waves in eurasia we report our investigation of the lg attenuation characteristics in eurasia using digital recordings from the incorporated research institutions for seismology chinese digital seismic network broadband stations to maximize the utilization of the current station and source distribution in the region we have derived a new technique known as the source pair receiver pair sprp method for lg attenuation measurement the procedure eliminates seismic source and site effects leaving behind decontaminated amplitude data from which regional wave attenuation is estimated for lg attenuation studies the sprp method is more flexible and of greater general applicability than its predecessor the reversed two station method chun et al 1987 the application of the sprp method to our time domain analysis of 33 regional and far regional seismic events has provided stable regional average for lg attenuation in periods of 1 6 s our time domain analysis aided by a damped least squares inversion algorithm has led to robust measurements of lg attenuation q and its frequency dependence in nine subregions of tectonic significance regions of active tectonics and seismicity generally have lower q0 than that in the stable continental interior subregional q and are found compatible with the published results in areas of relatively uniform geology values are comparatively poorly determined suggesting that they are susceptible to the presence of crustal heterogeneities along the wave paths

the tidal displacement field at earth s surface determined using global gps observations 1 we investigate the 3 d tidal displacement field on earth s surface recorded globally by 456 continuous global positioning system gps stations of igs spanning 1996 2011 for eight principal diurnal and semidiurnal tidal constituents in phase and quadrature amplitudes of the residual tidal displacements after removal of an a priori body tide model are estimated using the precise point positioning ppp technique on the daily gps data the resultant daily estimates are combined to derive final estimates for each tide at each station the results are compared with the predictions of eight recent global ocean tide models separately for coastal 307 and inland 149 stations we show that gps can provide tidal displacement estimates accurate to the level of 0 12 mm horizontal and 0 24 mm vertical for the lunar only constituents m2 n2 o1 and q1 and less favorably for solar related tidal constituents s2 k2 k1 and p1 although improved by ambiguity resolution most recent ocean tide models fit the gps estimates equally well on the global scale but do not agree well between them in certain coastal areas especially for the vertical displacements suggesting the existence of model uncertainties near shallow seas the tidal residuals for the inland stations after removing both body tides and ocean tidal loading otl furthermore show clear continental scale spatial coherence implying deficiencies of the a priori body tide modeling in catching lateral heterogeneity in elastic as well as inelastic properties in the earth s deep interior we assert that the gps tidal displacement estimates now achieve sufficient accuracy to potentially provide constraints on the earth s structure

transition from rifted continental to oceanic crust at the southeastern korean margin in the east sea japan sea 1 the southeastern korean margin documents the processes of continental rifting and seafloor spreading that eventually led to the opening of the southern part of the east sea japan sea two dimensional crustal structure of the southeastern korean margin was computed from ocean bottom seismometer data by tomographic inversion and iterative forward modeling the crustal structure shows the emplacement of high velocity 7 km s lower crust under the continental shelf and slope area associated with a rapid transition from rifted continental to oceanic crust the high velocity lower crust is interpreted as magmatic underplating formed by voluminous igneous activity during rifting magnetic modeling confirms its primary correlation with a prominent magnetic anomaly along the edge of the korean peninsula we suggest that the rifting and subsequent seafloor spreading at the korean margin was significantly controlled by the supply of magma in a region of hotter than normal mantle temperature

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

computation of mars transfer functions for nutations tides and surface loading abstract mars transfer functions for nutations tides and surface loading are computed for different models in order to study the influence of the physics of the interior on the planet s response to external forcing if the core is liquid there is a resonance at the free core nutation fcn period which must be taken into account the fcn period depends on the density of the core and consequently on the density jump at the core mantle boundary cmb and on the dimensions of the core the responses of mars forced by the solar gravitational attraction involve frequencies which could be very close to the fcn the observation of their amplitudes can in that case give us information about whether the core is liquid or not about its dimensions as well as about the density jump at the cmb we therefore consider several models for the interior structure of mars involving different normal mode frequencies and compute the transfer functions for nutations tides and loading as a function of the forcing frequency we show that the amplitudes of the semi annual tri annual and quadri annual nutations could be amplified by several ten percent or even several hundred percent by the fcn resonance depending on the fcn eigenfrequency value here annual means one martian year the same holds for the second degree diurnal tides and loading effects the impact of the core radius density and state on the body and load love numbers is analysed body and low degree load love numbers h and k can change by up to 25 for variations in the core radius of 200 km or for a change in the core state liquid solid the corresponding variations in the tidal gravimetric factor and the loading green s function are about 10 times smaller high degree load love numbers are more sensitive to the upper mantle rheology

a new test of earth tide models in central europe new improved ocean tide models allow a corresponding improvement in ocean tide loading computations during recent years various groups have made more accurate tidal gravity observations in central europe using gravimeters carefully calibrated on various calibration lines this progress with tidal gravity measurements and ocean loading corrections now allows a more comprehensive test of body tide models than was possible previously it is shown that the o1 and m2 gravimetric factors corrected using the latest ocean tide models are very consistent between the sites despite the different instruments and gravity calibration lines that have been used these observations allow constraints to be put on the anelasticity of the earth at tidal frequencies the corrected gravimetric factors are consistent with recent model results for both the elastic prem model and with 0 09 for an anelastic prem model with the q for dissipation in shear varying as frequency to the power

the effects of mantle anelasticity on nutations earth tides and tidal variations in rotation rate summary we model the effects of mantle anelasticity on luni solar nutations on tidal deformation on tidal variations in rotation rate and on the eigenfrequency of the free core nutation our results can be used to invert observations to solve for the anelastic contributions to the shear and bulk moduli of the upper and lower mantle we use specific anelastic models to numerically estimate the effects of anelasticity on these geodetic observables we compare our nutation estimates with observational results among our conclusions 1 mantle anelasticity is likely to be the most important source of damping for the free core nutation 2 present vlbi nutation results are in principle accurate enough to usefully bound anelasticity at diurnal periods but the discrepancy between the vlbi observed nutations and the 1984 iau nutation model cannot be explained by anelasticity and is not yet well enough understood to allow anelasticity to be determined from the data

detailed investigation of a spot on the core mantle boundary using digital pcp data abstract a number of deep earthquakes from the fiji tonga region were used to study the properties of the core mantle boundary cmb the investigation was restricted to an area with a diameter of only a few hundred kilometers at the cmb the use of a cluster of neighboring events yielding redundant sampling and rather good resolution the components of the investigation are i a classical stacking procedure to search for additional reflectors near the cmb ii a deconvolution of seismograms and a stack of the inferred reflector series for the same purpose iii a matched filter method to determine pcp travel times and pcp p amplitude ratios precisely and iv a comparison with synthetic seismograms to check the consistency of derived travel time residuals and pcp amplitude variations in the presence of cmb topography while we do not see any additional reflector for epicentral distances around 35 we detect by stacking seismograms recorded at 70 an additional phase which might be caused by a reflection from the top of d we show that pcp travel time residuals must not be interpreted as being caused exclusively by cmb topography an additional investigation of synthetics provides some constraints on dominant wavelengths and corresponding amplitudes of cmb undulations for wavelengths of 50 400 km the elevation cannot exceed 2 3 km if pcp is observed in this particular area

magnitude the relation of ml to mblg abstract the m blg magnitude developed by nuttli 1973 for the central united states is adapted to other regions of the world by incorporating a specific term for the spatial coefficient of anelastic attenuation using region specific values m blg values are determined for earthquakes occurring near the wwssn stations bks gsc and dug a comparison of the m blg values with published m l magnitudes shows that these two magnitude scales are essentially equivalent between magnitudes 3 to 5 because of this observation we now have a direct way of comparing eastern and western united states earthquake sizes for the purpose of adapting western strong motion data bases to the east and also for understanding teleseismic magnitude biases

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

models of the core mantle boundary and the travel times of internally reflected core phases topographic maps of the core mantle boundary cmb obtained by inverting different subsets of international seismological centre arrival time data involving either waves refracted through the boundary pkp or waves reflected from the topside pcp do not agree we report on the implications for models of cmb structure when data from bottomside reflections notably pkkp are included in the inversion travel time residuals with respect to a reference earth model prem of all core phases are positively biased but the mean residual is different for different phases and must be accounted for prior to inversion the new data illustrate that models of cmb topography can explain only a small fraction of the data variance the new cmb model involves both topography and a laterally varying boundary layer the cmb itself is smooth compared to previous results

verification of the ellipsoidal earth model with an inelastic and convective mantle using tidal gravity variations revisited summary tidal gravity observations can be used to validate theoretical estimation for inelastic response of the earth and its latitude dependence using gravimetric factors we used superconducting gravimeter sg data at five sites mets ahovi strasbourg sutherland canberra and syowa to validate theoretical estimation based on an existing method for the correction of ocean loading effect we tested eight global ocean tide models four old csr4 0 got99 2b nao 99b and fes2004 and four new tpxo7 atlas eot11a dtu10 and hamtide11a were tested we selected an optimal ocean tide model based on the criterion of the smallest misfit for the three main waves o1 k1 and m2 at each station as determinedbytheresidualbetweentheobservedloadingeffectandthemodelledoceanloading effect large discrepancies among the results of ocean tide models remained at mets

origin of internal flow structures in columnar jointed basalt from hreppholar iceland i textural and geochemical characterization basalt columns from hreppholar iceland show distinct internal structures produced by alternating brighter and darker bands through the column locally exhibiting viscous fingering features here we present geochemical and petrographic data retrieved from analyses of major and trace elements and mineral chemistry from a cross section of a single basaltic column this is combined with petrographic descriptions and data on crystal size distributions of plagioclase we use our data from hreppholar to test four existing models that have been proposed to explain banded structures inside columns 1 deuteric alteration 2 double diffusive convection 3 constitutional supercooling and 4 crystallization induced melt migration we find that the internal structures at hreppholar represent primary magmatic features because approximately 20 of the observed structures crosscut the column bounding fracture for each meter along the main axis of the column these features must thus have been formed before the column delimiting crack advanced major and trace element analyses show small but significant variations across the column and strong correlation between oxides like feo and tio2 as well as k2o and p2o5 the geochemical variations correlate with the presence of darker brighter bands visible on a polished surface and can be explained by a variation in the modal proportions of the main phenocryst phases specifically variable plagioclase and titanomagnetite content this banding enhances the internal structures apparent in the polished cross section from columnar joints at hreppholar the measured variations in major and trace element geochemistry as well as mineral chemistry are too small to distinguish between the proposed band forming models plagioclase crystal size distributions however display a systematic change across the column that is consistent with late stage migration of melt inside the column i e the crystallization induced melt migration hypothesis the central part of the columns have plagioclases indicative of slow cooling and these are also more steeply oriented i e subparallel to the column axis compared with plagioclases present in the more rapidly cooled edges this redistribution of melt within individual columns may significantly affect the cooling rate of columnar jointed lava flows and intrusions