finite element modelling of atmosphere loading effects on strain tilt and displacement at multi sensor stations summary strain and tiltmeter observations are composed of signals of different origin tides are a wellknown phenomenon that can be extracted from the time series by tidal analysis depending on the location of the station residuals however contain contributions of different magnitudes from ocean loading changes in atmospheric or hydrological loading anthropogenic induced signals and tectonics reductions of the residual variations are indispensable for extraction of for example the pure tectonical signal one of the challenges in view of the reductions is to understand transfer mechanisms between loading and local conditions such as topography cavity and geological features which lead to additional or modified deformations in this study systematic numerical modelling using the finite element method with elastic rheology is carried out to estimate these effects barometric pressure changes are used as example for the load to determine the additional deformations strain and tiltmeters are considered as instrumentation having nominal resolutions of 0 2 nstrain and 1 nrad respectively the cavity and the topographic effect are systematically investigated with sophisticated models incorporating typical topographic features such as a plain a hill flank and a valley representative for stations worldwide four observatories in central europe are modelled the geodetic observatory wettzell germany the sopron observatory hungary the geodynamic observatory moxa and the black forest observatory bfo both germany the modelling shows that cavity and topographic effects occur in the same order of magnitude and that both effects interact leading to deformations partly intertwined in a complex way this notwithstanding the results explain observed deformation signals at the observatories the systematic modelling helps to better understand the basic processes from which criteria for the selection of future observation sites are inferred

parameterization of the vertical transport of momentum by cumulus clouds part i theory abstract a scheme is developed to parameterize the vertical transport of momentum by cumulus clouds in which the effect of a cloud induced pressure field is included in addition a new form for momentum exchange between clouds and their environment is used the scheme incorporates a simple cloud model which includes both updraft and downdraft and specifies the cloud dynamic fields to enable us to determine the mean pressure gradient force across the clouds it is shown that in a typical environment with vertical wind shear the pressure gradient force is along the direction of the wind shear the equation governing cloud mean momentum together with the diagnostic equation for cloud induced pressure field is solved by iteration to evaluate quantitatively the horizontal pressure gradient force across the cloud and determine the cloud mean momentum application of the parameterization scheme to gate convective events will be presented in part ii of this paper

elastic wave velocities of forsterite and its β spinel form and chemical boundary hypothesis for the 410 km discontinuity a method for measuring elastic wave velocities at pressures up to 15 gpa has been developed velocities of forsterite and spinel were measured using a piston cylinder apparatus with a pulse echo overlap method for pressures up to 4 gpa and using a split sphere apparatus with a pulse transmission technique for higher pressures to validate the results volume compression incompressibility and rigidity were estimated from measured travel times and comparison was made between the present estimates and data from x ray brillouin and acoustic measurements the v p and k values for spinet are 3 and 8 higher than previous measurements at 10 gpa respectively velocity jumps in v p and v s due to olivine to spinel transition were about 1 34 and 0 80 km s 1 respectively very different from seismological observations of velocity jumps at the 410 km discontinuity which were concentrated around 0 45 km s 1 for the p wave and 0 22 km s 1 for the s wave velocity jumps in mantle peridotite were calculated using the experimental results and comparison was made between these estimates and seismological observations at the 410 km discontinuity the evidence does not support the phase change hypothesis and a chemical boundary was proposed as the origin of the 410 km discontinuity an eclogitic mineral assemblage might be an alternative for the composition of the transition layer

phase relation and physical properties of an al depleted komatiite to 23 gpa abstract knowledge of the mineralogical constituents of the earth s mantle depends heavily on high p experiments of pyrolite composition in order to understand the planetary interior better phase relations and mineral physics properties of compositions other than pyrolite may also be important high p and high t experiments were conducted on an al depleted komatiite which can be regarded as a kind of piclogite composition fourteen experiments were carried out along a model geotherm between 5 and 23 gpa and 1100 and 1600 c with a multi anvil apparatus analyses of quenched run products showed that in the studied komatiite the fractions of olivine and its high p polymorphs wadsleyite and ringwoodite are 40 50 vol pyroxene garnet phase transition occurs at 13 17 gpa while the respective values for pyrolite are 60 vol and 12 15 gpa the density and seismic velocity profiles of komatiite mantle were calculated using thermoelastic parameters of related minerals and they showed quite good agreements with those of seismic observations around the transition zone as well as those for pyrolite

pressure and temperature dependence of elastic wave velocity of mgsio3 perovskite and the composition of the lower mantle abstract simultaneous measurements of compressional p and shear s wave velocities and unit cell volume density have been conducted on mgsio 3 perovskite to 9 2 gpa and 873 k using ultrasonic interferometry in conjunction with x ray diffraction finite strain analysis of current data allowed us to determine the elastic moduli and their pressure derivatives independent of the pressure measurement the results are k s 253 2 gpa g 173 1 gpa k s p 4 4 1 and g p 2 0 1 the temperature derivatives of the bulk and shear moduli were tightly constrained from acoustic velocity measurements yielding k s t 0 021 2 gpa k and g t 0 028 2 gpa k p and s wave velocities and density profiles for a pyrolite compositional model consisting of magnesium silicate perovskite and magnesiowustite are calculated at lower mantle depths along a 1600 k adiabatic geotherm the results agree with those of seismic model prem within 0 5 0 5 and 0 3 respectively from 800 to 2600 km the effect of fe and mg partitioning between magnesium silicate perovskite and magnesiowustite on the calculated velocities and density is negligibly small compared to the effects of composition and temperature simultaneous constraints from p and s wave velocities and density support for a homogeneous lower mantle with pyrolitic composition

thermal equation of state of mg0 91fe0 09 2sio4 ringwoodite abstract in situ synchrotron x ray diffraction xrd experiments were conducted using the speed 1500 multi anvil press of spring 8 on mg0 91fe0 09 2sio4 ringwoodite rw whose composition is similar to that expected in the earth s mantle transition zone pressure volume temperature data were collected using a nacl or mgo capsule up to 21 gpa and 1273 k a fit to high temperature birch murnaghan htbm equation of state eos with fixed values of ambient cell volume v0 527 83 7 a3 and isothermal bulk modulus kt0 187 gpa yielded a pressure derivative of isothermal bulk modulus kt 4 41 1 a temperature derivative of bulk modulus kt t p 0 028 5 gpa k 1 and a volumetric thermal expansivity a bt with values of a 1 9 2 10 5 k 1 and b 1 2 4 10 8 k 2 these properties are consistent with the analysis using the thermal pressure th p eos the derived kt and kt t p are consistent with previous studies on mg2sio4 ringwoodite however consistent with measurements at 0 gpa the present equation of state yields significantly higher thermal expansivity than derived by diamond anvil experiments on mg2sio4 ringwoodite to 30 gpa and 700 k on the basis of the equation of state the density jump around 660 km depth expected for pyrolitic homogeneous mantle caused by ringwoodite mg perovskite mgpv magnesiowustite mw and garnet grt mgpv transitions was estimated the density jump calculated for pyrolite 9 2 is significantly larger than that across the 660 km discontinuity derived by recent seismological studies 4 6 one possible explanation for this is that the recent seismic data reflect only the sharp transition concerned with the rw mgpv mw transition

compressional and shear wave velocities of ringwoodite γ mg2sio4 to 12 gpa compressional and shear wave velocities of ringwoodite mg 2 sio 4 were measured on a polycrystalline specimen to 12 gpa at room temperature using ultrasonic interferometry techniques velocity measurements at ambient conditions yielded v p 9 86 3 and v s 5 78 2 km s finite strain analysis of the high pressure velocity data yields k 185 2 gpa g 120 1 gpa k 4 5 2 and g 1 5 1 for the elastic moduli and their pressure derivatives respectively the velocities and elastic moduli at ambient conditions are indistinguishable from aggregate properties of polycrystalline ringwoodite calculated using single crystal elastic constants c ij comparison of the current results on pressure derivatives of bulk and shear moduli with previous acoustic data on iron free ringwoodite to 3 gpa and iron bearing sample to 16 gpa indicated that the discrepancy can be explained by the pressure range of the experiments rather than iron content current results suggest that ringwoodite and wadsleyite posses very similar pressure dependence in elastic properties to the transition zone depth in a pyrolite mantle with 1400 c adiabatic foot temperature the wadsleyite to ringwoodite phase transition is characterized as a seismic reflector spreading about 20 km in width with a density jump of 2 1 and impedance jumps of 2 4 and 3 1 for p and s waves near 520 km depth which is consistent with seismic observations in long period data

elastic wave velocities of mg0 91fe0 09 2sio4 ringwoodite under p t conditions of the mantle transition region abstract experimental techniques have been developed to measure elastic wave velocities of hot pressed polycrystalline samples at high pressure and high temperature using a combination of ultrasonic interferometry and in situ synchrotron x ray observation in conjunction with a large volume kawai type multianvil apparatus kma with these techniques we have succeeded in precise measurements of the sound velocities of ringwoodite at pressures to 19 gpa and at temperatures to 1673 k equivalent to the conditions of the middle part of the mantle transition region a linear fitting of the present data on polycrystalline ringwoodite with a composition of mg0 91fe0 09 2sio4 yielded following parameters k0s 186 1 gpa ks p 4 3 1 ks t 0 018 1 g 119 1 gpa g p 1 2 1 and g t 0 015 1 which are in good agreement with earlier results at high temperatures and ambient pressure and those at room temperature and high pressures significant non linear decreases in vp and vs were noted at temperatures higher than 1200 k however suggesting that the elastic wave velocity measurements at temperatures corresponding to the actual mantle are needed to compare the laboratory data with the seismologically derived sound velocities

anisotropy of earth s inner core intrinsic attenuation from seismic normal mode models the earth s inner core the slowly growing sphere of solid iron alloy at the centre of our planet is known to exhibit seismic anisotropy both normal mode and body wave studies have established that when the global average is taken compressional waves propagate faster in the north south direction than in the equatorial plane recent body wave studies also indicate that this fast direction may be more attenuating and interpret this anisotropic attenuation in terms of anisotropic scattering due to inner core texturing here we use the earth s normal modes to study the attenuation anisotropy of both compressional and shear waves in the inner core as normal modes have wavelengths several orders of magnitude longer than estimates of inner core grain size any attenuation anisotropy quantified using normal modes must reflect the anisotropy of intrinsic viscoelastic attenuation of the crystalline inner core alloy by inverting zonal anelastic and elastic normal mode splitting function coefficients of twenty inner core sensitive modes we construct models of inner core intrinsic attenuation and velocity anisotropy we find that for compressional waves the north south direction is both fast and more strongly attenuating the existence of intrinsic inner core attenuation anisotropy can be interpreted in terms of anisotropic zener relaxation in the metallic alloy comprising the inner core such anisotropic zener relaxation has only been observed in the presence of solute atoms and is thus entirely consistent with the presence of a few atomic per cent of light elements in the earth s inner core

on reduction of long period horizontal seismic noise using local barometric pressure summary tilt from atmospheric loading has long been known to be the major source of long period horizontal seismic noise we try to quantify these effects for seismic data from the black forest observatory bfo which is known to be a very quiet station experimental transfer functions between local barometric pressure and horizontal seismic noise are estimated for two long time series by standard methods two simple analytical physical models are developed the local deformation model ldm and the acoustic gravity wave model twm subsequently these models with only two free parameters are fit using least squares to the observed seismic noise for time series of widely differing lengths the results are variable sometimes rather dramatic variance reductions are obtained and sometimes the reduction is hardly significant the method produces the best results when barometrically induced noise is high the resulting admittances for the ldm are compared to finite element calculations since the methods are simple and can result in conspicuous reductions in noise we provide one more reason for installing barometers at even the best broad band seismic stations

single crystal elasticity of ringwoodite to high pressures and high temperatures implications for 520 km seismic discontinuity abstract the single crystal elastic moduli of spinel structured mg 0 91 fe 0 09 2 sio 4 ringwoodite were measured to 16 gpa at room temperature and to 923 k at ambient pressure by brillouin spectroscopy a third order finite strain equation of state yields pressure derivatives of 4 1 2 and 1 3 1 for the adiabatic bulk modulus k s and shear modulus respectively the pressure derivatives of aggregate elastic moduli for all three polymorphs and of mg fe 2 sio 4 in the mg rich end are equal within the mutual experimental uncertainties with k s p t 4 1 4 3 and p t 1 3 1 4 a linear decrease of the elastic moduli and sound velocities with temperature adequately describes the data the temperature derivatives of k s and are 0 021 and 0 016 gpa k respectively an extrapolation of our data to transition zone pressures and temperatures indicates that the shear and compressional impedance contrasts associated with mg fe 2 sio 4 mg fe 2 sio 4 transition are sufficient to produce a visible discontinuity at 520 km depth even with only a moderate 30 50 amount of olivine moreover the partitioning of fe between mg fe 2 sio 4 and mg fe 2 sio 4 and majoritic garnet will produce a relatively sharp seismic discontinuity in the order of 10 15 km even when the latent heat of reaction is taken into account the visibility of the discontinuity in regional and global studies could be inhibited by large topography that would accompany any local variations in temperature or fe content the high v p contrasts observed in some localities are difficult to explain by the transition and are suggestive of a chemical boundary this is consistent with chemical heterogeneity in the transition zone probably related to subduction one of the possible explanations for high velocity contrasts near 520 km is a buried moho a boundary between garnetite former oceanic crust and mg fe 2 sio 4 enriched former peridotite layers

single crystal elasticity of γ mg0 91fe0 09 2sio4 to high pressures and to high temperatures sound velocities and elastic moduli have been measured on mg0 91fe0 09 2sio4 ringwoodite single crystals to 16 gpa and to 923k by brillouin spectroscopy a third order finite strain fit to the data yields pressure derivatives of 4 1 2 and 1 3 1 for the adiabatic bulk modulus ks and shear modulus respectively mg rich and mg fe 2sio4 have identical values of ks p and of p within the experimental uncertainties ks t and t for mg fe 2sio4 are 0 021 and 0 016 gpa k respectively our results indicate that the shear and compressional impedance contrasts associated with mg fe 2sio4 transition are sufficient to produce a visible discontinuity at 520 km even with a moderate 30 50 amount of olivine the generally low visibility of the 520 km discontinuity is likely due to its width and large amplitude topographic variations

pressure induced noise on horizontal seismometer and strainmeter records evaluated by finite element modelling summary barometric pressure induced noise is one of the major limiting factors in analysing longperiod seismological records especially the horizontal components are strongly affected the barometric pressure influence originates from the attraction by the air masses and deformations of the crust of the earth resulting in accelerations strain and tilts these factors are enhanced by the local topography and the installation site of the instrument although this influence is known for several years the physical transfer mechanisms are still not well understood by means of finite element fe analysis deformations caused by different pressure loadings are studied for moxa observatory the main topographic elements of the observatory surroundings like hill flanks and a valley in an area of approximately 2 5 km 2 are included in the model the gallery in which a long period sts 1 seismometer and two quartz tube strainmeters are installed is modelled with a high resolution of 5 m the fe model is exposed to three principle loading scenarios i uniform barometric pressure loading ii wind induced pressure on a hill flank and iii passages of pressure fronts as a linear elastic rheology is used the loading effects can be superimposed and scaled as necessary in order to get an estimate about the influence of cavity effects compared with that of topography the computations are redone for a model containing only the gallery but no topography additionally the influence of dipping layers and a possible cleft system on the pressure effects are studied from the fe analyses follows that all three scenarios can lead to significant tilts of approximately 0 1 to 0 7 nrad hpa 1 at the sites of the instruments this is the same order of magnitude observed in the seismometer data also the directions of the tilts are in agreement the deformation effects obtained for the strainmeters are too small by more than 1 order of magnitude a qualitative agreement between model results and observations can be found and the change in polarity occurring during the passage of a pressure front can be explained besides a direction dependence of the effects can be shown for the different components of the instruments as well as a dependence on the movement of the air masses anisotropy or a cleft system can modify the pressure influence regarding the order of magnitude up to a factor of 10 and the polarity of the effects a cleft system might be the explanation for the small effects observed in the n s component of the sts 1 seismometer

a preliminary investigation into the relationship between long period seismic noise and local fluctuations in the atmospheric pressure field summary the displacement response of an elastic half space to a plane pressure wave is examined in order to establish the conditions under which sources of this type can contribute significantly to the long period seismic noise field the study is restricted to pressure waves which propagate at velocities well below the seismic wave velocities characteristic of the half space the numerical studies indicate that pressure waves with amplitudes of 100 pbar or more can contribute significantly to the long period vertical background noise observed at the surface provided that the detectors are located on sections of alluvial fill or poorly to moderately indurated sandstones and shales whose thicknesses are greater than about a kilometre these same waves can also create significant tilt noise on long period horizontal seismographs located at or near the surface regardless of the rock type the seismic disturbances created by pressure waves decay rapidly away from the surface therefore it appears that it may be possible to eliminate the effects of atmospherically generated noise by placing the detectors at moderate depths

broadband seismic noise attenuation versus depth at the albuquerque seismological laboratory abstract seismic noise induced by atmospheric processes such as wind and pressure changes can be a major contributor to the background noise observed in many seismograph stations especially those installed at or near the surface cultural noise such as vehicle traffic or nearby buildings with air handling equipment also contributes to seismic background noise such noise sources fundamentally limit our ability to resolve earthquake generated signals many previous seismic noise versus depth studies focused separately on either high frequency 1 hz or low frequency

the effects of the atmospheric pressure changes on seismic signals or how to improve the quality of a station seismic investigations are mainly limited by seismic noise two microbarometers have been installed in the seismic vault of two different geoscope stations one at ssb and the other at tam all vertical components and most of the horizontal components show a significant correlation with pressure in order to correct the seismic signals from the atmospheric pressure noise a transfer function between the pressure data and the seismic data is inverted results show that after correction the noise levels reached on the horizontal components are similar between the two stations and the vertical components display noise levels below the low noise model as defined by peterson 1993 this technique reduces part of the noise and allows detection of small earthquakes and a better extraction of normal modes the analysis of the lowest normal modes of the earth excited by the m s 8 2 macquarie island earthquake is given to illustrate the perspectives of the method

earth motion caused by local atmospheric pressure changes summary observations have been made of the local atmospheric pressure field and the long period seismic noise fields both on the surface of the earth and in a mine at a depth of 183 metres the observations show that during windy intervals and in the period range 20 100 s there is a strong correlation between local atmospheric pressure changes and the noise recorded by a vertical seismograph located on the surface in contrast over the same range of periods there is no correlation between the seismic noise recorded in the mine and local atmospheric pressure changes except during the passage of acoustic waves it is shown that the noise in this pass band is not due to the buoyant response of the seismograph but is caused by the motion of the earth responding to atmospheric pressure changes

interface kinetics grain scale deformation and polymorphism deviatoric stress generated within subducting slabs by the olivine spinel transformation has been modeled by assuming the phases to be simply connected rather than comprising a mixture in which one phase is embedded within another here we use a simplified model to explain how transformation strain is incorporated into a continuum model and we then use the simplified model to explain quantitatively the origin of the unreasonably large deviatoric stresses predicted by existing slab models we review experiments on the transformation of single crystal samples and argue that they are consistent with the occurrence at the grain scale of deviatoric stresses comparable with those predicted erroneously to exist at the slab scale by those slab models using a simple example we show that although large deviatoric stresses can exist at the grain scale their average over a sample containing many grains can be hydrostatic this leads us to the problem of modeling the microscale structure we outline the therm

toward a single station approach for microzonation using vertical rotation rate to estimate love wave dispersion curves and direction finding abstract microzonation the estimation of shear wave velocity profiles of the upper few 100 m in dense 2d profiles is one of the key methods for understanding the variation in seismic damage caused by ground shaking events and thus for mitigating the risk of damage in the future in this article we present a novel method for estimating the love wave phase velocity dispersion using ambient noise recordings we use the vertical component of rotational motions inherently present in ambient noise and the established relation to simultaneous recordings of transverse acceleration in which the phase velocity of a plane sh or love type wave acts as a proportionality factor we demonstrate that the developed inversion technique shows comparable results to more classical array based methods furthermore we demonstrate that if portable weak motion rotational motion sensors are available and the installation of a seismic network or array is not possible a single point multicomponent approach for estimating the dominant direction of the incident wavefield and the local velocity structure will be feasible with similar performance compared to more classical techniques

elasticity of natural majorite and ringwoodite from the catherwood meteorite sound velocities and elastic moduli of natural polycrystalline majorite mg0 78fe0 21ca0 01 sio3 and ringwoodite mg0 75fe0 25 2sio4 from the catherwood meteorite were measured by brillouin spectroscopy these are the first acoustic measurements for such natural high pressure phases with fe contents comparable to that of the earth s mantle the adiabatic bulk modulus of majorite is ks 164 4 gpa and the shear modulus is 87 2 gpa which are typical values for garnet structured silicates both the elastic moduli and the sound velocities of natural cubic majorite are slightly lower than values for aluminosilicate garnets with comparable fe contents moreover the bulk and shear moduli of natural majorite are indistinguishable from those of pure mg majorite and the dependence of these moduli on fe content is small in contrast ringwoodite ks 193 3 113 2 exhibits a pronounced change in the aggregate elastic moduli and sound velocities with increasing fe content the addition of 10 fe to phase changes the velocity by an amount comparable to the velocity change across the transition in mg2sio4 it is therefore necessary to account for the effect of fe in constructing mineralogical models of the transition zone