mars interior structure and excitation of free oscillations based on available chemical models of the planet philos trans r soc london 349 1994 285 supply and loss of volatile constituents during the accretion of terrestrial planets in s k attreya j b pollack m s matthews eds origin and evolution of planetary and satellite atmospheres univ arizona press pp 268 288 icarus 126 1997 373 phys earth planet inter 112 1999 43 space sci rev 92 2000 34 a new set of global models of the martian interior has been constructed a model comprises four submodels a model of the outer porous layer a model of the crust a model of the mantle and a model of the core the first 10 11 km layer is considered as an averaged transition from regolith to consolidated rock the mineral composition of the crustal basaltic rock varies with depth because of the gabbro eclogite phase transition as a starting point for mantle modeling the experimental data obtained by bertka and fei j geophys res 102 1997 525 earth planet sci lett 157 1998 79 along the areotherm have been used iron content of the mantle being varied the measured or estimated up to now elastic properties for a set of mantle minerals are used seismic velocities determined from new high p t data on elastic properties are 2 3 lower than the velocities calculated earlier new high p t measurements of the density of fe fe fes and feh enable us to refine the core model taking into account available chemical models and the fact that noticeable amount of hydrogen could enter the martian core during its formation solar syst res 30 1996 456 such parameters as a ferric number of the mantle fe sulfur and hydrogen content in the core are varied the following tendency is seen the presence of hydrogen leads to the increase of the fe si ratio and decreases fe in the mantle due to the increase of the core radius the higher sulfur and hydrogen content in the core and the smaller mantle fe the less likely a perovskite layer exists the modeling shows that to obtain the fe si ratio up to the chondrite ratio of 1 71 more than 50 mol of hydrogen should be incorporated into the core in the second part of the paper based on the available estimates of the martian seismic activity and the sensitivity of current instruments the amplitudes for different types of free oscillations have been estimated it is found down to what depth the normal modes can sound the planetary interiors a marsquake with a seismic moment of 10 25 dyn cm is required for spheroidal oscillations with 17 to be detected these spheroidal modes are capable sounding the outer layers of mars down to a depth of 700 800 km

electromagnetic borehole fields in a layered dipping bed environment with invasion electromagnetic modeling of an induction sonde 1 100 khz in a dipping bed environment is a 3 d problem the capability for such an analysis is necessary for interpretation of oil well logs in offshore environments where most holes are deviated 3 d geometrical effects require vector field analysis the method accounts for transverse magnetic mode tm coupling arising from surface charges deposited by eddy currents passing through bed boundaries if borehole and invasion effects are included the only available rigorous analytical methods are finite elements or finite difference techniques these approaches require large scale computing in contrast our method is approximate and is an extension of the geometrical factor theory and born approximation the variational method does not require matrices and is numerically simpler than the more rigorous finite element method the method uses a new electric field vector integral equation developed by chew the formulation accounts for low frequency behavior a

influence of iron on the elastic properties of wadsleyite and ringwoodite 1 we investigate by first principles the influence of iron on the elastic properties of the b phase wadsleyite and g phase ringwoodite polymorphs of olivine the most abundant minerals of the upper and lower parts of the transition zone respectively our study aims to complement experiments to understand details of the 410 km and 520 km discontinuities the full elastic tensor cij bulk k and shear g moduli are determined under static conditions for b g mg1 xfex 2sio4 with x 0 125 wave propagation anisotropy in single crystals and polarization anisotropy in aggregates with preferred orientation are investigated and compared with those of iron free wadsleyite and ringwoodite for a thorough understanding of the effect of iron we examine the effect of iron on velocity contrasts due to phase changes and conclude that iron enhances dvp and dvs across the a b transition but suppresses them across the b g transition the latter might contribute to suppress locally the 520 km discontinuity if this has a significant contribution from the b g transition we show that lateral variation of iron dx produces lateral velocity heterogeneity ratios similar to those produced by lateral variations of temperature dt both producing ratios comparable to values extracted from seismic tomography studies however in contrast with dt dx produces negative values for density to longitudinal and shear wave velocity ratios this might be considered the fingerprint of lateral variations of iron concentration these negative ratios appear similar to results inferred from geodynamical models compiled by karato and karki 2001 for the upper mantle and transition zone

an analysis of tropical instability waves in a numerical model of the pacific ocean 2 generation and energetics of the waves this work was supported by the department of com merce noaa under grant na56gp0026 one of the au thors sm was partially supported by a nasa global change fellowship ngt 30288 another author ab was supported by a ucar postdoctoral fellowship

p v vp vs t measurements on wadsleyite to 7 gpa and 873 k implications for the 410 km seismic discontinuity the compressional p and shear wave s velocities for mg2sio4 wadsleyite have been measured to 7 gpa and 873 k using simultaneous ultrasonic interferometry and in situ x ray diffraction techniques from the velocity measurements we obtained the pressure and temperature derivatives for the elastic shear g and adiabatic bulk ks moduli g p t 1 5 1 g t p 0 017 1 gpa k ks 173 2 gpa ks p t 4 2 1 and ks t p 0 012 1 gpa k for the p and s waves we obtained vs p t 0 021 1 km s gpa vs t p 0 035 2 km s k vp p t 0 065 2 km s gpa and vp t p 0 038 2 km s k values in parentheses are standard deviations e g 1 5 1 1 5 1 independent equation of state analysis of p v t data provided an estimation of the temperature dependence for the isothermal bulk modulus of kt t p 0 022 12 gpa k and thermal expansion a bt coefficients of a 2 10 5 k 1 and b 2 5 10 8 k 2 using these data along with elastic properties for other mantle phases a velocity depth profile for a pyrolite model to 670 km depth is constructed using a finite strain method along a 1673 k adiabat in the transition zone the pyrolite model has a smaller gradient between 410 and 660 km than the body wave models from synthetic waveform analyses but converges with the seismic profiles at the bottom of the transition zone just above the 660 km discontinuity the pyrolite model has velocity jumps of 6 9 and 7 9 for p and s waves respectively over a thickness of 10 km for the phase transformation from olivine to wadsleyite which is in good agreement with short period p wave reflection data and a recent fine structure model c4 for both the velocity jumps and the thickness of the 410 km seismic discontinuity

diagnostic model of the three dimensional circulation in the upper equatorial pacific ocean abstract to investigate the processes that maintain the large scale annual average thermal structure of the equatorial pacific the three dimensional ocean circulation for a large area is determined from a diagnostic model applied to repeated meridional hydrographic sections along 150 w and 11o w from 5 n to 5 s geostrophic balances are used to determine velocity profiles from 0 to 500 db across the boundaries of the region zonal velocities across 150 w and 110 w at approximately 1 lattitude intervals from 5 n to 5 s and meridional velocities across 5 n and 5 s averaged over the zonal distance between 150 w and 110 w poleward wind driven flows across 5 n and 5 s based on climatological zonal wind stress are added to the geostrophic velocities in the mixed layers to achieve overall mass conservation the reference dynamic height field at 500 db is adjusted at four of the 21 stations by about 1 dyn cm horizontal nondivergence is used to determine meridional velocities between 0 75 and 5 latitudes

transition zone velocity gradients and the 520 km discontinuity stacks of long period global digital seismograph network gdsn seismograms at 110 to 180 epicentral distance reveal precursors to ss that result from underside reflections off upper mantle seismic discontinuities the 410 and 660 km discontinuities are obvious in these stacks but identification and modeling of other transition zone discontinuities are complicated by sidelobes from the 410 and 660 km reflections these sidelobes result from the limited bandwidth of the gdsn instrument responses and the effect of crustal reverberations on the ss reference phase the crustal effects can be minimized by restricting the records to oceanic bounce points where the 6 km thick crust has little effect on the long period waveforms over 2000 long period transverse component seismograms with oceanic ss bounce points recorded by the gdsn from 1976 to 1991 are manually edited aligned on ss and then stacked using a new procedure that weights the records by data quality the resulting image shows a clear reflection from a 520 km discontinuity that cannot be explained as a sidelobe artifact confirming earlier results of shearer 1990 1991 and revenaugh and jordan 1991 by stacking along the expected travel time curves for discontinuity phases the time versus range image of the precursor wave field is reduced to a single trace that measures upper mantle reflectivity versus time the features in this reflectivity profile are sensitive to the brightness and depth of the transition zone discontinuities and to the steepness of the velocity gradients between the interfaces using geometrical ray theory and assuming a constant velocity versus density scaling relationship i fit this reflectivity profile with velocity models of the upper mantle using both forward modeling and direct inversion the inverse problem is addressed by performing a deconvolution of the profile with the ss reference phase after a correction for attenuation followed by a direct mapping of reflectivity versus time into velocity versus depth velocity depth profiles resulting from these procedures are roughly in agreement with standard upper mantle velocity models except that the ss precursor data require a minor discontinuity near 520 km and a steeper gradient just below the 660 km discontinuity estimated discontinuity shear impedance changes are 6 7 1 1 at 420 km 2 9 0 7 at 519 km and 9 9 1 5 at 663 km the impedance change near 520 km is consistent with current mineral physics results for the olivine to phase change and places constraints on the fraction of olivine in the transition zone

do tropical cells ventilate the indo pacific equatorial thermocline source waters of the indo pacific equatorial thermocline are studied with a high resolution ocean model in the annual mean fields tropical and subtropical overturning cells are found that upwell at the equator and downwell at 5 degrees and 20 degrees poleward of the equator respectively tropical cells are common in ocean models but their role in ventilating the equatorial thermocline is obscure because the downwelled water is too warm to match the subsurface equatorial waters the tropical cells are much weaker when the overturning is considered in density coordinates when high frequency mass fluxes are included tropical cells are compensated by an eddy induced overturning seasonal variations and tropical instability waves are responsible for the compensation it follows that only subtropical cells transfer surface water to the equatorial thermocline strong tropical cells are shown to be an artefact

the three dimensional structure of an upper ocean vortex in the tropical pacific ocean in the equatorial pacific ocean easterly trade winds and the earth s rotation combine to drive surface currents away from the equator thereby causing cold nutrient rich subsurface water to upwell the front1 that forms between this upwelled water and warmer waters north of the equator is sometimes visible as a spectacular line in the sea 2 between 2 and 6 n westward propagating cusp shaped disturbances observed along this front3 have been attributed to the effect of dynamical instabilities in the system of zonal equatorial currents4 11but the connection between these phenomena remains unclear here we report extensive measurements from shipboard sensors satellite and drifting buoys which reveal the three dimensional structure of an anticyclonic eddy or vortex 500 km in diameter and centred at 4 n we suggest that cusp shaped disturbances of the front are caused by trains of large amplitude vortices which are driven by instability of the mean zonal shear we show that these vortices not only play an important role in the meridional transport of heat salt and momentum but are also associated with regions of intense horizontal convergence along the front where dramatic concentrations of marine life are observed

constraints on the structure of the east pacific rise from seismic refraction data university of washington seismic data taken during rose phase 1 have been used to study the structure of the east pacific rise in the vicinity of 12 n off axis but within 50 km of the axis we find that the oceanic crust can be modeled with a rapid change in velocity in the top 2 5 km a zone of low but uniform velocity gradient from 2 5 to about 5 5 km and a transitional zone about 1 km thick to mantle material there is also evidence for substantial anisotropy in mantle velocity gradients with a positive velocity gradient in the spreading direction and a negative velocity gradient parallel to the rise under the rise axis the data allow at most a very narrow zone of low velocity less than about 2 km wide in the crust

p wave mantle velocity structure beneath northern eurasia from long range recordings along the profile quartz high resolution seismic sounding of the mantle using two peaceful nuclear explosions pnes along the 3950 km long quartz profile in northern eurasia reveal major unexpected vertical and lateral mantle inhomogeneities in contrast to standard seismological earth models such as prem and iasp91 three rather than two mantle discontinuities are found between 400 and 700 km depth they are located at about 420 550 and 670 km depth lateral variations in depths amount to 10 20 km and associated p wave velocities vary by 0 1 km s 1 in the upper mantle the uppermost layer through which pn propagates extends down to about 100 km depth the mantle below this depth but above the 410 km discontinuity is characterized by alternating high and low p wave velocities in the depth range between 100 and 200 km the velocity fluctuates between 8 3 and 8 7 km s 1 and shows variations from shotpoint to shotpoint average velocities are clearly higher than standard seismological reference models this part of the mantle overlies a low velocity zone between about 200 and 300 km depth this channel also displays substantial lateral variation in depth which could be interpreted as a laterally variable asthenosphere beneath the west siberian basin the asthenosphere seems to be well established whereas it is only poorly defined under the uralian belt and the tectonic units to the northwest with the addition of more data from this and other profiles future aims include two dimensional and three dimensional tomographic modelling as well as modelling of petrological composition of the mantle down to 850 km depth beneath northern eurasia

sound velocities and elastic properties of fe bearing wadsleyite and ringwoodite the sound velocities and single crystal elastic moduli of phase wadsleyite and phase ringwoodite of mg fe 2sio4 with fe fe mg ratios of 0 075 and 0 09 respectively have been determined at ambient conditions by brillouin spectroscopy both compressional and shear wave aggregate velocities decrease with increasing fe content in both phases but the magnitude of this decrease is different for the two phases the adiabatic bulk modulus ks of fe bearing mg2sio4 ks 170 2 gpa is indistinguishable from that of the mg end member within experimental uncertainty whereas ks of mg fe 2sio4 increases rapidly with increasing iron content the shear moduli of both phases decrease with increasing fe content our measurements indicate that the velocity and impedance contrasts between olivine and mg fe 2sio4 are independent of fe content for mg rich compositions but the contrast for the mg fe 2sio4 transition increases significantly with increasing fe content the new data support a previous estimate of 40 10 for the olivine content of the upper mantle and suggest that less than 50 mg fe 2sio4 is sufficient to account for the observed impedance contrasts at depths of both 410 km and 520 km unless the effect of fe on elastic properties is accounted for it is difficult to account for both the 410 and 520 km discontinuities with a single olivine content

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

finite element analysis for model parameters distributed on a hierarchy of geometric simplices abstracta resurgence of interest in the problem of electrical or electromagnetic scattering from thin conductors either on a line or in a plane has been motivated in recent years by time lapse fracture monitoring in the near surface enhanced geothermal reservoirs and unconventional hydrocarbon plays however finite element modeling of small electrical features in large computational domains results in a disproportionately large number of elements concentrated in a volumetrically insignificant fraction of the mesh and it focuses computational resources away from areas of interest elsewhere such as receiver locations we have developed a novel hierarchical electrical model is proposed for unstructured tetrahedral finite element meshes in which the usual volume based conductivity on tetrahedra is augmented by facet and edge based conductivity on the infinitesimally thin regions between elements doing so allows a slender borehole casing of arbitrary shape to be coarsely approximated by set of connec

selected elastic moduli and their temperature derivatives for olivine and garnet with different mg mg fe contents results from ghz ultrasonic interferometry selected p wave acoustic travel times through single crystal samples of olivine and garnet with different mg mg fe ratios were measured at elevated temperatures from 293 k to 363 k using a newly developed ghz ultrasonic interferometer these high precision data allow us to examine aspects of the elasticity composition systematics of olivine forsterite fayalite and garnet pyrope almandine solid solution series for every 10 decrease in the mg mg fe content the p velocity of olivine along the b axis decreases about 3 and lnc22 t decreases about 7 for garnet ln c44 c11 c12 2 t decreases about 6 if such velocity composition systematics are typical and hold at the p t regime of the mantle only a 3 4 variation in the mg mg fe content of olivine is required to explain the lateral seismic velocity variation in the upper portion of the mantle within one tectonic region dlnvp l and 7 8 variation in the mg mg fe content to explain the 2 lateral seismic velocity variation of the upper mantle globally

the p wave upper mantle structure beneath an active spreading centre the gulf of california summary detailed analysis of short period travel time dt d and wave form data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km more than 1400 digital seismograms from earthquakes in mexico and central america recorded at scarlet yield 1753 travel times and 58 direct measurements of dt d as well as high quality stable waveforms the 29 events combine to form a continuous record section from 9 to 40 with an average station spacing of less than 5 km first the travel times are inverted using the tau method of bessonova et al the resultant model is adjusted to agree with the experimental p values further constraints arise from the observed relative amplitudes of mantle phases which are modelled by trial and error using wkbj synthetic seismograms chapman wiggins model gca which is appropriate for western mexico north of 20 latitude is similar to existing upper mantle models for shield tectonic continental and arc trench regimes below 400 km but differs significantly in the upper 350 km gca velocities are very low in this depth range the model catches up with the others with a very large velocity gradient from 225 to 390 km this well resolved feature is consistent with the shear wave model tna for western north america of grand helmberger the abundant data from 20 to 30 control the detailed shape of the 660 km discontinuity very large velocity gradients lie both above 620 660 km and below 661 680km a 2 8 per cent velocity change

a discussion of flow pathways in the central and eastern equatorial pacific abstract an eddy permitting global ocean model is used to interpret kinematics within the central and eastern equatorial pacific ocean from 160 e to the coast of america because of high levels of variability in this region observational studies of meridional flow are contradictory in particular as to whether the net flow is northward or southward unlike most oceanographic datasets model output can be analyzed at high temporal and spatial resolution providing clues as to real ocean behavior in the model a net southward flow occurs across the equator east of 160 w at most density layers throughout the year in the central pacific from 160 e to 160 w the net flow is northward but varies with season and occurs primarily in the mixed layer this is a key region for the flow of equatorial undercurrent water into the northern hemisphere the three dimensional flow is very complex and seasonally dependent it is vital that these flows are analyzed in an isopycnal framework or else the pathways are ve

stress determination in multianvil deformation experiments based on dislocation curvatures measurements application to wadsleyite and ringwoodite 1 the curvature of dislocation lines can serve as a probe for the resolved shear stress in multianvil deformation experiments this method is very well adapted to deformation experiments in the multianvil apparatus where the microstructure and in particular the dislocation density can be largely determined by early deformation stages on the contrary individual dislocation movements can adjust more rapidly to stress level changes and can thus record the last stress level borne by the specimen before it is quenched the method has been applied to dense specimens of wadsleyite and ringwoodite deformed at 15 to 22 gpa and 1000 to 1500 1600 c the resolved shear stress is very similar in wadsleyite 400 mpa and ringwoodite 350 mpa deformed at 1000 c showing that these minerals exhibit very similar rheological properties under these conditions

sverdrup and nonlinear dynamics of the pacific equatorial currents abstract the sverdrup circulation in the tropical pacific is constructed from satellite scatterometer winds compared with measured ocean currents and diagnosed in an ocean gcm previous depictions of the sverdrup circulation near the equator have shown only weak vertically integrated flows here it is shown that the actual transports are not weak this discrepancy could be due either to inaccuracies in the wind forcing or to sverdrup dynamics being too simple in this region scatterometer winds show a strip of positive curl along the sst front north of the equator in the eastern pacific that is due to wind speed changes induced by the front including that additional element of curl forcing greatly improves the realism of the sverdrup representation but the magnitudes of the equatorial transport are still too small by a factor of about 2 although the nonlinear advective and friction terms are small in the model momentum balance they are o 1 in the vorticity balance especially because their meridi

three dimensional topographic and bathymetric effects on magnetotelluric responses in jeju island korea summary magnetotelluric mt surveys have been conducted to investigate the volcanic structure in jeju island in the south sea of korea the island is oval in shape 31 km wide and 73 km long with a peak elevation of 1950 m at mt halla located in the centre of the island mt data were obtained in a wide range of frequencies in a mid mountain region and may be affected by distortion of electric fields due to topographic and bathymetric effects the purpose of this paper is to investigate the topographic and bathymetric effects on mt data for a four layered model having the topographic and bathymetric undulation of jeju island using an edge finite element method the model effectively reproduces a general feature of mt sounding curves observed on the island the topographic effect appears only at high frequencies whereas the sea effect causes a split of apparent resistivity curves in different polarizations at low frequencies since the island has a gentle slope of less than 10 except in the close vicinity of mt halla it has a similar effect of a change in thickness in the top layer in contrast the sea effect can be observed as quasi 2 d rather than 3 d along the major axis of the island and generates a parallel shift of the log apparent resistivity curve at low frequencies

theory of induction sonde in dipping beds the analysis necessary for the computation of the response of an induction sonde in dipping beds is developed the boundary value problem solved is for a bed of uniform thickness surrounded by two infinitely thick shoulder beds the source is a magnetic dipole oriented in an arbitrary direction and located in any of the three media the resulting electromagnetic fields in all three media are obtained from these fields induction logs are calculated for a focused induction sonde 6ff40 passing through a dipping bed under the assumptions of negligible borehole effect and no invasion the analysis is also used to obtain correction charts for dipping beds

sound velocities in olivine at earth mantle pressures the independent elastic constants of an upper mantle mineral san carlos olivine mg1 8fe0 2 sio4 were measured from 0 to 12 5 gigapascals evidence is offered in support of the proposition that the explicit temperature dependence of the bulk modulus is small over the range of temperatures and pressures thought to prevail above the 400 kilometer discontinuity and thus the data can be extrapolated to estimate the properties of olivine under mantle conditions at a depth of 400 kilometers in the absence of high temperature data at high pressures estimates are made of the properties of olivine under mantle conditions to a depth of 400 kilometers in contrast with low pressure laboratory data the predicted covariance of shear and compressional velocities as a function of temperature nearly matches the seismically estimated value for the lower mantle

3 d finite element analysis of induction logging in a dipping formation mark electromagnetic induction emi by a magnetic dipole located above a dipping interface is of relevance to the petroleum well logging industry the problem is fully three dimensional 3 d when formulated as above but reduces to an analytically tractable one dimensional 1 d problem when cast as a small tilted coil above a horizontal interface the two problems are related lay a simple coordinate rotation an examination of the induced eddy currents and the electric charge accumulation at the interface help to explain the inductive and polarization effects commonly observed in induction logs from dipping geological formations the equivalence between the 1 d and 3 d formulations of the problem enables the validation of a previously published finite element solver for 3 d controlled source emi

a zonal momentum balance on density layers for the central and eastern equatorial pacific abstract brown et al analyzed the kinematics of flow in the equatorial pacific ocean along time varying isopycnals in a three dimensional eddy permitting model here the dynamics of these flows is explored in the same model via the zonal momentum equation zme previous work has shown that the dominant terms of the zme on and near the equator are the pressure gradient wind stress and coriolis term in one model study the nonlinear and friction terms were significant but negated each other in this study with a higher resolution model and more realistic friction scheme it is shown that the nonlinear term is important along and north of the equator while the explicit friction term is negligible the part of the nonlinear term derived from high frequency eddy flows acts like a friction on the equatorial undercurrent while the remaining part of the nonlinear term from smooth flows enhances it in density coordinates meridional tropical cells lie on either side of the equator in the first half of t