| Number 10 | Fall, 1996 |
This is the tenth annual issue of the newsletter of SEDI, an IUGG Union Committee to Study the Earth's Deep Interior. Requests for additional copies of this issue, or for copies of the earlier issues, should be addressed to David Loper, Geophysical Fluid Dynamics Institute, Florida State University, Tallahassee, Florida 32306-3017, U.S.A, faxed to (904) 644-8972 or emailed to loper@gfdi.fsu.edu. Items for the next issue or notifications of change of address should be sent to the same address.
Special thanks are due to Frank and Joy Stacey for their efforts, above and beyond the call of duty, on behalf on their SEDI and AGU colleagues and accompanying persons, in organizing a scientifically successful symposium and an exemplary social program.
Four theoretical contributions, involving first principle studies and molecular dynamics calculations demonstrated great progress in the prediction of equation of state and phase stability of iron under the extreme pressure and temperature conditions of the Earth's core. M. Matsui (Kyushu U.) showed that densities and bulk moduli for the three candidate phases of the inner core hcp, fcc, and bcc are very similar but that the shear moduli are substantially different. D. M. Sherman (U. Bristol) calculate d the stabilities and equations of state of iron compounds with oxygen, sulphur, silicon, and carbon. In contrast to Fe-FeO compounds Fe3S is stable at core conditions, and Fe5S would match the density of the inner core. His calculated elastic propertie s of pure fcc, bcc, and hcp iron are quite different from those of the inner core, suggesting the presence of a considerable amount of a light elements or elements. R. Cohen (Carnegie Inst. of Washington) and L. Stixrude (Georgia Inst. Tech.) presented r esults of first-principles calculations for crystalline and liquid iron at core conditions. They find bcc iron to be unstable at inner core pressures and predicts elastic anisotropy for hcp iron that agrees well with the seismically observed anisotropy f or the inner core. Molecular dynamics calculations by A. B. Belonoshko and L. S. Dubrovinsky (Inst. Earth Sci., Uppsala U.) show that the experimentally determined equation of state of iron can be well reproduced, but his estimated melting temperatures a re much higher than those obtained from static melting experiments. F. D. Stacey (U. Queensland) pointed out complications in theoretical calculations related to liquid iron and the core. Based on a comparison of laboratory data on the bulk modulus and observed values for the core he argued that similar to solid iron, liquid iron must undergo phase transitions at high pressure that should be considered in the calculation of phase boundaries.
Four papers on high pressure experiments related to the melting curve of iron provided new explanations for the large discrepancies between the melting curves measured in the diamond cell and temperature measurements during shock experiments. R. Boehler (Max-Planck-Inst. Mainz) showed, on the basis of new data on the melting curves of several alkali halides measured in the laser-heated diamond cell up to 1 Mbar, that shock Hugoniot temperatures rise much faster with pressure than the melting temperature s and that shock temperatures for the solid overshoot the melting curves. For iron, he argued that there is no clear indication where melting occurs in shock experiments. This was supported by K. G. Holland and T. J. Ahrens (CalTech) who, on the basis o f new thermal diffusivity measurements during shock and by reanalyzing previous shock data, reported the disappearance of a previously reported kink in the P-T data at 2.4 Mbar. Their newly estimated Hugoniot crosses Boehler's melting curve at 2 Mbar and the temperatures are in excellent agreement with the thermodynamic estimates by Brown and McQueen. These new findings led O. L. Anderson (U. California, Los Angeles) and A. G. Duba (Inst. de Phys. de Globe, Paris) to correct their views presented at the meeting where they argued for the need of an additional triple point near 2 Mbar based on the previously reported shock temperatures. The statically measured melting temperatures below one Mbar from three different laboratories got further support from new measurements by H. K. Mao, G. Y. Shen, and R. J. Hemley (Geophysical Lab., Washington) who described refined methods for synchrotron X-ray diffraction that allow the detection of melting.
Two papers were related to planetary accretion. V. Zharkow (Inst. Physics of the Earth, Moscow) presented an accretion model for a Martian core incorporating hydrogen and sulphur and concluded that Mars does not have an inner solid core. Based on an ac cretion model for the Earth under reduced conditions, K. Lodders (St. Louis U.) argued that the alkali element contents of enstatite chondrites may be representative for the core.
Contributed by R. Boehler (Mainz).
The next paper on seismic shear wave dispersion by B.-h. Tan, I. Jackson, and J. D. Fitz Gerald (Australian National U.) presented results of shear modulus and attenuation versus temperature and seismic frequencies, ranging from 1 to 100 s periods on oli vine. The synthetic polycrystals were carefully prepared from crushed and cleaned San Carlos olivine hot pressed to a porosity of less than 1%. At high temperatures, both the shear modulus and Q are significantly different from ultrasonic data, and the question was raised during the discussion whether ultrasonic and other high frequency data are applicable to geophysics. On the other hand, attempts to relate and model dispersion effects over the entire frequency range from ultrasonic to seismic freque ncies would be useful.
R. Knoche (U. Bayreuth), S. L. Webb (Australian National U.) and D.C. Rubie (U. Bayreuth) next presented results of direct determination of sound velocities in olivine up to 12 GPa and 1800 K in the multianvil apparatus using the ultrasonic phase compari son buffer rod technique. P and S transducers were mounted on two of the opposing WC anvils and the low porosity polycrystalline sample was contacted by platinum buffer rods. The results agree well with the data of Duffy et al. and model and sound veloci ties for olivine agree well with observations for the upper mantle.
T. Gasparik (SUNY, Stony Brook) presented a wealth of complex new phase diagrams in the NCMAS system to pressures of 22 GPa and temperatures upper to the melting point and derived a set of parameters that fit the measured phase relations. He found a new sodium magnesium silicate.
J.D. Fitz Gerald, J.M.G. Shelley, and S.E. Kesson (Australian National U.) presented results for pyrolite composition glass heated to high temperatures and pressures of 70 and 130 GPa. Temperatures were not measured, but based on visual observations the authors suspect that temperature was high enough to drive reactions or disproportionation if such were favorable. Samples were recovered and examined by TEM. They found only the three phases magnesium rich perovskite (mp), calcium rich perovskite (cp), a nd magnesiowustite (mw). Partitioning of iron between mpv and mw followed a KD = 0.25 and showed no pressure dependence. No evidence for disproportionation or new phases was found. Na and Al partitioned into mw and Al was also found in mp. Densities for the assemblage after thermal effects are estimated agree well with seismic profiles and suggest chemical homogeneity or the Earth with pyrolite upper and lower mantles. They also suggested that penetrating slabs into the lower mantle would be denser mos tly by their cooler temperatures, but even on warming would maintain a slight chemical buoyancy by a density contrast of 0.6% which would facilitate plume formation at the core mantle boundary. In the discussion I. Jackson also stated that pyrolite works for lower mantle P and S wave velocities.
I. Suzuki and M. Sakai (Okoyama U.) presented compressional and shear moduli for polycrystalline modified spinel using the resonant sphere technique (RST). The sample was synthesized at 14 GPa and 1400K and a 2.2 m sphere was fabricated. Ambient values of K = 168 and G = 106 GPa were obtained. Implications for the earth depend on thermal assumptions.
J. Kung (Australian National U.), S.M. Rigden, and R.C. Liebermann (SUNY, Stony Brook) presented ultrasonic data on elasticity of ScAlO3 perovskite as an analogue for MgSiO3 perovskite in order to estimate pressure derivatives of elastic constants. They obtained K = 4.0 and G =1.85.
D. Yamazaki et al (U. Tokyo) presented the first studies of grain growth kinetics in MgSiO3 + MgO. This is very important for understanding rheology of the lower mantle. They converted forsterite to perovskite plus periclase in the multianvil apparatus , which produced a very fine-grained aggregate. They then followed the coarsening as a function of temperature and time at 25 GPa for times up to 30 hours and temperatures up to 1573 K. They found the parameters for the rate equation Dn - D0n = Ct where D is the grain diameter, t is time, and C = C0 exp ( - QA/RT). The values Q = 321 kJ/mole and n = 10.6 for MgSiO3, and 247 kJ/mole and n = 10.8 for MgO were obtained. The high exponent values imply very small growth rates, so that in a million years gr ains would only be 10 m and after a billion years they would still be less than 100 m large. In the discussion session R. Cohen and D. Loper asked why n is so large, whereas in many other systems it is usually about 3. I. Jackson suggested that it may be due to the two phase composition, and that in many cases the presence of a second phase can inhibit grain growth relative to a monophase aggregate. R. Boehler also addressed the problem of doing the growth measurements so close to the stability bound ary for perovskite and R. Cohen pointed out that a factor exp(- DG/RT) may be important near the phase boundary. Experiments at higher pressures should be performed to understand better this important issue.
D. Boness (Seattle U.) presented a summary of ideas about thermal and electrical conductivity in the lower mantle and their importance for understanding Earth dynamics. The issue is complicated because even if the properties of single phases were known, the texture of the rock is crucial to understand the net conductivities due to the problem of percolation paths.
R. Cohen (Carnegie Inst. Washington) and L. Stixrude (Georgia Inst. Tech.) presented results using first-principles methods based on the density functional theory (DFT). They discussed the phase transition in stishovite SiO2 to the CaCl2 structure which was verified last year by Kingma et al. The computations were done using the LAPW method which is a highly accurate method for solving the DFT equations, and the transition was found using so-called frozen-phonon calculations, where the nuclei are displa ced and the lattice is strained and total energies are computed laboriously as a function of strain and displacements. New results were presented for CaSiO3 perovskite using the newly developed LAPW linear response method which allows for direct computat ion of the dynamical matrix. In contrast to much previous theoretical and experimental work which showed CaSiO3 to be cubic, Stixrude and Cohen find it to be distorted at all pressures, with a transition to cubic at about 2000 K. The predicted distortio n is small enough to be impossible to observe in previous experiments but cold be important elastically if a transition occurs in the lower mantle. Cohen also presented MD results using the VIB model showing a melting slope for MgO three times greater th an found by Zerr and Boehler and suggested that there must be a problem with the experimental measurement since MgO is well understood theoretically and the theoretical DHm and DVm are reasonable and agree with earlier estimates and other materials. If t he experimental melting curve is correct, molten MgO must have an exotic electronic structure compared with crystalline MgO for which the theory gives good agreement with experiments and has proved predictive.
D. Sherman (U. Bristol) showed LAPW results for mw and discussed the NiAs transition at 135 GPa and the possibility of breakdown of mw to two phases. He performed computations on (Fe0.25Mg0.75)O of the equation of state and found it very close to an ide al mixture of FeO and MgO. He found a small non-ideal DVmix which he believes will stabilize mw. He discussed the gradual high-spin low-spin transition studied previously by Isaak et al. (1993). He discussed radiative transport using a localized pictur e and based on that found mw to be transparent to radiative thermal radiation. In the question period R. Boehler pointed out that mw is heated just fine with a CO2 laser and R. Cohen asked whether he had looked at the density of states of his actual comp utation, rather than the local model, so see whether it would be transparent or not.
L. S. Dubrovinsky and A. B. Belonoshko Uppsala U.) showed results for MD simulations for melting of MgSiO3 and MgO. They get agreement with R. Boehler for MgSiO3 and get a melting curve between that of Cohen and the experimental results of Zerr and Boeh ler. He also presented results for NaCl which show a higher melting curve than obtained by R. Boehler. Using his melting results he computed the melting eutectic for MgSiO3 + MgO at 5000 K and X = 0.55.
There were also a number of posters presented and discussion was lively. It was a fruitful and exciting session. Both theory and experimental techniques are being used together to help unravel the deep Earth. Progress on understanding the constituents of the deep Earth is advancing and quantities important for interpreting seismic observations and those needed for understanding rheology and dynamics of the Earth are being predicted and measured.
Contributed by Ronald Cohen (Geophysical Laboratory, Carnegie Institution of Washington)
J. Merriam (EOPG), Strasbourg) has shown the importance of the ocean loading corrections before interpretation of tidal data from superconducting gravimeters. He showed that the sensitivity is indeed about 5 nanogal/mm (ocean load/mean tidal height). The ocean tide maps, even from recent hydrodynamical and/or satellite altimetry ocean models, are not accurate enough. He proposes to correct for the ocean loading inside the tidal band by characterizing the dispersion assuming that the dynamic of the oc ean tide which produces it, is nearly linear. He showed that the FCN parameters are still correlated one another (real part of the resonance strength to the FCN-frequency; imaginary part to the quality factor). The reasons could be that the ocean loadin g are not correctly done because we are at the limit of the dispersion curve error bars, or that atmospheric loading had not be taken into account.
J. Hinderer et al (EOPG, Strasbourg) addressed also the question of the determination of the FCN parameters but rather taking a new approach based on a general non-linear estimation involving probability (bayesian inversion) and showed that the most prob able value of 1/Q is lower than what you get from the mean of others methods. If the ocean loading is not correct, there is a strong probability that you evaluate too low Q-values. In the second part of his talk, he showed that there is sufficient energ y in the atmospheric noise level around the FCN period, to excite that mode. In a third part, he reviewed the different possibilities of explaining the damping of the FCN and the change of the FCN period from its PREM value (460 days in inertial space) a nd its observed value (about 30 days less). The fact that the fluid is not a Poincare fluid might be important (10 days effect), but the most important effect is the increase of the core flattening of about 5%. Core-mantle gravitational coupling which f orbid any large relative motion must also be involved.
V. Dehant and P. Defraigne (Royal Observatory of Belgium) presented results from the computation of new nutations. They started from presenting the residuals between the observed nutations and the adopted ones by the IAU in 1980. They modified the theor y for an ellipsoidal rotating Earth with an elastic inner core, a liquid outer core and an elastic mantle by incorporating corrections for (1) mantle inelasticity, (2) ocean, (3) the FICN (Free Inner Core Nutation) (4) the effect of a new precession const ant on the TOM (Tilt-Over-Mode), and (5) the effects of increasing the core equatorial radius by 500 meters (corresponding to an increase of the core flattening of about 5%). There were still some unexplained differences on the prograde semi-annual nutat ion of which the suspected origin was the existence of a difference between the global Earth dynamical flattening associated to the hydrostatic equilibrium applied on the PREM densities and the one derived from the precession constant. Violation of hydro static equilibrium for the initial state of the Earth had then been considered by modeling mantle convection in a steady state Earth in which the mass heterogeneities are where tomography is giving them. The model is constrained for giving the right obse rved geoid, the right global Earth dynamical flattening and the right increase of the core flattening. The boundary displacements (at the ICB (Inner Core - Outer Core Boundary), CMB (Core-Mantle Boundary), 400 km depth, 670 km depth (phase transition), m antle-lithosphere surface) are computed and incorporated in the initial state of the Earth. New nutations can be computed. The resonance at the FCN is right on the observed value. The new numerical values are very close to the observed ones (at the lev el of 0.03 mas) except for the prograde annual, (0.08 mas) expected to be from the diurnal thermal effect of the atmosphere, and on the 18.6 year nutations, of which the observed amplitudes will be improved when a whole period would be observed by VLBI.
K. Lambeck (Australian National U.) has treated observations of sea-level changes since the time of the last deglaciation. He compared them with a model incorporating modeling of the ice sheet and of the rebound. The parameters involved are the viscosi ties in a number of layers as well as the lithosphere thickness. The optimum model from his comparison with the observations favours a 70 km effective thickness of the lithosphere and a strong contrast in the viscosity between the lower mantle (1022 Pa s) and the upper mantle (4-5 1020 Pa s).
P. Johnston (Australian National U.) examined the acceleration of the longitude of the orbit modes of different low-orbiting satellite like Lageos and Starlette. The idea is that when the gravity changes, there is an acceleration of the mode. He deduc es the time variation in the degree 2 part of the zonal Earth's gravitational potential. He also tried a solution for fitting this coefficient directly instead of the mode acceleration but showed that for a viscosity determination it has no impact. He d educes an average mantle viscosity of 4-10 1021 Pa s.
W. R. Peltier (U. Toronto) presented theoretical and numerical results of inferring the mantle viscosity from inversion of observations pertaining to glacial rebound. This problem is non linear and neither the viscosity nor the history of glaciation-deg laciation are well constrained a priori. He presented a solution to this delicate problem using an iteration procedure. This led him to stable estimations of the parameters. His viscosity profile is compared with others found in the literature and deriv ed from geoid matching. These profiles if scaled one to the other agree very well.
Contributed by Veronique Dehant (Observatory Royal de Belgique)
This presentation set the context for the remaining talks in the session, which were mainly concerned with numerical models of various convection related topics, with a strong focus on mantle plumes. G. Davies (Australian National U.) described n umerical experiments in cylindrical geometry on the generation and rise of thermal plumes, showing the applicability of a local Rayleigh number criterion in predicting the timing, size, and spacing of new plume heads. He illustrated the effects of time d ependence on heat flow and thermal structure of a long-lived plume, as secondary plumes are advected into the stable central plume. He also showed the effect on plume structure of a viscosity contrast and phase transformation at the 670 km level. S. Kin g (Purdue U.) also presented numerical experiments on plumes; he examined the influence of temperature-dependent viscosity on the shape of geoid and topography swells, and asked whether the shape of the swell permits us to constrain the morphology of the plume. Although plume morphology is strongly affected by temperature-dependent viscosity, the effect on the shape of the swell is relatively subtle.
A. Leitch (Australian National U.) presented a paper with M. Wells and G. Davies in which they estimated melting rates in a plume head beneath rifting lithosphere. The context for this study is to provide an explanation for the zone of thickened oceanic crust formed off the east coast of the US during the opening of the Atlantic. The required amount of excess melting can be produced by this kind of plume model but it is less easy to explain why the resulting zone of thickened crust is so narrow (or limited in time). B. Steinberger (Harvard U.), in a paper with R.J. O'Connell, considered the implications for plume conduits in a convecting mantle. They showed by means of a simplified dynamical model, how the surface distribution of mantle plumes might be expected to evolve under the influence of the surface plate motion and a reasonable return flow field. Plumes are advected, but extinguished if the slope of the conduit becomes too steep. This model is able to explain important features of the observed plume distribution, such a the apparent clustering of hotspots near ridges and their relative absence near subduction zones.
The two remaining talks were concerned with transient problems in mantle convection systems. S. Farrell (Monash U.) presented a paper, with G. Houseman, in which they investigated the effect on a convecting layer of an abruptly increased basal he at flow. The context for this study is the possibility of a two layered mantle in which sudden overturn of the lower layer rapidly heats the base of the upper layer. They showed that the timescale for propagation of this event to the surface can be expl ained by thermal diffusion into the lower boundary and increased upward flow rate of the thickened boundary layer. In the final talk, S. Butler (U. Toronto), with W. R. Peltier, modelled the problem of a potentially unstable cold layer at the 660 km endo thermic phase transition. Using a linearised stability analysis they investigated the influence of different parameters on the possibility of an avalanche instability in which this layer undergoes the phase transition and sinks catastrophically into the lower mantle. Phase transition kinetics play an important role in suppressing the instability.
I. Kumagai and K. Kurita (U. Tokyo) presented a poster describing tank experiments in which buoyant plumes are released and pass upwards through an interface at which density and viscosity decrease. In some experiments the plume head passes strai ght through the interface leaving the conduit behind. A second plume then forms at the interface, after a delay, thereby suggesting an explanation for "double-flood-basalt" events. T. Yanagisawa and Y. Hamano (U. Tokyo) also presented a poster, in which they described experiments designed to investigate the insulating thermal effect of a continent on the convecting mantle. They used a heterogeneous surface condition, with an insulating part representing a continent, and found that upwelling follows the thermal insulator when it is moved, although the timescale for the mantle to adjust is about four times the circulation time. Three other posters submitted to this session were not actually presented.
Contributed by Greg Houseman (Monash U.).
Anisotropy of the Inner Core: D. J. Stevenson (Caltech) addressed possible origins for inner-core anisotropy, concluding progressive growth of preferentially aligned grains can explain the observed anisotropy of the inner core. After many generations o f crystal growth, driven primarily by surface energy terms, small biases towards crystal alignment can be greatly amplified. Several mechanisms could provide the small strains required to bias the orientation of crystal growth such as, tides, lengthening of day, and deformation of the inner core as a result of mantle convection.
Evidence for Differential Rotation of the Inner Core: X. Song and P. Richards (Lamont-Doherty Earth Obs.) presented seismic observations supporting an inner-core rotation rate which is 1 deg. per year faster than the mantle. This revolutionary result a rises from measurements of systematic variations in the differential travel times of seismic waves which pass through the outer core (PKPbc) and the inner core (PKPdf). Differential waveform picks from a South Sandwich Islands to College Alaska path show a steady increase in PKPbc-PKPdf residuals of about three tenths of a second over the last 28 years. These observations combined with estimates of a 10 deg. difference between the inner cores anisotropy symmetry axis and its rotation axis gives an estima te of a differential inner core to mantle rotation rate of 1 deg. per year.
Review of Seismic Evidence for Ultra-low Velocity Zones Above the Core-mantle Boundary: D. Helmberger (Caltech), E. Garnero (U. C. Santa Cruz), and X. Ding (Caltech) reviewed evidence for a 5 to 50 km thick ultra-low velocity zone (ULVZ), up to 15% slow er than PREM, above the core-mantle boundary beneath the central Pacific and Iceland. The ULVZs are evidenced by anomalous SPdKS arrivals (SKS waves with two compressional legs diffracted around the outer core) and precursors to PcP. An ULVZ is found co ncurrently with a large scale central Pacific high velocity region (seen in SKKS-SKS studies) whereas no ULVZ is detected within the large scale low velocity region surrounding the Pacific. The relatively small ULVZ beneath Iceland is not accompanied by an anomalous high velocity region. Complicated SPdKS waveforms were modeled using dome-like low velocity zones.
Inversion for Lateral Velocity Variations in the D From Sd-SKS Differential Travel Times: B. Y. Kuo and K. Y. Wu (Academia Sinica, Taipei) presented the results of an inversion for D velocity structure using SKS-Sdiff differential traveltimes. Thes e measurements provide good global coverage of the D region. The differential traveltime measurements were corrected for upper-mantle anisotropy and lower mantle heterogeneity. The model consists of a D layer with constant thickness and a constant v ertical velocity profile and is parameterized using spherical harmonics up to degree 8. Both damped and undamped inversions have most of their power in the degree two harmonics. The preferred model was constrained to reproduce Sdiff residuals predicted by the D velocity model of Lay et. al. for India, Siberia, North and Central America. The model has fast circum-Pacific velocities, possibly imaging subducted slabs.
New Observations of PKKP Precursors and Estimates of Short-Wavelength CMB Topography: P. S. Earle and P. M. Shearer (U. C. San Diego) presented new observations of precursory energy arriving before PKKP. Stacks of over 2000 high-passed broadband seismo grams clearly image energy preceding PKKPbc by up to 50 s in the distance range 76 to 100 deg. The amplitude of precursory energy increases with time, with longer higher-amplitude precursor wavetrains observed at shorter distance ranges. Previous studie s explained PKKP precursors by scattering at the CMB. However, the time and distance trends observed in the data could not be explained by models with scattering occurring solely at the CMB, suggesting scattering contributions from the inner core.
On the use of Long-period Scattered Seismic Body-waves to Detect Mantle Plumes: JI Ying and H.-C. Nataf (Lab. de Geologie de l' ENS-Paris) discussed a search for mantle plumes. Long-period energy arriving between the body waves P and PP was back project ed to image possible plumes. Synthetic tests conducted on a velocity model generated from an idealized plume (a vertical cylinder extending through the mantle with a gaussian temperature profile having a maximum of 600 K and half width 125 km) showed sca ttered energy with an amplitude of 5% of the main arrival could be generated. Images produced by back projecting energy recorded on long period seismograms showed evidence for a plume associated with the Hawaiian hotspot. The anomaly is displaced in a di rection consistent with geodynamic predictions. However, the amount of scattered energy is much greater than that predicted by synthetic studies.
Imaging Global Topography on Transition Zone Velocity Discontinuities by Stacking SS Precursors: M. P. Flanagan and P. M. Shearer (U. C. San Diego) presented new maps of topography on the 410- and 660-km velocity discontinuities. Depth estimates were obtained from traveltime measurements of over 10,000 underside shearwave reflections from the 410- and 660-km discontinuities. The measurements were corrected for the effects of surface topography, crustal thickness and uppermost mantle velocity structur e. The new maps, having improved coverage over previous studies, show a depression of the 660-km discontinuity surrounding the Pacific. The 410-km discontinuity is depressed under most of the Pacific and elevated beneath the Southern Indian Ocean. More topography is seen on the 660-km discontinuity than on the 410- km discontinuity. Estimates of transition zone thickness, better constrained than the individual discontinuity depth measurements, appear greatest in regions of active subduction (Philippin es and Tonga).
Ancient Structures in the Mid-Mantle: J. C. Castle (ANU) and K. C. Creager (U. Washington) slant stacked data from several broadband and short-period networks in slowness and azimuth to illuminate reflections and conversions from near source impedance c ontrasts within the mantle near the Izu-Bonin trench. A clear signal from a horizontal reflector at a depth of 680 km is seen. Also imaged was a nearly vertical seismic discontinuity at a depth of 900 km running obliquely to the Izu-Bonin slab, suggesti ng past subduction occurred at a steeper angle.
Waveform Stacks of PKP Precursors: Evidence for Small-Scale Heterogeneity Throughout the Mantle: M. A. H. Hedlin, P. M. Shearer and P. S. Earle (U. C. San Diego) utilized high frequency precursors to PKPdf to study small scale heterogeneities (~10 km) within the mantle. Stacked images of high-passed filtered seismograms from the Global Seismic Network clearly show precursor energy which increases with time and range. The simplest scattering model to fit the observations is one in which fine-scale vel ocity heterogeneity is uniformly distributed throughout the mantle. The data do not support an increase in the concentration of scatters within the D region.
Global Distribution of Large Deep Earthquakes and its Possible Significance: E. A. Okal (Northwestern U.), S. H. Kirby (USGS), E. R. Engdahl (USGS) and W. C. Huang (Northwestern U.) relocated large (Mw > 6.7) deep earthquakes occurring since 1953. The seismicity is bimodal with peaks at depths of 400 and 600 km. The peak at 400 km is found in most subduction zones and the deeper events generally occur within the lowest 50 km of the Wadati-Benioff zone. The largest deep quakes with hypocenters near 6 00 km tend to be isolated from nearby earthquakes and occur near the spatial extremes of deep earthquake seismisity. It is suggested, in the largest deep events, dynamic stress generated from transformational faulting of extremely metastable olivine trig gers earthquakes on all nearby faults, thus, decreasing seismisity in the region.
Toward a Broadband Aspherical Attenuation Model: J. Bhattacharyya, M. Ritzwoller, A. Levshin, (U. Colorado at Boulder) and G. Masters (U. C. San Diego) discussed differences in recently published models of anelastic structure of the upper mantle. They investigated biases in surface- and body-wave measurements used to model anelastic variations. Coupled-mode synthetic seismograms show elastic focusing and defocusing can bias surface wave measurements. These effects can be decreased by incorporating an accurate 3-D elastic model in the anelastic modeling procedure. Also, body-wave measurements are slightly biased by interfering wavefronts resulting from 3-D elastic structure. They presented a preliminary dataset of broadband (80 - 500 s) attenuation measurements made using Rayleigh (R1-R8) and Love (L1-L6) waves from recent large earthquakes (Ms 3 7.0).
Growth Tectonics of the Inner Core Coupled with the Outer Core Dynamics: I. Sumita (U. Tokyo), S. Yoshida (U. Tokyo), M. Kumazawa (Nagoya U.) and Y. Hamamo (U. Tokyo) discussed an inner-core growth tectonic model and its implications for inner core an isotropy. In their model, crystals in the inner core are aligned under the stress field produced by Taylor-column type convection of the outer core. Models of crystal growth by lattice diffusion and grain boundary diffusion both predict a fast P wave ve locity in the north-south direction with the amount of anisotropy decreasing near the surface of the inner core (a result of a shear-stress-free boundary condition and compaction of the partially molten iron). Inner core growth models, which include the effect of compaction, predict transverse anisotropy near the inner-core boundary.
Super Plume Project - New Seismic Networks Towards High Resolution Imaging of Super Plumes in the Pacific and East Asia: D. Suetsugu (IISEE), and the Super Plume Project/Seismology Group presented the goals of a seismology data acquisition and analysis project. To better understand the dynamics of mantle plumes and subducting slabs three new seismic networks have been proposed. The South PAcific broadband seismic NETwork (SPANET), is a permanent network of 15 stations installed on Pacific islands. Da ta from this network will be used to develop models of 3-D velocity and Q structure beneath the Pacific. The Japan-Indonesian Seismic NETwork (JISNET), is a 5 year project consisting of 40 broadband stations installed throughout Indonesia to image the su bducting Indo-Australian plate. The Global Alliance of Regional NETworks (GARNET) project, utilizes existing local, regional, and national short-period seismic networks scattered throughout the globe to develop a massive database for the determination of fine earth structure such as topography on the upper-mantle discontinuities and on the CMB.
Contributed by Paul Earle (IGPP, San Diego).
K. Whaler (U. Edinburg) tried link the velocity maps deduced from secular variation of the geomagnetic field and the 3D result of Glatzmaier. Then, P. Roberts and T. Nakajima (U. California, Los Angeles) reported on their attempt to derive turbulent par ameters (eventually anisotropic) with a direct numerical simulation of buoyant convection in a Cartesian periodic box. They also showed how difficult it is to solve the layer along the tangent cylinder when you try to match the parameters of the Earth's core. Ph. Cardin (Ecole Normale Superieure, Paris) presented the results of an MHD experiment studying the interaction between a vortex of liquid Gallium and a transverse magnetic field. R. Kerswell (U. Bristol) argued that the precession is too energet ic to feed the dynamo! Many posters were presented in a session which didn't really work (AGU organisation, last day of meeting, missing posters, lack of discussion...). That was very disappointing.
Contributed by Phillipe Cardin (Ecole Normale Superieure, Paris).
The first talk by J. L. Le Moul et al was delivered by V. Courtillot (Institut de Physique du Globe). He gave an excellent summary of secular variation data which included the relatively precise data acquired recently from satellites and geomagnetic ob servatories to much less precise information obtained from paleomagneitsm over scales that extend beyond the past 100 million years. Courtillot argued that the paleomagnetic data could not be used to obtain reliable information on the details of the magn etic field above degree 2 (quadrupole field) in spherical harmonic terms. The next talk was by R. Merrill (U. Washington) who presented new analyses supporting Merrill and McFadden's contention that the geodynamo has occupied two fundamental regimes in t he past: a regime in which reversals occur and one in which they do not. M. Kono (U. Tokyo) delivered the third talk and argued that, excluding the large dipole field, it is better to model paleosecular variation with Gauss coefficients treated as zero-m ean random variables rather than using time-averaged field representations. This conclusion is contrary to that of the next talk by C. Johnson and C. Constable (U. C. San Diego), delivered by Constable, in which it was concluded that there is discernible longitudinal variations in the time-averaged paleomagnetic data. The final talk was delivered by C. Brton (AGSO, Canberra) and dealt with paleomagnetic data that show preferred longitudinal transition paths during a reversal. He showed that inclination shallowing in sediments could produce the observation that paths tend to cluster 90 degrees away from the sampling site, but only if the shallowing is very large.
The second half of the session involved poster presentations that significantly overlapped with discussions of numerous topics of SEDI interest. The posters include those of Hanamo and Habara (spherical harmonic analysis of data spanning the past 15,000 years); Yoshida and Hanamo (who argued that there is a correlation of a few broad seismic anomalies in the lower mantle and secular variation observed at the surface); Carlut and Courtillot (who argued that only the dipole and axial quadrupole fields cou ld be discerned in the time-averaged paleomagneitc data); Constable et al. (who analyzed the global magnetic secular variation data over the past 3000 years); Oda and Tsukuba (who presented new polarity transition data from deep-sea sediments from ODP leg 124 in the Celebes and Sulu seas); Tsunakawa and Nohara (who argued that reversal rates appear correlated with plate motions and suggested that cold slabs subducted to the core-mantle boundary were responsible; Shibuya (who compared the scatter of paleom agnetic directions from volcanics to those from sediments and found the later exhibit smaller dispersion on the average); and Hatakeyama et al. (who examined reversals and chemical changes in Archean banded iron formations.)
Because the discussions in the latter part of the session were wide ranging and on numerous topics that were very diverse, no attempt will be made here to report on the majority of the material discussed. An opening 5 minute (unscheduled) talk in the di scussion period was given by M. McElhinny who tactfully argued that far less could be resolved from paleomagnetic data than claimed in some (unspecified ) talks and papers. This led to many disagreements and lively discussions that were still going when this reporter chose to go to dinner.
Contributed by Ronald Merrill (U. Washington).
D. Gubbins and J. Bloxham (Harvard U.) reviewed dynamo theory and the energy sources for the dynamo, and J. Jacobs (U. Wales Aberystwyth) continued with an overview of deep earth structure: what we can infer on the size and properties of the core from tr avel-time observations and seismic modelling. A. Mazaud (CNRS-CEA, France) continued with paleomagnetism, 'the natural magnetic memory of the Earth', and gave a picture of the morphology of the geomagnetic field during polarity transition. K. Whaler rev iewed current work on core motions.
D. Kerridge (BGS Edinburgh) and R. Langel (NASA/Goddard) described survey measurements and derivation of main field models, and new developments in on-line access to observatory data. D. Winch (U. Sydney) described external field variations.
J. Bloxham and J. Neuberg (U. Leeds) reviewed changes in earth rotation, from the rapid variations caused by the atmosphere and the excellent agreement between theory and observation, to the decade variations associated with the core and the physical mec hanisms for core-mantle coupling. Andrew Jackson (U. Leeds) continued into the longer time scale with a description of recent advances in estimates of the day length from ancient eclipses.
Research discussions ranged over similar topics. J. Bloxham described the current state of a large-scale nonlinear dynamo calculation underway at Harvard. R. Holme (U. Edinburgh), speaking on planetary magnetic-field modelling, explained the inversion p rocess by which the external observed field is extrapolated down to the core to make inferrence on the forms of fluid motions. D. Gubbins presented a theory for core motions with diffusion, and highlighted some serious problems with the frozen flux hypot hesis under certain circumstances. S. MacMillan (BGS Edinburgh) gave exciting evidence of a new geomagnetic jerk, and A. Murray (U. Leeds) presented the fruit of her searches in the East India Company archives, a staggering 4,000 "new" observations of de clination from the 18th and 19th centuries.
G. Helffrich (U. Bristol) led the review of core seismology and homed in on the recent conclusions about anisotropy in the inner core. J. Neuberg continued with problems associated with finding CMB topography and/or lower mantle heterogeneity. The Fres nel zones for PcP bounce points overlap, suggesting the large topography derived from tomographic inversions of differential PcP-P travel times are due to noise. M. Kendall discussed the structure of D and presented new results using data from deep ear thquakes in South America recorded on the Canadian National Seismograph Network, which provide broad-band data for detailed analysis of D beneath the Caribbean. In particular, D appears to be anisotropic. An S-wave discontinuity was observed approxi mately 250 to 300km above CMB over most of the study area with approximately a 2.75% velocity contrast. Large amounts of S wave splitting, with SH always leading SV, are observed. Rays which turn above D show the same spliting as SKS and so the anisot ropy seems to be confined to D. Possible explanations are iron inclusions at the base of the mantle, subducted inclusions of cold basaltic material, higher velocity peridotite, or a layer rich in stishovite.
D. Shermann (U. Bristol) described the theoretical basis for studies of iron alloys under high pressure. First-principles density functional calculations were used to predict the equations of state and formation energies of Fe-FeO and Fe-FeS alloys unde r the pressures of the Earth's core. Solid solution between Fe and FeO remains energetically unfavourable up to core pressures. The instabilites are so large that no reasonable entropy term could stabilize an Fe-FeO solid solution at core temperatures. In contrast, the solid solution between Fe and FeS becomes favoured at core pressures as indicated by the formation energy of Fe3S. The presence of a light element like S or O is required to explain the observed density pattern in the core. It follows that the inner core is most likely an Fe-FeS alloy rather than an Fe-FeO alloy. The much lower density of the outer core may indicate the presence of an additional light element. Even if an additional light element is present in the outer core, the Eart h must be enriched in sulphur relative to potassium. The K/S ratio of the Earth must reflect the segregation of the core as an Fe-FeS eutectic during the early differentiation of the Earth.
Contributed by David Gubbins, Steve Gibbons, and Aoife O'Mongain
(U. Leeds).
Sakurai showed some tantalizing images of the slabs in the transition zone under the western Pacific , which agreed well with some of the observations made on the 900 km seismic discontinuity by Niu and Kawakatsu. Bercovici presented a self-consistent m odel based on the shallow-water equation which illustrates a bifurcation caused by the nonlinear coupling between temperature-dependent viscosity and shear heating. Bina presented a model of stress-state of slabs based on metastable phase transitions. T he mantle flushing event was the focus of the works by Nakakuki, Steinbach and Schroeder. In particular, Nakakuki showed the importance played by the thickness of the continental lithosphere in forming large plumes. Iwase and Honda discussed the effects of core-cooling on parameterizing thermal evolution. Yuen presented a model for producing extremely fast plumes from non-Newtonian and temperature-dependent rheology. Ogawa showed how multiple solutions can be developed in thermal-chemical evolutionary models. Kido showed that a second asthenosphere below the 660 km discontinuity is possible under oceans from his genetic algorithm inversion. Wei discussed about the state of stress in plates and Tanimoto presented a boundary layer model for measuring properties of steady-state plumes from tomography. Maruyama discussed regional flushing events in back-arc basins.
There were many lively exchanges between the "gaijin" and the Japanese scientists and students. The workshop concluded with a sumptuous sushi- beer party , which continued on to a karaoke bar in the "shita-machi" Nezu in Tokyo. Abstracts of this worksh op can be accessed over the WEB, http://banzai.msi.umn.edu/japan.html
Contributed by David Yuen (U. Minnesota).
The Symposium started with an invited talk by M. Ritzwoller and J. Resovsky (U. Colorado) on the constraints brought by normal modes on the deep mantle. Ritzwoller presented a US-flavored review of the topic, with emphasis on the need of considering cou pling between modes to determine accurate spectra. The recent occurence of large deep earthquakes, the improvment in station coverage and theoretical treatment, make it possible to retrieve 'structure coefficients' up to degree 10 for some modes. The pr edictions of global tomographic models are good, but they lack short wavelengths. Large heterogeneities in D are not required by these data. Then VanDecar presented tomographic images of the mantle beneath South-America, obtained with his colleagues u sing arrays of portable broadband seismographs. The Nazca slab is seen down to 1400 km. An amazing slow anomaly extends deep beneath the Parana basin. VanDecar insisted on the importance of chemical heterogeneities. Neele and his colleagues cast doubt upon the long-wavelength topography of seismic discontinuities obtained from PP or SS precursors. Using Kirchoff synthetics, he showed that localized slab-induced topography yields spurious long-wavelength large-amplitude deflections after inversion. He proposed a new method to retrieve the correct signal. The transition from seismology to geodynamics was performed by two presentations on mineralogical modeling in a convecting mantle. Vacher and his colleagues presented three seismic profiles derived f or different adiabats. He showed that three separate discontinuities were predicted in cold regions. In the discussion, Estabrook exclaimed that this matched PP precursor observations perfectly. Matas and his colleagues showed a new method to derive mi neralogical compositions and phase transitions in mantle conditions, based on the minimization of the Gibbs energy. They concluded that the 660 km transition would have no effect on plumes rising across it.
There was then a series of presentations on numerical modeling of mantle convection. The Nantes group, with Choblet, Deschamps, Labrosse, Sotin and their colleagues showed their recent results on convection with temperature-dependent viscosity in 2D and 3D, and on scaling laws derived from these, and applied to mantle convection history. Van den Berg discussed the transition between Newtonian and non-Newtonian states, in an extended Boussinesq approximation. The next topic was the behavior of slabs in a convecting mantle. Insergueix and colleagues focused on the effect of slab dip on the thermal structure in the slab and in the mantle, as well as on the influence of surface plate velocities. Two presentations, one by Christensen, the other by Olbertz and colleagues, dealt with the effect of trench migration on the fate of subducted slabs. Christensen showed that if lower-mantle viscosity is high, then a trench roll-back of 2 cm/year is enough to flatten the slab above the 660 km transition. Olbertz observed similar behaviours, but had problems with slab sticking to the over-riding plate. She concluded that a wide variety of slab behavior was to be expected in the present day Earth. Hansen modelled plumes at high Rayleigh numbers and for large vis cosity variations in 2D. He found that the entrainment of surrounding mantle in the plume was very small. We then turned to the core. Majewski discussed the migration of FeS and FeO in the liquid core. Dellar investigated the formation of coherent str uctures in the outer core. Brito and his colleagues presented applications of Joule heating measurements performed in liquid gallium to magnetic dissipation in the core.
The poster session had results on velocity contrasts across Europe from Rayleigh wave Monte Carlo inversion (Lomax and Snieder), on the inversion of P-wave amplitudes and travel times (Klaus and Neele), and more about magneto-dynamic structures in the ou ter core (Dellar). Two beautiful posters were devoted to numerical modeling of mineral properties: molecular dynamics melting of mantle phases (Vocaldo and Price), and ab initio calculation of the seismic velocity discontinuity between forsterite and wad sleyite.
The last session was devoted to D. Schweitzer presented PcP and ScP observations at short distance (9-29 degree) below Europe. Time residuals of up to 2 s were obtained between these two waves. O'Mongain and colleagues looked at PcP at larger distan ces (65-80 degree), recorded on the arrays of western US. Precursors to PcP did not show up clearly. Schimmel and Paulssen presented evidence for ScS precursors at short distance (less than 30 degrees). They interpreted these as reflexions at the top o f D, some 180 km above the CMB. Focusing by undulations is required to explain the observed amplitudes. Engdahl presented work by van der Hilst and his colleagues on tomographic mapping of the D layer. Using a new high-quality data set of P wave pi cks, they inferred heterogeneities of ñ0.6% in D Sylvander and Souriau obtain much larger heterogeneities (up to ñ10%) by inverting P waves diffracted by the core, from the ISC catalog. Emery and her colleagues investigated S diffracted waves, trying to constrain velocity gradients and anisotropy in D by using both SH and SV data. Finally, Kendall and Silver showed examples of an S+ScS phase with a 5 seconds splitting. They find that SH is faster than SV in D by up to 3%. SKS seems unaffected. They proposed an interpretation in terms of slabs residuals.
Overall, this was a very interesting and lively Symposium. The core was poorly represented. It should receive more emphasis next time.
Contributed by Henri-Claude Nataf (Ecole Normale Superieure, Paris)
Mark Boyd (Conoco) chaired the first morning session on seismology. Paul Davis (U. C. Los Angeles) described the results of seismic experiments in the former Soviet Union and elsewhere for anisotropy within the mantle. George Helffrich (U. Bristol) des cribed some new results on core-mantle boundary topography, and Guy Masters (U. C. San Diego) discussed stratification in the core, revisiting the main topic of his PhD thesis (supervised by Jack). Finally, ColinThomson (Queens, Ontario) gave a new devel opment of surface waves in anisotropic media.
John Chamberlain (Phillips Petroleum) chaired the second session. It was pleasant to have some contributions from atmospheric geomagnetists, a field Jack contributed to early in his career. Ian Axford (MPI Munich) reviewed current knowledge about the S olar Corona, Roger Banks described recent results from an MT experiment in the Kenya rift, and David Orr (York U., Ontario) discussed hydromagnetic waves in the magnetosphere. The session concluded with Al Duba (Lawrence Livermore National Lab.) discussi ng conductivity effects of carbon and hydrogen on olivine and Jean-Paul Poirier (Institut de Physique du Globe, Paris) on the cooling of the Earth's core, in which he concluded the inner core is a relatively young feature.
On Tuesday, the first session was chaired by Mike Kendall (U. Leeds). Keith Aldridge (York U.) discussed elliptic instabilities in laboratory experiments on rotating fluids and the earth's core. Doug Smylie (York U.) also discussed core dynamics in the context of a problem Jack worked on early in his career. Lalu Mansinha (Western Ontario) described experiments to test the law of gravity and introduced the interesting concept of gravitational permeability. Kurt Lambeck (Australian National U.) descri bed results for postglacial rebound from new analyses of sea level changes around the UK and western Europe.
Paleomagnetism dominated the next session, chaired by Frank Lowes (U. Newcastle upon Tyne). Ken Creer (U. Edinburgh) gave results from lake sediments covering the last 100,000 years and found intriguing periodicities in the paleosecular variation recor d, while Don Tarling (U. Plymouth) was able to identify Milankowitz cycles in the paleomagnetic record. Ted Evans (U. Alberta) gave a discussion of rock magnetic effects of ultra-fine particles and Wyn Williams (U. Edinburgh), in another rock magnetic ta lk, described the results of numerical simulations of multi-domain grains. John Shaw (U. Liverpool) described a novel approach to thermal demagnetisation using microwave heating, a new development with exciting potential.
The final session was chaired by Rosemary Hutton (U. Edinburgh). Andrew Jackson (U. Leeds) discussed the crustal field and long wavelength anomalies. Jeremy Bloxham (Harvard U.) described an on-going numerical simulation of the geodynamo, and Jean-Loui s LeMoul (Institut de Physique du Globe, Paris) gave an application of wavelet analysis to the geomagnetic record in identifying jerks.
The meeting finished with Kathy Whaler's inaugural lecture at the University. A set of papers is planned for a special issue of Physics of the Earth and Planetary Interiors.
Contributed by David Gubbins (U. Leeds).
A main topic of the meeting was dynamo theory which ranged from basic models to applications to galactic magnetic fields. The Herzenberg dynamo was revisited by Moss, Brandenburg and Soward and a new class of oscillatory solutions was reported. An asym ptotic theory of dynamo waves and their application to the sun was presented by Sokoloff, Kuzanyan and Galitzky. Anvar Shukurov showed a way in which sign changes in the observed magnetic field of the galaxy M 31 could be explained through a non-axisymme tric model. A highlight of the meeting were the new videos of numerical simulations of an Earth-like dynamo which Gary Glatzmaier (Los Alamos National Lab.) presented from his continuing collaboration with Paul Roberts (UCLA). The structures of bifurcat ing dynamo solutions in the case of convecting rotating spherical fluid shells have been studied by Hirsching, Wicht, Ardes, Tilgner and Busse and were presented by the latter author. In a similar spirit dynamos in rotating sphere are approached by the P otsdam group (Fuchs, Rdler, Rheinhardt, Schler) based on forces corresponding to a prescribed axisymmetric velocity field. Helmut Fuchs presented this work. Generation of magnetic fields through the dynamo process is also likely to occur in proto-stel lar disk as Axel Brandenburg demonstrated through his numerical simulations. A central role in this process is played by the Balbus-Hawley instability which represents the instability of the Keplerian rotation law in the presence of a weak magnetic field . Two papers by Primavera, Rdiger and Elstner and by Drecker, Kitchatinov and Rdiger, each presented by the first author, considered the influence of boundary conditions and the role of non-axisymmetric modes in this instability. With the development of liquid sodium flow technology in recent decades it has become feasible to realize homogeneous dynamos in the laboratory. Andreas Tilgner reported on the progress in the construction of such an experiment at the Forschungszentrum Karlsruhe and presente d his numerical simulation of the planned dynamo.
A number of special topics must be investigated to gain a better understanding of the dynamos operating in the Earth and in the Sun. The question whether magnetic buoyancy can drive the solar dynamo was addressed by Thelen. The challenges posed by the observational evidence about the history of the solar cycle were pointed out by Peter Frick who showed evidence for strong oscillations of the solar diameter when the solar cycle was weak and vice versa. The influence of turbulent boundary layers on the dynamics of the Earth's core was addressed by Anufriev and Hejda. The latter subject is of particular importance in understanding various asymptotic states (Ekman state, weak Taylor state, classical Taylor state) of dynamos which were discussed by Ivan Cupal. Mathematical methods dealing with certain singular points in the basic equations were addressed by Petr Svacek. The influence of magnetic fields on convection in mushy layers, such as those believed to exist at the outer boundary of the Earth's inner core, was discussed by Bod'a, Guba and presented by Guba. An important subject of rotating fluid dynamics are Stewartson layers which are surfaces of high shear parallel to the axis of rotation. Rainer Hollerbach showed how these layers are modifi ed and eliminated as the Elsasser number becomes of the order E1/3 where E is the Ekman number.
Another major topic of the meeting was the dynamics of convection in the presence of a prescribed magnetic field. The classical problem of the onset of convection in a rotating sphere with a magnetic field has been extended by Walker and Barenghi in tha t poloidal as well as toroidal axisymmetric fields were considered. Magnetically driven instabilities can occur even when the density is stably stratified. The latter instabilities are influenced by the electromagnetic boundary conditions in dependence on the stratification in the plane layer model, i.e. strongly (slightly) influenced for uniform (non-uniform) stratified layer as was found by Brestensky, Sevcik and Simkanin and presented by the last author. Another paper by the Bratislava group dealt w ith the weakly nonlinear problem of convection in a planar layer with an azimuthal magnetic field, i.e. derived from the above mentioned linear problem by considering the non-linearity from the modified Taylor's constraint. This paper by Brestensky, Reva llo and Sevcovic was presented by the second author. Convection in a compressible fluid permeated by a vertical magnetic field is a topic motivated by observations at the surface of the sun. Paul Matthews explained the rich dynamics arising in this prob lem and illustrated it through computer generated videos. Already in the case of an incompressible electrically conducting fluid novel dynamic features are found when a magnetic field is applied to a convection layer. Examples from the case of convectio n in a layer heated from below with a vertical magnetic field (Busse and Clever) and from the case of convection driven by centrifugal buoyancy in a cylindrical layer (Petry, Busse and Finocchi) were described by Busse.
Even without magnetic fields convection in rotating spheres still provides some new and challenging problems. Topography at the boundary can induce new modes of instability connected with a strong geostrophic shear as has been demonstrated in the paper by Bassom and Soward which was presented by the latter author. The influence of the Prandtl number on turbulent convection in a rotating sphere and the competing roles of polar and equatorial convection were discussed by Tilgner on the basis of his joint work with Busse.
Through the attractive social activities arranged by the organizers of the conference the participants became familiar with the interesting history, customs and activities of the people living in the region of Slovakia where the conference was held.
Abstracts of the papers presented at the meeting can be obtained by writing to the organizers [brestensky@fmph.uniba.sk]. Proceedings of the meeting are scheduled to appear within the next 12 months.
Contributed by J. Brestensky (Comenius U.) and F. H. Busse (U. Bayreuth).
Details of the EUG Meeting can be obtained from EUG 9 Office,
EOPG, 5 rue Renee Descartes, F-67084 Strasbourg Cedex, France; tel: +33
88 41 63 93 or +33 88 45 01 91; fax: +33 88 60 38 87; e-mail: eug@eopg.u-strasbg.fr.
For more information contact either covenor ( at ceperley@uiuc.edu
or cohen@quartz.ciw.edu) or check the web at http://granite.ciw.edu/aspen/aspen.thml.
If you are interested, please send an e-mail to Helmut Harder
at hfh@willi.uni-geophys.gwdg.de and you will receive further circulars
(communication with participants will be only by e-mail)
18-28 August 1997. The Second Circular for this Assembly, which will include scopes for Symposia and Workshops, registration materials, and information on accommodations, will shortly be distributed. by the Local Organizing Committee. To receive further information contact the Secretariat, Geophysical Laboratory, University of Thessaloniki, GR-540 06, Thessaloniki, GREECE (Tel: 30 31 998526; Fax 30 31 998528; E-mail: iaspei@olymp.ccf.auth.gr). You may also consult the IASPEI home page address on the Worl dWideWeb at http://www.csd.net/~bergman/iaspei/ and at a mirror home page shortly to be set up in Greece. Sessions at this assembly either co-sponsored by SEDI or otherwise of interest to the SEDI community include the following.
S8 Mantle Rheology and Geodynamics: Inverse Problems and Geophysical Phenomenology (Co-Sponsored by CMG and SEDI). Conveners: W.R. Peltier (Canada) and K. Lambeck (Australia), B. Hager (USA), R. Sabadini (Italy), S. Singh (UK). [Prof. W. Richard Peltier, Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 1A7, CANADA; Tel: 1 416 978 2938; Fax: 1 416 978 8905; E-mail: peltier@atmosp.physics.utoronto.ca]
S14 Structure and Evolution of the Earth: Geophysical Observations, Laboratory Constraints, and Modeling (Joint with SEDI). Conveners: T. Shankland (USA), A. Chopelas (Germany), S. Honda (Japan), H. Paulssen (The Netherlands), J.-P. Poirier (France), D. K ondopoulou (Greece) [Thomas J. Shankland, Earth & Environmental Sciences Division, MS D443, Los Alamos National Laboratory, Los Alamos, NM 87545, USA; Tel: 1 505 667 4907; E-mail: shankland@lanl.gov; Fax: 1 505 667 8487]
S19 Slab Structure and Dynamics of Deep Subduction. Conveners: R. van der Hilst (USA), M. Gurnis (USA), C. Lithgow- Bertelloni (USA), D. Rubie (Germany), M. Weber (Germany), N. Delibassis (Greece). [Prof. Rob van der Hilst, Department of Earth, Atmospheri c and Planetary Sciences, Massachusetts Institute of Technology, Room 54-514, Cambridge, MA 02139, USA; Tel: 1 617 253 6977; Fax: 1 617 253 9697; E-mail: hilst@mit.edu]
S21 Hotspots and Plumes: Origin, Ascent, and Interaction With the Lithosphere. Conveners: H-C. Nataf (France), U. Achauer (France), U. Christensen (Germany), J. Phipps-Morgan (USA), J. VanDecar (USA), A. Vafidis (Greece). [Dr. Henri-Claude Nataf, Departem ent Terre- Atmosphere-Ocean, Ecole Normale Superieure, 24, rue Lhomond, F- 75231 Paris Cedex 05, FRANCE; Tel: 33 1 44 32 22 04; Fax: 33 1 44 32 22 00; E-mail: nataf@geophy.ens.fr]
W3 Towards Reference Earth Models (Co-Sponsored by SEDI). Conveners: G. Masters (USA), B.L.N. Kennett (Australia), Y. Ricard (France). [Prof. Guy Masters, Institute of Geophysics and Planetary Physics, Scripps Institute of Oceanography, University of Cal ifornia, San Diego, MC A-025, La Jolla, CA 92093, USA; Tel: 1 619 534 4122; E-mail: gmasters@ucsd.edu; Fax: 1 619 534 5332]
1.01 The effect of Composition and Boundary Conditions on the
Earth's Core; J. Lister (U. Cambridge) and D. Loper.
1.02 Geomagnetic Secular Variation and Dynamo Theory; D. Jault (Institut
de Physique du Globe, Paris) and D. R. Fearn.
1.03 Numerical Models of Planetary Convection and the Dynamo; K. Zhang
(U. Exeter) and P. Hejda.
1.09 Reversals and excursions: Records and processes; E. Herrero-Bervera
(U. Hawaii) and P. Camps.
5.11 Global and Regional Modeling of the Geomagnetic Field and its
Variations; A. Jackson (Leeds) and V. Papitashvili.
Full information about the assembly may be found on the web at http://www/irfu.se/iaga_97/html
SEDI 1 Images of the Earth's Deep Interior: J.-P. Montagner (Institut
de Physique du Globe), J. Hinderer (U. Alberta), R. Sabadini (U. Bologna).
SEDI 2 Physical and chemical constitution of the Earth: Ph. Gillet,
R. Boehler (Mainz)
SEDI 3 Cooling, mixing and phase transitions within the Earth: J.-P.
Poirier (Institut de Physique du Globe), U. Christensen (Gottingen)
SEDI 4 Laboratory Modelling and deep Earth dynamics: H.-C. Nataf (Ecole
Normale Superieure, Paris), F. H. Busse (U. Bayreuth)
SEDI 5 Core mantle interactions: J.-L. Le Moul (Institut de Physique
du Globe), D. Gubbins (U. Leeds)
SEDI 6 Geodynamo, theory and observation: D. Jault (Institut de Physique
du Globe), J.-P. Valet (), D. Fearn (U. Glasgow)
SEDI 7 Nature and role of the inner core: A. Souriau (OMP, Toulouse),
H. Wanke
SEDI 8 Deep interiors of terrestrial planets: Ph. Logonne , T. Spohn
(W.-Wilhelms U.).
For further information, please contact http://www.geologie.ens.fr/SEDI or
Philippe CARDIN
program committee
Departement Terre Atmosphere Ocean
Ecole Normale superieure
24 rue Lhomond
75231 Paris cedex 05 FRANCE
tel: 33 1 44 32 22 12
fax: 33 1 44 32 22 00
email: cardin@geophy.ens.fr
Gauthier HULOT
Local organising committee
Departement de Geomagnetisme
Institut de Physique du Globe de Paris
4, place Jussieu
75252 Paris cedex 05, FRANCE
tel: 33 1 44 27 24 12
fax: 33 1 44 27 33 73
email: ghulot@ipgp.jussieu.fr
1. N. Tchouikova, P. Stroev, E. Koryakin, A. Grushinsky, T. Maximova.
The Earth's crust model from seismic and gravity data.
2. N. Tchouikova, S. Kazaryan. The preliminary unequilibrium dynamic
model of the Earth's envelopes.
3. V. Zharov. The models of the atmospheric tides and their connection
to the Earth's rotation.
4. N. Tchouikova, V. Zharov. The nutation for unequilibrium Earth's
model.
5. S. Pasynok. The free oscillations of the Earth's inner core for
unequilibrium Earth.
6. Yu. Barkin. The effects of geophysical processes on the dynamics
of the Earth's internal core.
7. N. Tchouikova, N. Alakhverdova, S. Kazarjan. The theory and the
method to search for the total sources of the global gravity and magnetic
field anomalies.
8. V. Zharov, V. Krajnov. The laser gyroscop: the first experimental
observations of the Earth's rotation.
9. M. Nagoga, A. Loginov. Computer maintenance and other works with
soft-and hardware.
This activity has been supported by the Russian State Foundation on Fundamental Research and by programs "Astronomy" and "Universities of Russia". The results of this activity are to be presented at the annual session of our regular Geodynamics seminar n amed "Sagitov readings - 96", on November 21, 1996 in Sternberg Institute. In addition. we plan to organize in the next year the conference named "The global geodynamics and the Earth"s rotation" in Ufa, Bashkortostan (the finest place in Russia on the B elaya river, South Ural).
A book entitled "The Earth and its Rotation" by V. N. Zharkov, S. M.
Molodensky, A. Brzezinski, E. Groten and P. Varga was published this year
by Herbert Wichmann Verlag, Huthig GmbH, Heidelberg, Germany, ISBN 3-87907-283-3.
Panel members included representatives from disciplinary panels (past and present) as well as individuals who have not previously served on NSF panels, and represented a wide range of subdisciplines involve in SEDI research. The CSEDI panelists also rea d seven proposals that contributed to SEDI program goals that were reviewed by the discipline programs (Geophysics and Geochemistry) to compare the quality of proposals submitted to the CSEDI program with those of the disciplines. Panelists concurred tha t the same quality of proposals were being funded in CSEDI as in the discipline programs.
The results of the competition are summarized in the list of awards. Twelve new awards were made for seven research projects, and two awards were made to support conferences or workshops. The program was already carrying commitments for CSEDI projects submitted in prior years, so funds available for new awards were limited to just under $700K. However, matching funds were contributed from a number of discipline programs (Geophysics, Geochemistry and Petrology, Instruments and Facilities, and Tectonics ) for several of the new CSEDI awards, which enabled us to fund more new starts than expected. The total expenditure for CSEDI proposals in Fiscal Year 1996 was approximately $1.2M, which includes funds committed in prior years as well as matching funds from other EAR programs.
Fiscal Year 1997: The National Science Foundation will hold a
second CSEDI "Special Emphasis" competition in fiscal year 1997. The details
of the program can be found in the announcement published a year ago for
fiscal year 1996. The publication number is NSF 95-155. Those interested
in submitting CSEDI proposals in this submission cycle should note that
the deadline for submission is January 20, 1997.
Contributed by Brian Kennett, Australian National University.
The first item of business was a report by Philippe Cardin of plans for the SEDI 1998 Symposium, "A Journey to the Center of the Earth" to be held in Tours, France (see report above). There followed announcements of a number of upcoming meetings of inte rest to SEDI; see reports above. The next item of business was the question of a logo for SEDI. A committee consisting of D. Loper and O. Anderson was charged with developing a logo and presenting it to the membership for approval (see following item). There next was some discussion of SEDI sponsorship of meetings. The points were made that (1) such action provides visibility for SEDI and (2) sponsorship does not imply financial assistance. There was some discussion of the competition between SEDI Sy mposia and the newly established Gordon Conference. It was agreed that Kurt lambeck would write Mike Gurnis, the convenor of the 1998 Gordon conference, regarding this matter. The last item of business was a report by Brian Kennett of the status of the Doornbos Prize.
Logo. An ad hoc committee consisting of Orson Anderson and Dave Loper have developed a candidate logo for possible adoption by SEDI. SEDI members, particularly those on the executive committee, are invited to send their comments regard ing this proposed logo to Dave Loper. Also, alternative possibilities are solicited. So those of you with an artistic bent and a good computer drawing package have a go at it.
Email server. This is to remind you that a SEDI email server exists. At present it contains the names of roughly 80% of the approximately 750 SEDI members. Anyone registered can distribute a message to the other 600 by sending it to s edi-mail@gfdi.fsu.edu. anyone not registered can become so by sending a two-line message "subscribe, quit" to sedi-mail-request@gfdi.fsu.edu.
Website. A website has been recently established for SEDI.
This may be found at http://gfdi.fsu.edu/~sedi/. In particular, all the
past issues of the DEEP EARTH DIALOG can be found there. Comments on possible
improvement of this site are encouraged; send them to the secretary.