|Number 3||November 21, 1989|
This is the third 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 Flui d Dynamics Institute, Florida State University,
Tallahassee, Florida 32306-3017, U.S.A. Also news item for the next issue
or notifications of change of address should be sent to the same address.
In addition to the regularly scheduled scientific sessions, SEDI sponsored a special Symposium on Saturday afternoon, 29 July. The symposium consisted of four invited lectures: Some Problems of Physics of the Earth's Interior by V. N. Zharkov (Institute for Physics of the Earth, Moscow, U.S.S.R.), Electrical Conductivity of the Deep Mantle by J. P. Poirier (Institut de Physique du Globe, Paris), Seismic Resolution at the Core Mantle Boundary by D. Doornbos (University of Oslo, Norway) and Dynamic Crysta llization and the Development of Compositional Convection C. Jaupart (Institut de Physique du Globe, Paris). It was the consensus of those in attendance that this was the best session of the Exeter meeting; its success was due in large part to the effort s of its convenor, J.-L. Le Mouël . Noteworthy are the experimental results of J. P. Poirier indicating that the electrical conductivity of the lower mantle is much larger than the extremely low values reported by Jeanloz's group at Berkeley and the obse rvational results reported by D. Doornbos that the core-mantle boundary itself must be fairly smooth; the source of the seismically inferred roughness must lie in the lowermost mantle.
A quadrennial report of activities related to IAGA working group I-2, Theory of Planetary Magnetic Fields and Geomagnetic Secular Variation, has been prepared by D. Loper. Anyone wishing a copy of this report should contact him at the address listed pre viously.
The meeting began with brief oral reports of (a) the first SEDI symposium at Blanes in June, 1988, by E. R. Benton, (b) the Dynamo Workshop held in Liblice, Czechoslovakia, in July, 1988, by I. Cupal, (c) the second SEDI symposium to be held in Santa Fe, New Mexico in August, 1990, (d) the Western Pacific Geophysics Meeting to be held in Japan in August, 1990 by T. Yukutake, (e) a SEDI workshop to be held at the European Geophysical Society Meeting in Copenhagen in April, 1990, by D. Doornbos.
There then followed reports of the activities of several of the established national SEDI groups including Canada, Japan, UK and USA. These activities are reported on separately in later sections of this newsletter. Scientists from several countries, i ncluding France, India and USSR, expressed their intention to establish additional national SEDI groups.
The present officers of SEDI (E. R. Benton, Chairman; D. Doornbos, Vice-Chairman; D. Loper, Secretary) are serving four-year terms which expire at the time of the Vienna General Assembly in 1991. It was agreed that E. R. Benton should select a Nominatin g Committee from among the current members of the SEDI Executive Committee. This Nominating Committee will be charged with nominating new officers to serve from 1991 to 1995. These new officers will be elected at a SEDI business meeting at the Vienna Ge neral Assembly.
Next those attending the meeting heard brief reports on a number of projects of interest to SEDI participants, including the following. (a) ISOP (D. Doornbos): a progress report appears later in this issue. (b) INTERMAGNET (A. W. Green): a progress re port appears later in this issue. (c) the Dynamic Global Magnetic Environment (R. van der Voo & J. Hermance): A workshop on this topic is being planned with the sponsorship of the U.S. Geodynamics Committee. It will concentrate on the use of geomagnetic data. (d) Consortium on Array Magnetometers (J. Hermance): A consortium of not-for-profit research institutions is preparing a proposal to NSF for 100 flux-gate magnetometers. (e) MFE/Magnolia & Geomagnetic observing system on EOS (R. Langel & J.-L. Le Mouël ). (f) The Use of Submarine Cables (T. Yukutake): Efforts centered in Japan are underway to make use of under-sea telephone cables in the Pacific area for electromagnetic measurements. (gamma) Hefest Project (M. S. Zhdanov): This is a project jo int between the Soviets and the Italians to do deep electromagnetic sounding (to 100 km depth) using a MHD power supply located in Italy. (h) Paleointensities (R. Coe): This is an attempt by a group of paleomagneticians to determine accurate paleointensi ties over the past 100 myr or so using lava flows.
As the final item of business, it was moved and seconded that the chairman of SEDI petition the president of IUGG to allow SEDI to have the opportunity to propose Union Symposia for IUGG General Assemblies. After a brief discussion, the motion was appro ved.
The symposium led off with a talk by S. Karato (Minnesota) on the relationship of seismic velocity inhomogeneity and its expected effect on rheology. Duffy, Tyburczy, and Ahrens (Caltech) discussed recent studies of the stability of hydrous minerals an d the implication for subduction of water. A major number of papers dealing with subducting plate penetration into the lower mantle was presented by Jordan (MIT), Fischer (Lamont) and Creager (Seattle). Gaherty and Lay (Michigan) reported a study of S, ScS, sS and sScS wave forms from earthquakes in slabs which penetrated the D" layer. They, Schwartz (Santa Cruz) and Beck (Livermore) are attempting to separate slab effects from D" shear wave anomalies. The structure of D" was also discussed in papers given by Doornbos and Hilton (Oslo) and Wysession and Okal (Evanston). Sugi (Tokyo), Kikuchi (Yokohama), Fukao (Nagoya) and Suzuki (Sapporo) reported on mechanical models of the subducting slab based on earthquake mechanisms. New approaches to applicati on of long period surface waves were presented by Romanowicz (Paris) and Tanimoto (Caltech) who are inverting these data for spatial attenuation and density variations, respectively. SV diffracted waves and the S-wave structure of the lower mantle were d iscussed in papers by Vinnik (Moscow) and Haddon (Ottawa).
Mantle viscosity and post-glacial rebound were discussed in papers from the Toronto group (Peltier, Solheim and Mitrovica). Models which attempted to explain mantle-wide convection and allow a chemically stratified mantle were presented by Silver (Carne gie) and Olson (Baltimore).
The symposium ended with some reports of analog laboratory experiments on boundary stability (Kincaid, Giannandrea) and a new look at the energy budget of the core and core-mantle boundary by Olson. He concluded, in contrast to previous results, that pa tterns of core convection are not driven by mantle convection and compositional buoyancy dominates over thermal buoyancy everywhere in the outer core.
The workshop was deemed necessary because of a recent spate of quite conflicting reports on the temperature of the liquidus of iron at high pressure, and because there has been no forum at national meetings for the various authors to discuss the sources of these discrepancies. The workshop was exciting as well as illuminating. The protagonists did not waver in their certainty, but they did present in detail all the auxiliary and associated experiments and calculations which had not been published befor e. This allowed the audience to appreciate the reason for their certainty.
After the workshop the question still remains: is the liquidus temperature - at high pressure - the larger value found by J. Bass, T. Ahrens, R. Jeanloz and A. Williams, or is it lower as found by M. Brown and R. McQueen, or is it still lower as found by R. Böhler? All of these scientists have very good track records, and outside of this distinguished group, who is to say any of them are wrong? By bringing all of them together at the workshop, we were able to get some very illuminating discussion.
An analysis of shock-wave and isothermal-compression data by J. R. Grover, including the porous-iron data, a theory of melting and the electronic specific-heat contribution, constrained melting to about 5600-6300 K at 2.43 Mbar. This allows both the val ues reported by M. Brown and R. G. McQueen and the values reported by R. Jeanloz and his colleagues.
R.Böhler reported new data using a laser-heating configuration for the diamond cell in which the whole iron sample is bathed in a laser beam. This new data agrees with his previous results which indicate convergence of the g-liquid and e-g boundaries at lower pressures; that is, there are low values of the coordinates of the e-g-l triple point. Bass presented new shock-wave data on stainless steel tending to confirm his original high values reported for the iron meeting Williams discussed many previo usly unpublished details on his diamond-cell melting experiment supporting his announcement of very high values of melting temperature published in Nature.
The apparent low coordinate values of the gamma-epsilon-gamma triple point estimated by Böhler, if true, would disallow the interpretation of the solid-solid transition, seen by Brown and McQueen, as a transition from fcc to hcp iron. Böhler's work indic ates that there may be yet a fourth triple point. In support of this view a theoretical calculation of M. Ross and D. Young suggested the presence of a third bcc phase at the highest P and T. This new phase would be the highest pressure phase of iron an d would be the major constituent of the Earth's core, not fcc iron (gamma) nor hcp iron (gamma), as players in the field have previously maintained. Not all members of the workshop were enthusiastic about this new complication of the phase diagram, but i t received support from W. Bassett, who showed that the thermodynamics of phase diagrams for the transition metals allowed the existence of a high-pressure high-temperature bcc phase as well as a low-pressure bcc phase (i.e., ordinary everyday iron).
Because the melting temperatures reported by Williams and Bass are markedly higher than those of Böhler and of some theoretical calculations, these two speakers were aggressively questioned about their methods by members of the workshop in an effort to u nderstand origin of the differences. Although there was no resolution of the problem, attention was focused on two areas requiring further investigation: 1) an identification of melting in a diamond cell by visual observation of texture or shape changes in the iron sample, and 2) accurate determination of the thermodynamic state of the interface between shocked iron and the transparent anvil material. M. Brown, W. Nellis, and D. Schiferl all presented detailed critiques of the shock pyrometry and high-t emperature diamond-cell experiments. The outcome of this dispute will have important consequences for our understanding of the Earth's interior.
The other general theme of the workshop was the problem of the composition and thermodynamic state of the Earth's core. G. Masters reviewed recent seismological measurements of wave travel times through the core and long-period oscillations of the whole Earth and their implications for the structure of the core. Evidence for strong attenuation of waves in the inner core suggests that it is heterogeneous, possibly in a liquid-solid, two-phase state. Optimized models fitted to the seismic data show an a verage density of about 13.0 g/cc in the inner core, and a density jump of 0.5-0.6 g/cc across the inner-outer core boundary. E. Knittle reviewed the problem of solid-liquid equilibrium in the Earth's core. Diamond-anvil experiments on the melting of Fe S and FeO compounds suggest that ideal melting-point depression behavior is closely followed at high pressure, but that FeO greatly depresses the melting temperature, in contrast to the lesser effect produced by FeS. W. Bassett showed that nickel impurit ies greatly compress the phase diagram to lower temperature values. D. Boness discussed the electronic structure of iron at core conditions. A. Jephcoat presented new data on the room temperature isotherm of Fe and Fe-Ni alloy to 2.8 Mbar, a new record for x-ray diffraction in the diamond cell.
People interested in attending the Symposium should write to one of the organizers whose addresses are given below. They will then receive further circulars containing information about registration, accommodation, abstract deadlines for contributed pre sentations, and provisional programs. The scientific sessions will be held at St. John's College, in which a limited number of rooms have been reserved to house participants and their families. Santa Fe is, of course, an attractive, famous and historic city that offers many opportunities for the sightseer. Scientific sessions will start early on the morning of Monday August 6, and end during the afternoon of Friday August 10, 1990. The registration fee will be $150 for participants and $50 for each fa mily member.
Dr. Gary Glatzmaier
Institute of Geophysics and Planetary Physics
Los Alamos National Laboratory
Los Alamos, NM 87545
Dr. Paul Roberts
Institute of Geophysics and Planetary Physics
University of California
Los Angeles, CA 90024
There will be a SEDI business meeting in conjunction with this Symposium. Anyone wishing to contribute an item to the agenda of this meeting, contact E. R. Benton, Department of Astrophysical, Planetary & Atmospheric Sciences, University of Colorado, Bo x 391, Boulder, CO 80309, U.S.A. In particular, the topic, venue and convenors for the third SEDI symposium, to be held in the summer of 1992, are to be decided at this business meeting. Suggestions and nominations are welcomed.
A second AGU-SEDI symposium was convened as a Union session at the Spring 1989 AGU meeting in Baltimore by C. Voorhies (NASA Goddard) on the subject of Earth core properties, processes and core-mantle interactions, covering geophysics of earth polar moti on, length of day, core topography and core dynamics, free oscillations, magnetic field variations and constraints from paleomagnetism. A total of 11 invited talks were given in 2 half-day sessions, highlighted by the first presentation outside the Sovie t block by S. I. Braginsky, on Some new results in geodynamo theory.
At each of the AGU meetings held during the 1988-89 academic year, the EDIC held business meetings. For copies of the minutes of these meetings, contact the secretary of the U.S. SEDI Committee: Thorne Lay, Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109.
A project entitled The Earth's Central Core is being organized with T. Yukutake (Univ. Tokyo) as chief investigator and Y. Honkura (Tokyo Inst. Tech.) as secretary. This project will encompass four topics: (1) Structure and physical properties (Y. Hamam oto); (2) Long-term geomagnetic variations and liquid core motions (Y. Honkura); (3) energy and material balance (M. Kumazawa); (4) Structure of the internal boundaries and related dynamics (Y. Ida). For more complete information concerning these activit ies, contact Takesi Yukutake, Earthquake Research Institute, Tokyo University, Bunkyo-ku, Tokyo 113, Japan.
A successful workshop on ISOP was held during the recent IASPEI General Assembly in Istanbul. Both scientific and organizational issues were discussed, and the workshop was followed by a planning meeting attended by representatives of most of the larger countries. There was a strong feeling that an initial experimental period of ISOP operation should be started as soon as possible. It was also recognized that funds are required to support training course and workshops in the initial stages of the proj ect and to coordinate ISOP both in the initial stage and during full-scale operation. A tentative timetable was adopted, provided the required funds can be secured, and an Executive Committee was formed to implement the plan. Members of this Committee a re Berrocal (Brazil), Denham (Australia), Doornbos (Norway), Engdahl (U.S.A.) and Kondorskaya (U.S.S.R.). T. Jordan (U.S.A.) will serve on matters concerning the ISOP Science Plan. A copy of the report of the workshop may be obtained from E. R. Engdahl, U. S. Geological Survey, Denver Federal Center, P. O. Box 25046, MS 967, Denver, CO 80225, U.S.A.
If a semi-permanent secretary is deemed desirable, the question arises
of whom that would be? The current secretary would be willing to continue
provided some satisfactory arrangement is made to remove the burden of
the routine activities such as mainta ining the mailing list and preparing
and distributing the DIALOG. Alternatively, someone else might be found
to assume the position on a continuing basis.
One possible funding format is to consolidate modest amounts from a number of sources, such as national funding agencies. These monies might be funnelled through IUGG. The National Science Foundation of the US appears willing to cooperate in this arran gement.
We scientists who are actively investigating the structure of the Earth's deep interior have in SEDI a new organizational tool to assist us. We should decide how to make best use of this tool.
1. Should the SEDI secretariat be a semi-permanent office?
2. Whom would you recommend as secretary?
3. What regular activities should SEDI perform?
4. How should the routine SEDI activities be financed?
5. What new directions should SEDI attempt to foster?
6. Whom would you like to nominate for SEDI executive committee?
In addition, any further comments concerning these issues will be welcomed. Action will be taken on these items at the Santa Fe Symposium in August, 1990. Send your response to E. R. Benton, Department of Astrophysical, Planetary and Atmospheric Science s, Campus Box 391, University of Colorado, Boulder, CO 80302, USA or via electronic mail to "Benton firstname.lastname@example.org".
The potential of SEDI can be realized only if those who it may benefit scientifically chose to participate. An important way you can participate in the immediate future is to respond to this questionnaire. Please take the time to give a thoughtful repl y to these questions.
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