Deep Earth DIALOG

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.


Summaries of meetings of interest to SEDI


The Sixth Scientific Assembly of IAGA at Exeter, England

The Sixth Scientific Assembly of IAGA was held at Exeter, England, from 24 July through 4 August, 1989. The sessions of particular interest to SEDI participants included Session 1.4 on Core Mantle Interactions convened by I. A. Eltayeb (Sultan Qaboos Un iversity, Oman), Session 1.5 on Observational Constraints on Planetary Dynamo Theories, convened by J.-L. Le Mouël (Institut de Physique du Globe, Paris), J. Cain (Florida State University, U.S.A.), C. Voorhies (NASA Goddard, U.S.A.) and M. Prevot (Univer site des Sciences et Techniques do Languedoc, Montpellier, France) and session 1.6 on Recent Developments in Dynamo Theories, convened by P. H. Roberts (University of California, Los Angeles) and F. Krause (Akademie der Wissenschaften der DDR, Potsdam, Ea st Germany). The proceedings of the first of these is to be published as a special issue of Geophysical and Astrophysical Fluid Dynamics. Session 1.5 was notable for the size of the audience relative to the size of the room. The speakers were barely ab le to move due to the audience crowded up to their toes.

 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.


SEDI business meeting at Exeter

In the morning of 29 July, 1989, preceding the SEDI symposium discussed above, a business meeting of SEDI was chaired by E. R. Benton, Chairman of SEDI, and attended by 40 scientists from a total of 13 countries. This report constitutes the official min utes of that meeting.

 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 25th Scientific Assembly of IASPEI at Istanbul, Turkey

As part of the 25th Assembly of the International Association of Seismology and Physics of the Earth's Interior (IASPEI) held in Istanbul, Turkey, from 21 August to 1 September, 1989, a three-day symposium on The Earth's deep interior and dynamics of sub ducting slabs was organized by S. Karato (Department of Geology and Geophysics, University of Minnesota) and co-sponsored by the IASPEI commission on the Lithosphere, the International Commission on the Lithosphere and SEDI. This summary of the symposium was prepared by T. Ahrens.

 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.

Report of a Workshop on the Physics of Iron

The accurate determination of the equation of state and phase diagram of iron at high pressures and temperatures has long been of the greatest importance for geophysics. A comparison of the density of the liquid outer core of the Earth with that of pure iron at the same pressure and temperature reveals that the core must be composed of iron together with elements of lower atomic weight. Similarly, the melting temperature of pure iron at 3.2 Mbar, i.e., at the boundary between the liquid outer core and solid inner core, must be an upper bound on the temperature of this boundary. At a recent workshop, held from June 14 to 16, 1989, at Los Alamos, physicists and geophysicists met to review and evaluate current experimental data on iron at high pressures and to correlate these data with models of the Earth's core. This workshop was sponsored by the National Science Foundation and the Institute of Geophysics and Planetary Physics of the University California, and convened by T. J. Shankland (Los Alamos Na tional Laboratory), D. Young (Lawrence Livermore National Laboratory) and O. Anderson (University of California at Los Angles). The proceedings of the workshop will be published as a special section of JGR red. This report was prepared by O. Anderson.

 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.

Second SEDI Symposium at Santa Fe, New Mexico, August, 1990

A SEDI Symposium on Reversals, secular variation and dynamo theory is to be convened by Gary Glatzmaier (Los Alamos ), Jean-Louis Le Mouël (Paris) and Paul Roberts (Los Angeles) at Santa Fe, New Mexico, from 5 to 10 August, 1990. This Symposium will ai m to advance knowledge of the physical state of the core and lower mantle in order to understand better the fluid mechanics of core motion and the generation of the main geomagnetic field. The current status and implications of the paleomagnetic and arch eomagnetic data will be a central part of the proceedings, as will the analysis of secular variation data. The scope of the Symposium will also include physical properties of the Earth's deep interior including the results of high pressure studies, the s eismic structure of the core-boundary region and the determination of core surface motions and fields. The following have been invited to be lead speakers at the symposium: Barraclough, Benton, Braginsky, Burlatskaya, Coe, Doornbos, Glatzmaier, Gubbins, Hoffman, Jordan, Kent, Kono, Langel, Lawrie, Le Mouël , Lund, Merrill, Morrison, Soward and Stevenson.

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
Fax: 505-665-3107
'phone: 505-667-7647

 Dr. Paul Roberts
Institute of Geophysics and Planetary Physics
University of California
Los Angeles, CA 90024
Fax: 213-206-3051
'phone 213-206-2707

 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.

Projects and National Activities


U.S. SEDI Activities

In mid 1988 the U.S. SEDI Committee was established as a Committee of the AGU as the Earth's Deep Interior Committee (EDIC) with the goals and organization as described in DIALOG #2. This committee organized the first AGU-SEDI symposium at the Fall 1988 AGU meeting in San Francisco on the subject of Lower mantle dynamics: plumes, slabs the D" layer and interactions with the core. This symposium, convened by G.Schubert (Univ. California, Los Angeles) was very successful, with 2 8 papers being presented in 3 half-day sessions, and resulted in published proceedings which appeared only 7 months following the symposium; see the July 1989 issue of Geophysical Research Letters (16, 601-636). Gerry Schubert and AGU should be congratul ated for a remarkably prompt publication of these proceedings.

 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.

Canadian SEDI Activities

The Canadian SEDI group has adopted the acronym CANSEDI, and is showing itself to be quite active under the chairmanship of D. Crossley of McGill University, and with the guidance of an executive committee composed of W. Cannon (York Univ.), R. Haddon (G eol. Survey of Canada), R. Langley (Univ. New Brunswick). C. McCammon (Univ. British Columbia), J. Merriam (Univ. Saskatoon), R. Peltier (Univ. Toronto) and D. Smylie (York Univ.). The CANSEDI group is presently circulating among its membership a working proposal outlining a number of research projects related to SEDI, including the study of long-period gravity variations using superconducting gravimeters, geodynamical applications of VLBI data, dynamo theory and paleosecularvariation, mineral physics, m antle convection and seismic tomographic studies. For further information on this proposal, or other activities of CANSEDI, contact David Crossley at the Department of Geological Sciences, McGill University, Montreal, Quebec H3A 2A7, Canada.

European SEDI Activities

The first SEDI Workshop of the European Geophysical Society will be convened by D. J. Doornbos (Oslo) and D. Gubbins (Leeds) at the EGS General Assembly in Copenhagen on 27 April, 1990. The aim of this workshop is to bring together the results of studie s of the structure and dynamics of the Earth's interior. Studies from a wide range of disciplines, e.g., seismology, geomagnetism, geodynamics and mineral physics, will be relevant. Representative topics include the geodynamo and secular variation, core -mantle boundary and interactions, the nature of mantle discontinuities, inverse methods, etc. For further information contact Durk Doornbos, Institute for Geophysics, University of Oslo, Postbox 1022, Blindern, 0315 Oslo 3, Norway or David Gubbins, Depa rtment of Earth Sciences, University of Leeds, Leeds LS2 9JT, U.K.

Japanese SEDI Activities

A subcommittee for the Study of the Earth's Central Part has been established in the National Committee for Geodesy and Geophysics of the Science Council of Japan, with T. Yukutake (Univ. Tokyo) as chairman and T. Yagi (Univ. Tokyo) and Y. Hamato (Univ. Tokyo) secretaries. This group held a workshop on The Earth's central core in Tokyo from 2 to 3 February, 1989, and is planning a second domestic SEDI workshop in Tokyo in April, 1990.

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.

ISOP Progress Report

SEDI has endorsed the establishment of an International Seismological Observing Period (see DIALOG #1 for a description of ISOP). ISOP can be viewed as a period of organized global cooperation in observational seismology, invol ving both analog and digital stations, serving to provide arrival times and possibly other waveform parameter data for phases from designated events. Emphasis will be on later arrivals, including S and core phases, with the goal of improving the data bas e used for tomographic imaging. A recent study makes it clear that even relatively crude data of later arrivals can produce substantial improvement in resolution of Earth structure. Besides providing crucial new data on the earth's interior, this projec t would have an important educational (feedback) function vis-à-vis seismologists and analysts at the stations.

 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.


INTERMAGNET is a non-exclusive program of world-wide data exchange between geomagnetic observatories. Its goals are to (1) establish and maintain digital geomagnetic observatories in remote areas; (2) standardize geomagnetic measuring and recording equi pment and (3) establish a real-time world-wide data exchange using existing meteorological satellites. INTERMAGNET is governed by an executive council consisting of R. L. Coles (Canada), A. W. Green, Jr. (U.S.A.), J. L. Le Mouël (France) and W. F. Stuar t (U.K.). Current participants include the U.S. Geological Survey, the British Geological Survey, the Institute of Geophysics and Planetary Physics of Paris and the Geological Survey of Canada. A number of other national groups are expected to join in t he near future. Also, a number of automated ocean-bottom geomagnetic observatories are being planned. For more information concerning INTERMAGNET, contact A. W. Green, Jr., U.S. Geological Survey, MS968, Denver Federal Center, Box 25046, Denver, CO 8022 5, U.S.A.

Future of SEDI

There are a number of important questions concerning the future of SEDI, on which the Chairman seeks the advice of the readers of the DIALOG. These questions relate both to the administrative and financial structure of SEDI and to its future scientific activities.

Administrative structure

As noted above, the current officers of SEDI are serving four-year terms which expire in August, 1991. It has been suggested that continuity of leadership is desirable. One possible format, modelled after the IUGG, is to have the policy-making offices o f Chairman and Vice-Chairman turn over on a regular basis while keeping a relatively stable secretariat.

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.


SEDI receives $12,000 from the IUGG every four years. Currently, this money is being used by the chairman of SEDI, E. R. Benton, to assist the travel of scientists to SEDI-related scientific meetings. The administrative costs of SEDI, such as the prepa ration and mailing of this DIALOG, are being borne by resources presently available to the secretary, D. E. Loper. This is not a stable situation. If SEDI is to fulfill its potential and be a positive factor in the development of geophysics, a firm base of administrative support is necessary. The formation and early development of SEDI was facilitated by the enthusiasm of creating something new and constructive. However, a different sort of effort is needed for the long run. In particular, the routin e tasks should be turned over to a competent administrative assistant, allowing attention of the officers to be focused on the new directions which SEDI can foster.

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.

Scientific Activities

The principal objective of SEDI is to foster and facilitate cooperative studies of the structure, composition, energetics and dynamics of the Earth's deep interior, particularly the lower mantle, the core and the core-mantle boundary region. Specific pr oblem areas of interest include: the geomagnetic dynamo and secular variation; paleomagnetism and the evolution of the Earth's deep interior; core composition, structure and dynamics; dynamo energetics and the structure of the inner core; core cooling and the core-mantle boundary region; core-mantle boundary shape, coupling and the rotation of the Earth; lower-mantle composition, structure, convection and plumes.

 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.


The Chairman of SEDI requests your input on these issues discussed above. He would appreciate your response to the following questions:

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".

 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 reply to these questions.

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