Deep Earth DIALOG
|November 16, 1987
This is the first of a series of newsletters about activities and developments related to the new IUGG Union Committee, SEDI: Study of the Earth's Deep Interior. In addition to providing information, it is hoped that the newsletters will provide a sense of community for those interested in the Earth's deep interior. The name of the newsletter was chosen to emphasize these functions; one definition of dialog is "a conversation between two or more persons: an exchange of ideas and opinions." The success of this newsletter (and of SEDI itself) will depend in large part on the level of interest and participation by the scientific community. A significant portion of this participation will be in the form of items contributed to DEEP EARTH DIALOG. These items should be sent to David Loper:
via post to:
Geophysical Fluid Dynamics Institute,
Florida State University,
Tallahassee, Florida 32306-3017, U.S.A.
via Telex to:
via SPAN to:
via BITNET to:
via Telemail to:
These news items could include meeting announcements, notification of planned projects, informal reports of recent meetings or projects, news of significant scientific breakthroughs, questions for discussion, comments on questions previously posed, etc. When sufficient contributions have been received, an issue of the DIALOG will be distributed.
We have compiled an address list including all those we know of who may have an interest in SEDI, and this first issue of the DIALOG is being sent to everyone currently on the list. This is not meant to be exclusive. If you know of anyone wishing to be on the address list, send the name and address to David Loper.
At the IUGG General Assembly in Vancouver, there was a strong feeling of good will toward SEDI, even though it has as yet no clearly stated agenda. It remains to be seen whether this good will will be translated into good works. Perhaps the dialog can begin by discussing how this potential can be transformed into actions. Specifically, lets begin by addressing the following questions.
(1.1)* What should we try to accomplish under SEDI? Here "we" is taken to mean the entire SEDI community, not merely the officers or executive committee. Perhaps few would argue that the ultimate goal of SEDI is an enhanced understanding of the past e volution and current thermal, dynamical and chemical state of the Earth's deep interior and how these affect the structures and processes observed at the surface of the Earth. The question here is: what more specific goals should we set? One obvious goa l is to "solve the geomagnetic dynamo problem" (see the section on a brief history of SEDI). What are some others?
(1.2) How should we try to accomplish these goals? That is, how can SEDI aid in the accumulation and dissemination of knowledge concerning the Earth's deep interior. It should be emphasized here that SEDI is not a funding agency. It has a modest budg et from IUGG for things such as this newsletter, but it cannot alone bear the cost of funding scientific projects, travel, and the like. What activities can we plan and carry out? One activity already planned is biennial workshops or symposia (see the s ection on the first SEDI symposium on page 4). Should we issue resolutions and recommendations? If so, can we develop a mechanism to reach a consensus without having a meeting?
(1.3) The dissemination of knowledge can take several forms: (a) dissemination among those active in SEDI; (b) dissemination to the scientific community at large; (c) dissemination to the general public. One problem is that our interest group is geo graphically widespread, with many in the so-called third world countries being quite isolated. It is hoped that this newsletter will help to lessen this isolation. What else can we do to strengthen our sense of community? Another problem we face is tra nsmission of our message to the appropriate funding agencies. We in the deep-earth community commonly take a back seat to the more visible geophysical and astrophysical communities. What can we do as a group to counteract this? What can we do specifica lly to enhance the dissemination of knowledge concerning the Earth's deep interior to the general public?
We hope that you will help to make the DIALOG and SEDI successful;
let us hear from you.
- A Brief History of SEDI
- The first SEDI symposium
- SEDI-related meetings
- National SEDI Groups
- ISOP: The International Seismic Observational Period
A Brief History of SEDIThe following history is presented to orient those of you who are unfamiliar with the sequence of events which led to formation of SEDI. The events were set into motion by a letter dated February 22, 1985, from David Loper to a number of scientists inqu iring whether progress toward solving the geomagnetic dynamo problem might be facilitated by coordinating our research activities, perhaps mounting a concerted effort to solve the geomagnetic dynamo problem. The response to the letter was favorable.
The next developments took place at the IAGA Scientific Assembly in Prague, Czechoslovakia, in August, 1985. Partly, but not entirely, in response to the letter, on August 8, 1985, the IAGA Working Group I-2 (on Theory of Planetary Magnetic Fields and Geomagnetic Secular Variation) called for the creation of a project entitled International Study of the Earth's Core and Lower Mantle, with acronym ISECALM. This project would have the geomagnetic dynamo problem as one important component, but would also encompass other topics, including core-mantle coupling and its effect on Earth rotation, heat flux into the lower mantle, thermal plumes in and electrical conductivity of the lower mantle, short-term secular variation, and fluid motion at the top of the core. The matter was discussed further during a subsequent informal meeting at that IAGA Assembly on August 13, 1985, and E. R. Benton and D. E. Loper were asked to co-chair an effort to obtain approval for ISECALM as an official program of IAGA and IUGG .
Subsequently a workshop was convened at the International Center for Theoretical Physics (ICTP) at Trieste, November 6-8, 1986, under the joint sponsorship of the U.S. National Science Foundation and the Third World Academy of Sciences of the ICTP. The 23 scientists in attendance participated in the preparation of a proposal requesting the formation of a new IUGG Union Committee to Study the Earth's Deep Interior. Thus the acronym SEDI came to replace ISECALM. The proposal included an appendix discuss ing a number of scientific questions and problems of interest to SEDI, including: 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: structure, convection and plumes. The proposal also made a number of recommendati ons concerning current or proposed observational programs. Copies of the IUGG proposal and the minutes of the Trieste meeting are available from D. Loper.
The proposal was approved at the recent IUGG General Assembly in Vancouver, creating a new Union Committee for SEDI. The officers for the first four years are E. R. Benton of the University of Colorado as Chairman, D. Doornbos of the University of Oslo as Vice-Chairman and D. E. Loper of Florida State University as Secretary. The officers, with the advice and consent of an executive committee, will be responsible, among other things, for seeing that biennial scientific meetings are held in even numbere d years. Other functions of SEDI are to be determined by the needs and participation of the scientific community. Anyone with suggestions or opinions on the possible activities of SEDI are encouraged to communicate them to one of the officers. Their ma iling addresses and telephone numbers are:
Prof. Edward. R. Benton,
Department of Astrophysical, Planetary and Atmospheric Sciences,
University of Colorado, Boulder , CO 80309-0391
Prof. Durk Doornbos,
Institute of Geophysics,
University of Oslo, Blindern, 0315 Oslo 3, Norway
Prof. David Loper,
Geophysical Fluid Dynamics Institute,
Florida State University,
Tallahassee, Florida 32306-3017, U.S.A.
The first SEDI symposiumThe first SEDI symposium will be held at Blanes, Spain, on June 23-25, 1988. This will be in conjunction with the regular biennial meeting of the Committee on Mathematical Geophysics (CMG). The full meeting will run from June 20-25. The tentative plan is to have Monday, Tuesday and Thursday devoted to topics principally of interest to the CMG, then have the SEDI symposium Thursday evening, Friday and Saturday. The CMG portion of the meeting and the local arrangements are being organized by Antoni Cor reig (Facultat de Fisica, Universitat de Barcelona, E- 08028 Barcelona, Spain; Tel. 34-3-330-7311), and the SEDI symposium is being arranged by Joe Cain (Department of Geology, Florida State University, Tallahassee, FL 32306, U.S.A.) and David Loper.
The CMG Conference will stress two themes. The first is Nonlinear Dynamical Systems in the Geosciences (geophysical fluid dynamics, earthquake dynamics, cellular automata, fluid flows in the Earth, turbulence, transport phenomena, self organization, per colation, electromagnetic fields in nonlinear media, molecular dynamics, etc.), convened by Jorge Lomnitz-Adler and M. Vishik. The second is Philosophies and Applications of Inverse Theory (Bayesian inference or not, Monte Carlo methods, against lineariz ation, neural networks, nonlinear inversion of waveforms, the accuracy of 3D Earth models, helioseismology, geodesy, etc.), convened by Brian L. N. Kennett and Daniel Rothman. Speakers having accepted invitations by mid-October 1987 are: C. J. Allègre, G . Backus, G. Dreyfus, V. I. Keilis-Borok, B. B. Mandelbrot and Y. Pomeau. For further information, contact Antoni Correig.
The SEDI symposium will be divided into five half-day sessions with an experimental format. Each session will begin with an invited introductory lecture on a specified topic. Then there will be a poster presentation (all contributed papers will be pres ented as posters), in the form of an extended coffee break. Next there will be one or two invited talks reviewing the current status of the topic. Finally there will be a group discussion period, led off by a brief summary of the posters. The five topi cs are (1) Physical properties and phase changes at the inner-core boundary and core-mantle boundary, (2) Core structure and oscillations, (3) Dynamics of the core (4) Lower mantle structure and convection (5) Core-mantle boundary topography and intera ctions. Invitations to speak have been extended to T. Ahrens, D. Giardini, R. Haddon, R. Jeanloz, T. Jordan, T. Lay, J.-L. Le Mouël, P. Melchior, H. K. Moffatt, T. Ringwood, P. H. Roberts, G. Schubert, D. Smylie and J. Wahr. A formal notice of this symp osium will be distributed shortly.
In subsequent years, the meetings of SEDI and the CMG may be held separately, but it is hoped that they will be carefully coordinated so that they complement each other in schedule and topics.
SEDI-related meetingsIn addition to the regular biennial meetings, other scientific meetings will be informally designated as SEDI-related activities. For example, the meeting on "Nonlinear dynamics of rotating magnetic systems", organized by Paul Roberts and held August 4- 7, 1987, at UCLA, was so designated.
A NATO Advanced Study Institute on "Geomagnetism and Paleomagnetism" is to be held at the University of Newcastle upon Tyne, April 9-27, 1988. For information, contact Ann Codling, School of Physics, University of Newcastle upon Tyne, Newcastle upon Tyn e NE1 7RU, United Kingdom. There will be a two-day break in the middle of this ASI, to allow attendance at the Royal Society discussion meeting on "Seismic tomography and mantle circulation" to be held in London, April 13-14, 1988.
The Geophysical Institute of the Czechoslovakian Academy of Sciences is sponsoring an international meeting of "New Trends in Geomagnetism" at the Castle of Liblice, Czechoslovakia, from June 27 to July 1, 1988. The meeting will be divided into three pa rallel symposia: A. Sun-Earth connection and geomagnetic field. B. Modern methods on rock magnetism and paleomagnetism C. Earth-core boundary and geodynamos. The third of these is designated as a SEDI-related activity. For further information conc erning this meeting, contact Ivan Cupal, Geophysical Institute, Czechoslovakian Academy of Sciences, 141 31 Prague 4, Czechoslovakia; Phone (0042-2) 766051, 762546; Telex 121546.
A NATO Advanced Study Institute on Tomography in Geophysics is to be held at Les Houches, France, in August, 1988. For information contact Mr. J. Zinn-Justin, Service de Physique Theoretique, CEN Saclay, F-91191 Gif-sur-Yvette, France.
National SEDI GroupsThere has been a move to establish national SEDI groups. The British were the first to form one and have held a number of meetings. The chairman of the British group is Raymond Hide (Geophysical Fluid Dynamics Laboratory, Meteorological Office, Brackne ll, Berkshire RG12 2SZ, United Kingdom) and the secretary is David Gubbins (Department of Earth Sciences, University of Cambridge, Bullard Laboratory, Madingley Rise, Madingley Road, Cambridge CB3 0EZ, United Kingdom).
The Canadians held an organizational meeting of their national group at the IUGG General Assembly in Vancouver. For further information about this group and their current activities, contact David Crossley, Department of Geological Sciences, McGill Univ ersity, Montreal, Canada.
While the French have not yet formed a national group, they have an ongoing coordinated program of study of the Earth's core; see the article by Vincent Courtillot in the October 28, 1986, issue of EOS.
The possibility of forming a United States national group will be discussed during the Fall Annual Meeting of the AGU in San Francisco this December. Anyone wishing to participate is welcome to attend the discussion, which will be held in Room 401 of th e Civic Center at 8 PM on Monday, December 7, 1987.
ISOP: The International Seismic Observational PeriodIt is a cliche (but not hyperbole) to assert that the three-dimensional maps of seismic heterogeneity are revolutionizing our thinking about machinery that drives plate tectonics and produces the magnetic field. At the SEDI workshop in Trieste last Nove mber, Prof. T. H. Jordan (United States) proposed to establish an "International Seismological Observing Period" (ISOP) whose purpose would be to provide a new and much improved data set for mapping the three-dimensional structure of the Earth's mantle an d core using the existing global network of over 1500 permanent seismic observatories. During the ISOP, the arrival times and other attributes of high-frequency seismic phases from a specially designated set of events would be reported by the global netw ork to the International Seismological Centre (ISC) and distributed to the seismological community. A resolution supporting the proposal was adopted by the SEDI workshop.
The arrival times of high-frequency teleseismic phases have been routinely collected by the ISC and other organizations for many years. Although primarily for locating earthquakes, these data have proved very valuable for tomographic mapping. Recent st udies have made it clear, however, that the arrival-time data included in the ISC bulletins represent only a small subset of the information potentially recoverable from the seismograms. Particularly valuable constraints on deep earth structure can be ob tained from later-arriving seismic phases such as S, ScS, PKP2, PnKP, which are not now systematically reported to the ISC. Many of these phases are well-recorded on the high-frequency seismometers operated at most observatories.
Jordan outlined plans for the ISOP to the IASPEI Commission on Practice at the IUGG General Assembly in Vancouver last August. Most of the equipment, personnel, and expertise need to implement the project are already in place, so the funding requirement s are small. The primary needs are for enhanced organization, careful planning, and extended communications by the international seismological community. Although Jordan emphasized that a specific project plan will require some effort to think through, he suggested that it be initiated by an organizational period of perhaps one year during which the participating countries could, if possible, upgrade instrumentation and acquire additional expertise. Reporting strategies could be tested and statistical checks on measurements established. This would be followed by a three-year observing period for the collection and distribution of a geographically dense set of high-frequency arrival times. Although he nominal period could be longer, three years seems to be about the minimum time needed to sample global seismicity. Throughout the ISOP, efforts would be made to improve the quality of the arrival time data, with special emphasis placed on maintaining accurate timing and utilizing polarization informati on (e.g., picking shear-wave arrivals from horizontal components).
The ISOP proposal has been received with considerable enthusiasm by the international seismological community. In Vancouver, resolutions supporting its implementation was passed at the IASPEI plenary session. The Commission on Practice established a spe cial working group under the chairmanship of Dr. J. Hjelme (Denmark) and charged this group with the responsibility for organizing the ISOP and coordinating ISOP planning and activities with SEDI. A resolution in favor of the ISOP was also passed by Work ing Group 6 of the International Lithosphere Program. For further information regarding ISOP plans, contact Prof. T. H. Jordan, 54-518, Dept. Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA 02139 (T.Jordan/Omnet).
* Question number y in DIALOG issue #x is labeled (x.y) for ease of future reference.