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1998-04-25

The Crafoord Prize 1998

The Royal Swedish Academy of Sciences is to award the 1998 Crafoord Prize in geosciences with special emphasis upon “the dynamics of the deeper parts of the Earth" to Don L. Anderson, California Institute of Technology, Pasadena, USA and Adam M. Dziewonski, Harvard University, Cambridge, USA “for their fundamental contributions to our knowledge of the structures and processes in the interior of the Earth"
The 1998 Crafoord Prize is valued at 500 000 US dollars. The prize will be presented to the prizewinners at a ceremony on 16 September 1998.

Great disasters the best source of knowledge about the inner Earth


We live upon an unstable planet. The continents move, volcanoes erupt and earthquakes afflict large areas. Cynically expressed, the greatest disasters afford the best information on the Earth´s interior. Yet advances in digital technology and the extremely sensitive instruments for measuring seismic movements within the Earth´s crust have now led to better analyses and interpretations of seismic data even from smaller but more frequent earth tremors. Two of the world´s most prominent researchers in the area, Don Anderson and Adam Dziewonski, have been awarded the 1998 Crafoord Prize for their outstanding research into the composition and dynamics of the Earth.

Don Anderson and Adam Dziewonski, both separately and jointly, have studied earthquakes. On the basis of seismological studies they have together developed a generally accepted standard model of how the Earth is organised and of the dynamics of the processes, at its core and in its mantle that govern continental drift, volcanism and earthquakes.

That the continents move was proposed by Alfred Wegener in the 1930s, but this was not proved until the 1960s. Some parts of southern South America are moving westwards at speeds of up to 15 cm a year, while the Philippines move fastest. These and other movements within the Earth lead to continental drift and earthquakes. The unsettled areas around the Pacific Ocean are now fairly well mapped, but what are the underlying mechanisms of continental movement, earthquakes and volcanic activity?

Don Anderson and his team have researched changes in the Earth arising because of the pressure deep down in its mantle. Sudden changes in the rock types at depths of 400 km and 660 km are explained by conversions of the rock types to contain minerals that are entirely unknown at the Earth´s surface. At 400 km the mineral olivine, common in lava, changes to spinel, a high-pressure mineral. At 660 km, the mineral perovskite is formed, a mineral otherwise only produced in the laboratory at very high pressures and temperatures. Anderson´s research has shown that such changes in the composition of the mantle may explain the occurrence of tensions in the earth´s crust that can lead to earthquakes. Anderson and his research team have also used seismic data to study convection currents in the mantle, decisive for understanding continental drift and volcanism on Earth. Recently, Anderson has also used geochemical and chemical-isotope methods for mapping not only Earth´s development. These studies are also of importance for the understanding of the development of the Moon and the planets Mars and Venus.

The speed and nature of seismic waves give important information on temperature and mineral density. Adam M. Dziewonski is a pioneer in our understanding the properties of seismic waves and how they are propagated through the Earth. Through detailed studies of the great Alaska earthquake in 1964 Dziewonski and his co-workers succeeded in forming a picture of the interior of the Earth: the Earth has a solid inner core and a fluid outer core consisting chiefly of iron. Outside the core there is the mantle and then the crust composed chiefly of silicates. Seismic waves crossing the core change direction - are anisotropic. This, Dziewonski considers, is because of thermal convection (hot currents) in a direction determined by the orientation of the metallic iron crystals in the solid core. Recently the team observed that the inner core is rotating 2-3 degrees faster than the surface. Current research may well show whether this is caused by the processes that may perhaps also explain earth magnetism.

Seismic tomography
Dziewonski and his co-workers have successfully improved methods of analysis and interpretation of seismic data and developed what is termed global seismic tomography (corresponding to computed tomography in medicine).

Seismic tomography employs differences in the seismic velocity of waves propagating themselves through rock types of different temperatures. In this way it is possible to chart how cold plates from the Earth´s crust and the upper layer of the mantle (the lithosphere) sink down through the mantle towards the border of the fluid outer core. Pieces of the puzzle are being added to our knowledge of the Earth´s global geochemical cycle.  

Don L. Anderson was born in 1933 in Maryland, USA and received his doctorate in geophysics at the California Institute of Technology CALTECH in 1962. He has been a leading figure in "deep Earth" research since the 1960s. He was Director of the Seismological Laboratory of the California Institute of Technology from 1967-1989. Don Anderson published his "Theory of the Earth" in 1989, a remarkable synthesis of his broad and provocative research and a guide for geo-researchers from different fields for future exploration of the dynamics of the deep parts of our Earth.

Adam M. Dziewonski was born in 1936 in Poland. After receiving his doctorate in Cracow, Poland in 1965 he travelled to the USA for post-doctoral research, where he continued his career as a seismologist. He worked in Dallas, Texas until 1972, when he became Associate Professor at Harvard University. In 1976 he became Professor of Geology at the Department of Earth and Planetary Sciences and from 1994 he is Frank B. Baird, Jr. Professor of Science at Harvard.

Perina Stjernlöf
perina.stjernlof@kva.se
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