A revised view of continental tectonics is emerging from the research of an MIT professor who has made the first statistical evaluation in the West of long-secret gravity-field data for a large section of the former Soviet Union.
Dr. Marcia K. McNutt of the Department of Earth, Atmospheric and Planetary Sciences, played a leading role, in collaboration with Mikhail G. Kogan of the Institute of Physics of the Earth, Moscow, in making the Russian data available to colleagues throughout the world. They published their findings in a recent issue of Science Magazine.
Gravity-field data help geologists understand the nature of the various layers deep below the Earth's surface, giving clues to the influence those layers have on the formation of mountain ranges and other surface features, like the Tibetan Plateau.
The data also have important economic and strategic values which lead many nations to keep information for their territories under wraps. The information is of vital importance in finding and extracting mineral resources, oil and gas, especially for terrain where surface features are obscured by forests. Information on gravity-field data can also be used to measure subsurface stress.
Some nations believe that a knowledge of gravity data can aid the targeting of intercontinental ballistic missiles. This was the original reason for the classification of the Soviet data, but now a more important Russian imperative has led to the release of the data to help stimulate the economy.
The basic geologic question Professor McNutt sought to answer in reviewing the Russian data was: When continental blocks such as Italy, Arabia and India collided with the southern border of Eurasia why were narrow mountain belts created in the west and very broad ones in the east?
Her conclusion: Differences in the lateral strength of the upper mantle control intracontinental deformation. The difference between western and eastern Eurasia, she found, can be explained by the presence of a low-viscosity zone in the uppermost mantle beneath eastern Eurasia that is absent in the west.
Professor McNutt's statistical analysis of the Russian data shows that the location of the change in viscosity corresponds with the geologic boundary between the older shields and platforms of the Baltics, Russia and Siberia with the younger, geologically active mountain belts of eastern Asia.
"Our conclusions from dynamic modeling of gravity and seismic velocity anomalies from northern Eurasia point to a revised view of continental tectonics according to which the physical properties of the upper mantle to depths as great as 400 km (248 miles) are affected by the thermal structure and stress history of the overlying continents, and that lateral variations in these physical properties in turn dictate patterns of intracontinental deformation," Professor McNutt and her Russian colleague wrote in their paper, "Gravity Field over Northern Eurasia and Variations in the Strength of the Upper Mantle," (Science, January 22).
Professor McNutt and Dr. Kogan have been working together for about 10 years to gain access to the data that the former Soviet Union spent 30 years and the equivalent of $2 billion acquiring. Their success means a 20-percent increase in the land area available for gravitational analysis at wavelengths less than 2,500 km (1,550 miles).
The information is of great interest to scientists because data derived from satellites "currently predict correctly only 50 percent of the total gravity spectrum over northern Eurasia at wavelengths greater than 1,000 km (620 miles) and only 75 percent at wavelengths greater than 3,000 km (1,860 miles)," she said.
The Soviet data-an estimated 10 million point measurements-were derived by the Topographic Service of the Armed Forces of Russia at a resolution of 10 km (6.2 miles) using airplanes and helicopters, Professor McNutt said.
Despite the value of the data, it was nearly lost, however. The original paper records were never entered into computers and were beginning to crumble, Professor McNutt said.
It was the breakup of the Soviet Union that finally led to success for Dr. Kogan in his long quest to make the data available to his scientific colleagues in the west. His first step, after gaining permission, was to arrange a consortium of western companies interested in oil and mineral exploration of Russia. Through the consortium, computer equipment was made available and the data were recorded electronically.
Professor McNutt praised her Russian colleague, whom she met 10 years ago in France at a scientific conference, not only for his perservence in pressing his request for access to the data, but for his courage.
Dr. Kogan, a Jew, was excluded from membership in the Communist Party, a virtual requirement for advancement, influence and, most important, security in the former Soviet Union, Professor McNutt said. Yet, he kept up his efforts to make the data available.
"This was a very good outcome of political change," Professor McNutt said. But she also sees a tragic side for science in the dissolution of the former USSR.
"The Soviet system of science was very powerful," she said. "It was held in high esteem, and while researchers didn't always have the best equipment, in some areas they made unsurpassed theoretical contributions. But now, there is not enough money to support scientists because the infrastructure has fallen apart. Many scientific institutes have shut down. The average pay a scientist can command might provide bread for a month. Students are being told to pick potatoes.
"Those scientists with foreign contacts have had some success securing funding from abroad, but there is no way that I can see that the Russians will be able to maintain their output of science. The National Science Foundation has helped out to some extent with certain projects of the former Soviet Union, but these are difficult economic times in this country as well and we probably can't support much Russian science from the US.
"Russia is encouraging its scientists to get involved in projects that will make money. I hate to see this emphasis on applied science. the Soviets had such a strong commitment to pure research. Once they start looking only at the bottom line, they won't be doing much research."
A version of this article appeared in the March 31, 1993 issue of MIT Tech Talk (Volume 37, Number 27).