Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

lundi 8 décembre 2003

Last week, a study released by Princeton University said that geoscientists have captured images of the interior of the Earth by using techniques similar to body scanning by physicians. This study also revealed in-depth structures which might explain how our planet is changing -- and aging.

The scientists used tremors from earthquakes to probe the inside of the planet just as sound waves allow doctors to look inside a mother's. The technique, a greatly refined version of earlier efforts, produced a surprisingly sharp image and yielded the first direct measurements of giant spouts of heat, called mantle plumes, that emanate from deep within the planet.
Mantle plumes are believed to cause island chains, such as the Hawaiian Islands and Iceland, when the Earth's crust passes over the column of heat. Although accepted by most scientists, the existence of mantle plumes has been fiercely contested by a minority of researchers in recent years.

Here is an illustration of how these mantle plumes are *moving* under ourselves (Credit: Jamie Painter, Visualization Scientist, Copyright The Regents of the University of California, Link).

Mantle plumes

Another geophysicist from Princeton, Jason Morgan, proposed the existence of these mantle plumes thirty years ago.

"This is the first visual evidence that mantle plumes exist," said Raffaella Montelli, a Princeton geoscientist and the lead author of a paper published online by the journal Science on Dec. 4. "There is still a very open debate, but we are saying 'Look, here they are; you can see them.'"
The scientists used data from more than 3,000 seismographic stations around the world. The stations monitored tremors from more than 86,000 earthquakes since 1964. The seismic waves change speed slightly when they encounter different temperatures and materials in the Earth, said Princeton professor Guust Nolet. In particular, the waves slow down when they encounter warm spots where the rock is very slightly softer than in cooler spots.

The researchers identified 32 plumes, but they got some surprises. Some of these plumes were very well correlated with known hotspots. Some others, like under Yellowstone National Park, were not found by this extensive survey.

The research paper has been published by Science. Here is a link to the abstract of this paper, "Finite-Frequency Tomography Reveals a Variety of Plumes in the Mantle" (registration needed).

Scientific American also published an article on this subject, "Earth's Elusive Mantle Plumes Detected At Last."

Sources: Princeton University News release, December 4, 2003; Science, December 4, 2003; Scientific American, December 5, 2003

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