Imaging the center of the Earth
Scientists from several U.S. universities had a bright idea. They've adapted the industry tools developed for oil and gas exploration to use the data provided by more than 1,000 seismic observatories to image the Earth's mantle 2,900 kilometers beneath Central and North America. The team wants now to image the whole globe. It also thinks that these new imaging technologies could improve how we look for oil in or beneath geologically complex structures such as the Gulf of Mexico salt domes, but do we really need this?
This project involved many researchers at the Massachusetts Institute of Technology (MIT), Purdue University, the University of Illinois and the Colorado School of Mines. And it was led by Robert van der Hilst, professor of earth, atmospheric and planetary sciences (EAPS) and director of MIT's Earth Resources Laboratory.
Below is an image showing how "seismic waves from earthquakes penetrate the Earth's mantle and scatter back at the core-mantle boundary to detectors on the surface. Nearly 100,000 such recordings are used to illuminate the planet's deep internal structures" (Credit: Rob Van Der Hilst, MIT). And here is a link to a -- slightly -- larger version of this picture.
Here are more details about how the scientists got their idea to mix oil industry tools and earthquake data.
Deeply propagating waves generated by large earthquakes hit the core-mantle boundary and bounce back-as if from a mirror-to the Earth's surface. Each time one of these waves hits an underground structure, it emits a weak signal. "With enough data, we can detect and interpret this signal," van der Hilst said. Using data from thousands of earthquakes recorded at more than 1,000 seismic observatories, an interdisciplinary team of earth scientists and mineral physicists led by van der Hilst pinpointed the details of deep earth structures.
The idea for the research reported in Science was born over breakfast in a Cambridge, Mass., Au Bon Pain some five years ago, when Maarten de Hoop, an applied mathematician at Purdue University, and van der Hilst realized that they might be able to pair up the industry tools and the earthquake data to study the core-mantle boundary in ways never before possible.
Anyway, the researchers obtained some surprising results. While the core mantle temperature is supposed to be about 3,700 degrees Celsius in North America, it only reaches 500 degrees Celsius in Central America.
For more information, this research work has been published by Science under the name "Seismostratigraphy and Thermal Structure of Earth's Core-Mantle Boundary Region" (Volume 315, Issue 5820, Pages 1813-1817, March 30, 2007). Here is a link to the abstract. The full paper is apparently available from the Science here in HTML format. At least, it looks accessible through Rob Van Der Hilst's publications page.
Sources: Massachusetts Institute of Technology news release, via EurekAlert!, April 6, 2007; and various websites
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