New technique uses seismic ’garbage’ to view Earth’s interior
Frees seismologists from tyranny of waiting for earthquakes
Seismologists have long relied on earthquakes or expensive tools like explosives to help create images of Earths interior, but a new method created by University of Colorado at Boulder (CU-Boulder) researchers will produce quicker, cheaper and clearer images.
Rather than waiting for earthquakes, the researchers have recovered surface-wave information from normal seismic noise that is constantly produced by fluctuations in the Earths atmosphere and oceans. Measuring surface waves is important because the information helps scientists get a clearer picture of the Earths interior, according to Michael Ritzwoller, director of CU-Boulders Center for Imaging the Earths Interior.
The method is described in the March 11 issue of the journal Science.
“This new technique will give us a better fundamental understanding of the planet by providing much better resolution of Earths interior,” Ritzwoller said. “It also will diminish what is known in seismology as the tyranny of earthquakes, which means having to wait for an earthquake to happen to do our jobs.”
The new method promises significant improvements in the resolution and accuracy of crust and upper mantle images down to 60 miles or more within the Earth, particularly when used with seismic projects like USArray, according to Nikolai Shapiro, a research associate in the Center for Imaging the Earths Interior and the studys chief author.
Coupled with existing and emerging technology, such as USArray, the new measuring technique will lead to a better fundamental understanding of the structure of the planet and may help save lives in the process, Ritzwoller said. A component of the National Science Foundations (NSF) EarthScope program, USArray includes hundreds of portable seismometers that in coming years will be moved over the entire country, producing images of the Earths interior to aid in earthquake risk assessment.
“The authors application of what used to be seismic noise to the detailed mapping of the crust and upper mantle will have significant impact on earth science and on seismic hazard mitigation,” says James Whitcomb, head of NSFs deep earth processes section, which funded the research. “This innovative research foretells whats to come from EarthScope.”
Researchers have for years been constructing tomographic images of Earths crust and upper mantle from waves generated by earthquakes. That method, known as seismic tomography, reconstructs Earths inner structure on a computer screen, slice by slice. The new technique is similar, but is based on organizing ambient seismic noise, which is typically discarded as seismic “garbage.”
Seismic tomography is like doing a medical CT scan of the Earth, Ritzwoller said. But when people have a CT scan, doctors are in control and can make images at will. Seismologists cant control when an earthquake happens, so they can either wait for another one or set off explosives to create their own image-generating waves.
“To move beyond these limitations requires observational methods based on seismic sources other than earthquakes, which is what our method offers,” said Shapiro.
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Earth Sciences (also referred to as Geosciences), which deals with basic issues surrounding our planet, plays a vital role in the area of energy and raw materials supply.
Earth Sciences comprises subjects such as geology, geography, geological informatics, paleontology, mineralogy, petrography, crystallography, geophysics, geodesy, glaciology, cartography, photogrammetry, meteorology and seismology, early-warning systems, earthquake research and polar research.
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