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David Bricker (Before May 21)
University Communications

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University Communications

Last modified: Wednesday, May 18, 2011

IU-led project will help scientists see into North America's rocky innards

May 18, 2011

BLOOMINGTON, Ind. -- A new project led by Indiana University researchers and funded by the National Science Foundation will strategically position 120 seismometers placed to image a key part of the deep roots of North America.

The $1.3 million, four-year undertaking is part of NSF's EarthScope program, which seeks to cover the entire U.S. with a grid of seismometers, strainmeters, and GPS devices for the purpose of better understanding seismic activity and predicting earthquakes.


Image courtesy of Earthscope, a National Science Foundation program

EarthScope Program scientists are deploying thousands of seismic, GPS, and other geophysical instruments to study the structure and evolution of the North American continent and the processes that cause earthquakes and volcanic eruptions. Shown is the complete grid of sensors that, used in concert, will give scientists the clearest picture yet of American geological phenomena.

Print-Quality Photo

"The stable part of the Earth's mantle in our part of the world is the very basis for our continent, yet we know so little about it," said Principal Investigator Gary Pavlis, an IU Bloomington geophysicist. "This is about seeing the un-seeable, using brand new imaging tools and techniques. EarthScope is essentially an upside-down telescope that will allow us to look inside the Earth."

The latest installation of EarthScope convenes experts from IU Bloomington, the Indiana Geological Survey, and the University of Illinois at Urbana-Champaign. About $700,000 of the grant total will stay in Bloomington.

A seismic array of sensors works a little like sonar -- in the sense that the equipment must pick up vibrational information to "see" what lies beneath. A single sensor wouldn't tell scientists very much at all. A vast network of the sensors, on the other hand, can pinpoint the source of vibrations and their speed, even the nature of the rock through which vibrations pass.

To see how EarthScope works, see this visual representation of Earthscope sensors in action shortly after a February 2008 earthquake in Nevada: (animation by the Incorporated Research Institutions for Seismology).

While it's true that the Midwestern U.S. is less seismologically active than the western U.S., small earthquakes do happen on a regular basis here.

The New Madrid seismic zone, which runs from northern Arkansas to Kentucky, produces about 100 earthquakes a year, most too weak to be felt, or felt well beyond the quakes' epicenters. Similar faults to the New Madrid exist below Illinois, Indiana, and Kentucky, among others, but little is known about the rock within, around, and below the fault zones.

"The reason the central part of the North American continent is so flat is that it sits atop what geologist call a 'craton,' a stable part of the crust and upper mantle that hasn't deformed much at all for billions of years," Pavlis said. "All continents have a core, a craton, which is very stable, and does not break apart easily. It's not clear what geologic processes create these stable plate interiors or how much they can deform to produce earthquakes like the New Madrid earthquakes of 1811-1812."

The area Pavlis and his team will deploy seismic instruments is centered around the Illinois Basin, a 400-mile-long oval-shaped formation that underlies the lower two-thirds of the state of Illinois, the southwestern half of Indiana, western Kentucky and areas within Tennessee and Missouri. The basin tells the stories of ages past as the Earth's crust was bowed downward, as deep as 15,000 feet below the surface in the case of the Ordovician layers (about 450 million years old).

The Illinois Basin is major source of the area's coal and natural gas and is currently being studied as a possible storage reservoir for carbon sequestration. A better model of the basin's architecture could therefore have consequences for energy prospecting and environmental protection.

Pavlis said his group will use modern seismic imaging technologies to better understand how the continent in this region was assembled, how such structures are related to the Illinois Basin, and how the region became part of the craton of North America.

To speak with Pavlis, please contact David Bricker, University Communications, at 812-856-9035 or (before May 21) or Steve Hinnefeld, University Communications, at 812-856-3488 or (after May 21).