Underneath the flat expanse of much of Illinois is a basin that University of Illinois researchers can study by measuring tiny earthquakes from dozens of sensors.

Stephen Marshak, a UI geologist, is a leading investigator on this portion of EarthScope, a nationwide grid of sensors that will help to generate a three-dimensional picture of the ground beneath our feet.

The sensors are moved every 18 months or so, and 120 seismographs are about to look at a section of southern Illinois, Indiana and Missouri that Marshak likens to a sort of upside-down Himalayas in variation of depth.

The Illinois Basin is a major source of the area's coal and natural gas, as well as a potential reservoir for carbon sequestration.

Indiana University is the principal researcher in the project.

The new project includes the UI, Purdue University and both states' geological surveys.

The $1.3 million, four-year project is funded by the National Science Foundation.

In time, the entire nation will have been covered with a grid of seismometers and strainmeters, which measure the distance between two points, as well as GPS devices.

The project will study the structure, evolution and dynamics of the continent.

Marshak said the many small earthquakes in the region help give a picture of the shape of the space, with dozens of meters; datapoints are compared.

"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," according to an Indiana University release. "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."

You can view a demonstration of the sensors after a 2008 earthquake in Nevada at http://bit.ly/n8CMQx

When complete, the seismic array will extend from the Ozarks in southeastern Missouri through southern Illinois and Indiana through northern Kentucky.