The earth is always in motion. And as its mantle plates deep underground move and shift, they groan, moan, pop and crack. But much of it happens so slowly — just 5 to 7 centimeters a year — that the sound has to be sped up and amplified so that it can easily be heard by the human ear.
Sometimes, though, the earth moves a lot faster, creating the large-scale devastation associated with such natural disasters as the 2008 Sichuan earthquake in China or this year's quake in L'Aquila, Italy.
Looking for answers by looking at the earth's interior structure
Scientists still don't know why there are earthquakes, says Stephen Gao. The seismologist has worked in Africa, China and Siberia, and is currently heading a research team for EarthScope, in Rolla, Missouri.
EarthScope is part of a huge project to seismographically map the continental U.S. and Alaska. "The idea is to use 400 seismographs to cover the whole U.S. in about 14 years," Gao explains, adding that the information that will come from those monitors is designed to help scientists predict, not prevent, earthquakes. "[But if] you can predict one, then you can do something to lessen the damage caused by an earthquake," he points out. "People can come out of their house and camp outside. You can shut down the power, the natural gas lines. In that situation, you can reduce the damage a lot."
EarthScope began putting down seismometers on the U.S. west coast in 2002 and is moving its operations eastward across the country. The project is currently entering the area of the New Madrid fault zone, in Missouri and several nearby states. It's the site of one of the most powerful earthquakes ever recorded in North America.
Finding the right locations for monitoring movement
The placement of the 400 seismometers is critical. To ensure complete coverage they are being laid out on a massive grid, with stations about 70 kilometers apart. Because the instruments are highly sensitive, they can't be too close to roadways or large trees. Both give off vibrations that could create false readings. So, here in Missouri, open cow pastures and hay fields are the best locations.
Gao has enlisted the help of four students to identify possible seismometers sites.
One of them is Ben Williams, a graduate student at Missouri University of Science and Technology, where Gao teaches. He explains the reason the seismometers are set in a grid. "Because rather than seeing what's going on under the ground at a specific point, they can pool the resources from all of these seismometers and that's what's able to give them more of a visual picture of what's going on. Rather than having just one point and seeing what's going on there, you have 20 points per state seeing what's going on at all times."
Senior geology major Alicia Metzger from Missouri State University adds that the sensitive instruments measure any sort of vibration. "They also perform what they describe as a CAT scan, so that way we get an idea of what the mantle and underneath the ground here — the bedrock — looks like. The whole project together collectively will be able to give us a picture of what's going on in the North American plate."
Keeping landowners in the loop
Today, the two students are double-checking one of their candidate sites to make sure it's still suitable. Kirby Farms is a scenic cattle ranch off the beaten path, with rolling hills and bright green meadows.
Owner James Kirby jokes that he's allowing EarthScope to set up a station on his property because they offered him a large amount of money, then adds, seriously, "No, they just came out and told me what they were going to do and wanted to know if we'd go along with it. Why not? We have a fault line, the New Madrid, on the eastern side of Missouri. If they gain some information, it will be something."
Metzger says they like to keep the land owners involved in what they're doing. "We'll send them newsletters regionally for their areas quarterly, that way they get an idea of what's going on in their areas what's involved with their seismometers."
Kirby hauls out the all terrain vehicles, and the students make the bumpy ride out to the site where they take some readings. They determine that it is a good location for a monitor.
Workers will soon build a small underground station at Kirby Farms by digging a deep hole and reinforcing it with concrete. Then a network of sensitive equipment, wires, and meters will be installed to monitor the earth's activities. Through the use of cellular telephone and satellite signals, the station will transmit data for the next two years.
Data to advance many scientific fields
While the 14-year project, funded by the National Science Foundation, may seem lengthy in human terms, Gao says it's miniscule in geologic terms. But he says one of the important things about this study, is that scientists don't have to wait until it's finished to begin analyzing the data. EarthScope makes it available to everyone via the internet through live streaming.
"People are already starting to publish things," Stephen Gao reports. "So we are actually doing several things at this date. We are trying to map the structure of eastern Nevada, for example. We are trying to see why there are some very strange structures in New Mexico and Colorado. There are papers already being published and on the way. You don't have to wait for the end."
As researchers learn more, the information will be used to help educate the public about earthquake science and safety. And scientists and engineers hope to use what they learn from EarthScope to design stronger earthquake-resistant structures, and improve earthquake and volcano predictions.