Work crews in Oklahoma were assessing damage Monday after an earthquake shook a small community near Oklahoma City over the weekend.
At least 10 aftershocks have been reported and experts say more could be felt for months to come.
The latest quake occurred after a spike in tremors that have hit the heartland over the last two years. It buckled roads, damaged houses, and has scientists scratching their heads.
The unusual 5.6 magnitude quake that shook Oklahoma over the weekend was the strongest ever felt in the state, an area better known for a different kind of natural disaster -- tornadoes.
"I woke up immediately. I didn't know what was happening. I thought it was a tornado that had suddenly come up," Chris Steele, a resident of Prague, Okla., said.
"And I looked out the window and you could see the stars, so then I realized it was another earthquake," he said.
The quake's epicenter was near the tiny town of Sparks, located about 44 miles northeast of Oklahoma City. See map of area affected.
But the rumbling was felt from Texas to Wisconsin.
Geological experts are struggling to explain what's described as a dramatic increase in seismic activity throughout America's heartland.
Another quake shook the same area in October 2010. It was recorded as Oklahoma's second largest quake.
Seismologist Austin Holland, who works for the Oklahoma Geological Survey, said there are actually fault lines criss-crossing the heartland.
Although they're small, seismic pressure can build up.
"The plate boundaries are squeezing the central part of the United States from all the interactions of the tectonic plates surrounding North America," Holland told CBN News.
"You have an earthquake that occurs, and that changes the stress ever so slightly next to it, and so another earthquake occurs, and it's just sort of like a zipper unzipping. It kind of just goes down the line," he explained.
Before 2009, Oklahoma only saw about 50 small quakes a year, most too small to be felt.
But in 2010, more than 1,000 earthquakes shook the state.
This has experts concerned that it's only a matter of time before a "big one" hits middle America.
"Earthquakes are a national hazard. It's in these areas, away from California, away from the places we think about, where there can be some of the greatest risk," Dr. David Applegate, associate director for natural hazards at the U.S. Geological Survey, told ABC's "Good Morning America."
The state of Arkansas is also experiencing a drastic increase in earthquakes.
The federal government has been preparing agencies in the heartland for the possibility of a major earthquake.