A small earthquake was reported early Friday morning near Florence, typical in magnitude of what commonly registers in the state.

But how frequent are earthquakes in Alabama and what risks do they pose?

The U.S. Geological Survey, which documents earthquakes across the country, finds that most events in Alabama are similar to what was recorded in Northwest Alabama — magnitude 2.8. There were no reports of anyone feeling or noticing the earthquake, which was a little more than a mile below the Earth’s surface.

In 2017, Alabama had 18 small earthquakes detected.

“Most of the earthquakes in Alabama are small, at magnitude 2 and sometimes larger,” said Paul Caruso, a geophysicist with the U.S. Geological Survey in Golden, Colorado. “You don’t have the long fault lines in Alabama like the San Andreas or New Madrid faults that extend hundreds of miles.”

Those fault lines cause the most concern in the United States, with San Andreas running 750 miles through heavily populated areas of California near the coast.

New Madrid, beginning south of Memphis and stretching into Illinois, however, has a troubling history. While it has not been the site of major damage since more than 200 years ago around the time of the Louisiana Purchase, it once shook a majority of the country.

“New Madrid is capable of magnitude 8 or larger,” Caruso said. “The 1811-1812 New Madrid earthquakes made church bells ring all the way to Boston.”

The likelihood of an earthquake impacting Alabama would come from New Madrid, but how much is only speculation.

“That’s hard to say what the impact would be,” Caruso said. “Most of the areas where you have injuries and larger destruction is where you find tall buildings and a lot of population.”

Even so, Cullman County is considered an emergency staging area if New Madrid did anything like what happened in the early 1800s.

Documentation of the event tells of stream and river banks collapsing and waterfalls forming. The event, which was actually a series of earthquakes and aftershocks, also caused the formation of Reelfoot Lake by obstructing streams in what is now Lake County, Tennessee.

The earthquakes and aftershocks measured 7.0 to 7.9 from what geologists have determined.

Caruso said the fault runs closely with the Mississippi River.

“We often find that around fault lines. Rivers have a way of finding the weakest rocks and eroding them,” he said.

Alabama’s larger documented earthquakes have occurred in various locations around the state, from a 4.8 measurement in 1997 southeast of Tuscaloosa near Eutaw to 4.6 in 2003 at nearby Fort Payne.

“Those are about the largest we’ve found, but they haven’t been centered in heavily populated areas with the tall buildings,” Caruso said. “New Madrid is the largest fault east of the Rocky Mountains, but nothing has been seen like what happened in the 1811-1812 events in that part of the country.”