Things were shaky in Oklahoma on Saturday, but the 5.6 magnitude earthquake in Lincoln County was not all that abnormal.
The quake, which hit 45 miles northeast of Oklahoma City at 10:53 p.m. Central Time, was the largest in the state's history and occurred less than 24 hours after a 4.7 magnitude quake hit in almost the exact same spot.
It was felt in Illinois, Kansas, Arkansas, Tennessee and Texas, and there have been at least ten after-shocks of magnitude 3.0 or higher.
Twelve homes were damaged and three people were injured when a chimney fell on them, according to a local Fox affiliate. Additionally, a major highway buckled in three places.
We're in tornado country, man, Joey Wakefield, emergency management director for Lincoln County, told Reuters. These earthquakes, it just scares the hell out of everybody here.
But, Lincoln County is also in earthquake country.
There are three fault lines in the area: the Meers fault, the Wilzetta fault and the uncertain Crooked Creek fault on the Kansas-Oklahoma border.
Seismologists now think that the Wilzetta fault, also known as the Seminole uplift, was responsible for the quake on Saturday. It was the result of a right-lateral strike-slip faulting, the same kind of movement that causes earthquakes on the San Andreas fault in California, according to Trembling Earth.
The Wilzetta fault has been active for 320 million years. It has been relatively quite for recent eons, but a nearby seismic belt near Oklahoma City has been rather active recently.
There have been a number of significant earthquakes in the United States this year. Like Oklahoma, the Virginia earthquake in August was an unexpected and unpredictable event. That 5.8 magnitude tremor was felt up and down the East Coast.
Is the earthquake rate anything to worry about? Not really. In the big picture of American earthquakes, these two events were not unusual at all.
In Alaska on Sunday, an earthquake comparable to Oklahoma hit on the outer islands. In the past week, there have been about 300 total earthquakes in the state alone.
Still, aside from Alaska and the West Coast, there were almost no other quakes in the United States in the last seven days. Before Oklahoma, there were only minor earthquakes in Tennessee, Missouri and Virginia, the highest registering a magnitude 2.4, which is 1,000 times less powerful than the 5.6 magnitude quake near Oklahoma City.
Additionally, the rate of earthquakes in Oklahoma has spiked in recent years. Up until 2009, the state had an average of about 50 quakes per year, but in 2010 there were over 1,000, according to the Daily News. Even more shocking is that this dramatic increase could be man-made.
Residents in Oklahoma and Arkansas, which has also had an increase in the numbers of earthquakes recently, blame injection wells. In the process called fracking, natural gas companies blast through shale and bedrock using a fluid to release natural gas. Some suspect that his could have tectonic repercussions.
There are currently 181 injection wells in Lincoln Country, Okla.
Natural gas companies and some Oklahoma seismologists dismiss the claim that the earthquake was anything but natural. The Oklahoma Geological Survey also added that while the number of quakes has increased in the past two years, it is not inconsistent with historical data, according to CNN.