The magnitude 5.6 earthquake in Oklahoma on Saturday night felt was as far as Wisconsin, U.S. Geological Survey geophysicist Jill McCarthy said.
“We have had eight recorded earthquakes (in Oklahoma) in the past 24 hours or so,” she said.
McCarthy is the team chief scientist with the National Earthquake Information Center in Denver, Colo.
A 4.7 magnitude temblor was reported early Saturday, followed by the 5.6 magnitude earthquake just before 11 p.m., which was the strongest in state history.
A series of smaller earthquakes was reported between the largest quakes, sometimes referred to as aftershocks.
“Aftershocks are earthquakes too, but usually we talk about the main event. They just represent the cluster of activity that happens after a bigger quake,” McCarthy said.
Aftershocks typically decrease rapidly with time, but whether or not a stronger earthquake is in our future cannot be predicted, she said.
Oklahoma is not near a plate boundary, McCarthy said, but seismic activity in the state is not uncommon and the cause of them is not known.
“They're a little bit more anomalous, but they're not necessarily unusual,” she said.
“We're unsure what that origin is,” McCarthy said.