Forty-eight earthquakes have rattled the ground in Oklahoma in the past week, contributing to one of the most earthquak-fraught months on record in the state.
According to the U.S. Geological Survey, Oklahoma has recorded 148 earthquakes of at least a 2.5 magnitude in the past 30 days.
The numbers have made it one of the shakiest states in the United States.
"Certainly there's been a big change in the amount of earthquakes and people are feeling them," said Daniel Lao Davila, assistant professor of geology at Oklahoma State University. "I am in my office and every day or two I feel a brief shaking. These are small, magnitude 2 or magnitude 3, but you can feel them."
"There really is a hot spot right now in Oklahoma," he said.
Lao Davila said that before 2008, Oklahoma used to have on average three earthquakes per year that registered as magnitude 3 or higher.
Since 2008, they've registered "hundreds" per year, he said. That's more than their neighbors in Kansas but less than, say, California or Alaska, which sit on active fault lines.
"For the cause well we really don't know. These earthquakes have been occurring all throughout the central Oklahoma," he said.
Old fault lines that run beneath Oklahoma and parts of Kansas and Tennessee could have become reactivated, or the earth's crust could be under significant stress, or the earthquakes could be induced by subsurface activity like oil and gas production , he said.
"In my opinion it could be a mixture. It could be natural stress, and then in some areas it could be induced," he said.
Lao Davila said that geologists at Oklahoma State, the University of Oklahoma, and the U.S. Geological Survey are studying the earthquakes in Oklahoma to try and understand their cause, but in the meantime he said it is critical for residents to become educated about what to do in case of a serious quake.
"I would say the most important thing for people is to be aware that this seismic hazard is present in Oklahoma and people should learn, they should educate themselves for how to prepare for an earthquake, how to be sure they'll be safe in case another magnitude 5 occurs," he said.