This past weekend seven small earthquakes hit central Oklahoma over a 14-hour period, according to the U.S. Geological Survey.
This weekend's temblors are the latest in a growing number of earthquakes across Oklahoma, Texas and Kansas that scientists say could be caused by hydraulic fracturing for oil and natural gas, The Associated Press reports.
Typically fracking, which requires drillers to blast water, sand and chemicals deep into the underground rock formations to free oil and gas, causes micro quakes that are barely strong enough to record on equipment.
So far, Oklahoma has had more earthquakes this year than California, according to a PBS article.
As of last month, Oklahoma has racked up 190 earthquakes of magnitude 3 or greater. California, on the other hand, has only recorded 71 earthquakes this year.
Proponents of fracking argue the method is safe, and credit the boom for record oil and gas production in the U.S.