Between 1978 and 2008, Oklahoma had just two earthquakes with a magnitude over 3.0. In 2014, thus far, there have been around 200 such earthquakes there, more even than the highly unstable state of California. (They've had 140.) Experts believe the unusual increase in earthquakes is linked to the number of wastewater wells connected to oil
and gas drilling. Wastewater wells occur when oil and gas companies inject wastewater deep underground. Scientists believe that the wastewater acts as a lubricant in existing fault lines, causing more movement. Hydraulic fracturing, commonly known as fracking, has also been linked to earthquakes, though the majority of Oklahoma's tremors were caused by wastewater wells.