So far in 2014 Oklahoma has had more earthquakes than California, and many experts believe that the unusual seismic activity is linked to the sharp increase in oil and gas drilling operations and the number of wastewater wells in the state, CNN reported.

Data from the U.S. Geological Survey shows that between 1978 and 2008 the average annual number of earthquakes with a magnitude of 3.0 or more within the state's boundaries was two. In less than six months of 2014 so far there have been 207 tremors of such magnitude registered. By comparison, California has recorded 140 such earthquakes over the same period.

The increase started in 2009, when 20 quakes over 3.0-magnitude occurred and that doubled to 43 the next year. The number kept rising over the following years, with the exception of 2012, the CNN said. According to meteorologist Chad Myers these numbers are likely to keep going up, as seismic activity in Oklahoma seems to be linked to the practice of oil and gas companies to inject fracking wastewater in deep wells underground. Myers believes that hydraulic fracturing is unlikely to create new faults but said that injections may be lubricating existing ones that have been inactive for many years.

Although such quakes are not strong enough to cause damage, they still raise concerns among scientists because the long-term effect of injections is not known.