April 19, 2012. Government scientists are focusing on the disposal of wastewater from oil and gas drilling as the possible cause of scores of earthquakes that have shaken the central part of the U.S. since 2000. Researchers think the increased seismic activity may be linked to wastewater injected into the ground by oil and gas drilling operators. U.S. Geological Survey researchers found that for three decades prior to 2000, seismic events in the nation's midsection averaged 21 a year. They jumped to 50 in 2009, 87 in 2010 and 134 in 2011. The findings add to pressure on the industry over a drilling process known as hydraulic fracturing -- or fracking -- that has sparked concerns the method may provoke earthquakes and taint drinking water. The study was discussed the same day that the U.S. Environmental Protection Agency released the first regulations to combat air pollution from gas wells.