A general view shows the aftermath of an earthquake and tsunami that hit the northern port of Iquique, April 2, 2014. The earthquake, with a magnitude of 8.2, struck off the coast of northern Chile near the copper exporting port of Iquique on Tuesday even
A general view shows the aftermath of an earthquake and tsunami that hit the northern port of Iquique, April 2, 2014. The earthquake, with a magnitude of 8.2, struck off the coast of northern Chile near the copper exporting port of Iquique on Tuesday evening, killing six and triggering the tsunami that pounded the shore with 2-meter (7-foot) waves. REUTERS/Francisco Alcayaga Motta REUTERS/Francisco Alcayaga Mot

The sharp growth in the number of earthquakes in Oklahoma, U.S., have been found not to be borne out of natural seismic causes but due to the massive injections of wastewater by oil and gas extraction.

Made up of just four wells, those facilities have managed to trigger over 100 small to medium earthquakes in the past five years, a study published on Thursday by the journal Science said. These four wells pump 4 million barrels of water a month to 3.5 km beneath the surface.

Those four wells, when combined, inject over 5 million gallons of water a mile or two into the rock formations underground, the study found. And this happens every day.

"That buildup of fluid creates more pressure that has to go somewhere," Katie Keranen, study lead author Cornell University seismologist, told AP.

Many of the quakes triggered off by the massive drilling were found to have occurred much farther away from the wells.

The research noted that since 2008, the small town of Jones has experienced over 2,500 earthquakes greater than magnitude 3.0, representing 20 per cent of the total in the central and western U.S. in that particular period alone.

"There are large regions in the state that are lighting up with quakes," Keranen said. "It's a very profound increase."

Data from the U.S. Geological Survey showed that over 300 earthquakes above magnitude 3.0 had occurred from 2010 to 2012 in the central and eastern U.S., compared to the average annual rate of only 21 from 1967 to 2000.

For Oklahoma, from 2008 to 2013, an average of 44 earthquakes of magnitude 3 were felt every year. For 2014, there have been 233 so far, Keranen said.

Researchers found the water diffused through underground moves faster and farther, triggering quake fault lines that already were likely ready to move, she said.

"You really don't need to raise the pressure a great deal," Keranen said.