An increase in seismic activity in Oklahoma since 2009 may be in part related to activity associated with oil production, the U.S. Geological Survey finds.

"In Oklahoma, seismicity rates since 2009 far surpass previously observed rates at any time during the 20th century," Susan Hough, a USGS seismologist, said in a statement. "Several lines of evidence further suggest that most of the significant earthquakes in Oklahoma during the 20th century may also have been induced by oil production activities."

Energy consultant Wood Mackenzie said Oklahoma shale was on par with the Eagle Ford basin in Texas and the Bakken shale in North Dakota with production expected to pass 1 million barrels of oil equivalent per day by 2020.

Oklahoma is the No. 5 oil producer in the nation. Wood Mackenzie said energy investments in the region should top $4 billion for 2015.

The USGS found many of the larger earthquakes reported in the emerging shale state are tied to industrial activity.

A magnitude 5.7 earthquake in 2011 was the last major seismic event reported in Oklahoma. The largest before that was a 5.7-magnitude quake in 1952, which USGS seismologists concluded was tied to oil production in the state.

USGS said the disposal of wastewater in deep underground wells is potentially leading to more earthquakes.

"Deep injection of waste water, now recognized to potentially induce earthquakes, in fact began in the state in the 1930s," Hough said.

Oklahoma Gov. Mary Fallin has expressed concern about the increase in the number of earthquakes tied loosely to the oil and gas industry in her state.