By Heide Brandes
OKLAHOMA CITY (Reuters) - Oklahoma earthquakes may have been related to oil production activities as early as the 1930s, a study released this week by the U.S. Geological Survey said.
Oklahoma has seen a surge in seismic activity in recent years and is recording 2.5 earthquakes daily of a magnitude 3 or greater, a rate 600 times greater than observed before 2008, the Oklahoma Geological Survey said in April.
"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," Susan Hough, USGS seismologist and lead author of the study, said in a statement on Tuesday.
"Deep injection of waste water, now recognized to potentially induce earthquakes, in fact began in the state in the 1930s," she said.
The study says the recent earthquakes in central and eastern United States may be primarily caused by the injection of wastewater in deep disposal wells.
Many people have associated the process of hydraulic fracturing, or fracking, with earthquakes. But the U.S. Geological Survey said in April that the actual hydraulic fracturing process, which involves injecting water, sand and chemicals deep underground to break up rock formations, is only occasionally the direct cause of felt earthquakes. (http://on.doi.gov/1KGiLzy)
The latest study tracked how wastewater injection evolved over time, with an increase around 1950.
"Waste water injection has a strong correlation to the increase in earthquakes," said Morgan Page, USGS seismologist and co-author of the study.
"The results further demonstrate that, while the rates seen in recent years are unprecedented, induced earthquakes are likely nothing new in Oklahoma."
Oil production in Oklahoma has more than 100 years of history.
Before a 2011 magnitude 5.7 earthquake in Prague, Oklahoma, the largest measured earthquake in the area was the 1952 magnitude 5.7 El Reno earthquake, which the study concludes was likely induced by activities related to oil production near Edmond, Oklahoma.
On Wednesday, the Oklahoma Insurance Commission issued a mandate to insurance providers giving them 45 days to inform customers whether or not policies would cover damage caused by induced earthquakes.
The Oklahoma Corporation Commission and other government agencies have taken steps to curtail earthquakes linked to disposal wells.
Most recently, the commission issued a plan to reduce the risk of induced earthquakes in Cushing area, home to major oil storage hubs, by changing the operations of 13 disposal wells.
(Reporting by Heide Brandes; Editing by Jon Herskovitz and Mohammad Zargham)