Washington:
A sharp rise in earthquakes in the Midwestern state of Oklahoma is due to an increase in wastewater injection from oil and gas operations in recent years, researchers said on Thursday.
This year, Oklahoma has surpassed California, long known as the leading seismic state, with 190 quakes greater than magnitude 3, compared to 71 in California.
"These earthquakes are part of a 40-fold increase in seismicity within Oklahoma during 2008-2013 as compared to 1976-2007," said the report in the journal Science.
The culprit is a handful of injection wells used to bury massive amounts of wastewater from operations to separate oil and gas, as well as hydraulic fracturing, or fracking.
Most of the state's 9,000 injection wells are not a problem, but four of its high-volume wells are, pumping more than four million barrels (477,000 cubic meters) of water underground each month, said the report.
These temblors can travel as far as 22 miles (35 kilometers) from the injection site.
The volume of wastewater disposal has doubled in central Oklahoma from 2004 to 2008, said the research led by Katie Keranen, professor of geophysics at Cornell University.
For some regional context, Oklahoma's earthquakes constituted nearly half of all central and eastern US seismicity from 2008 to 2013, the report found.
"Modern, very high-rate injection wells can therefore impact regional seismicity and increase seismic hazard," said the study.
Keranen described induced earthquakes as "one of the primary challenges for expanded shale gas and unconventional hydrocarbon development."
She urged companies to avoid wastewater disposal near major faults and follow standard best practices to reduce the risk.