OKLAHOMA CITY, April 18 (UPI) -- Even with action taken to control human-induced seismic events tied to oil and gas, the USGS reported more than a dozen minor quakes in Oklahoma in a week.
The U.S. Geological Survey reported there were 13 quakes in Oklahoma and one just over the northern state border in Kansas since last week. The largest were two magnitude-3.5 quakes recorded Tuesday in the north-central part of the state. Magnitude-3.0 and magnitude-2.5 quakes were recorded by the USGS on Sunday.
A March report from the USGS found central U.S. states have experienced a dramatic increase in seismic activity over the past six years. Between 2009 and 2015, there have been an average 318 quakes in the region, against an average of 24 in the 35 years ending in 2008. The average rate last year was 1,010.
Regionally, the report said the disposal of oil and gas-related wastewater is the "primary reason" for the increase in seismic activity in the central United States. Many states, including Oklahoma, have active management plans for wastewater injection as a way to curb tremors.
Oklahoma Gov. Mary Fallin in January approved $1.38 million in one-time costs to support earthquake research in the state. State energy regulators, meanwhile, have called on energy companies to reduce the amount of wastewater disposed in underground wells in an effort to curb seismic activity. A plan for western Oklahoma went into force in February and expansions to a risk area in the central part of the state have been made.
Oklahoma is among the top oil- and gas-producing states in the nation, with its oil accounting for about 4 percent of the national total. One of the largest oil fields in the country is in central Oklahoma.