OKLAHOMA CITY (Reuters) – Oklahoma’s oil and gas regulator released a wide-ranging plan on Tuesday to scale back use of wastewater injection wells in western Oklahoma, just days after a 5.1 magnitude quake rocked the state.

Seven counties are affected by the plan, which is the largest push yet in western Oklahoma to curb seismic activity linked to wells to dispose of saltwater, a natural byproduct of oil and gas work.

Saltwater disposal needs have grown in tandem with the growth in horizontal drilling and hydraulic fracturing, or fracking, in recent years.

The plan by the Oklahoma Corporation Commission includes a voluntary order that covers 245 disposal wells over a 5,200-square mile area. More than 40 percent of injected volumes will be cut back.

Tim Baker, director of the commission’s Oil and Gas Conservation Division, said the directive had been in the works since October due to a need for a larger, regional response. The counties covered include some that have not yet experienced an increase in earthquakes.

“This plan is aimed not only at taking further action in response to past activity, but also to get out ahead of it and hopefully prevent new areas from being involved,” Baker said in a statement.

The plan will be phased in over four stages in the next two months, as sudden stoppages could actually create more seismic events, Baker said.

The disposal wells into the Arbuckle formation are operated by 36 companies, including Sandridge and Chesapeake Energy.

Oklahoma was struck by a magnitude 5.1 earthquake on Saturday morning, the third-strongest quake ever recorded in the state, which has experienced a surge in seismic activity in recent years, the U.S. Geological Survey reported.

Concerns about the increase in earthquakes in Oklahoma led to Governor Mary Fallin to use $1.4 million from the state’s emergency fund for earthquake research.

Baker said that money, as well as a grant from the Oklahoma Energy Resources Board and the Groundwater Protection Council, will help fund additional equipment and staff at the Corporation Commission.

Oklahoma, which has been shutting in some wastewater wells since August, has about 3,500 disposal wells.

(Reporting By Heide Brandes; Editing by Terry Wade and Sandra Maler)