4.5 Oklahoma earthquake comes after rule changes for fracking wells

An earthquake with a magnitude of 4.5 that struck near the U.S. crude oil hub of Cushing, Oklahoma on Saturday occurred just days after regulators imposed new rules meant to prevent temblors in the area and said more changes were possible.

The Oklahoma Corporation Commission (OCC), which regulates the state's oil and gas industry, ordered companies on Sept. 18 to shut or reduce usage of five saltwater disposal wells around the north-central Oklahoma city of Cushing.

Saltwater, a normal byproduct of oil and gas work, is put into deep disposal wells that scientists say have contributed to a rash of small and medium-sized earthquakes in Oklahoma since 2009.

At the time of its latest directive, the OCC said its "plan may be altered as more data is made available".

On Sunday, some people on social media, fearing a quake could cause a fire or explosion in Cushing in the future, were already calling for tougher rules.

"This needs to stop," read a comment at NPR's StateImpact. "The injection wells & fracking are wrecking Cushing."

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

Saturday's quake reported by the U.S. Geological Survey was shallow and centered 5 km (3 miles) from Cushing. [L1N12A0K6]

There were no reports of injuries or damages to the vast network of pipelines and tanks that make up the U.S. oil storage hub, which serves as the reference point for futures traded on the New York Mercantile Exchange.

The Cushing quake was the second significant quake to hit the state in a day, the USGS said, after one with 4.4 magnitude struck near Medford, about 80 miles (130 km) northwest of Cushing, on Saturday morning.

Noticeable quakes, above magnitude 3.0, now strike Oklahoma at a rate of two per day or more, compared with two or so per year before 2009.

Despite resistance from oil producers, the OCC has previously required disposal well operators to show they are not injecting water below the state's deepest rock formation, a practice believed to contribute to seismic activity.

The first set of rules the OCC issued on Aug. 4 told 12 operators of 23 wells that they had 60 days to reduce the amount of saltwater being injected into wells.

The standards have affected only a fraction of the state's approximately 3,500 saltwater disposal wells.

(Reporting By Terry Wade; Editing by Mark Heinrich)