From the Independent - increase in magnitude 3.0 or greater earthquakes linked to underground disposal of wastewater from oil and natural gas production.
"A magnitude 5.6 earthquake in Oklahoma has brought fresh attention to the practice of disposing oil and gas field wastewater deep underground.
The United States Geological Survey said the quake happened at 7.02am on Saturday, in north-central Oklahoma, on the fringe of an area where regulators had stepped in to limit wastewater disposal.
The shallow quake struck nine miles northwest of Pawnee, where there were no immediate reports of injuries. Damage in the town appeared to be minor.
An increase in earthquakes in Oklahoma that are magnitude 3.0 or greater has been linked to underground disposal of wastewater from oil and natural gas production."
The full article can be read here.