The U.S. Geological Survey reports a magnitude 4.0 earthquake and three smaller temblors have struck Oklahoma.
The survey reported that the magnitude 4.0 quake hit Saturday south of Medford in north-central Oklahoma. Three smaller temblors — with magnitudes of 3.5, 3.0 and 2.8, all struck near Perry.
No injuries or damage were immediately reported. Geologists say damage is not likely in earthquakes below magnitude 4.0.
Thousands of earthquakes have been recorded in Oklahoma in recent years, and many have been linked to the underground injection of wastewater from oil and natural gas operations.
Regulators have directed oil and natural gas producers to close some disposal wells or reduce the volume of fluids they inject.