The earthquake happened about 4 p.m., and measured 3.2 on the Richter scale, said Jim Lawson, chief geophysicist at the Oklahoma Geological Survey.
The first aftershock, measuring 2.6, was six minutes later and a third, 2.1 on the Richter scale, hit at 5:45 p.m.
Reports came into the survey office of people feeling the quake in McAlester, Lamar, Okmulgee, Holdenville and Weleetka.
"We do have occasional earthquakes in this part of the state,” Lawson said. "There's usually three a year in that area, but because they're smaller, they're generally not felt by anybody.”
Lawson said the quake was naturally occurring and caused by differential forces acting across a fault in that area.
"What's causing them to change, I do now know,” Lawson said.
Lawson invited anyone who feels a quake or wants more information about earthquakes in Oklahoma to visit the survey's Web site at www.okgeosurvey1.gov/
