LANGSTON, Okla. (AP) -- The U.S. Geological Survey has recorded nine earthquakes in Oklahoma since about 9:30 p.m. Friday, the largest being a magnitude 4.0.
The U.S.G.S. says the 4.0 magnitude quake was recorded at 10:05 p.m. Friday about seven miles south of Langston. The other quakes ranged from magnitude 2.4 to 2.9 and all but four were near Langston. The others were near Stillwater, Choctaw, Cherokee and Crescent.
No injuries or damage are reported.
Geologists say earthquakes of magnitude 2.5 to 3.0 are generally the smallest felt by humans.
Scientists are studying why earthquake activity has increased in Oklahoma and whether it is connected to wastewater disposal related to oil and gas production -- but have found no answers.
The energy industry denies that the method is to blame for the increase.