The earthquake that shook Kansas and four other states this morning was one of the strongest ever recorded in Oklahoma.
The earthquake struck at 9:06 a.m. about six miles east of Norman. At least two people sustained minor injuries. Minor damage — primarily to windows and fallen items — was reported.
"You definitely would have felt it in Wichita," said Don Blakeman, a geophysicist with the U.S. Geological Survey's earthquake information center in Golden, Colo.
Tremors in Wichita lasted for about a minute.
The U.S. Geological Survey initially rated the quake a 4.5 and later dropped it to a 4.3. But research seismologist Austin Holland said the Oklahoma Geological Survey measured it at 5.1. The higher figure would make the temblor the state's second-strongest since records began.
Don Blakeman, a geophysicist with National Earthquake Information Center, said the quake was felt up to 170 miles away. Tremors were felt in parts of Kansas, Arkansas, Missouri and Texas.
Don Steeples, who teaches earthquake seismology at the University of Kansas, said the energy impact of a 4.3 earthquake is equivalent to about a half-million pounds of exploding dynamite.
"My guess is the earth in Wichita probably moved up and down less than a tenth of an inch," he said.
An earthquake occurs when a rock slips on either side of a fault.
"That causes a vibration that goes until it dies out," Steeples said. "A tremor just means something shakes."
He said he wasn't sure how much of Kansas felt the tremors, but said he had confirmed reports from as far away as Emporia.
Kansas historically has not been a prime player in the world of earthquakes.
"It's relatively benign," Steeples said. "Nothing like California but also more active than places like North Dakota."
Kansas typically sees about a dozen earthquakes with a 2.0 magnitude each year, he said.
"We get a 4.0 every couple of decades or so and a 5.0 every century," Steeples said.
Kansas' last significant earthquake occurred in June 1989, when a 4.0 was registered at the epicenter about 20 miles northwest of Hays, he said.
Every 24 hours, more than 1,000 earthquakes occur somewhere in the world.
Over the last year or two, there has been a series of earthquakes in Jones and Spencer, Okla., which are near Norman.
A magnitude-5.5 earthquake struck El Reno, just west of Oklahoma City, in 1952, and another struck in northeastern Indian Territory in 1882, according to records at the U.S. Geological Survey. The Oklahoma Geological Survey rated that quake at 5.0. Quakes of 4.4 magnitude struck Hughes County in 1939 and Coal County in 1997.