SPARKS, Okla. (AP) -- Oklahomans more accustomed to tornadoes than earthquakes suffered through a weekend of temblors that cracked buildings, buckled a highway and rattled nerves. One quake late Saturday was the state's strongest ever and jolted a college football stadium 50 miles away and was followed early Sunday by a jarring aftershock.
There were no reports in the hours after the quakes of any severe injuries or major devastation.
"That shook up the place, had a lot of people nervous," Oklahoma State wide receiver Justin Blackmon said of the late Saturday quake, the strongest of a series of quakes. "Yeah, it was pretty strong."
The magnitude 5.6 earthquake Saturday night was centered near Sparks, 44 miles northeast of Oklahoma City, and could be felt throughout the state and in Kansas, Missouri, Arkansas, northern Texas and some parts of Illinois and Wisconsin, said geophysicist Jessica Turner at the U.S. Geological Survey. A magnitude 4.7 quake early Saturday was felt from Texas to Missouri.
Turner told The Associated Press that the subsequent magnitude 4.0 quake that struck at 3:39 a.m. Sunday was an aftershock centered some 36 miles east of Oklahoma City in the same region. Like Saturday night's quake, she said it was another shallow quake occurring about 3 miles underground, but experts had no immediate explanation for the spurt in seismic activity.
Following the quakes or numerous small aftershocks, several homeowners and businesses reported cracked walls, fallen knickknacks and other minor damage. But in Shawnee, the fire department said one spire on the administration building at St. Gregory University had been damaged and another one was leaning, according to KWTV in Oklahoma City.
An emergency manager in Lincoln County near the epicenter said U.S. 62, a two-lane highway that meanders through rolling landscape between Oklahoma City and the Arkansas state line, crumpled in places when the stronger quake struck Saturday night. Other reports Sunday were sketchy and mentioned cracks in some buildings and a chimney toppled.
"Earthquake damage in Oklahoma. That's an anomaly right there," Todd McKinsey of Moore told The Oklahoman newspaper after the magnitude 5.6 temblor centered 50 miles away left him with cracked drywall.
Oklahoma typically has about 50 earthquakes a year, and 57 tornadoes, but a swarm of quakes east of Oklahoma City contributed to a sharp increase in the number of temblors. Researchers said 1,047 quakes occurred last year, prompting them to install seismographs in the area. A cause of the uptick wasn't known.
Saturday night's earthquake jolted Oklahoma State University's stadium shortly after the No. 3 Cowboys defeated No. 17 Kansas State. The crowd of 58,895 was still leaving when it hit, and players were in the locker rooms beneath the stands at Boone Pickens Stadium.
The temblor seemed to last the better part of a minute, rippling upward to the stadium press box.
"Everybody was looking around and no one had any idea," Oklahoma State quarterback Brandon Weeden said. "We thought the people above us were doing something. I've never felt one, so that was a first."
The magnitude 4.7 earthquake that struck the area early Saturday was also widely felt, but emergency officials said no injuries were reported at area hospitals right after that.
"Nothing is destroyed or anything like that," Prague City Police Department dispatcher Claudie Morton told the Tulsa World after the Saturday morning quakes.
A few hours before dawn Sunday, the latest quake set nerves on edge anew.
At the Prague Community Hospital in the region, registered nurse Jessie Plumb said no injured people had come into the emergency room by Sunday morning. But she said she and other hospital staffers felt the 4.0 magnitude quake before dawn while on the second floor of the building.
"It kind of gave a little bit of a shake, a little bit of rock `n roll," she told AP by phone. "I would say it was 20 or 25 seconds." She said she was anxious because of the number of quakes concentrated in her region in so short a span and the fact that they were so strong.
Saturday's late-night quake was slightly less in intensity than a temblor that rattled the East Coast on Aug. 23. That 5.8 magnitude earthquake was centered in Virginia and was felt from Georgia to Canada. No major damage was reported, although cracks appeared in the Washington Monument, the National Cathedral suffered costly damage to elaborately sculpted stonework, and a number of federal buildings were evacuated.
Turner said the Saturday night quake was Oklahoma's strongest on record.
USGS records show that a 5.5 magnitude earthquake struck El Reno, just west of Oklahoma City, in 1952 and, before Oklahoma became a state in 1907, a quake of similar magnitude 5.5 struck in northeastern Indian Territory in 1882.
She said an active spate of quakes began occurring in the region in February 2010 and added the latest activity appears to be part of that trend. She also said the magnitude 4.7 quake early Saturday appeared to be a prelude to Saturday night's more potent quake and Sunday's was an aftershock. "If these are going to continue to happen, we can't predict," she told AP.
But she said experts were still puzzling out why the latest quakes were concentrated in such a small geographic area around Sparks.
"The largest earthquake is a 5.6 and we call that the main shock," she said. "Everything before that 5.6 we consider a foreshock including the 4.7. Everything after the 5.6 we consider an aftershock."
Oklahoma Geological Survey researcher Austin Holland told Oklahoma City television station KOTV that the earthquake and aftershocks occurred on a known fault line.
Residents in Prague and Sparks felt an intense shaking, but for those farther away the quake was more of a dull rumble, he said.
"It shakes much more rapidly when you're closer to it," Holland said. "Because it's a large earthquake, it's going to rumble for a while."
The Prague police dispatcher Morton said her office was swamped with calls, mostly from jittery locals expressing their alarm. She said residents told her that picture frames and mirrors fell from walls and broke, drawers worked loose from dressers and objects tumbled out of cabinets.
"Oh, man. I've never felt anything like that in my life," Morton told the Tulsa newspaper. "It was the scariest thing. I had a police officer just come in and sit down and all the sudden the walls started shaking and the windows were rattling. It felt like the roof was going to come off the police department."