【案例】
For a Weekend, Oklahoma is Earthquake Country
![]() Sue Ogrocki/Associated Press
Jess Burrow, left, and James Patterson, looked over the damage caused by Saturday's earthquake in Sparks, Okla.
By SARAH MASLIN NIRPublished: November 6, 2011
But on this Saturday and Sunday, the earth moved — at least 23 times — and football was not involved.
The quakes, powerful by Midwestern standards, shook towns about an hour’s drive northeast of Oklahoma City. They began early Saturday and continued intermittently through the weekend.
Late Saturday night, the area experienced the strongest earthquake ever recorded in the state. No serious injuries were reported, but minor damage to roads and buildings was reported, according to the Sheriff’s Department in Lincoln County, the epicenter for many of the quakes.
Geological activity in the region has increased in recent years, and earthquakes have occurred with greater frequency and intensity. The big quake on Saturday night, which occurred at 10:53, had a preliminary magnitude of 5.6, according to the National Earthquake Information Center, a division of the United States Geological Survey.
The Geological Survey said Saturday night’s quake was shallow, about three miles deep, and that the epicenter was four miles east of Sparks, which is about 44 miles northeast of Oklahoma City.
That quake followed smaller ones earlier in the day, including one at 2:12 a.m. with a preliminary magnitude of 4.7. Its epicenter was in Prague, about 50 miles east of Oklahoma City.
Since mid-2009, the state has had 10 times more earthquakes than normal, said Austin Holland, a research seismologist with the Oklahoma Geological Survey. In 2010, the earth beneath Oklahomans’ feet moved more than 1,000 times, but only 100 or so were strong enough to be felt.
“We have not a clue,” Mr. Holland said of the increase. “It could be a natural cycle; we just don’t know.”
Unlike earthquake-prone California and Japan, Oklahoma does not rest atop the fractious areas where two tectonic plates rub against each other. But the state’s geophysical activity has only been surveyed in earnest for about 50 years, Mr. Holland said, making it difficult to draw conclusions or put the recent activity into context.
But the state does have faults that are buried deep, like the Wizetta Fault, also known as the Seminole Uplift, east of Oklahoma City, where pressure can build.
“You still get earthquakes within the plate. That doesn’t mean there’s a plate boundary, but there’s a fault,” said Don Blakeman, a geophysicist at the National Earthquake Information Center.
That pressure is released as tremors like those that startled residents over the weekend in Prague, Okla., where the visible damage on Sunday morning included chimneys that had collapsed onto houses. In a house on North Road, a china cabinet was emptied of its contents, which were smashed, Mr. Holland said. Parts of Highway 62 between Prague and Meeker buckled, he said.
In Lincoln County, cracks ran up the brick courthouse in Chandler after a smaller quake early Saturday morning, said Justin Reese, who runs the Boomarang Diner there.
Since the Saturday night quake, there have been 11 aftershocks that measured above 2.5 on the Richter scale, Mr. Blakeman said.
Mr. Holland said the intensity of the Oklahoma earthquakes “could go either way.”
But this being Oklahoma, the football fans in Norman and Stillwater were not to be outdone by any earthquake on Saturday.
In Norman, the University of Oklahoma Sooners beat the Aggies of Texas A&M, 41 to 25, and in Stillwater, the Oklahoma State Cowboys defeated the Kansas State Wildcats, 52 to 45.
http://www.nytimes.com/2011/11/07/us/oklahoma-earthquake-sets-a-record.html?_r=1&ref=us
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