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Archive for Monday, October 4, 2004

Kansas earthquakes rarely leave residents shaken

October 4, 2004

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Californians are cleaning up after a series of earthquakes struck the state last week, but deep below the surface in Kansas, the earth may also be rumbling.

Kansas has long been known for its tornados, but it can have at least a dozen earthquakes a year, thanks to its own subsurface earth movements.

"Most of the time you are not going to notice them," said Rex Buchanan, associate director of the Kansas Geological Survey at Kansas University.

That's because most of the Kansas temblors register below 3.0 on the Richter scale, the seismic measurement used for earthquakes.

Nevertheless, a buried granite mountain range across the state, extending from Oklahoma City to Omaha, Neb., has its faults.

Most notable is the Humboldt fault line on the eastern boundary of what is called the Nemaha Ridge. It extends from near El Dorado up to the Manhattan and Wamego area. West of Nemaha Ridge is the Midcontinent rift.

While most Kansas quakes are unnoticeable, larger ones can occur. On the night of April 24, 1867, one did.

A quake centered near Wamego cracked walls and loosened bricks on buildings in northeastern Kansas. Chimneys were knocked down and a newspaper office wall crumbled in Paola, according to geological survey accounts. Some people were injured. The quake was felt as far north as Dubuque, Iowa.

"It was felt very strongly in Lawrence," said Don Steeples, vice provost and geophysics professor at KU. "There wasn't any serious structural damage, but things were knocked off shelves and there was general alarm."

Scientists have since estimated that quake to have been as strong as 5.7 on the Richter scale, or slightly stronger than the one last week that shook Parkfield, Calif., and the central part of that state.

The 1867 quake is the largest recorded in Kansas. But there have been other, similarly sized earthquakes, including one in 1904 in Dodge City.

Western and central Kansas quakes could be caused by an earth uplift that stretches from about Wichita to the Black Hills in western Nebraska, Steeples said. It could have caused about a dozen quakes during the past 20 years felt in Rooks, Graham, Ellis and Russell counties.

Some small quakes may be the result of man's actions, Buchanan said. Some in western Kansas might have resulted from injection of salt water to squeeze more production out of oil wells, he said.

In May 1999, the ground shook in Wyandotte and Johnson counties. Two office buildings on a hill near Interstates 635 and 70 in Kansas City, Kan., had to be evacuated and later torn down because of damage. Lines of cracks, some at least a foot wide and deep, crossed the asphalt parking lot.

"We believe that was caused by the collapse of a roof to an old limestone mine," Steeples said.

During a 12-year-period from December 1977 to June 1989, a geological survey seismograph recorded more than 200 earthquakes in Kansas and Nebraska. The largest was a 4.0 on the Richter scale and the smallest a 0.8. Because of lack of funding, KGS no longer has a seismograph.

A quake like the one in 1867 probably occurs in Kansas once every 200 years, Steeples said.

"We don't know when the next one will be, we just know that sooner or later it will come," he said.

Buchanan isn't concerned.

"It's not on my list of things to worry about," he said.

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