Why so many quakes in Okla.?

12/20/2009 12:00 AM

12/20/2009 12:08 AM

JONES, Okla. —During a typical year, Jones residents will feel one or two earthquakes. This year there have been 25 since March, according to the Oklahoma Geological Survey.

"I can tell you what's going on, but we don't know why," engineering geologist Ken Luza said.

Equipment coming to the state next year might help answer some questions.

Luza said he's not aware of any faults near Jones, but thousands of unnamed faults lie deep in the state's subsurface.

"Now, we usually average about 50 earthquakes per year in Oklahoma," Luza said. "So it's not unusual to have earthquakes. But what seems unusual is that they seem to be concentrated in eastern Oklahoma County."

Paul Wallis of Jones describes the earthquakes as "the boom and the shake."

Wallis said Thursday night's earthquake and another early Dec. 13 were the ones his family has felt most strongly.

"That one last night... we were actually putting the Christmas tree up, and the top went to shaking," he said.

He said he was in bed Dec. 13 when a boom startled him awake around 2:30 a.m.

"I think the boom woke me up, and I was sitting up when the shaking was taking place. We've got the train track that runs about 50 yards from the house, and it was about two or three times louder than that," he said.

His wife was downstairs working on the computer and ran upstairs.

"Her and the girls went to squealing," Wallis said.

When a rash of earthquakes happen in one location over an extended time, Luza said, it's called a swarm. They usually occur over a few days to a week.

"It's unusual to see it last eight months," he said.

Luza said there are only 15 seismograph stations in the state. That's enough to narrow the location of the epicenter to about a six-mile radius.

But it's not enough to get an exact location of the quake or depth, or to be able to tell whether the ground there was moving up and down, side to side or both, he said.

"To measure that, we'd need more seismograph stations, and they are coming," Luza said.

Beginning next year, Project Earth Scope, which is funded by the National Science Foundation, will bring in an additional 25 seismograph stations to Oklahoma. That will give the state a total of 40.

The equipment will be housed in Oklahoma for a two- to three-year study, then moved to another state.

But during that short window, Luza said, researchers will be able to collect data they have never had access to.

"We're hoping this will give us the opportunity to look at the data and maybe we'll be able to say something more definitive as to why," he said.

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