NORMAN — A swarm of rumblings this year beneath the state’s red dirt is shaking off misconceptions consigning earthquake tremors to the West Coast.

“They can and do happen everywhere,” said Bob Pierce, of the Incorporated Research Institutions of Seismology, as he installed a seismometer — used to record earthquake data — earlier this month on a rancher’s land about 11 miles southeast of Tecumseh. “Some places they’re happening all the time, you just can’t feel it.”

The Oklahoma Geological Survey records more than 50 earthquakes a year in Oklahoma, said Austin Holland, seismologist for the organization, adding that Oklahoma — typically flagged for stirring cyclone touchdowns along the corridors of Tornado Alley — has always had small earthquakes, which he credited to periods when the land was stretched apart, Arbuckle mountains were pushed up and large basins developed.

So far, the research group has charted 34 earthquakes in Oklahoma, including one on Feb. 27 in Lincoln County that reached a magnitude of 4.4, which is forceful enough to be felt indoors and rattle dishes and windows.

Dissecting shakes

Local scientists are scratching their heads to pinpoint the backstory to the shaking stir that’s rocked the state this year.

“We’re not really certain,” said Holland of this year’s quake numbers, noting similarities to tremor occurrences in 2004. “It’s sort of the nature of earthquakes. They often cluster temporarily and then are quiet for awhile. It’s all within the realm of possibilities.”

Randy Keller, director of the survey, also credited advancements in technology and citizen awareness for the higher number of earthquakes. The Oklahoma Geological Survey, for example, has a component on its Web site for people to report feeling an earthquake.

“We just have an incomplete history of these small earthquakes,” said Keller as he surveyed the installation of the seismometer near Tecumseh.

Ins and outs of quakes

According to the U.S. Geological Survey, earthquakes typically occur when two faults within bedrock, usually miles deep, slide past each other.

Keller said there are likely faults deeply buried in the state where the latest rumblings have occurred, noting the trend of reported shakings streaming through the middle of the state — mostly in Oklahoma, Lincoln and Canadian counties — which he referred to as the Nemaha structures.

The rumblings, however, can’t be linked to named faults, since they remain undetected below the Earth’s surface, Holland said.

“We don’t have a fault map we can put them on. We can’t see inside the Earth,” he said, adding that the only time an earthquake in Oklahoma has ruptured the surface was along the Meers fault line, which runs west of Lawton.

The last movement along this fault was 1,200 years ago, measuring a magnitude of 6 plus, said Ken Luza, engineering geologist at the survey. Luza is also known as Mr. Meers Fault by Keller, since he was one of the researchers who studied the fault’s scarp — the displacement that occurred when its movement broke the Earth’s surface — in the 1980s.

“If anyone was ever going to be afraid of a large earthquake coming somewhere, that’s the one,” Keller said. “But that’s not likely.”

Keller has a running theory that there is a rift zone extending from the Great Lakes to Oklahoma, adding that the Midcontinent Rift remains narrow until it reaches the plains of Kansas, where it begins to spread into Oklahoma. 

View from the inside

Whether this scenario is true could be determined within the next few years as 400 seismometers, like the one buried near Tecumseh, are installed every 45 miles through the country, rotating to a new location every two years.

EarthScope, a collaboration of scientists and educators based at Oregon State University, is leading the project, planting seismometers that will record earthquakes that occur locally, regionally and throughout the world.

The images, available on EarthScope’s Web site at www.earthscope.org, will be used to paint a three-dimensional, detailed picture of the Earth’s mantle to study the characteristics and origins of earthquakes and their faults, so scientists can better predict quakes.

“You name it, I’ve probably been to your hometown and dug a hole in it,” said Pierce, who has been installing these devices, which migrate west to east, for the last five years.

Pierce said the devices already have disproved several scientists’ theories of faults in states like Washington, where the seismometers have ended their temporary stint.

Oklahoma has 18 seismometers buried beneath its red dirt, part of an eventual total of 39.

While the installation isn’t complete, Holland credited the devices with tracking a more accurate location of a swarm of six earthquakes that occurred in a three-day period earlier this year. He said during a chain of similar rumblings in 2004, only one location could be pinpointed.

“Most of what we’re seeing in Oklahoma is small earthquakes,” Holland said. “Even the ones that people feel … still small earthquakes. It’s hard to get one that’s big enough to be seen, since our stations are very spread out. Having a dense system like this is very expensive, and it’s already making a difference.”

The array of stations, placed in isolated areas — mainly private land — for better readings, will stay in Oklahoma for two years before continuing the trip east.

Some of the devices, however, will remain under the supervision of the Oklahoma Geological Survey. Holland said he is writing a grant to adopt these stations.

“It’s a godsend that we’re getting all these stations during this increase of earthquake activity,” Holland said. “I’m having a hard time keeping up with the data.”

Nanette Light 366-3541 nlight@normantranscript.com