Oklahoma Earthquakes 2010: What's the Cause?

(Oct. 13) -- Sooner shakeup! Residents of Oklahoma were jolted this morning by something entirely unexpected: an earthquake that struck the state around 9 a.m. local time, damaging several buildings, causing minor injuries and rattling people in five other states.

The quake was centered five miles east-northeast of Noble and eight miles southeast of Norman. The U.S. Geological Survey originally categorized the quake at 4.3 magnitude, but the Oklahoma Geological Survey later came out with its own assessment of 5.1 (for comparison, the quake that devastated Haiti earlier this year was categorized initially as a 7.0).

Just what accounted for the variation in measurements?

The Oklahoma Geological Survey Observatory explains:

These are two different estimates of an earthquake's size. They are two common seismological methods for determining the size, or magnitude, of an earthquake, which cannot be measured directly. They often have discrepancies similar to those that we are seeing for this earthquake. It is entirely possible that the magnitude estimates will change over time as further work is done to measure the size of the earthquake.

Worryingly for Oklahomans, the state's geological survey notes that similar earthquakes could occur "at any time." In fact, though several outlets reported that this was the first quake in years, the Oklahoma Geological Survey disagreed, pointing out that a 4.1 earthquake had occurred in February, and that 2010 was overall a banner year for earthquakes in the state. Indeed, a cursory look back through the year in the eyes of local publications reveals a spate of observed earthquakes in early 2010.

What causes Oklahoma earthquakes, though?

All scientific parties are in agreement that the state is riddled with fault lines, including the Meers fault, which could be to blame, but others hypothesized that increased oil and gas drilling activity could have played a part as well. As NewsOK reported:

Most quakes are close to "plate boundaries," those zones where the earth's huge tectonic plates bump and grind against each other, slide or plow over and under one another, said Estella Atekwana, professor of hydrogeology at Oklahoma State University. But here in the middle of the continent, she said, "We are not in an area that is tectonically very active."

Atekwana, who studies plate tectonics, said energy for Oklahoma's quakes must then come from other forces. Those could include buried faults that have yet to be identified, or even oil and gas drilling processes, she said.

And as News9 reported:

Other geologists said production wells have not been tied to earthquakes, but disposal wells, where the saltwater and other fluids used in oil and gas production are injected back into the earth have been shown, in some cases, to cause small quakes.

Of course, one of the major companies behind such activities, New Dominion LLC, argues that its own scientific testing has not found any link between disposal wells and the uptick in quakes recently.