The Irving, Texas area experienced 11 earthquakes between Tuesday and Wednesday, prompting further speculation about the role of fracking in seismic events.
The first, a 2.3 magnitude quake, hit around 7:30 AM on Tuesday; the last, a 2.7 magnitude quake, came Wednesday morning around 10. The strongest of the 11 was a 3.6 magnitude quake—classified as "significant" by the U.S. Geological Survey.
Earthquake experts with Southern Methodist University, who are installing more more seismographs in the area, say it's too soon to pinpoint the cause.
In November, Irving was hit by another series of earthquakes—five in a four-day period—an event that sparked some to question whether fracking operations were responsible.
Such increased seismic activity appears to be a historic anomaly. From the National Geographic:
"It's premature to speculate on the causes of the earthquakes," says Brian Stump, a seismologist and professor at Southern Methodist University, in Dallas, who is studying the recent temblors.
Earthquakes in the area had been virtually unknown until relatively recently. "If we go back prior to October of 2008, the historical record indicates there might have been one earthquake in 1950, but that was about it," says Stump.
Since then, there have been more than a hundred seismic events in the area, known as the Fort Worth Basin.
Though the Railroad Commission, which regulates the oil and gas industry in the state, dismissed any such connection, Stump added that fracking wastewater injection wasn't being ruled out as a possible cause.
"Historically, it has shown that in some places that they've triggered small to moderate earthquakes,” local fox4news.com reports Stump as saying.
The U.S. Geological Survey and the Oklahoma Geological Survey stated last year that fracking wastewater injection was "a likely contributing factor to the increase in earthquakes" in Oklahoma, and a study released this week found that a strong quake that hit Ohio in March 2014 was likely caused by fracking.