Updated Thursday 12:30 p.m. ET.
A rare series of earthquakes in northern Texas has residents asking if oil and gas activities are responsible for the shaking, which has left people rattled but did not cause significant damage or injuries.
A series of nine earthquakes ranging in magnitude from 1.6 to 3.6 shook the Dallas region over a period of less than 24 hours late Tuesday and early Wednesday. The shaking was felt in Dallas, Irving, and surrounding towns. Residents of those areas have flooded Twitter with accusations that the quakes were caused by oil and gas activity.
Scientists say they won't know the cause of the temblors for perhaps a year, but that it's possible industrial activities could have played a role. A scientific study published this week concluded that several small earthquakes near Youngstown, Ohio, in March were caused by fracking activities near a fault.
In Texas, "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.
Stump and other scientists have published research finding "a plausible link" between some recent earthquakes and waste injection wells in the area. The wells are created by shooting polluted water from fracking or other industrial activities deep into the earth, often at high pressure, to dispose of the waste. (Learn about a possible link between a rise in earthquakes in Oklahoma and injection wells.)
But the seismologist notes that "there are those that disagree" with his findings.
Stump is part of a team that's deploying instruments in the area to better measure the specific characteristics of the earth and to map the area's fault lines. Scientists will then analyze the data over the coming months.
Tuesday's and Wednesday's quakes are the fourth significant sequence of seismological events since 2008. Other recent quakes have struck near the Dallas/Fort Worth International Airport and in the northern part of the basin.
Link to Injection Wells?
A growing body of research suggests that wastewater injections may lubricate faults and trigger earthquakes, although some industry representatives have downplayed the possibility of a link. (Learn more about fracking and quakes.)
The Railroad Commission of Texas, which regulates the oil and gas industry in the state, recently ordered companies to check local seismic records before they open a new waste disposal well. The ruling came after residents of the town of Azle, outside Fort Worth, complained that recent earthquakes there may have been spurred by new injection activities. Scientists are currently studying the question.
Stump says that it's difficult to link any one earthquake with an injection well. "But by studying a number of events, my hope is that we can come to an understanding of these processes," he says.
Elizabeth Cochran, a seismologist with the U.S. Geological Survey in Pasadena, California, says it often takes about a year of analysis to determine the cause of an earthquake.
"What we typically do is put out additional instrumentation, which allows us to get better location data, and then we can look at where the faults are in relation to any injection wells and determine how likely it is that a particular sequence is related to that or not," says Cochran, who has studied the link between injection wells and earthquakes in Oklahoma.
"There have been a number of studies that have pointed toward wastewater injection as a cause, not for every single seismic event but perhaps for a significant portion of those events," says Cochran, pointing to research from Oklahoma, Kansas, Texas, and elsewhere.
On top of a significant uptick in Oklahoma earthquakes in recent years, Cochran says she has seen an increase in the number of aftershocks. "That's a fundamental change in tectonic events," she says, "which tend to behave in a predictable way, so it has to be driven by something.
"It suggests that there could be some sort of forcing, which would potentially point to injection."
Chad Warmington, president of the Oklahoma Oil and Gas Association, recently told National Geographic that it's too early to know if injection wells are responsible or if the rise in earthquakes in his state is part of a natural cycle.
"We are concerned about it because we live here, but we don't want to have a knee-jerk reaction and have a bunch of regulation put on us that is not effective in minimizing the risk of seismic activity," he said.
The Texas Bureau of Economic Geology did not respond to a request for comment Wednesday.
The Texas Bureau of Economic Geology, which studies geologic issues for the state, said on Wednesday that it did not have someone available to comment.