WASHINGTON -- The swarm of earthquakes went on for months in North Central Texas, rattling homes, with reports of broken water pipes and cracked walls and locals blaming the shudders on the fracking boom thats led to skyrocketing oil and gas production around the nation.
Darlia Hobbs, who lives on Eagle Mountain Lake, about a dozen miles from Fort Worth, said that more than 30 quakes had hit from November to January.
We have had way too many earthquakes out here because of the fracking and disposal wells, she said in an interview.
While the dispute over the cause remains, leading geophysicists are now saying Hobbs and other residents might be right to point the finger at oil and gas activities.
It is certainly possible, and in large part that is based on what else weve seen in the Fort Worth basin in terms of the rise of earthquakes since 2008, William Ellsworth, a U.S. Geological Survey seismologist, said in an interview Thursday.
Ellsworth said the Dallas-Fort Worth region previously had just a single known earthquake, in 1950.
Since 2008, he said, there have been more than 70 big enough to feel. Those include earthquakes at the Dallas-Fort Worth airport that scientists linked to a nearby injection well.
Ellsworth briefed his colleagues on his findings Thursday at the Seismological Society of Americas annual meeting in Anchorage, Alaska.
Researchers also are investigating links between quakes in Kansas, Oklahoma, Ohio and elsewhere to oil and gas activities. USGS seismologist Art McGarr said it was clear that deep disposal of drilling waste was responsible for at least some of the earthquakes in the heartland.
It is only a tiny fraction of the disposal wells that cause earthquakes large enough to be felt, and occasionally cause damage, McGarr said. But there are so many wells distributed throughout much of the U.S. they still add significantly to the total seismic hazard.
While causes are under debate, its well established that earthquakes have spiked along with Americas fracking boom. The USGS reports that an average of more than 100 earthquakes a year with a magnitude of 3.0 or more hit the central and eastern U.S. in the past four years.
That compares with an average rate of only 20 observed quakes a year in the decades from 1970 to 2000.
Regulators in Ohio found what they said was a probable connection between small quakes in the northeast corner of that state and the process of hydraulic fracturing, or fracking, in which high-pressure water and chemicals are pumped underground to break up shale rock and release the oil and natural gas inside.
But the USGS considers it very rare for fracking itself to cause earthquakes. Far more often the issue is quakes caused by the disposal of the wastewater into wells.
Fracking produces large amounts of wastewater, which companies often pump deep underground as an economical way to dispose of it without contaminating fresh water. Injection raises the underground pressure and can effectively lubricate fault lines, weakening them and causing quakes, according to the USGS.
Its a sensitive issue because the fracking boom has brought jobs and economic development, as well as abundant energy, and states are often hesitant to interfere.
Oklahoma has been struck especially hard. Since 2009, the earthquake activity in Oklahoma has been approximately 40 times higher than in the previous 30 years, according to the Oklahoma Geological Survey, which says its researching whether oil and gas activity is playing a role. Oklahoma has recorded more than 300 earthquakes this year, including 11 in a single day this week.
Most of the earthquakes connected to oil and gas activity are small, although a 5.7 magnitude quake in Central Oklahoma was felt as far away as Milwaukee and destroyed 14 homes. The Oklahoma Geological Survey disputes studies that link the 2011 quake to injection wells.
The Texas Railroad Commission, which regulates the oil and gas industry in that state, is also skeptical of the link between earthquakes and drilling.
The commission bases its regulation on science and facts, and at this time staff have no information or science that warrants limits to drilling or hydraulic fracturing in Texas, spokeswoman Gaye McElwain said in an email.
USGS seismologist Ellsworth said that near Fort Worth, two disposal wells were close enough to the earthquakes to be responsible. He said more research was needed to determine whether they were the cause, or whether the natural gas production itself in the Barnett Shale was responsible.
Ellsworth and his colleagues, including seismologists from Southern Methodist University, in their presentation Thursday ruled out the idea that the falling level of a nearby lake might be contributing. But he said they couldnt entirely reject the possibility of other natural causes _ despite earthquakes being virtually unheard of in the region before 2008, a time frame that matches the start of the fracking boom.
Hobbs, of Eagle Mountain Lake, Texas, said shed lived in the area since 1967 and never even considered the possibility of earthquakes.
Its spooky, she said.
The federal government has left decisions on earthquake regulations for wastewater injection wells to the states, some of which have decided theres enough evidence to take action. Arkansas banned new injection wells in a large region and Ohio has tightened its seismic rules.
Texas Railroad Commission spokeswoman McElwain said geology varied greatly from state to state. There are more than 144,000 disposal wells nationwide and very few and relatively minor seismic events have been documented, according to commission Chairman Barry Smitherman. The commission announced March 28 that its hired a seismologist to look into the issue.
Some in North Central Texas say the railroad commission is too slow to act and hasnt taken the earthquakes seriously enough.
If they dont think the wells are the cause of the earthquakes, then let them put them in their backyard and not in ours, said Lynda Stokes, who trains dogs and horses in Reno, Texas, and is also the part-time mayor of the town of about 3,000 people. Well be happy to share.
There are also worries in Kansas, where residents want to know whats caused a recent surge in earthquakes in the south-central part of the state, an area where oil and gas production is on the rise. Gov. Sam Brownback has appointed a task force to look into it.
Part of the problem in getting answers is a lack of seismic monitoring equipment in Kansas, a state without a big history of earthquakes.
Being able to capture these things better is pretty important, said Rex Buchanan, the interim director of the Kansas Geological Survey.
Buchanan, a member of the governors task force, said it wasnt clear whether the nearby injection wells were playing a role in the quakes.
Its a possibility, but I dont think anybody is willing to go that far, at least nobody that is looking at this seriously at this point, he said.
USGS seismologist McGarr attributes the quakes to drilling in the Mississippian Lime shale formation, which straddles the Kansas-Oklahoma border.
There is little doubt that these earthquakes are due to the injection wells in that field, he said.