Earthquakes in Cleburne? Some North Texans suspect drilling behind recent quakes
ThereÂ’s a whole lotta shakinÂ’ goin on.
Cleburne experienced four earthquakes since Sunday, residents are getting shaky and some geologists arenÂ’t ready to rule out North Texas natural gas production as the cause, though they stop short of calling it a definite, direct correlation.
The earthquakes began Sunday evening with an episode that registered a magnitude of 2.6, according to the U.S. Geological Survey. (Earthquakes that cause damage usually are about twice that.) A second earthquake came Monday registering 2.3 – less than a week after a June 2 earthquake that registered a magnitude of 2.8.
“Most folks are not necessarily scared or worried about it,” said Cleburne City Manager Chester Nolen after the first three earthquakes. “We’ve got some people, they’re worried that it’s due to the gas drilling, then we’ve got some scientists who say, ‘oh it’s all due to gas drilling.’”
Nolen said he didnÂ’t feel all the earthquakes, but did notice one that rattled dishes and windows in his home.
“On the first one and third one I did not [feel anything], and I was sitting in my office,” he said. “On the second one I was sitting on my butt watching the basketball game and I felt it.”
After the initial three quakes had gained national attention for their novelty, earthquakes No. 4 and No. 5 struck Tuesday evening.
The City of Cleburne had about 100 calls regarding the initial three earthquakes, and Nolen isnÂ’t quite ready to chalk it up to natural gas drilling.
“I was born on a Gulf Oil Co. lease and put myself through college working on drilling rigs and working as a roustabout,” Nolen said. “I don’t believe it’s the approximate cause. I’m not going to say it’s not but I’m not certain it’s the cause.”
An earthquake expert said natural gas production could be the culprit, although itÂ’s never for certain.
“It’s very hard to say what causes any earthquake,” said Cliff Frohlich, associate director and senior research scientist with the Institute for Geophysics at the University of Texas at Austin. “That said, I’ve spent a fair amount of time looking at these events over the past several months. I think most reasonable people with earthquake training probably would say they’re related to the gas production.”
He said there have been about 100 tiny earthquakes picked up since October 2008.
“What’s unusual about them, the ones we can locate, they appear to come from almost exactly the same spot,” he said, “and natural quakes tend to form a cloud, they’re not so localized. Also there isn’t a history of tectonic quakes in North Texas.”
Residents shouldn’t be concerned because these are “little tiny quakes,” Frohlich said. Drilling-induced earthquakes tend to be small elsewhere in Texas, and hydraulic fracturing doesn’t cause a big enough disturbance to generate bigger earthquakes.
“I’d be extraordinarily surprised if these caused a 5 or a 6,” he said.
What causes Texas quakes?
According to Texas Earthquakes, which Frohlich co-wrote and published in 2003, drilling itself does not cause earthquakes.
“However, earthquakes in some parts of Texas may be induced by the pumping of fluids at oil and gas fields or by the injection of fluids to dispose of chemical wastes … Moreover, while there are tens of thousands of oil and gas wells in the state of Texas, in only a few fields does evidence indicate that oil and gas pumping induces earthquakes.”
Drilling has been known to cause earthquakes in some parts of the state, according to a 1998 report by the GovernorÂ’s Division of Emergency ManagementÂ’s Department of Public Safety. The report was revised in 2001.
“In northeastern Texas the greatest hazard is from very large earthquakes (magnitude 7 or above) which might occur outside of Texas, particularly in Oklahoma or Missouri-Tennessee,” according to the report. “In south-central Texas the hazard is generally low, but residents should be aware that small earthquakes can occur there, including some which are triggered by oil or gas production.”
The largest quakes caused by oil and gas production in North Texas have been in Lamar, Gregg, Denton and Cooke Counties, among others. The largest earthquake registered 4.2 and struck in April 1934, according to the report.
Many geologists stop short of calling correlation between drilling activity and earthquakes a definite causal relationship, however, itÂ’s clear the incidence of earthquakes has increased as Barnett Shale production increased during the past two decades.
Since 1975, there have been only a few cases of earthquakes within 100 miles of Fort Worth, according to the U.S. Geological Survey. Barnett Shale production grew steadily since the 1980s, but really picked up speed in the late 1990s and early 2000s.
In 2003, there were almost 3,000 producing wells in the Barnett Shale, according to the Railroad Commission of Texas, and three incidences of earthquakes within 100 miles of Fort Worth, according to the U.S. Geological Survey.
In 2008, there were more than 10,000 producing wells and 10 occurrences within 100 miles of Fort Worth. Since the beginning of 2009, there have been seven occurrences of earthquakes.
The director of the Barnett Shale Energy Education Council, Ed Ireland, said he has received calls from reporters but no concerned citizens. He said the industry knows as much about earthquakes and their causes as anyone else: not much.
“What I hear from all these geologists is basically they don’t know,” he said. “It hasn’t been studied and whether or not there is any relationship between drilling and earthquakes, what I hear them saying is it’s not known. Some of these geologists have said there has not been a proven relationship and others say it’s possible.”
jtronche@bizpress.net
