About 16 hours after the largest earthquake on record in North Texas shook Venus and parts of surrounding cities, the event was the talk of the morning at the Shell station at U.S. 67 and Farm Road 157.
“Everybody is asking, ‘Did you feel it? Did you feel it?’” said Maria Tanguma, who works at the convenience store.
Tanguma herself did not feel the magnitude-4.0 quake that struck at 5:58 p.m. with an epicenter 3 miles north-northwest of Venus and 6 miles south of Mansfield, according to the U.S. Geological Survey.
But her mother in Mansfield did, as did people in Arlington, Alvarado, Burleson, Cleburne, Dallas and Grand Prairie.
With more than 50 earthquakes having rattled North Texas since November 2013 and this one being the strongest, is it time to add quakes to the list of disasters that area residents need to prepare for?
Jana Pursley, a geophysicist with the U.S. Geological Survey, said, “I wouldn’t say that any area is safe from having a major earthquake, only that major earthquakes are unlikely in some areas.
“Texas is not an area we’ve seen associated with major earthquakes.”
After Thursday’s quake, SMU researchers say, it’s time to re-examine what we believe.
“This illustrates that we all need to think about the possibility of larger earthquakes in the region where we live,” Brian Stump, SMU Albritton Chair in Geological Sciences, said in a statement.
With a magnitude of 4.0, Thursday’s quake was about 16 times as powerful as the magnitude-3.4 quake that struck the same area in November. By comparison, the magnitude-7.8 earthquake in Nepal was about 120 times as powerful as Thursday’s quake.
Jamie Moore, Johnson County’s emergency management coordinator, said two mobile homes sustained minor damage. No other damage was reported. The earthquake lit up Twitter and Facebook more than the county’s 911 operations, Moore said.
Texas Railroad Commissioner Ryan Sitton came from Houston to help inspect natural gas wells and disposal sites in the area of the quake and said “not the slightest” damage had been found.
The Railroad Commission notified four disposal well operators Friday that they must conduct well and reservoir testing. Five wells are within 100 square miles of the estimated epicenter. The operators voluntarily agreed to shut down temporarily to conduct the testing within days, the commission said in a statement.
Taking pressure readings and making other observations will gather more information that could help explain the role that fracking and other drilling activity may play in the rise in earthquakes, Sitton said.
“The engineer in me loves the data,” he said.
SMU researchers said the earthquake was part of a series of smaller quakes that their team has been following in the Midlothian area. Some 23 earthquakes have been recorded within 12.4 miles of the Venus location since 2009, with five of them registering higher than magnitude 3.
“I don’t think any of us was surprised by Thursday’s event,” Heather DeShon, SMU associate professor of geophysics, said in a statement. “There have been a series of magnitude-3 and greater earthquakes in the Johnson County area. If you have movement on a fault and change the stresses, you increase the likelihood of additional earthquakes. In other words, one earthquake frequently leads to another.”
In late April, the U.S. Geological Survey released preliminary models to forecast how hazardous ground-shaking could be in the areas with sharp increases in seismic activity. The models aim to calculate how often earthquakes are expected to occur in the next year and how hard the ground will likely shake.
Unlike, say, San Francisco, North Texas is not known to sit atop an active fault line, said Pursley, the geophysicist.
“Some fault lines have surface expression, and many of those are active,” she said. “Other faults don’t have surface expression and aren’t active, so we don’t know they’re there. But they can become active.”
Most likely cause
Wastewater injection wells and other processes tied to oil and natural gas drilling are the most likely cause of a rash of earthquakes that hit in the Azle and Reno area northwest of Fort Worth, according to a scientific study published last month.
An article in the science journal Nature Communications says the 27 earthquakes in that region from November 2013 to January were in an area where no earthquakes had been reported or felt in 150 years, leading them to link the quakes to nearby wells.
Seismologists already suspected that hydraulic fracturing — which injects water, sand and chemicals deep into rock formations to free oil and gas — can cause small quakes that are rarely strong enough to register on monitoring equipment.
But fracking also generates vast amounts of wastewater, which is then pumped into injection wells that send the waste thousands of feet underground.
Concerns about the connection between drilling and earthquakes has been heightened lately with a series of quakes in Irving, with much of the activity occurring near the old Texas Stadium site. The exact cause of those quakes has not been determined, and DeShon didn’t want to speculate.
Other studies have pointed to a link between wells and quakes, especially in Oklahoma and southern Kansas, an area that has had more than 950 magnitude-2 or higher earthquakes this year, according to the Geological Survey.
Last month, the Oklahoma Geological Survey said it’s “very likely” that most of the state’s recent quakes were triggered by the injection of wastewater from oil and natural gas operations. The agency investigated dozens of earthquakes in central and north-central Oklahoma.
In 2009, researchers from SMU and the University of Texas at Austin began investigating small quakes at Dallas/Fort Worth Airport that occurred from October 2008 to May 2009. They published their study in March 2010.
The quakes stopped after Chesapeake Energy, in August 2009, shut down one of two injection wells it operated on DFW property.
UT Austin researchers reviewed seismic data collected in several locations in the Barnett Shale from November 2009 to September 2011. Cliff Frohlich, senior research scientist at UT’s Institute for Geophysics, released a study in August 2012 concluding that “injection-triggered earthquakes are more common than is generally recognized.”
Both studies also said it is “plausible” that injection wells triggered the quakes. Frohlich is a co-author of the article in Nature Communications. DeShon said in 2014 that researchers hope additional study would allow them to be more “precise.”
When asked whether the drilling might cause catastrophic earthquakes, DeShon said last month that the occurrence of any earthquake increases the chance for more.
“The faults that we’ve looked at so far are not long enough … for a truly catastrophic earthquake. That doesn’t mean these faults we know of don’t have the potential to cause an earthquake of a 4 or 5 [magnitude] that could cause damage in an area like North Texas, which has not been built to seismic-safety engineering standards,” she said.
On Thursday, Tom Fayo of Alvarado felt the jolt at his home in an RV park.
“I thought it was a tornado coming through at first,” said Fayo, who experienced California quakes in the 1970s and ’80s when he was a truck driver. Thursday’s event was nothing like that, he said. But, he added, “I think it may just be a matter of time.”
Staff writer Max B. Baker contributed to this report, which includes material from the Star-Telegram archives.
Patrick M. Walker, 817-390-7423
The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter scale, magnitude is expressed in whole numbers and decimals. For example, a magnitude of 5.3 might be computed for a moderate earthquake, and a strong earthquake might have a magnitude of 6.3. Because of the logarithmic basis of the scale, each whole-number increase represents a tenfold increase in measured amplitude. As an estimate of energy, each whole number corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number.
Source: U.S. Geological Survey