Another small earthquake vibrated Irving Sunday night: a magnitude of 2.5 at 7:46 p.m., according to the U.S. Geological Survey. That makes 17 in the last week in North Texas, most of them around the old Texas Stadium site in Irving. As the quakes continue, speculation circulates as to what's causing them.
The double-digit swarm of small quakes has the Dallas City Council and Dallas County Judge Clay Jenkins talking about how to get ready for a bigger one.
Jenkins hosted a conference call Friday with 50 local emergency management directors, FEMA and the U.S. Geological Survey.
“The experts think that if this reaches up into the 4s of the Richter Scale, given the shallow nature of where these earthquakes are compared to the deeper earthquakes compared to other parts of the country and the continent, there could be some structural damage,” Jenkins said.
Jenkins says unreinforced brick, cinder block or stone buildings are at greatest risk. So far, there's been no damage. The strongest of the quakes has measured a magnitude of 3.6.
Jenkins says seismologists are working hard to try to figure out what’s going on.
A couple of water-cooler theories are floating around. They center what happened several years ago on two pieces of real estate in the quake zone near State Highways 183 and 114.
One thought is that the vibration from the implosion of Texas Stadium, which sits above the Balcones Fault, changed the stresses along the fault and that energy is now being released in the form of minor to moderate earthquakes. That idea made seismologist Brent Blanchard laugh.
“To actually try to connect that to a scientific theory that a vibration that really transfers energy about 10 feet into the ground at the most would cause earthquakes hundreds of feet or miles underground is pretty much without merit,” Blanchard said.
Blanchard heads up Protec Services in New Jersey. It’s an international vibration consulting company and was among several to set up equipment to monitor the Texas Stadium implosion in 2010.
Blanchard says his monitors on the river levees about 900 feet away didn’t pick up anything from the series of dynamite charges and 6 million pounds of concrete and steel crashing down.
"Even seismographs over top of underground utility lines that were about 60 feet away and running right next to the stadium, those detected minimal vibrations," Blanchard said. "We're talking about point-0-0-something."
Blanchard says there’s no way the stadium implosion is the culprit.
Another suspect being talked about: the inactive natural gas well about a mile north of the stadium. Could natural gas drilling and fracking be the cause of the quake and shake?
A study last summer by the USGS, Cornell and University of Colorado-Boulder linked Oklahoma earthquakes to fracking waste-water injection wells. The nearest such well to the Irving quake zone is more than 10 miles away at the far north end of D/FW International Airport near Flower Mound.
A study published recently by the Seismological Society of America shows a link between fracking and earthquakes in Poland Township, Ohio. A co-author of the study, Michael Brudzinski, says they found the series of five earthquakes were centered half a mile from six gas wells and happened only during the hours drillers were fracking. But fracking at the Irving well ended in 2009, and that makes Brudzinski discount drilling activities.
“It’s hard to believe that fracking that took place many years ago would be resulting in earthquakes today,” Brudzinski said.
He says it appears North Texas seismologists looking for clues will have to drop fracking as a credible suspect.
On Monday, the Dallas City Council discusses emergency plans for earthquakes.
SMU seismologists have deployed more seismographs in Irving following the recent earthquake activity. We've reported before on SMU's efforts to study North Texas earthquakes. Here's another story on SMU's efforts.