No one really has any idea what's causing the "swarm" of earthquakes along the Irving Dallas border. What is known is that this is a new phenomenon. None of us who grew up here in the DFW area can ever remember having this kind of problem with the ground shaking – and certainly not with almost a dozen noticeable quakes in 24 hours.
Circumstantial evidence points to "human-induced seismicity" as the oil and gas industry folks call it, although one can't be certain. Ground zero for these earthquakes is along the Balcones Fault, about the oldest geographical feature in Texas – clocking in at one billion or so years old. It's the same fault that runs down Highway 67 and then I-35 by way of the limestone escarpment in Cedar Hill and Midlothian, the one the cement plants there mine for raw material. It snakes up to the Texas – Oklahoma border in less dramatic fashion, including along the Trinity River bottomland where the Irving/Dallas quakes are being recorded.
What's also known is that when you apply new pressures, or re-arrange the pressures, to an existing fault, you get movement. That why deep injection of anything – fracking wastes at a well disposal site or CO2 at existing wells, have been linked to triggering earthquakes – especially where there are already faults.
This is what was probably happening in December 2013 through January and February of 2014 in and around Azle, when that part of the Metromess was experiencing it's own earthquake "swarms." There are at least two injection wells in the vicinity that were at the center of many of the quakes and since their pressures and volumes have been decreased, those swarms have decreased as well.
We know that a couple of fracking waste injection wells at DFW airport on the edge of Irving were closed because of suspected links to earthquakes they were causing.
"And an earlier study by scientists at Southern Methodist University (SMU) and UT found links between disposal wells near the DFW airport and induced earthquakes for a series of quakes in 2008 and 2009. The study specifically looked at two injection wells in the area that were built in 2008. Seven weeks later, earthquakes started. “Were the DFW earthquakes natural or triggered by activities associated with natural gas production, most likely saltwater injection to dispose of brines?” the report asked. The study said yes, the “correlations are consistent with an induced or triggered source.”
Those DFW airport wells have been closed for years, but with millions of gallons of waste being stored deep underground, are they still capable of causing pressures on the Balcones and/or faults that feed the Balcones? We know less about the geology underneath us than we do the deep space above us.
In the middle of the earthquake swarm there are two gas wells on the University of Dallas campus – one that was producing until 2012 and one where the casing failed and shut down early on. They've been there since 2009 but we don't know the recent history of either.
No new drilling or injection activity is known to have occurred at or near the sites of the most recent earthquakes.
We've come a long way from the original perceived foil hat territory of fracking activity causing earthquakes. When many of us first heard about this association, it sounded like science fiction. Now we know it's science fact. Even the oil and gas industry concedes that injection wells have a connection to earthquakes. That's a huge change in the debate since only a few years ago.
What is less known, and what the industry does not concede yet, is that fracking alone has been linked to earthquakes.
A 2012 British study found fracking itself caused small earthquakes near Blackpool.
The report, undertaken by independent experts and commissioned by the UK’s Department of Energy and Climate Change, looked at the relationship between fracking operations by the Cuadrilla company at Preese Hall well, near Blackpool in Lancashire, and small earthquakes between April and May of 2011 – the largest a magnitude 2.3. The report agreed with previous studies that the earthquakes were caused by the process.
It said the stress in the fault was pre-existing and the hydraulic changes made by fracking initiated the earthquake sequence.
The same thing happened in Canada with fracking near the Horn River Basin.
"…a report released recently by the B.C. Oil and Gas Commission sheds light on the huge shale gas deposits in northeastern B.C. Quakes recorded by Natural Resources Canada ranged from 2.2 to 3.8 on the Richter scale, below the 4 mark and thus deemed minor.
"The investigation has concluded that the events observed within remote and isolated areas of the Horn River Basin between 2009 and 2011 were caused by fluid injection during hydraulic fracturing in proximity to pre-existing faults," the commission said in its report."
We don't know what's causing the Irving quakes, but we do know that fracking alone has been known to cause the size of earthquakes being recorded there now. To suggest that only injection wells have been linked to quake activity is just plain wrong.
We're messing with Texas geology in a way that we haven't before, in areas of the state where we haven't before. We really don't know what the long-term consequences of that messing are.