A recent spate of earthquakes in the Dallas area, centered around the old Texas Stadium in Irving, has raised concerns that hydraulic fracturing, or fracking, is the cause. Making that correlation may be understandable, but it's almost certainly wrong.
The good news is that the series of earthquakes has been relatively minor — with the largest ranging in magnitude between 2.5 and 3.6 — and any damage appears to be generally limited to wall and ceiling cracks in a few homes.
But when news reporters ask those homeowners and other Irving residents if they have any idea what might have caused the quakes, some suggest that it could be fracking — a decades-old process that forces water into underground shale formations, driving oil and natural gas out of the fissures to be extracted.
The reporters almost never follow up with facts, thus leaving the fracking speculation unchallenged.
Fortunately, seismologists are investigating the Irving quakes. They have pointed out that there is no active fracking nearby.
While there are two wells in the earthquake vicinity, one never produced anything and the other was shut down in 2013, according to Craig Pearson, a staff seismologist for the Texas Railroad Commission.
These days, fracking gets blamed for almost anything that happens out of the ordinary. However, independent scientific studies have been unable to detect a connection between fracking and earthquakes.
The "evidence" for a connection is generally limited to anecdotal assertions.
There is another possibility: waste water injection wells, which are used to dispose of the water-chemical mixture used in the fracking process. The suggestion is that the water lubricates the lithologic layers and helps them slip, causing a quake.
However, even for seismologists who think there could be a connection between earthquakes and injection wells, they point out that the impact is usually within six miles of the injection well site.
The injection well closest to the Irving epicenter is 10 miles away.
While earthquakes are not common in the Dallas-Fort Worth area, they have happened — especially over the past five years. And the U.S. Geological Survey (USGS) has been studying them.
There was, for example, a magnitude 2 quake on Jan. 6, 2012, about midnight, located six miles north by northwest of Dallas and about 12 miles southwest of Plano — that is, around Irving — according to the USGS. (I was up that night and felt it).
It turns out that Dallas sits atop an ancient mountain range, the Ouachita Mountain system, whose subterranean roots extend through a good swath of south and north central Texas, sweeping up into Oklahoma, Arkansas and Mississippi.
Though some of the range has been buried over the millennia, the tectonic plates that formed it are still there, and they can slip.
And that raises an important point: The USGS concluded that 2012 quake originated about three miles under the surface — roughly 16,000 feet — as have the recent quakes.
That depth provides another reason fracking or injection wells are unlikely to have been a factor — injection wells typically don't go deeper than 10,000 feet.
So what's causing the Dallas-area earthquakes if it isn't fracking?
The seismologists confess they don't know. And that's not unusual.
In fact, the number of major earthquakes is up all over the world, including an unusual cluster in Connecticut this month, and also estimated to be originating about three miles down. But no one is blaming that cluster on fracking, because there isn't any.
Tom Parsons, a USGS research geophysicist, and Eric L. Geist, a USGS researcher, published a report last year pointing out that there were about twice as many major earthquakes globally in the first half of 2014 as the average since 1979.
However, the vast majority of those quakes were outside the United States, whereas fracking is largely restricted to only some parts of the U.S. The authors concluded that the increase in quakes was within normal parameters and not a result of any specific actions.
Indeed, a quick look at the USGS global map indicates that seismic activity is fairly low in the U.S., compared to the rest of the world, where there is virtually no fracking.
People understandably want answers when they feel the earth shake. But correlation is not causation.
At this point, the scientists just don't know the Irving earthquakes' cause. We are probably on safer ground — even if less-stable ground — to say that it's Ouachita's fault.