By Merrill Matthews
A recent spate of earthquakes across the United States has raised concerns that hydraulic fracturing, or fracking, is the cause.
Several states with strong fracking industries have seen an uptick in seismic activity. North Texas, for example, has undergone a flurry of earthquakes. Oklahoma experienced more magnitude-3 earthquakes last year than California. Earlier this month, Michigan suffered an earthquake with a magnitude of 4.2.
Some have suggested 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.
Making that correlation may be understandable, but it’s almost certainly wrong.
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, and one that has more scientific support: waste water injection wells, which are used to dispose of the water-chemical mixture used in fracking. The suggestion is that the water lubricates the lithologic layers and helps them slip, causing a quake.
However, seismologists point out that the impact is usually within six miles of the injection well site, yet the closet injection well to some of the recent Texas quakes was 10 miles away.
The problem is that the public, but also the media, don’t seem to recognize the difference. In fact, some Texas geologists recently complained that when they suggest that waste water injection wells may have caused some of the Texas tremors, the media report fracking as the problem.
Geography may better explain some of the trembles. Dallas sits atop an ancient mountain range, the Ouachita Mountain system, that covers a good swath of south and north central Texas, sweeping up into Oklahoma, Arkansas and Mississippi. Though the range has been buried over the millennia, the tectonic plates that formed it are still there, and they can slip.
That raises an important point: The USGS concluded that a 2012 quake originated about three miles under the surface — roughly 16,000 feet. That depth provides another reason why fracking or injection wells are unlikely to have been a factor on many of the quakes — injection wells typically don’t go deeper than 10,000 feet.
So what’s causing these earthquakes if it isn’t fracking? Seismologists don’t know. And that’s not unusual. In fact, the number of major earthquakes is up all over the world, including a recent cluster in Connecticut. 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 noting that there were about twice as many major earthquakes globally in the first half of 2014 as the average going back to 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, the USGS global map indicates that seismic activity is fairly low in the United States 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. The likely fault in most quakes is geology.
Merrill Matthews is a resident scholar with the Institute for Policy Innovation in Dallas, Texas. Follow at twitter.com/MerrillMatthews.
