Although Texas has had its share of both natural and man-made disasters, earthquakes are not something most Texans worry about much. The geology of much of Texas is more or less flat limestone layers left over from the time when a giant sea covered much of the state. We are pretty far away from the edges of tectonic plates, unlike places such as the west coast of the U. S., where earthquakes are a constant threat. So when the small North Texas town of Azle had an earthquake a year or two ago, it was an unusual event. It was a small one, but more and more followed. In the month-long period ending today (Dec. 29), Azle has had ten earthquakes large enough to be noted by the website earthquaketrack.com, whose data comes from the United States Geological Survey. The smallest was magnitude 2.8 and the largest was 3.6, which is enough to rattle windows and cause minor structural damage.
This would be simply a matter of scientific curiosity were it not for the possibility that these earthquakes, as well as similar ones in other parts of Texas and the U. S., are related to oil- and gas-drilling activity. Specifically, the process called "fracking" involves sending lots of water treated with chemicals down a potential oil or gas well, then pulling it out again and disposing of it in underground injection wells that are deep enough so the injected fluids don't mix with groundwater. At least, that is the intention.
Drillers have done fracking for many years, and according to a website operated by the U. S. Environmental Protection Agency, Texas has over 52,000 Class II injection wells, which are typically the type used by fracking operations. But only in the last five to ten years has fracking become a widespread practice near populated areas of North Texas, where the Barnett Shale formation has become the focus of intense exploration and drilling. In the interests of full disclosure, my father-in-law received some money for mineral rights related to drilling near his former home in Fort Worth, which he no longer owns. And my sister lives in Cleburne, some 30 miles south of Fort Worth, which has experienced a few earthquakes of its own in recent months. Cleburne is near a lot of fracking activity and injection wells too.
Suppose there is a connection between shoving lots of water underground and triggering earthquakes: what then? Is this a matter of engineering ethics concern? I would certainly think so.
The parties most directly involved are (1) the oil and gas drillers, (2) the people living in areas subject to these strange earthquakes, (3) the organizations paying for and benefiting from the drilling, (4) local, state, and federal regulatory authorities, and (5) the general public, which is not directly affected by the earthquakes, but benefits in some way from increased domestic supplies of fossil fuels, and is possibly harmed by the general increased risk of earthquakes in the future. But identifying the concerned parties is only the first step.
From a legal point of view, the situation is extremely fuzzy. Although there have not historically been a lot of Texas earthquakes, there were enough for U. T. Austin geology professor Cliff Frolich and his colleague Scott Davis to write a book about them in 2002. I have read that book, and the impression I got was that Texas is not under any existential threat from a "big one" like California is due for. Rather, there are lots of little faults here and there, and every so often one of them gets tense enough to snap, like a third-grade teacher the day before Christmas vacation. Frolich wrote a report back in 2009 on a cluster of earthquakes near Cleburne, where he confirmed that numerous injection wells had been operating. After installing a special array of seismographs, he detected even more earthquakes than the standard USGS network did, and in the abstract of the report he stated, "A plausible hypothesis to explain these observations is that injection only triggers earthquakes if injected fluids reach and relieve friction on a suitably oriented, nearby fault that is experiencing regional tectonic stress." What he's saying in ordinary English is something like this: Earthquake clusters are like doors that have both a lock and a key. The lock is the local conditions of stress and orientation that make the fault ready to let go, and the key is the water coming in from the injection wells. When the key fits in the lock, the door opens and in comes an earthquake.
Seismic data on earthquakes is easy to come by; besides the USGS data, there are other online databases and the information is relatively easy to find and read. The question of where injection wells are and how much fluid is injected is a harder one to answer, although the Texas Railroad Commission (named that for historical reasons), which is the state regulatory agency for oil and gas drilling, has a database on injection wells that will yield such information to diligent inquiry. I diligently inquired for about five minutes this morning and turned up a bunch of wells across Eagle Mountain Lake from Azle, but nothing right in the town. But maybe Azle sits on the lock, and the key flowed under the lake from the other side, so to speak.
I'm no geologist, or lawyer either. If Azaleans (or whatever you call citizens of Azle) get tired of being shaken awake at 2 A. M. and organize a class-action lawsuit, their lawyers would have a rocky road to travel (so to speak) in order to prove to the satisfaction of a civil-trial jury that such-and-such injection wells directly caused so-and-so earthquake. The only similar legal issue I can think of would be a lawsuit concerning structural damage caused by dynamiting for quarries and similar purposes. In those types of cases, all the plaintiff has to show is that at Time A before the blast, the damage wasn't there, and right afterward at Time B it was, and usually it's easy to show that because the physics of shock propagation is pretty well known and hard to argue against in court.
That is far from the case for these earthquake clusters. In defense of their practices, fracking drillers state correctly that they have been doing fracking for many years in Texas and elsewhere, and nobody much noticed any earthquake clusters back then. My own guess is that they just happened to be fooling around with keys where there weren't any locks. But now that the fracking activity is so visible near populated areas such as the Dallas-Fort Worth area, people have begun to notice the clusters and start putting two and two together.
So far, no one has been seriously injured or killed in a recent Texas earthquake cluster in areas where injection-wells are suspected as the cause. As long as the damage remains minor, the general good will enjoyed by the oil and gas industry in Texas will probably continue, especially if they keep spreading around those royalty payments of a thousand dollars or so to anyone in the neighborhood of an active well. But if we get a seriously bad earthquake that results in injuries or deaths near a place where injection wells are operating, watch for the legal and regulatory picture to change fast. For my sister's sake, as well as the fracking industry, I hope that never happens.
Sources: The book Texas Earthquakes by Cliff Frolich and Scott Davis was published in 2002 by the University of Texas Press. An abstract of Prof. Frolich's report on the Cleburne earthquake cluster is accessible at http://www.pnas.org/content/early/2012/07/30/1207728109.abstract. The EPA website with statistics on Class II injection wells can be found at
http://water.epa.gov/type/groundwater/uic/wells.cfm. I referred to articles in a Russian news website on the Azle earthquakes, published at
http://rt.com/usa/texas-fracking-earthquakes-azle-445/
and data on the Azle earthquakes from the earthquake website
http://earthquaketrack.com/us-tx-azle/recent. I also referred to the Wikipedia article on Azle.
