It’s time to think out-of-the-box in regards to the influence of hydraulic fracturing and deep injection wells to seismicity. The relationship of these activities to seismic activity is strong and most likely correct to some degree. But could there be other contributing factors?
Anyone experienced in experimental design methodology knows that factors causing a response typical typically consist of only a few variables. Out of a large number of possible variables, these key variables have a significant influence the response of interest. Of these, only one or two may be single component variables. The remaining variables are interactive. That is, the interaction of two, typically overlooked, variables, may act as one. Independently they might not have a significant effect, but together they have a large influence on the response in question Traditional experimental techniques, such as one factor (variable) at a time experimentation, would not likely find these two-factor interactive variables.
Two shale gas processes have been attributed to seismic events.
First is hydraulic fracturing, which are known to cause micro-seismic events about magnitude -2, a slip of one tenth of mm, generating less energy than a gallon of milk falling off a kitchen counter These events are minuscule and not felt but measurable. They pose no public health or safety risks and occur on a continuous basis around the earth.
The second process, deep wastewater injection wells, induces more active seismic events, typically between 1 and 4 on the Richter scale. These earthquakes are typically felt but rarely cause damage. The estimated frequency of earthquakes of this magnitude is about 1.3 million a year around the world.
Most geologist know that under the right conditions, every time pressure is applied or reduced from an underground rock formation there is at least a small risk of a seismic activity.
These disturbances also include mining operations, driving piles for bridge and building construction, in seismically active areas.
Another possible cause of seismicity in the Dallas Fort Worth Region is road construction. Whether an independent or an interactive factor, road work can induce earth quakes, especially when drill shafts and piers are constructed for bridges and overpasses.
“Dallas-Fort Worth has the best and most extensive freeway system of a major metropolitan area on a per-capita basis when considering lane-miles of freeway and tollway, centerline miles, the quantity of multi-level interchanges, grid-style network, and percentage of freeways/tollways with frontage roads.
“According to a 2010 article, Dallas-area traffic has been among the worst in the nation for years, and for many commuters it’s about to get a lot worse before it gets better. Call it growing pains, or just one big mess, but construction has either already started or soon will on no fewer than a half-dozen of the most heavily traveled – and already backed up – traffic corridors in North Texas, as the region embarks on what may be the most aggressive road-building program in the country.” 
In closing, both shale gas drilling and road construction are as common in North Texas, as cowboy boots and pickups. Again, this is not to say that injecting hydraulic fracturing flowback in deep wells is not a major factor causing earthquakes in the DFW region, but it may not be the only cause.
 Dallas-Fort Worth Texas-Size Ambition, http://www.dfwfreeways.info
 Dallas-Fort Worth area highway improvements come with a heavy toll, DallasNews.com Star-Telegram, April 17, 2010; http://www.dallasnews.com/news/transportation/20100417-Dallas-Fort-Worth-area-highway-improvements-6755.ece
The opinions expressed in this article are solely those of the author Dr. Barry Stevens, an accomplished business developer and entrepreneur in technology-driven enterprises. He is the founder of TBD America Inc., a global technology business development group. In this role, he is responsible for leading the development of emerging and mature technology driven enterprises in the shale gas, natural gas, renewable energy and sustainability industries. To learn more about TBD America, please visit: http://tbdamericainc.com/