The shaking around Azle and Reno, which I will hereafter refer to as "San Andreas Minor," has attracted the attention of the U.S. Geological Survey precisely because the area has almost no record of seismic activity. A few studies, including one recently from SMU, point to correlation between the epicenter of the earthquake swarms and the locations of underground injection wells for fracking wastewater.
However, there isn't enough granular, on-site seismic data to draw hard conclusions yet. It's thought that the injection alters the bedrock stresses on faulting in this area, inducing slippages that produce quakes like the magnitude 3.6 detected in near Azle just a few days ago. The USGS says this is entirely possible, but to arrive at that degree of certainty, it needs more data, which is why it just lent SMU four seismic monitors to be positioned in private homes, public buildings and schools in the area.
Another entity with an intimidating acronym, Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL), will provide some 15 sensors to the effort. "We are first going to focus in on where the earthquakes have been occurring -- about a five- to six-mile area near Reno and Azle," said Heather DeShon, SMU associate professor of geophysics. "How long the monitors remain depends on continued seismicity. We're thinking a few months."
SMU will not disclose the location of the sensors for data integrity reasons, but they will not be deliberately placed near injection wells so that a link, if it exists, can be confirmed without bias.
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Unfair Park spoke with a geophysicist from USGS' National Earthquake Information Center in Golden, Colorado, about why it needs better on-site monitoring. It's detecting each of these earthquakes, but it can't differentiate them. "What an earthquake is, whether it's induced or natural, when rock breaks and stored-up energy is released, seismic waves -- like sound waves -- in the rocks, each of our instruments records how ground moves, and that doesn't look any different regardless of what the source is."
And that's why this locational data are so important.
By the day, the position of the Railroad Commission of Texas -- charged with regulating injection wells -- becomes more and more untenable. Despite several studies identifying a strong correlation between these wells and seismic activity, the agency maintains that no real evidence of a link has been found. This despite the fact that researchers have linked injection wells to quakes in the Haynesville Shale of East Texas, and that Chesapeak Energy shut down two injection wells near DFW Airport and one near Cleburne because of earthquakes.
Last time EnergyWire checked, the agency had visited the site of a single injection well in the area. It's not clear what the agency would do even if it did launch a diligent investigation. The agency's rules don't address earthquakes as a cause for regulatory action.