- © 2016 by the Seismological Society of America
Researchers (Frohlich et al., 2016) from the University of Texas at Austin and Southern Methodist University recently developed a new question‐based system for categorizing Texas earthquakes as either natural or man‐made.
Unfortunately, this new test is a significant step backward. Frohlich et al. (2016) appears to reject the science‐based, integrated subsurface engineering and geomechanics approach as advocated by more than 80 national and international subject matter experts. The test also runs counter to the approach recommended by the National Academies and the U.S. Environmental Protection Agency (EPA), and it arbitrarily skews the conclusion away from natural causes. This article will explore these shortcomings and provide some recommendations for improvements.
A question‐based system, where researchers answer conditional questions to determine if an earthquake may be man‐made, is a useful tool for exploring an inherently complicated subject. An earlier question‐based system developed by Davis and Frohlich (1993) focused on downhole pressure and fluid pathways:
Are these events the first known earthquakes of this character in the region?
Is there a clear correlation between injection and seismicity?
Are epicenters near wells?
Do some earthquakes occur at or near injection depths?
If not, are there known geological structures that may channel flow to sites of earthquakes?
Are changes in fluid pressure at well bottoms sufficient to encourage seismicity?
Are changes in fluid pressure at hypocentral locations sufficient to encourage seismicity?
The premier U.S. scientific organization has also articulated the importance of subsurface factors. In its comprehensive 2013 report, the National Research Council of the National Academies concluded:
Increase of pore pressure above ambient value due to injection of fluids and decrease in pore pressure below ambient value due to extraction of fluids have the potential to produce seismic events. For such activities to cause these events, a certain combination of conditions has to exist simultaneously …