How do we know if an earthquake is tectonic or anthropogenic?
As I scroll through memories to file them away in the limited catalog that is my brain, I’m reminded of a question I once posed during a seminar presentation. The presentation was by one of the research committee members that was commissioned by the U.S. Department of Energy to study human-induced seismicity, done in June 2012. When the presentation
concluded finished, I asked, “Did the committee ever investigate anything else [other than human activities related to oil and gas extraction] that might be causing the recent activities in the midwest?” A faculty member stepped-in to declare that they are submitting a paper correlating mid-continent seismicity to oil and gas extraction; which, still didn’t answer my question. If the answer to my question is “No, we only seek to determine whether earthquakes are human-induced, and not ask what else could be causing a deviation in what we think is normal seismicity.” then this is (to me) a non-scientific approach — post a comment below as I would love to hear your thoughts on this.
This post is merely a philosophical question that is spawned from that unanswered question.
Mind you, I am not asking how we can tie earthquakes to oil and gas. We know that. We know that either pumping fluids in or out of the ground, the pressure around the rocks change. Some may strengthen the fault (making it less likely to slip or develop a new fault) and some may weaken the fault (making it more likely to slip or develop a new fault). The first known case of the latter is well-documented, when Rangley, Colorado suddenly became seismically active in the 1960’s. Since then, there have been about a dozen cases in the U.S. that clearly document human involvement in earthquake triggering. There have been numerous more intraplate earthquakes that are not (or not yet, if you wish) tied to human activities, and are deemed tectonic. We try to fit these earthquakes into a model where humans are implicated, if that doesn’t fit, then it must be the other — so what’s the big deal?
The big deal is that determining whether earthquakes are caused by human activity is socially biased and politically charged. When the ground rumbles and buildings start to wiggle, we want to know where to point the proverbial finger of blame. When, in most cases, the finger points to nature, media outlets and politicians can’t really stir it to a frenzy. Really, what can people do other than move somewhere else that’s not earthquake-prone. Now, if the finger points to man (or corporations), people tend to get excited about tarring and feathering the culprit. Some seismologists say, mid-continent earthquakes are definitely anthropogenic. Some seismologists say, only a handful of earthquakes are human-induced and that they might be aftershocks from previous large earthquakes. Keep in mind that these people are working with the same data! Identical observations, different hypotheses.
When the New Madrid earthquakes happened in the early 1800’s, nobody claimed foul on fracking and no politician placed an embargo on oil and gas industries (probably because they didn’t exist yet). If the New Madrid earthquakes were to happen in present time, how are we (scientists, the public, media, etc.) going to view them?