Thanks to fracking and other injection processes, small earthquakes are the new normal in the American interior. That poses another, more ominous question. What does the Big One look like in Oklahoma? Canada recently earned the dubious honour of the World's Largest Fracking-Triggered Earthquake, while Oklahoma continued to deny its even-bigger quakes had anything to do with fracking. But that doesn't change the cold, hard facts of a constant low-level swarm of shaking in Oklahoma and Kansas.
The problem is that these aren't on a classic tectonic boundary, and we don't have much history on which to base our predictions. Tectonic boundaries are the edges between the tectonic plates that make up the surface of our world. They can move together, apart, out side-by-side, triggering earthquakes as they get stuck then break free. Oklahoma State University geology professor Todd Halihan gets to the heart of the problem in an interview with Emergency Management, lamenting:
The predictions kind of suck. We're somewhere between a couple of liquor bottles falling off the shelf and complete Armageddon. And that's not particularly comforting or useful, so you should probably take some steps to prepare people for what to do that is logical in a case of uncertainty.
What the United States Geological Survey (USGS) does know is that these induced earthquakes don't follow the same patterns as those in California and the Pacific Northwest. At a normal tectonic boundary, all these tiny earthquakes would be the harbinger of doom foreshadowing a major earthquakes. But for induced earthquakes, the seismic activity relates to how much wastewater is being injected into the subsurface, dropping off when injection ceases. At least, it should.
That's where the next problem comes in. All these tiny earthquakes that are mostly scary shaking with little damage might be reactivating ancient fault lines. The USGS is still trying to get a handle on making 50-year predictions for the interior, but they aren't yet willing to rule out the possibility of up to a magnitude 7 earthquake. That would be on par with San Francisco's Loma Prieta or Los Angeles' North Ridge earthquakes -- except in a region utterly unprepared for it.
All these small quakes are shallower than their coastal kin, so the shaking is less dissipated when it hits the surface. Worse, the interior is home to stiffer soils, so shaking is felt more intensely. Pair that with buildings designed to resist the strong winds of tornados, not the shaking foundations of earthquakes, and you've got a recipe for disaster. Even breaching the magnitude 5 barrier was enough to cause damage, a genuine moderate-scale earthquake at magnitude 7 would be catastrophic.
USGS will be coming out with new hazard maps this autumn, hopefully reflecting new lessons learned about induced earthquakes in the past few years. The next question will be if city planners update their seismic codes to match.