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The US Geological Survey (USGS) regularly comes out with handy maps that explore earthquake hazards around the United States. California is usually the flashing red focal point.
But this year's map is different. For the first time ever, the USGS has also decided to include the risk of earthquakes caused by humans — quakes thought to be set off by the injection of wastewater from oil and gas operations.
That changes the picture considerably. A bunch of regions east of the Rocky Mountains are now at risk of "damaging shaking" from man-made quakes that could affect buildings, pipelines, and other infrastructure. Nearly 7 million people live in these areas.
The agency's forecast for 2016 looks like this:
The first thing you'll notice is that California, which sits right on the boundary between the Pacific and North American tectonic plates, is still most at risk from naturally occurring earthquakes. The USGS estimates a 10 to 12 percent chance of a "damaging" quake in the Bay Area this year. (This is the first time the agency has done one-year forecasts.)
But then there's Oklahoma. A wide swath of this state also has a roughly 10 percent chance of a "damaging" earthquake this year, according to USGS. That's new. Oklahoma isn't naturally a hotbed of seismic activity. But since 2008, as the state's oil and gas industry has expanded, the region has seen hundreds of small earthquakes, usually magnitude 3.0 or smaller. Now USGS is warning that even bigger seismic shocks — tremors that could damage buildings — are possible.
Oklahoma's population faces the biggest risk, but USGS notes that Kansas, Texas, Colorado, New Mexico, and Arkansas also face some risk from "induced" earthquakes — an area that encompasses some 7 million people. The agency doesn't predict how big the quakes will be, exactly, it just pegs the odds of some sort of "damaging" earthquake this year.
As part of its assessment, the USGS also identified more than 21 regions east of the Rocky Mountains where human activity has induced earthquakes since 1980:
Oklahoma has unexpectedly become the earthquake capital of the United States in recent times, with hundreds of small earthquakes each year. And most experts now point to the boom in oil and gas operations since 2008 as the culprit.
Oklahoma has a number of "dewatering" operations that separate out crude oil from briny mixtures pulled up from wells
— a process that helps salvage otherwise-unusable oil. That leftover water then gets injected back underground into disposal wells so that it doesn't contaminate local freshwater supplies.
Wastewater disposal comes with a catch, however: Injecting all that water back underground both pushes the crust in the region downward and increases pressure in cracks along the faults. That makes those faults more prone to slippages and earthquakes.
Relatedly, the process of hydraulic fracturing, or "fracking," involves injecting water, chemicals, and sand underground at high pressures to crack open shale rock and extract oil and gas. Fracking itself doesn't seem to be causing earthquakes. But after the well is fracked, the wastewater needs to be pumped out and disposed. And, again, when it's put into underground disposal wells, that can raise the risk of earthquakes.
Most of Oklahoma's 9,000 wastewater wells don't seem to be causing any problems. But a 2014 Science study, led by Katie Keranen of Cornell, suggested that a handful of high-activity wells were likely responsible for the sharp uptick in seismic activity in central Oklahoma since 2008:
Just four injection wells southeast of Oklahoma City appear to have been responsible for one-fifth of the seismic activity since 2008. These wells are part of a dewatering operation owned by the oil/gas company New Dominion and inject some 4 million barrels of wastewater underground each month.
The Science study also noted that pressure from the wastewater wells travels through the subsurface farther than anyone thought. The four high-activity dewatering wells are capable of triggering seismic activity in a 772-square-mile vicinity.
That could explain, for instance, why the town of Jones, Oklahoma, has seen thousands of small earthquakes since 2008 despite the fact that there are no wastewater wells in the immediate vicinity.
It's worth noting that, so far, these earthquakes have been too small to do serious damage or endanger lives. Still, they have stirred up concern among some Oklahoma residents, and regulators are now considering whether additional rules may be necessary.
Further reading: Last year, Buzzfeed's Dan Vergano did an excellent deep dive into man-made earthquakes in the Midwest.
