New Map Shows Rise in Human-Caused Earthquake Risk

The USGS map is the first to include quake risks related to human activity, largely tied to the fracking boom in the central states.

Picture of a map of damage from natural and induced earthquakes

The new USGS map shows a risk hot spot in Oklahoma similar to the one in southern California.

Illustration by USGS

By Sarah Gilman

PUBLISHED March 28, 2016

Most people associate Oklahoma with weather-related disasters: tornado outbreaks, massive wildfires, Lawrence of Arabia-style dust storms, tumbleweed maelstroms. But thanks to oil and gas wastewater injected deep into the ground, parts of the state can now also claim the dubious distinction of being among the most likely places in the United States to experience a damaging earthquake in 2016.

On Monday, the U.S. Geological Survey unveiled an earthquake hazard forecast for the central and eastern parts of the country that for the first time includes human-caused quakes, referred to in technical parlance as "induced seismicity." The report suggests that seven million people in parts of Oklahoma, Kansas, Colorado, New Mexico, Texas, and Arkansas face increased risks from human-induced earthquakes in the next year.

The risks appear most widespread and significant in north-central Oklahoma and a tiny sliver of southern Kansas, where a large area has a 5 to 12 percent chance per year of an earthquake that can cause buildings to crack and, in rare cases, collapse. That's comparable to risks in parts of more seismically famous California, USGS scientists said at a press conference on Monday.

The USGS decided to include induced seismicity in the new map because of a well-documented and sharp increase in the number and severity of human-made earthquakes in the central and eastern U.S. starting in 2009, largely tied to the energy industry.

"We want to help people understand how much concern they should have with these earthquakes," said lead author Mark Petersen, chief of the agency's National Seismic Hazard Mapping Project.

Underground Air Hockey

The oil industry recently boomed in Oklahoma and elsewhere due to advances in horizontal drilling and hydraulic fracturing—also known as fracking—a controversial practice that involves firing a slurry of water, sand, and chemicals into the ground to release trapped hydrocarbons. Along with the fracking fluids, the oil or gas that rises to the surface tends to come with copious amounts of brackish groundwater, which energy companies dispose of by reinjecting into the earth.

In parts of Oklahoma, this wastewater injection has increased five to tenfold. At the same time, earthquakes of magnitude 3.0 and greater spiked from fewer than 100 between 1970 and 2009 to almost 600 in 2014, and a whopping 907 in 2015.

Most of the water is going into a layer of rock called the Arbuckle Formation, which may transfer water pressure to the still deeper basement rock layer, where the earthquakes are triggered. As water input has increased, so has the pore pressure in already stressed faults there, allowing their sides – usually clamped tightly together – to slip more easily past each other.

"Think about an air hockey table," Oklahoma Geological Survey Director Jeremy Boak explained in an interview. "When it's off, the puck doesn't slide that freely." But when the air blows, creating a little cushion of pressure, the puck glides like a dream.

In Oklahoma, injected water helped produce the state's largest ever recorded earthquake – a magnitude 5.6 in Prague in 2011 that toppled chimneys and inspired at least one lawsuit against industry to cover injuries and property damage. Theoretically, injection or smaller induced earthquakes themselves could trigger even larger quakes, USGS scientists said, since the state has a fault that, prehistorically, has produced a magnitude 7 temblor.

Other industrial activities can induce seismicity too, such as building large reservoirs and mining, though none of those causes are emphasized in the latest USGS report.

Legal Rumblings

These seismic maps are mostly used to develop emergency plans, building safety standards, and insurance rates. That means the new projection of induced earthquake risk could see citizens and communities in affected areas shouldering more of the financial burden for drilling's ripple effects, Johnson Bridgwater, director of the Sierra Club's Oklahoma Chapter, told National Geographic.

The percent of homeowners holding earthquake insurance policies in Oklahoma has risen in recent years to around 10 percent – similar to California. Considering that Oklahoma wasn't much of a seismic risk until the fracking boom, some citizens and nonprofits are trying to hold energy companies accountable.

Two significant temblors that shook Oklahoma City and Edmonds over the 2015 holidays resulted in lawsuits from homeowners. And the Sierra Club's state chapter recently filed another earthquake suit against energy companies after a magnitude 5.1 quake struck near the Kansas border in February.

"Oklahoma citizens are now having to open their own pocketbooks for insurance protection," Bridgwater said. "And they're obviously upset and think industry should have to cover that."

Also, while previous maps looked at natural risk over longer timeframes, induced seismicity can vary rapidly along with shifts in policy or the market, so the USGS adjusted the timescale of the new map to just one year. USGS's Petersen noted that some parts of the country where induced quakes were more common for a time are now forecast to have far less seismic risk.

"Something is going right in Ohio," he said, which shows that regulatory changes like reducing injections can mitigate the potential quake hazards.

Conditions are already changing in Oklahoma. Boak says the collapse of oil prices has led to steep declines in wastewater injection in the 25-county area that has been most impacted. He expects new calls by the Oklahoma Corporation Commission, a state regulatory agency, to further curtail underground disposal and keep those numbers down.

Though there have been more than 200 quakes in Oklahoma so far in 2016, Boak said he is "guardedly optimistic" that there will be an overall reduction by the end of the year.

http://news.nationalgeographic.com/2016/03/160328-earthquakes-map-risks-usgs-science/