U.S. to Map the Risks of Man-Made Earthquakes

Move Follows Rise in Frequency of Quakes in Regions With Increased Fracking

Wall Street Journal
1 May 2014
By Tamara Audi

ANCHORAGE, Alaska—A rise in the frequency of earthquakes in regions with increasing oil and gas extraction is prompting scientists for the first time to assess risks of man-made quakes and include them on federal maps that influence building codes and public policy.

The new mapping, which the U.S. Geological Survey hopes to release later this year, is likely to put regions of the central U.S. not typically thought of as earthquake zones on notice for greater seismic hazards. Unlike West Coast states at high risk for major quakes, like California, other areas typically aren't as prepared to handle strong temblors.

The USGS regularly maps hazards from naturally occurring quakes, alerting building engineers and local governments to the probability of moderate and strong shaking in their regions based on fault lines and seismic studies. The agency said that in the wake of research showing increased seismic activity in certain regions—including two strong 2011 quakes in Colorado and Oklahoma—it decided to release a separate map to evaluate the risk of man-made quakes, called induced quakes.

"We've never done this before," said Justin Rubinstein, a USGS seismologist working on the assessment. "We've never tried to consider induced earthquakes in hazards."

An average rate of more than 100 earthquakes a year above a magnitude 3.0 occurred in the four years from 2010 to 2013 in the central and eastern U.S., compared with an average rate of 20 events a year observed from 1970 to 2000, according to the USGS.

"The number of earthquakes within central and eastern United States has increased dramatically over the past few years, coinciding with increased hydraulic fracturing," or fracking, and the subterranean disposal of wastewater from oil extraction, said the Seismological Society of America, an organization of quake scientists, at its meeting here on Thursday.

Mr. Rubinstein said the USGS remains "agnostic" on the causes of the increase. "We're not here to point fingers," he said, adding that "an increase in earthquake rate" for any reason "implies that the probability of a larger earthquake has also risen."

Greater hazard risks could prompt communities to better prepare for quakes, or increase insurance costs.

There generally is an accepted link between quakes and human activity, but there is debate about which specific activities and sites might cause temblors, and how large an induced quake might get.

"It's very complicated and difficult to assess whether a quake is induced or not," said Hal Macartney, a geologist who works in the oil and gas industry. "There's still a lot of uncertainty." He added that the industry is attuned to the issue, and some operators have installed their own monitors to measure quakes and try to figure out "how to mitigate" any potential risks.

Gail Atkinson, a professor of earth sciences at Western University in Ontario, Canada, said induced quakes can cause more intense shaking on the surface because they tend to occur at shallower depths than many naturally occurring quakes. But she and other scientists said more access to data from regulators and industry operators is needed to fully understand the risks.

The mapping effort comes as regulators, industry officials, politicians and scientists begin to grapple with how to measure and respond to potential quake risks from human activities in the aftermath of a jump in seismic activity in Oklahoma, Texas, Arkansas, Ohio and Colorado.

Last month, Ohio state officials said they believed the "likely source" of a series of small quakes there was fracking activities. Ohio will require additional seismometers to more closely monitor tremors.

Other states are focused on how wells used to inject fluids deep underground and dispose of millions of gallons of fracking wastewater might be contributing to quakes.

Wastewater disposal after oil extraction appears to cause larger quakes than fracking, researchers said. In that process, oil is extracted with salt water. The remaining brine, or wastewater, is injected into the ground. The pressure caused by that can put stress on an existing faults and trigger quakes, some scientists contend.

In 2011, wastewater disposal appears to have caused a magnitude 5.3 quake in Colorado and a 5.6 quake in Prague, Okla., the USGS said. That quake caused light damage to more than a dozen homes in the area.

A spokesman for the American Petroleum Institute didn't immediately respond to a request for comment. In the past, the group has said there is not enough data to confirm a link between tremors and injection wells.

Scientists and industry officials estimate there are about 35,000 wastewater wells in the U.S. A small fraction of those are believed to be linked to quakes, seismologists said.

On Thursday, new research unveiled at the Seismological Society of America conference said that quakes can be triggered up to 30 miles away from the site of wastewater disposal, a greater distance than previously thought, said Katie Keranen, an assistant geophysics professor at Cornell University who led the study.

—Russell Gold contributed to this article.

Write to Tamara Audi at tammy.audi@wsj.com