Towns on the Great Plains are built to withstand tornadoes. Earthquakes are a new thing.
A cluster of central states surrounding Oklahoma now faces the highest risk of earthquakes induced by human activities "such as fluid injection or extraction," according to a short-term seismic forecast by the U.S. Geological Survey.
The report, which for the first time includes quakes that may be linked to oil and gas production, comes after an alarming six-year rise in the incidence of quakes throughout the central and eastern U.S. There, some seven million people, concentrated near Oklahoma City and Dallas-Fort Worth, face an increased risk of earthquakes.
There were more than 1,000 quakes last year with a magnitude greater than 3 on the 10-point Richter scale, up from an annual average of 24 between 1973 and 2008. The states facing the highest risk from human-induced quakes are, in order, Oklahoma, Kansas, Texas, Colorado, New Mexico, and Arkansas, according to the report, published Monday. The largest populations at risk live in Texas and Oklahoma.
Scientists predict that any damage would probably be on par with some of the cracking in homes and commercial buildings already witnessed since the oil-and-gas boom began. North-central Oklahoma is the most prone to quakes this year, according to the research, with a 12 percent risk.
The link to the energy industry is largely based on wastewater from wells subjected to hydraulic fracturing, or fracking, the engineering advance that let drillers free hydrocarbons trapped in shale. The production process yields a lot of water, which may be disposed of by injecting it into storage wells. That is the practice suspected in the increased earthquake activity.
As the number of quakes in Oklahoma, Texas, and other central states has risen in the last decade, so has concern among local residents, environmentalists, and regulators. Oklahoma saw a 5.1-magnitude temblor in February, coincidentally three days before the Sierra Club sued three companies under a federal law governing dangerous waste disposal. It’s the latest in a string of accusations against companies involved in the disposal of wastewater.
Linking wastewater injection to tremors in general is easier than linking any particular earthquake to a wastewater operation. The ground slips the same way in either case. Instead, scientists are “looking at the sequence as a whole,” said Justin Rubinstein, deputy chief of the USGS’s induced-earthquake research. They have to seek out where changes have been made to industrial operations “and how the seismicity has changed in response to that.”
Shutting facilities in some areas has led to a decline in quakes. Kansas put in place new rules in March 2015 and has subsequently seen a decline in the shakes, according to the USGS. An earthquake “swarm” in central Arkansas in 2010-2011 led to the shutdown of some wastewater injection there, and another drop in seismic activity. The USGS has yet to see a similar development in Oklahoma.
“New regulations, new restrictions on injection have changed the earthquakes,” Rubinstein said, “but for Oklahoma specifically we’re waiting for more data to come in.”
It's difficult to project induced quakes, in part because companies don’t disclose in real time the amount of wastewater they’re injecting underground, and at what pressures. Federal and state regulators may only ask for annual disclosures of monthly disposal activity.
A recent journal study by scientists with the Geological Survey concluded that water injection wells with the highest rates, greater than 300,000 barrels per month, are more frequently associated with quakes than lower-volume wells, and that managing these injection rates may be a good way to reduce quake risk.
Monday's report is an update to the USGS's 50-year seismicity projections, which are updated every six years and used in building codes and by insurers.
(Updates with map, chart, and USGS comments.)