Earthquakes caused by human activity will now be included in the U.S. Geological Survey's seismic risk maps, the agency said on Monday after a sharp rise in temblors linked to wastewater disposal wells used by the oil and gas industry in Oklahoma.
The seismic risk maps are used by emergency management officials as well as the country's major engineering and design associations to guide how strong to construct buildings.
"By including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the U.S.," Mark Petersen, Chief of the USGS National Seismic Hazard Mapping Project, said in a statement.
Some 7 million people in the Central and Eastern United States live or work in areas threatened by so-called induced seismicity, and in parts of these regions, the damage caused by earthquakes could be at parity with that seen in high-hazard regions of California, the USGS said.
Oklahoma is at the greatest risk for hazards associated with induced seismicity, the USGS said, followed by Kansas, Texas, Colorado, New Mexico and Arkansas.
Oklahoma in 2015 experienced 907 magnitude-3.0 or greater earthquakes, compared with just two of similar size in 2009. In February, a 5.1-magnitude temblor shook the area around Fairview, Oklahoma - the third strongest recorded in the state.
The uptick in quakes has prompted serious concern among locals, particularly those in close proximity to the oil storage hub at Cushing, Oklahoma, which is home to some 66 million barrels of oil and the delivery point for the widely-traded West Texas Intermediate futures contract.
"We have had some earthquakes that were way to close to those tanks," said Michael Teague, Oklahoma's Secretary of Energy and Environment.
The disposal of saltwater — a natural byproduct of oil and gas drilling — into wells has been tied to earthquakes. Oklahoma regulators have already ordered many wastewater well companies to curb operations.
The USGS said building code committees are still determining whether to include induced earthquakes in their revisions, in part because they could be temporary.
The American Society of Civil Engineers is already in the process of publishing 2016 guidelines that do not take into account man-made earthquakes. But the group does not anticipate updating those standards again until 2022.
"There is always a delay in design codes adapting the USGS Seismic Hazard Maps," said Muralee Muraleetharan, a civil engineering professor at the University of Oklahoma.