OKLAHOMA CITY – Busted bricks and cracked windows were revealed Monday after some of those most powerful earthquakes in Oklahoma in the past year rattled the northern part of the state.
Oklahoma residents have gotten used to feeling rumbles from a spike in earthquakes blamed on wastewater injection wells from oil and gas production, but most don't cause damage. The threshold for damage usually starts at 4.0, and two quakes measuring a 4.2-magnitude hit Sunday evening in the Breckenridge and Enid areas, about 70 miles (113 kilometers) north of Oklahoma City, according to the U.S. Geological Survey.
Homeowners and business owners also reported split walls and bricks falling down.
"We're not used to 4.2 magnitude earthquakes," said Garfield County Emergency Management Director Mike Honigsberg.
Oklahoma averaged just one magnitude 3.0 earthquake a year before 2009. But that number jumped to 903 in 2015, before declining to 304 last year. The strongest earthquake on record in the state was a 5.8 magnitude in 2016 near Pawnee.
Oklahoma regulators have directed several oil and gas producers to close or reduce the volume of injection wells, and the number of quakes has since declined. People can usually feel local earthquakes at 2.5 magnitude.
Sunday's quakes are the strongest since a magnitude 4.3 struck in September near Medford in northwestern Oklahoma, according to Oklahoma Geological Survey seismologist Jacob Walter.
"These earthquakes are consistent with wastewater injection," Walter said. "Right now we're looking at the aftershocks."
Walter said there had been about 10 aftershocks of magnitude 3.0 or below.
Walter said the threat of earthquakes will continue, even if injection wells were ended immediately, because of the pressure built up from past injections.
"The earthquake severity hazard will be high for the next several years because of the energy in those fault systems from previous, historical wastewater injection," Walter said.