|The quake shook part of the sandstone facade off an old bank|
building in Pawnee, Okla. (Photo from Tulsa Public Radio)
Oklahoma once had one or two noticeable earthquakes (3.0 magnitude or greater) a year. Now it has hundreds, and Saturday morning it had a quake that tied for the strongest in the state's history, a 5.6-magnitude temblor that damaged a few buildings in Pawnee and was felt in at least eight states.
"The quake was so strong in Joplin, people there were worried it was the New Madrid Fault in far eastern Missouri, the site of the United States' strongest earthquake ever, in 1812," John Durkee of Public Radio Tulsa reported.
The U.S. Geological Survey has attributed Oklahoma's increased seismic activity to injection wells used to dispose of drilling waste from horizontal hydraulic fracturing, the leading method for producing oil andgas in the U.S. "The quake prompted state oil-and-gas industry regulators to order the shutdown of disposal wells in a more than 700-square-mile area near the quake’s epicenter," Paighten Harkins reported for the Tulsa World.
USGS placed the epicenter of the quake eight to nine mikes northwest of Pawnee and about four miles underground. "Preliminary information from the Oklahoma Geological Survey indicates the earthquake was a 'strike-slip event' off the southern edge of the Labette Fault, a major fault that runs through Pawnee and into Osage County," Harkins reported.