Earthquake Rattles Oklahoma; One Of Strongest Recorded In State

An earthquake struck northern Oklahoma early Saturday morning, rattling houses and waking residents in the region around Pawnee, about 74 miles north of Oklahoma City. Preliminary measurements show the quake had a magnitude of 5.6 — believed to be one of the strongest in state history.

The quake was felt in five states, according to the U.S. Geological Survey: Oklahoma, Kansas, Missouri, Arkansas and Texas. It struck just after 7 a.m. local time, at a depth of 6 kilometers (3.7 miles).

The epicenter was around 8 miles northwest of Pawnee, a town of less than 3,000 people. Shortly after the large quake hit, at least four additional temblors struck the same area, with the strongest having a magnitude of 3.6; all of them were shallower than the first quake.

According to the National Weather Service's Tulsa office, the earthquake ties the strongest quake in Oklahoma history at 5.6 magnitude. The previous record breaker hit on Nov. 5, 2011, the agency says.

Public Radio Tulsa — where the quake was strongly felt — describes the scene:

"Police in Pawnee report some windows were broken and homes sustained damage to the the outside facade. There have been no reports of injuries.

"The quake struck just after 7 a.m on Saturday morning. It was nearly four miles deep.

"Social media was alive with people feeling the quake from Dallas to Springfield, Missouri. 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 State's strongest earthquake ever in 1812."

A number of smaller earthquakes have hit northern Oklahoma in the past week — including one that struck the same area as today's quake on Thursday, with a 3.2 magnitude. Since last Saturday, a string of similar quakes have hit an area west of Pawnee, including at least eight with a magnitude of 3 or higher.

In Oklahoma and other regions that are experiencing a spike in earthquakes, a consensus has emerged that they're linked to the underground injection of wastewater brine that's generated from fracking in oil and gas production, as Public Radio Tulsa reported last month.

The station says the Oklahoma Geological Survey is now working on a six-month study of injection wells to get a grip on how to cut the chances that operations "inadvertently induce a seismic event," as an oil industry representative said last month.

The U.S. Geological Survey says that Saturday's strong quake "occurred as the result of shallow strike-slip faulting."

More from the USGS:

"Locations across the central and eastern United States (CEUS) have been experiencing a rapid increase in the number of induced earthquakes over the past 7 years. Since 2009 rates in some areas, such as Oklahoma, have increased by more than an order of magnitude. Scientific studies have linked the majority of this increased activity to wastewater injection in deep disposal wells in several locations. However, other mechanisms such as fluid withdrawal, enhanced oil recovery, or hydraulic fracturing processes can also result in induced earthquakes."