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Oklahoma's record-tying quake was predicted, more expected

FILE - A seismograph monitor shows small earthquakes from around Oklahoma outside the Oklahoma Geological Survey on the campus of the University of Oklahoma in this Friday, Jan. 8, 2016 photo. (Keaton Fox/KOKH)

Like a weather forecast that was spot on, seismologists said a large, damaging earthquake was likely in Oklahoma, some predicting the strength would be at least a 5.0 magnitude.

Saturday's quake was a 5.6 magnitude, and may be revised up still.

"Saturday's quake had a slightly larger energy release than the Prague 5.6," United States Geological Survey geophysicist Daniel McNamara said. That could lead to the preliminary 5.6 magnitude to be bumped up to make it the state's largest earthquake on record. Teams from the USGS are coming to Oklahoma now to install new sensors and gather new data.

"I don't think we're very likely to have a magnitude 6 earthquake, which would be a pretty big earthquake, but I wouldn't be surprised to have a 5," Jeremy Boak, the director of the Oklahoma Geological Survey, said in an interview on Jan. 8, 2016.

Since that interview, Oklahoma has recorded two quakes that measured in the 5 range. The first was Feb. 13 near Fairview. It was a 5.1, according to United State Geological Survey data.

In Oklahoma, four magnitude 5 quakes have rattled the state in recorded history, including the two this year. The other two were a 5.6 magnitude near Prague in 2011, the other a 5.5 near Yukon in 1952.

In 2016, while the total number of earthquakes is down, the larger, more damaging earthquakes make up a large percentage of those types of quakes in history.

2016 has recorded 50 percent of all the 5.0's in history. Of quakes magnitude 4.0 or higher, 20 percent of all of those magnitude quakes in history were recorded in 2016. Oklahoma has recorded 17 4.0 quakes or higher so far. The only year higher is 2015, which 29.

Large earthquakes typically beget large earthquakes, said USGS seismologist Daniel McNamara.

"There will certainly be large M4 aftershocks associated with the M5.6," McNamara said by email from his office in Colorado.

Faults, new and old

McNamara tweeted that the aftershocks shows a previously unknown fault had been discovered.

Something similar happened in Edmond earlier in 2016 after a series of magnitude 4 quakes rattled the area, though that fault is "quiet for now" McNamara said.

Oklahoma has an extensive series of faults, but most run in the southern portion of Oklahoma. The areas where quakes are centered are mainly to the north, maps show.

"In Oklahoma, you have naturally occurring earthquakes that could be up to a 5 [magnitude]," McNamara said. "The Meers fault in southern Oklahoma had a history that could've produced a 7 [magnitude] 1,200 years ago."

But those quakes happened on occurrences between 500 and 1,000 years in between them. Having two 5 magnitude quakes is certainly out of line with the natural history, McNamara said.

Risk from wastewater injection wells

As the state continues to shut down injection wells across portions of northern Oklahoma, the risk for significant earthquakes remains.

Regardless of where you live, you should prepare your home for shaking, especially if you live near wastewater injection sites, he said.

"Where are you most likely to generate an earthquake, and in the case of wastewater injection, and in reservoir management, they're both human activities that can be managed to potentially avoid large earthquakes," McNamara said in February. "Citizens should be aware they could go through strong shaking and just try to prepare your home. Tie down large bookshelves and computer monitors and televisions and things like that that could fall and fall on you or your children."

"If [shaking] were to occur, say, on the Edmond fault near Oklahoma City, or in a place like Cushing, where the large oil storage facility is, then you'd have considerably more damage," McNamara said.

McNamara also tweeted a graph showing Oklahoma's energy release from quakes has nearly tripled as larger quakes begin to make up the bulk of Oklahoma's seismicity.

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