Fault map


ENID, Okla. — The factors are aligned for Oklahoma to have another damaging earthquake, magnitude 5.7 to 6.0, but exactly when it could happen is unclear.

U.S. Geological Survey research geophysicist Daniel McNamara said the fault orientation in Oklahoma is optimal for producing earthquakes.

There are several as­­pects of earthquakes, and determining the next possible large one, which includes data like size, the fault system, orientation and alignment.

“Faults that are aligned in a particular optimal orientation — which if you know compass directions, would be N45E — so not directly north or east but halfway between. So that orientation is optimal for producing earthquakes in Oklahoma,” McNamara said. “Many of the fault systems are of that orientation.”

McNamara said the 5.6 magnitude earthquake that shook Prague in 2011 was of such fault orientation.

“So we look at the orientation and the size of the fault to see if the size of the fault is large enough to produce a big earthquake and if the orientation is optimal,” he said.

McNamara said USGS cannot predict exactly when another large quake will occur, but the factors are there.

“I would say there are numerous fault systems in Oklahoma that are producing magnitude 4s that could rupture into a larger earthquake, very similar to what happened in 2011 in Prague,” he said. “There are at least 13 fault systems that have the same type of behavior as Prague ...”

Last week, Oklahoma Corporation Commission di­­­rected two wastewater injection disposal wells in Alfalfa County to halt operations and 23 other wells in the county to reduce volume after several earthquakes were recorded, including one that measured magnitude 4.7.

On Monday, more than three quakes rattled near Cherokee, ranging in magnitudes from 4.4 to 3.0.

“The Cherokee faults tend to be not as big as some of the southern Oklahoma faults,” McNamara said. “The region we looked at in most detail is in Cushing. There are two active fault zones there that intersect with a very large regional fault system that produced the Prague (5.6).”

Cushing is the largest crude oil hub in the world. So much so, Reuters reported that ConocoPhillips overhauled how it plans for earthquakes in regard to crude tanks.

McNamara said the Cherokee faults are not as well known as others, even though there is an increase in 4.0-plus magnitude earthquakes. He said USGS does not know the extent of the faults in terms of depth, which makes it difficult to forecast a larger earthquake.

Most of the activity is in northwest Oklahoma, McNamara said.

But activity appears to be starting back up near Cushing. McNamara said in October, the Cushing fault “reactivated” again and had three 4.0 magnitude earthquakes in three weeks.

“These faults are 5 to 10 kilometers depth, and they don’t come to the surface of the earth,” McNamara said. “We only know about them through geologic mapping from the oil industry, but we don’t know about all of them, just stuff that is non-proprietary at this point, or that they’ve already maybe produced from so it’s not proprietary information.”

For future predictions, McNamara said USGS will need more data. USGS is working to add collaborations with the oil and gas industry to learn more fault locations and wastewater injection amounts in regard to seismicity, he said.

“There are volumes for many of the wells, but it is a monthly reporting,” he said. “When the OCC becomes interested in an area like Cushing or Cherokee, they may limit the volume allowed and then they require the companies to report on a daily basis. So you get much higher resolution data out of them, which is great for us because then we can look at real fine daily seismicity variations correlated with wastewater.”

McNamara said he doesn’t blame oil and gas companies for not wanting to share information.

“However, with the government we’re not going to be competitive for producing oil and gas,” he said. “We just want to know about the fault structures.”

McNamara said the 5.6 magnitude earthquake near Prague could happen in other regions, it’s just a matter of when.

“Just about any of the fault structures that have produced magnitude 4s over the last two years seem like they could produce a larger earthquake,” he said.

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