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‘Small’ Probability Of Large Aftershock After Utah Earthquake

SALT LAKE CITY, Utah – Seismologists called the Wasatch Front’s 5.7-magnitude earthquake “moderate-sized,” but a large quake for Utah. Fortunately, they were not expecting “the big one,” or anything in the order of a 7.0 magnitude earthquake in the aftermath.

The 5.7 magnitude earthquake Wednesday was the largest to rattle the Beehive State in nearly 30 years. It was followed by a couple of aftershocks of as much as 4.6 magnitude.

Officials spoke over and over about social media chatter claiming seismologists said an earthquake as big as a 7.0 or 9.0 was imminent.

Not true, they said. A magnitude 9.0 earthquake was not even possible for the size of the fault lines along the Wasatch Mountains.

The said the chance of something bigger than Wednesday morning’s earthquake diminished as soon as it happened.

“There is no imminent prediction or imminent expectation of a magnitude-7.0 earthquake,“ said Keith Koper, director of the University of Utah Seismograph Stations.

Koper said there will be a lot of aftershocks, into the hundreds, and even thousands. However, he said there was no evidence of another large earthquake to come.

The seismologist said there’s only a 4 to 5 percent probability that there will be an earthquake larger than the 5.7. That’s a small probability, and as time goes on that probability decreases.

“We have had several strong, or moderate-sized aftershocks” said Koper. “The largest one was 4.6. We do expect aftershocks to continue, and to feel aftershocks for weeks, at least for days.”

Koper called Wednesday’s incident a normal faulting earthquake, which means that the earth’s crust is stretched sideways, and one side of the fault slips downward on the other side of the fault. It’s a typical kind of earthquake for this area, he said.

“In terms of what people should expect, they should expect hundreds to thousands of more, smaller earthquakes, (and) aftershocks that are going to play out of the next several weeks,” said Koper.

Bob Carey is the earthquake program manager for the Utah Department of Emergency Management. He reminded everyone in the state that this was a good time to review their emergency plans with their family.

He and the seismologist saw this earthquake as a wake-up call for preparedness.

“This is the earthquake that I’ve always wanted to have happen,” said Carey. “I know that sounds nutty, but now we can understand that we can actually have it.”

Carey said Utah seismologists have been warning residents for years to prepare for the “Big ONE.”

“It’s not that we’ve been barking at the moon for all of these years, because it kind of feels like that,” he said. “Now we have something that we can point to, that is evidence that we can have this, and this is just a little one.”

The earthquake program manager reminded everyone not to panic, but to be prepared.

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