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New report reveals 'disconcerting' earthquake risk along Wasatch Front

By Katie McKellar  |  Posted Apr 18th, 2016 @ 8:34pm


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SALT LAKE CITY — The probability that at least one magnitude 6.75 earthquake could rattle the Wasatch Front in the next 50 years is 43 percent, a new report found.

The soon-to-be-released report was previewed Monday, giving earthquake experts the clearest earthquake risk forecast to date.

The new statistics are scientifically thrilling, said the report's lead author, Ivan Wong, but they also tell a sobering story.

"Think about that. That means flipping the coin, 1 out of 2 chances that we will have a big earthquake in the next 50 years," Wong said. "There is a really good chance that (Utah) will undergo a large, damaging earthquake in the Wasatch Front region. You can't get around that."

State emergency management officials already say a major earthquake is the worst potential natural disaster facing Utah, according to projections from federal loss estimations.

But Monday's new statistics "redefine the problem," said Bob Carey, earthquake program manager for the Utah Division of Emergency Management.

"This is a big deal. We've just increased our chances of having a major earthquake by quite a bit. We used to talk about a 15 percent chance in the next 50 years, now it's more than double. That's disconcerting," he said.

"Earthquake Probabilities for the Wasatch Front Region in Utah, Idaho and Wyoming" is the first comprehensive study of its kind for Utah, compiled by 14 scientists who assessed quake likelihood based on new geologic information on the timing and locations of large, prehistoric quakes on known faults in the region.

The full report is expected to be released in roughly two weeks, Wong said.

It's the result of ongoing research, including geologists' field studies of rock records throughout the Wasatch Front, to help predict and gauge the havoc a major earthquake could reap in the region, which is home to 80 percent of Utah's population of 3 million.

"The problem is we don't know exactly when that earthquake will occur. It could occur later today, tomorrow, days, months or years down the road. But we know in the next 50 years, it's 1 out of 2," Wong said.

The Wasatch fault is the most likely fault in the region to generate a major earthquake, having an 18 percent chance of a magnitude 6.75 or greater quake in the next 50 years, according to the report. However, the study includes probabilities of many other mapped and unmapped faults that contribute to the chances of an earthquake in the region. When considered together, the fault records increase regional probabilities of a quake.

"This area, outside of California or Washington, now we understand has the highest hazard and the highest risk anywhere within the western U.S. These are really some sobering thoughts," Wong said.

As severity of the earthquakes decrease, their probabilities rise, the report shows. The chance that a magnitude 5 earthquake or greater could hit the Wasatch Front is an alarming 93 percent.

(Photo: Aaron Thorup, Working Group on Utah Earthquake Probabilities)

"The hazard and risk in the Wasatch Front region is higher than we had anticipated. I don't think anyone in the (study's) working group expected that the probabilities would be as high as they are," Wong said. "So the attitude that the big one will not occur in one's lifetime, that threat cannot be ignored and we need to change that attitude."

Carey said he hopes the new statistics will urge state leaders to be aware of the impending threat and make policy accordingly, such as encouraging seismic retrofits of buildings that pose safety risks. He has said there are about 165,000 unreinforced brick buildings in the state, which would cause about 55 percent of deaths in an earthquake.

"I understand the Legislature has competing things, but we can't ignore this problem anymore," Wong said.

He noted that Utah should be doing more to retrofit its schools.

"It saddens me, personally, to see that Utah has not taken the measures to take care of the schools," Wong said. "Roughly 10 percent of schools is a collapse danger. That means your kids could be in school when the school collapses. That is a very sobering observation, and frankly I think something needs to be done."

All Utahns should take the new probabilities to heart, said Joe Dougherty, spokesman for the Utah Division of Emergency Management. He hopes the probabilities will motivate Utahns to prepare their families for the worst-case scenario earthquake.

"For us, (the new probabilities) sound like reality," Dougherty said. "In the past, we've had kind of a broad range of possibilities, but now we know within our lifetimes and likely within our kids' lifetimes that that earthquake is going to happen. And that should wake a lot of people up."

Monday's statistics were released just in time for the annual earthquake drill, the Great Utah ShakeOut. Nearly 1 million Utahns plan to participate in Thursday's drill.

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