OGDEN — As Utah earthquake expert Bob Carey sees it, the question isn’t if a big earthquake will someday shake Utah and the Wasatch Front.
It’s going to happen.
The more germane question is when. When will pent up energy in the Wasatch Fault, the north-south fault line running through Weber County, let go, release and rattle the area?
Carey, response and recovery bureau chief for the Utah Division of Emergency Management, can’t say, but when it does, the impact could be dramatic. He prepared a report estimating the impact of an Ogden-centered quake, and if one measuring 6.5 on the Richter scale struck, it would potentially kill 378 or more people, obliterate 12,657 buildings, destroy 42 bridges and cause $7.76 billion in economic losses.
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“This is kind of our imagination. But this is hard science at work, also,” Carey told a group of Weber County emergency management officials and others. “Some version of what I’ve described, you’re going to see.”
He’s not aiming to induce panic. Rather, Monday’s presentation, part of a four-day seminar organized by the Weber County Emergency Management Office, was meant to give the attending emergency management officials a sense of what they could be facing if an earthquake hits.
Carey also hopes the information serves another purpose — raising awareness among the general public of the threat. “It would be nice if they got nervous,” he said, and took steps like preparing family response plans.
Based on geological studies of past earthquakes that have struck along the Wasatch Fault, the Brigham City area is most overdue for a temblor, followed by the Salt Lake City area, Carey said. Hundreds of years or much more sometimes passes between the most devastating earthquakes. But the entire Wasatch Front area is potentially at risk.
A 2016 study by the Utah Geological Survey, in cooperation with the U.S. Geological Survey, estimated that there was a 43 percent chance of a large earthquake measuring a magnitude of 6.75 or more over the next 50 years along the Wasatch Front. It estimated there was a 93 percent chance of a more moderate earthquake measuring magnitude 5 or more. Echoing Carey’s cautionary remarks, the study said the Wasatch Fault was the most likely fault line to generate a large earthquake, with an 18 percent chance of such a temblor in the coming 50 years.
The 250-mile Wasatch Fault, made up of 10 segments, extends from Malad City, Idaho, south to Fayette in central Utah, according to the Utah Geological Survey.
Per Carey’s study, using modeling developed by the U.S. Federal Emergency Management Agency, here are some of the estimated effects of a magnitude 6.5 quake in Weber County:
Deaths: Some 378 people would die if the earthquake were at 5 p.m., with 424 dying in a 2 p.m. temblor and 470 dying if it happened at 2 a.m.
The varied number of people at homes, schools and businesses at the different hours accounts for the differences. Another 1,500 to 1,800 people would sustain serious, potentially life-threatening injuries and 3,800 to 5,100 people would suffer light injuries.
Building damage: Nearly 40,000 of the 78,000 buildings in Weber County would sustain at least moderate damage, with 12,657 of those being completely destroyed.
Single-family residences, which account for the vast majority of buildings, would likewise account for the majority of damaged and destroyed structures. Of the varied building types, unreinforced masonry structures, like brick homes, would account for 72.4% of the structures that were destroyed.
Drinking water: Most structures would lose access to drinking water for a month, and by the three-month mark, nearly 65,000 of the 78,000 buildings would still be without.
“This is the biggest problem aside from structural damage,” Carey said. “This is a big deal. We’ve underplayed it for years.”
Economic losses: Of the total estimated economic loss, $7.76 billion, most of that, $6.23 billion, would come from capital losses like structural and building content damage. Income losses due to the interruption of business operations would total around $1.28 billion while damage to the transportation network, roads most notably, and utilities would account for the rest.
The economic impact could have long-term ramifications.
“This can be a community killer. If you can’t recover, people leave,” Carey said. Such potentially dramatic effects “should motivate the people who make decisions about us.”