SALT LAKE CITY — Roughly 1 in 3 Salt Lake County homes could crumble in the event of a major earthquake that experts say could rock Utah’s urban corridor at any time.

That’s according to a Deseret News analysis of the number of Salt Lake County homes built of brick or other brittle blocks prior to 1975 — types of houses that experts say are likely to collapse in a magnitude 7.0 quake or higher.

The homes aren’t supported by steel that would allow them to bend enough to avoid deadly collapse in a large earthquake.

"They’re like a house of cards. There’s actually nothing tying them together," said Bob Carey, earthquake program manager for the Utah Division of Emergency Management.

More homeowners have fortified such "unreinforced masonry" houses against such a disaster in recent years, and some have even received help from Salt Lake City and the federal government in the process.

The chimney of the McEntire home is secured to the roof in Salt Lake City on Wednesday, April 18, 2018. The McEntires used the Fix the Bricks program to retrofit their home.

Still, 33.5 percent of stand-alone homes in Utah’s most populous county fit the definition of unreinforced masonry, the riskiest manmade shelter during an earthquake, according to Carey. They make up an estimated 76,000 single-family houses, out of a total of 226,500 in the county.

That’s according to state emergency managers’ estimates that consider county assessor data from 2010, the most recent available. Carey and his colleagues use federal disaster modeling software to map potential destruction, but they caution that the numbers are a best guess, not an exact representation.

Some of the homes may have been upgraded to withstand collapse, but there’s no comprehensive record of such improvements.

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The risky homes are characterized by their makeup of brick, cinder blocks or adobe and pose such a big risk because their roofs, chimneys and parapets often sit neatly on top, unattached by much more than gravity, said Audrey Pierce, program manager of a Salt Lake City initiative that connects homeowners seeking retrofits to federal dollars.

"The roof can slip off and collapse," Pierce said. "That is what we’re trying to avoid."

In January, a crew of five upgraded the 100-year-old Sugar House home of Maddie and Trevor McEntire, peeling back the roof and drilling it down into the walls with "humongous screws," they said.

The parents of three children — ages 5, 2, and 10 months — now feel "so relieved, like we can actually see ourselves owning a home for the long term," Maddie McEntire said. "We bought in the area because we loved the charm. But we really were kind of naive in thinking that these homes would last forever."

Harrison Rather, left, and Ben, Evelyn and Rose McEntire play outside the McEntire home in Salt Lake City on Wednesday, April 18, 2018. The McEntires used the Fix the Bricks program to retrofit their home.

The couple became nervous the more they read about a possible quake, but found it was difficult to get earthquake insurance for their unreinforced home, she said. Shortly after moving there in March 2016, Trevor McEntire went to City Hall to secure a permit to build a garage and spotted a flyer advertising Fix the Bricks, the city’s retrofit program.

The family was among the first to sign up, and paid about $4,000 of the total $17,000 bill, with the bulk covered by federal grants through the program.

"You just can’t beat the peace of mind," Maddie McEntire said.

Not included in the count of at-risk homes are roughly 100 apartment and condominium buildings within county borders — those that are three stories or higher. They also are vulnerable because they were built from the same materials prior to 1975, when states strengthened building codes following California’s deadly San Fernando earthquake. The multi-unit buildings pose a big risk because so many people live there.

Not surprisingly, the historical districts of Utah’s most populous cities and towns, snaking from Ogden to Provo, have the highest concentrations of unreinforced masonry.

And Salt Lake City will feel the most impact, with several census blocks where more than 4 in 5 buildings are made of unreinforced masonry. One such area is Rose Park. Another is the southwest portion of the Avenues, brimming with mid-19th century homes, as well as an area east of Liberty Park and northwestern Sugar House.

But the Yalecrest neighborhood near the University of Utah is the worst offender, with 9 in 10 brick-and-mortar buildings.

Outside of the capital city, over half of homes in tracts within Weber County’s Ogden and Riverdale areas are predicted to be at-risk. The same goes for parts of Sandy.

Utah’s urban corridor, home of roughly 4 in 5 Utahns, straddles the most active portion of the Wasatch Fault. The boundary of the plates deep below the ground traces Utah’s main artery, I-15, along a 140-mile stretch from Brigham City to Nephi.

Predictions from geologists of the effects of a magnitude 7.0 quake paint a hellscape along the route.

The rupture will yank the ground 8 feet higher in places, effectively turning lowlands into quicksand and sending hundreds of rock slides into neighborhoods, according to a 2015 report from the state’s seismic commission.

The cost of bracing a chimney and securing a roof together — considered the most basic and important seismic upgrades — varies greatly depending on the home, but can run $15,000 or more, depending on the home. For multi-unit buildings, the cost ratchets up much higher, said Pierce.

One major historic community bucks the trend. Logan has fewer reinforced masonry buildings and more new ones.

Carey speculates that redevelopment following a destructive magnitude 5.9 earthquake in the Cache Valley during August 1962 could have caused a shakeup in how people built homes and businesses there.

The Aug. 30, 1962, edition of the Deseret News describes caved-in ceilings, collapsed walls and cracking facades following the quake, though no serious injuries were reported. Still, the quake reduced portions of the Logan Printing Company’s walls to rubble and collapsed the roof of a pool hall.

One man, James Cook, told the Deseret News at the time it was "just like an airplane hitting the north end of the house."

But earthquakes aren’t generally on the minds of today’s Utahns, notes Ralph Becker, the former Salt Lake City mayor who tried to prod the Utah Legislature to pass a bill requiring seismic evaluations for apartment buildings as they are converted to condos.

"This is a perfect time," Becker recalls thinking, because building owners would be set to turn a profit from the sale and theoretically could pony up for any needed upgrades.

The measure brought by Salt Lake Democrat Larry Wiley, a building inspector, also would have required building owners to disclose the results of the evaluation at closings of sales. It foundered without enough support for several years before his retirement in 2014.

"We’ve got sort of a blind view of seismic risk here, because of the way the Wasatch Fault works. We don’t see earthquakes every few months," or even every couple years, Becker said.

The last major quake to shock Salt Lake City hit 1,400 years ago, according to the Utah Seismic Safety Commission, which calculates that the tremors take place roughly every 1,300 to 1,500 years and enough stress has built up to unleash another. But a smaller quake took place in and around what currently is Nephi 300 years ago, Carey notes.

In 2016, Salt Lake City stepped in to help secure federal dollars for city homeowners to pay for retrofits, but residents like the McEntires still are on the hook for 25 to 30 percent of the cost.

But historic apartment buildings haven’t made as much progress, said Audrey Pierce, program manager for Fix the Bricks.

"It is a goal of ours and a priority for us," Pierce said. "But it’s just been a lot harder to tackle, so we haven’t really gotten there yet."

But for property managers, a 25 to 30 percent share of the cost still is exorbitant, Pierce said. The price tag, which she did not disclose, recently turned one building owner away after initial discussions with the program.

Fix the Bricks has upgraded 15 homes, with five more under construction. Two-dozen who signed up in 2016 are currently awaiting various rounds of federal, state and city approval.

The paperwork-heavy process can take more than a year in its entirety, so Pierce encourages those who can afford the upgrades to pursue them on their own. A second wave of 100 homes from 2017 are next in line.

"We can’t actually secure and protect the entire home, but what we can try to do is make it so that people can still get out of the home and maybe even possibly still live in it after the earthquake," Pierce said. "We’re trying to mitigate the death and the injury that we have to deal with after the earthquake. That’s the ultimate goal."

The Great Utah Shakeout

The annual, statewide drill is planned for Thursday at 10:15 a.m.

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