SALT LAKE CITY — Scientists say Utah's Wasatch Front faces a 1-in-7 chance of being hit by a magnitude-7.0 earthquake — the size of the tremor that devastated Haiti last week — sometime in the next 50 years.
If it hits at the worst-possible time — in the middle of a winter night — government computer models estimate that it could kill about 3,000 people, injure another 42,000, damage more than a third of all buildings and cause at least $35 billion in economic loss.
More than 60,000 people would need public shelter during freezing temperatures. Most power, water and communications would be out initially, and may not be restored in some areas for months. Fires could be widespread.
Police and firefighters would be so overwhelmed that they could not reach many people for days, so neighbors would need to rely on each other for help.
That may not be as bad as what's now unfolding in Haiti — where the Red Cross fears 50,000 people may have died and most buildings were damaged in some cities. Still, a 7.0 quake in Utah would be horrific. That said, damage and suffering could be reduced if residents plan and take precautions now.
"It's been about 1,300 years — plus or minus 650 — since the Salt Lake City segment (of the Wasatch fault) had an earthquake of that magnitude," said University of Utah seismologist Jim Pechman.
He adds an ominous statistic: "They happen there, on average, about every 1,300 years," or about the same length of time since the last one occurred.
So does that mean Utah is due for a "big one"?
"They don't go off like clockwork," Pechman said, and it depends how much pressure has built up on the fault. "There's a lot of variability in that."
He said the probability of a large quake on the Salt Lake City segment of the Wasatch fault (one of 10 independent segments of that fault system) is somewhere between 1-in-10 to 1-in-7 in the next 50 years. "If you look at the Wasatch Front as a whole, it would be higher," he said, about 1-in-7 odds overall.
Pechman notes that the Salt Lake City segment of the fault has been expanding an estimated 1.2 millimeters a year recently. Scientists say as pressure builds along a fault, it is like slowly stretching a rubber band until it suddenly breaks.
Scientists say a worst-case scenario quake in Utah would be centered in mid-Salt Lake Valley, and would be felt in seconds from Brigham City in the north to Santaquin in the south, and from Tooele in the west to Coalville in the east. It would affect 80 percent of Utah's population.
Shaking in Salt Lake County would be so severe that no one would be able to stand without falling. Unsecured hot-water heaters would shake loose in many homes, and broken gas lines would start fires. Bookcases, furniture and debris would fall and injure many. Some people trying to run out of buildings would be killed by falling debris. Collapsing buildings would kill many.
A 7.0 quake would quickly create a ledge or "scarp" that could stretch for nearly 30 miles along the main fault — roughly following Wasatch Drive in the south valley, and following Highland Drive and 1300 East in the central and northern parts of the valley.
Pechman said that scarp, or ledge, would be about 3 feet high — but would be up to 9 feet tall in places. As the scarp forms, it could snap utility lines and block transportation across it, and topple houses around it.
Bob Carey, earthquake preparedness director for the Utah Division of Homeland Security, says two small valley faults would likely also shake "in sympathy" with the larger Wasatch fault, and also form smaller scarps.
The Taylorsville fault roughly follows I-215 northward from 4700 South to Rose Park. The Granger fault runs diagonally from a point near 2700 West and 5400 South to near North Temple and 5600 West.
Besides the three scarps blocking east-west traffic and relief efforts, Carey said lands along the Jordan River are expected to "liquefy" or act like quicksand in the quake, meaning bridges may collapse. "As a planning strategy, we're not counting on any of the bridges across the Jordan to be accessible," Carey said.
So he says Salt Lake County would be divided into six slices not easily accessible to each other. They would be the area east of the Wasatch fault scarp, between it and the Jordan, from the Jordan to the Taylorsville fault, from it to the Granger fault, and from it to the Oquirrh Mountains.
Computer models developed by the state and the Federal Emergency Management Agency estimate quake damage — and predict that casualties could vary greatly depending on the time of day that a big quake hits.
Carey said a 7.0 quake hitting in the middle of the night, for instance at 2 a.m., would cause the most casualties: an estimated 2,920 dead, another 1,480 with life-threatening injuries, another 9,360 with non-life-threatening injuries but still needing hospitalization, plus 31,430 with "Band-Aid" injuries.
He said fatalities would be greater during the night because many older homes in Utah are "unreinforced masonry buildings," made of bricks on bricks without reinforcing steel. The brittle structures don't flex well in quakes and can snap like chalk. Upgrades — such as better attaching of roofs to walls — can make them safer.
"More fatalities and injuries come from this building type than any other (in a quake). So this would lead to higher fatality rates at night," Carey said.
In comparison, a quake that hits during drive-time rush hour, say 5 p.m., "is safer because a larger portion of the population is in transit and not in buildings," Carey said. Models predict fatalities then would be down by 16 percent compared to a middle-of-the-night quake, and other injuries would be down by 20 percent.
The safest time for a big quake may be during the workday because more people would be inside commercial buildings that "tend to be newer, which means they were built to a higher seismic code," Carey said.
Fatalities during an afternoon quake, compared to a middle-of-the-night quake, would be down about 20 percent, and other injuries would be down about 26 percent, Carey said.
Of note, state officials just a few years ago predicted casualties in a 7.0 quake would be almost twice as high as they predict now. But Carey said developers of computer models found errors in predictions of ground shaking. "When this error was corrected, it significantly lowered the casualty estimates," he said.
Carey said models predict that 38 percent of all buildings in the area would suffer at least moderate damage. He said they predict that economic losses from damage to buildings and their contents would be more than $34 billion.
Models also predict that more than 62,000 people would need public shelter — which could be dire if an earthquake hits during freezing temperatures in winter. Nearly 100,000 households would be displaced here in a 7.0 quake, but not all would need public shelter as they huddle with friends or family.
Carey expects all cell phones and landline phones to go down initially. "Whether it's due to damage or overuse, they always go down," he said.
"The power is still going to go down. That's going to be for eight to 12 hours. And then when it does come back, it's going to be spotty," Carey said, adding that 80 percent of areas should have it restored within 30 days — a time frame that should be similar for restoring telephone systems.
"Water systems will take longer," he said. "We could see some areas without water for three months." Sewer systems take even longer. He said he expects natural gas "to perform a little better" because of upgrades to pipes and systems recently.
Carey said police and firefighters would likely be overwhelmed in a 7.0 quake, and neighbors will likely need to depend on each other for help for the first hours and days. That is why the state has encouraged neighborhoods to form Community Emergency Response Teams. Many local cities offer CERT training.
Carey said personal and family preparedness is also wise. For example, officials have said that in a 7.0 quake, residents may need to depend on their "72-hour" kits of supplies for five days or more for food, water and other basics. A book by the state on earthquake dangers and how to prepare is available online at quake.utah.edu.
The state and Federal Emergency Management Agency's Region 8 are also developing a catastrophic earthquake plan for the Salt Lake area. Carey said FEMA figures that a big quake hitting the Salt Lake area "would be the worst thing that could happen in the region," which is one reason for the planning.
Carey said, "We are in the infancy of that. The process is going to work towards a full-scale exercise with FEMA in March of 2012, where we will spend three days doing a full-scale exercise" to simulate emergency response and likely problems.