7.0 earthquake: If the big one hits Utah's Wasatch front

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.

QUAKE ODDS

"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.

QUAKE DESCRIPTION