The 6.0 magnitude quake that hit the Nevada city early Thursday morning left it strewn with the wreckage of older buildings - and that's the kind of damage to expect from a Wasatch fault earthquake, a University of Utah seismologist said Thursday.

Geophysics professor Robert B. Smith, former director of the university's seismograph station, said the Wasatch fault that runs between Brigham City and Levan stretches the Earth's crust four inches every year.

That constant elasticity is "pulling the West apart," he said. "It's a rubber band being loaded."

And it will snap.

Mathematical calculations based on regional earthquake history shows a one-in-four chance of a big quake of magnitude 6.5 to 7.5 will happen here in the next 50 years.

Or maybe tomorrow.

The Wells quake is considered moderate. But even a moderate earthquake of 5.5 to 6.5 magnitude, if its epicenter were in a Wasatch Front city, would be devastating, Smith said.

The Wasatch fault is is 350 kilometers long - about 217 miles - and divided in segments, Smith said. Those segments in a large earthquake would act as if the loaded rubber band shot a rock into a windshield: break lines speed outward from the ding until the whole thing shatters.

"The crack propagates and has a velocity of roughly the speed of sound," Smith said.

That means a fracture would travel a 20-mile fault segment in six seconds, collapsing unreinforced brick buildings and homes in an instant and possibly shearing underground water, electric, sewer and natural gas lines along the way and causing billions of dollars in damages.

That doesn't mean post-earthquake cities would be smoldering ruins, as newer buildings are engineered to withstand seismic activity, Smith said.

Still, the Wells quake, moderate as it was, "is going to be remembered as something that caused a lot of damage," Smith said.

Unfortunately, he added, memories are short.

"We all say we're going to make preparations, but we don't. People have the tendency with earthquakes [to remember] for about a week," he said.

There's not much individuals can do to defend themselves in a 7.5 magnitude quake, but they can allay damage by retrofitting masonry homes to make them safer. Smith said people also should pull together the standard, basic emergency 72-hour kits of food, water and batteries and make plans for how to contact families and friends - the sorts of advice available from multitudes of public-safety and church Web sites.

But the best preparedness comes from land-use planning and government. Officials understand they have a huge responsibility, but tend to treat earthquakes as a problem far in the future they won't have to deal with, Smith said.

"They want to know what's going to happen in the next year or so, not the next 100 years," he said.