Smith, who co-wrote a study looking at that possibility, said in 2006 that a 7.3 on the Wasatch fault could lead to valley tilting that would permanently flood areas along the eastern shore of the Great Salt Lake. He said then that he thought a 7.0 would be too small to do that, but he had not done computer modeling on it.

He added that a 7.5 is considered to be the maximum credible size for an earthquake along the Wasatch fault.

Areas that would have been flooded include Salt Lake City International Airport, and much of that city west of I-15 and roughly north of I-80 — plus some downtown areas. Much of Davis County could also have been affected, including areas in Centerville and Farmington west of I-15.

Also, major dams above Salt Lake City, Ogden and Provo survived the 2008 quake. But had it hit 20 years earlier — before major seismic upgrades to dams — officials said structures such as Mountain Dell, Pineview and Deer Creek dams likely would have failed, causing devastating flooding below, on top of other destruction by the quake.

First response

Carey said in 2006, as he predicted the damage from such an earthquake, "It would be a catastrophic event. It will go well beyond our ability to take care of it."

Now, amid the overwhelming damage and casualties, relatively few police and fire officials are on duty to try to handle it — if they can get across collapsed bridges, quake scarps and through debris to reach those in need, and if their sometimes-old police and fire stations did not collapse and trap equipment (as some did).

"When you look at someplace like Sandy, and it has 80,000 people and they have (only a few dozen) firemen or so on duty, it's very limited what they will be able to do," Carey said back in 2006.

Also, emergency planners long figured that even among those few on-duty firefighters and police who are available, many would go home to check on their own families — making emergency response even more short-handed.

"Hurricane Katrina showed that many police and first responders may go home to take care of their families," Brian Garrett, director of the state Office of Emergency Services, said in 2006. It happens again after this earthquake.

Carey predicted in 2006, again correctly, that first responders would rely on emergency training to do a quick triage on disasters facing them. They give priority to "hospitals, nursing homes and maybe elementary schools" that sustained severe damage or collapse where many who cannot help themselves are in dire danger.