It's a scenario Salt Lake County residents have been hearing about for years, and one emergency responders and government officials hope they're ready for when it happens.
Earlier this month, more than 70 people from Salt Lake County government, including Mayor Peter Corroon, members of the Unified Fire Authority and Salt Lake County Sheriff's Office, as well as other state and city leaders and members of the private sector, went to Emmitsburg, Md., to put their battle plan for a major disaster to the test.
"Overall it went very well. The response was very good. We were very proficient at the response to the disaster," said UFA deputy fire chief and Salt Lake County Council Chairman Michael Jensen. "Those already used to responding to those calls did a very good job."
Federal Emergency Management Agency paid for the group to travel to Maryland to find out how the county's disaster plan would work in a mock disaster. The plan is supposed to cover all types of catastrophes from tornadoes to terrorist attacks, Jensen said.
Salt Lake County's disaster for the drill last week was a 7.0 earthquake with the epicenter on the county's east bench near I-80 and Highland Drive.
But rather than having a disaster that involved only first-responders or people from one department, this scenario was different because it involved people from numerous government and even private agencies, said Salt Lake County Emergency Services coordinator Robert Flowers, a former top FEMA official.
"(The drill) focused on the big picture of all the different people who get involved with disasters, and what their roles are," Corroon said.
In addition to first-responders from the county, others who traveled to Maryland to participate included leaders from Taylorsville, Davis County, Salt Lake County Health Department, the University of Utah, the Red Cross and LDS Disaster Services.
"That was one of the greatest benefits ... getting to know each other by spending a week together," said Corroon, who noted it was better to meet the other agencies now rather than being introduced for the first time after a real disaster has already happened.
Corroon said one of the main points he learned from the drill was, "An elected official should not try to micromanage the experts, such as the first-responders," he said.
What officials discovered is that while the county is already at the top of its game in terms of emergency first-responders, where a little work is needed is the recovery effort.
"Once the earthquake stops shaking, once the flood waters recede, how do you work together to bring back your businesses? Rebuild your roads?" Corroon said.
It can take months, and sometimes even years, for counties to recover from large-scale disasters, Jensen said. Once the immediate disaster is over, he said county government leaders need to think about how to establish a good foundation to rebuild.
Specifically, Flowers said improvements could be made with disaster declaration, how to allocate resources amongst different jurisdictions including money received from the federal government following a disaster declaration.
"We did OK. I'd give ourselves a passing grade on the recovery. There were just certain areas we could improve on," he said.
The last time the county traveled to Maryland to take part in a drill like this was 15 to 20 years ago, Jensen said.
Flowers said he has been instructed by Corroon to plan similar exercises in Utah in the near future. He hopes future drills might also include private citizens to prepare them for when "the big one" hits.
"I know citizens get tired of hearing that, but that's what (will really help them)," Flowers said.If citizens are happy with eating nothing but bread and water following a disaster, the county will be able to help them, he said. But if they want more than that, it's best to brush up on their self-reliance preparations now.