A magnitude 7.5 earthquake on the Teton Fault could cost more than half a billion dollars and temporarily displace hundreds of households in Jackson Hole, a new report suggests.

The fault, which runs 35 miles along the base on the Teton Range, has been “ominously silent” since it last erupted in an earthquake nearly 5,000 years ago, said Wallace Ulrich, a Teton County resident and former state geologist. Most faults in the region undergo an earthquake every 800 to 1,000 years, researchers say.

Ulrich oversaw the 132-page report “Wyoming Earthquake Hazard and Risk Analysis.” A Teton Fault quake would have the biggest economic impact of 16 earthquake scenarios the report examined across Wyoming, according to geologists with the Wyoming State Geological Survey who assembled the document.

“The Teton Fault is one of the largest potential faults on the state,” study co-author and state project geologist Seth Wittke said in a telephone interview from Laramie. “So you’d expect a maximum-magnitude earthquake to create a lot of [economic] losses.”

The results are estimates and not “set in stone,” Wittke said (see box on 26A for methodology).

Such an earthquake would impact Teton, Lincoln, Park, Sublette and Fremont counties. Teton County would be hardest hit, with an economic loss of $494 million from damage to buildings alone.

“Moderate to heavy damage would be likely within 20 miles of the fault, including the communities of Moran, Wilson, Jackson and Moose,” the report says. “Light damage is predicted to extend out to 35 miles from the epicenter, including Alta and the Rafter J area. [V]ery light damage can be expected up to 50 miles from the epicenter near West Thumb, Alpine and Bondurant.”

Of the roughly 12,000 buildings in Jackson Hole and surrounding communities, the earthquake would damage nearly 4,000, including St. John’s Medical Center.

There’s a 72 percent chance the hospital would be damaged extensively, the report said.

The majority of the hospital would probably be closed for several weeks, study authors wrote.

“The Saint John’s Medical Center would be less than 1 percent functional the day of the earthquake,” the report said. “Functionality would increase to 3 percent by day seven, and 28 percent by day 30.”

All of the region’s highways and all but two of its 95 bridges would likely survive the earthquake intact. The report did not say which two bridges would be damaged.

Also, the report did not mention landslides and avalanches that could close roads. Nor did it discuss potential damage to the Jackson Hole Airport runway.

A substantial quake would cause $46 million to damage to roads, bridges and other transportation infrastructure in Teton and Sublette counties, the report predicts.

Only one of the region’s three police stations and five of the region’s 10 fire stations would remain open. Emergency services at Grand Teton National Park headquarters at Moose and Jackson Hole Airport, which would likely be close to the epicenter of the quake, would be especially hard hit, according to the report.

Of the fire departments, the one at the airport would sustain the most damage, followed by the Teton park fire department stationed at Moose. Next on the damage list would be both fire departments in Wilson, and the Jackson Hole Fire/EMS station in Jackson.

Of the police stations, the earthquake would damage the Jackson Police Department headquarters and the Teton County Sheriff’s Office, where emergency dispatch is located. The damage would be so severe that operations would be only at half force after one week.

Only the police station in Alpine would escape mostly unscathed.

The quake would temporarily close all but five of the region’s 16 schools. The Teton Science Schools’ Journey School has the highest chance of extensive damage.

Next on the damage list would be by C-Bar-V Ranch and Davey Jackson Elementary School. Kelly Elementary, Alta and Bondurant elementary schools would experience little damage, according to the projections.

The hardest-hit fire departments and schools would be operating at only about 50 percent capacity after a month.

“Seeing how long it would take some of these emergency facilities to get back to even 50 percent surprised me a little bit,” Wittke said.

The study authors did not include estimates of death and injury because they were too hard to calculate given Jackson Hole’s highly variable tourist population, Wittke said. The Jackson Lake Dam, which some geologists say could rupture during a Teton Fault earthquake, also was not analyzed.

A Teton Fault quake would damage 803 households severely enough to make them uninhabitable. About 400 people would require shelter.

The quake would cut power to more than 800 households and cut off drinking water to 2,792 homes. It would cost $4.5 million to repair utilities such as power, water and sewer in Teton County.

The quake would create 174,000 tons of debris.