The 3.9 magnitude quake originated southeast of Wallsburg around 12:15 a.m.
People all over the Wasatch Back felt it, from Heber and Midway to Park City and Kamas.
About 10 miles from the epicenter, Mary Hammond said the shaking woke her up in downtown Heber.
“My dogs woke us up before we actually felt anything, and I knew something was up,” she said. “Shortly after, the house started to sway – pretty intense.”
In Midway, also about 10 miles from Wallsburg, Lynne Allred said she and her husband felt strong tremors from the basement of their house.
“It’s the strongest Utah earthquake I’ve ever felt,” she said. “I’ve felt a few over my years, but none of them like this.”
Although the quaking woke many in the community, experts say Thursday’s tremors are considered relatively weak.
Utah Division of Emergency Management’s Genevieve Keys said the earthquake early Thursday morning was about 100 times less powerful than the 5.7 magnitude quake in Magna back in March of 2020.
“Earthquakes are measured on a scale of a factor of 10,” she said. “So, each number you go up [in magnitude], you go up by a factor of 10.”
Keys said more immediate tremors are unlikely. A couple of aftershocks followed Thursday’s event, but none was strong enough to feel.
“This event is really nothing out of the ordinary – we have earthquakes like this all the time below our feet,” she said. “This one was just strong enough to get our attention.”
Katherine Whidden is a research scientist at the University of Utah’s Seismograph Stations. She said people don’t usually notice earthquakes below a 3.0 magnitude.
To cause damage, she said the tremors need to register a magnitude of 5.5 or higher.
Whidden said it’s a common misconception that a weak earthquake relieves the stress that could trigger stronger tremors.
“When you go up one magnitude unit, the shaking goes up by a factor of 10, but the energy released goes up by a factor of 30,” she said. “So, this was a 3.9, let’s round to 4.0. To relieve the stress of even a magnitude 5, we would have to have 30 of these earthquakes to offset a 1 magnitude unit larger earthquake. And then that keeps going up – so if it was 2 magnitude units larger, we would need 900 of the little earthquakes to offset it, and that’s just not happening.”
Whidden noted Wasatch Back residents shouldn’t be too worried about high-magnitude earthquakes – those are more likely across the Wasatch Front.
Keys said when you feel the ground shake, drop to the ground, cover your head and neck, and stay put until the earthquake ends.
More information about earthquake preparedness is available from Be Ready Utah.
