What are frost quakes?
Temperatures across the United States plummeted today, with parts of the Midwest experiencing wind chills of 40 degrees below zero - and that's in Celsius.
What's causing these odd sounds?
So, what's going on here?
"Cold enough for some Sun Dog Millionaires and so cold you could actually see the ice crystals in the air that cause said sundogs", resident Colin Rankin wrote on Twitter.
As that water underground suddenly freezes into ice, it then expands, causing the surrounding soil and rock to crack. But meteorologists in the Grand Forks, North Dakota, NWS office laughed when contacted by Live Science with the question and said they'd never heard the term "frost quake" before.
"Frost quakes are usually not picked up on seismographs because they aren't generating a true seismic wave", said Jones.
Most often, frost quakes occur between midnight and dawn, when temperatures are coldest, and in areas with little snow on the ground, since a layer of snow will insulate the ground from the falling temperatures.
First, the ground has to be saturated with water - like it is in the Chicago-area right now with all the snow being dumped in the region.
Another possible form of cryoseism that people are hearing right now is when artificial materials - asphalt, concrete, etc - contract in the extreme cold, and fracture under the intense pressure.
In mid-January, reports of frost quakes also popped up in IN and CT when a deep freeze settled in after Winter Storm Harper, reports Brian Donegan for The Weather Channel.
Frost quakes have been reported across the US Midwest - including Ohio, Chicago and Pennsylvania. But it will be hard to confirm if the quakes actually happened; the booms they create may sound powerful, but frost quakes are actually "very small compared to even a small natural disaster", John Bellini, a geophysicist with the U.S. Geological Survey, tells Alicia Fabbre of the Naperville Sun. Let us know in the comments, below!