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“Frost quakes” shake Ontarians out of bed

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For the last two weeks, loud booming sounds—likely caused by “frost quakes”—have jolted southern Ontarians out of their slumber in the middle of the night.
 
These tremors, also known as cryoseisms, occur during sudden, drastic drops in temperature—in recent weeks, by the way, temperatures across Ontario have dipped below -20 degrees Celsius.
 
At such low temperatures, deep groundwater starts to freeze and expand, causing the ground to crack.
 
“And it seems like the cracking occurs very explosively, very suddenly. And when it does so, it can actually cause the ground to vibrate (and) cause a loud boom,” says John Ebel, professor of geophysics at Boston College.
 
Because temperatures are coldest at night, the loudest cracks have occurred in the early hours of the morning. Some have even compared the sound to that of an “explosion” or a “distant bombing.”
 
While cryoseisms can cause thunderous sounds, they are local weather events that are far weaker than traditional earthquakes, according the Maine Geological Survey. “In some cases, people in houses a few hundred yards away do not notice anything.”
 
Consequently, the instruments at Earthquake Canada are not sensitive enough to detect “frost quakes.” So, it can only assume that’s what people are hearing based on reports from the public.
 
And there have been plenty of those—so many, in fact, that a Toronto-based graphic designer decided to create an interactive map that shows where people have been hearing these explosions from the ground.
 
The mapmaker, Ashley King, asked people on Twitter to send her their postal codes if they’d heard a quake.
 
While most incidents have occurred in large cities, possible “frost quakes” have also been heard in rural Ontario, including one report from just outside Kawartha Highlands Provincial Park and another as far north as Parry Sound.