Canadians are experiencing a rare phenomenon as part of the polar vortex that has descended over the central part of North America.

Meteorologists call the incidents “frost quakes” and they can produce a sound as strong as a sonic boom.

The “quakes” happen when ice and rain seep into the ground and then the temperature falls so low that it freezes, causing the earth to split open as during an earthquake.

The phenomenon shocked residents of Toronto who thought someone was breaking into their homes or that gunfire had erupted in their neighborhoods. Toronto police reported hundreds of calls from worried residents over loud, unexplained noises.

Some residents told London’s Daily Mail that the quakes were strong enough to wake them from sleep and make dishes rattle.