Did you hear it?
© Frederick Florin/AFP/Getty Images

On Christmas Eve, many people in and around Toronto reported hearing a loud "boom," like something had fallen on their house.
Around 11 p.m. Christmas Eve, people reported hearing a loud "boom" in Toronto, Newmarket, Aurora, Belleville, Richmond Hill, and Sutton. Not only was the boom heard, but it rattled houses, leaving many to believe that a tree had fallen on their rooftop.
Loud boom in #YorkRegion around 11pm last night. Heard in #Newmarket #Aurora and #RichmondHill. #meteor? #earthquake? #sonicboom? #santa?

- Rob Jones™ (@blindedbtflash) December 25, 2013

@NebulousNikki that's what we thought too! Lots of neighbours heard it too. Can't figure out what it was... #Kingston

- Kate Kaminska (@katekaminska1) December 25, 2013

@NebulousNikki @RodSinclair1 same in Durham / Brooklin. Over 20 friends in area reporting it at 7:45, again around 11 and about midnight

- Micheline Robichaud (@SweetMinxy) December 25, 2013
But so far, there hasn't been an official explanation.

Even more mysterious is that some people reported hearing booms at other times during the day as well, ranging from 2 p.m. to 6 p.m. to 1 a.m. on Christmas morning.

The United States Geological Service (USGS) didn't record any seismic event in Ontario yesterday, and there were no reports to the American Meteor Society.

So what was it?

The most likely explanation is that it as a cryoseism, also known as a frost quake.

Cyroseisms are rare, localized seismic events that occur when a sudden drop in temperature freezes the groundwater, which then expands and cracks the soil and rock. The crack will release a sudden burst of explosive energy, resulting in a loud noise and the shaking of the ground. They usually occur between midnight and dawn.

Temperatures north of the city - in Newmarket, Richmond Hill, and Sutton, for example - were a chilly -20 C or colder on Christmas Eve.

On January 18, 2000, when temperatures were near -20 C in Sadowa, Ontario, 12 frost quakes were recorded in two hours.

Cryoseisms are rare, but they seem to be more common around the Great Lakes.

Two similar events took place in the U.S. in 2011 and 2007.

According to media reports, in 2011, residents in southwestern Ohio and Indiana reported being awakened by a loud boom as well as the shaking of their homes.

A similar incident occurred in 2007 in Ohio.

What is similar about these events and the Christmas Eve events is that all of them had recently experienced an ice storm.

Is this the answer to the boom of Christmas Eve? We won't know for sure, but it does seem to be the most likely explanation.

Then again, it could just have been a very noisy Santa.