Could it not have been a smaller version of one of these? Why 'frost quakes'?!
Speculation and confusion swirled after a loud boom could be heard through parts of northwest Calgary on Tuesday afternoon.

It was enough to rattle the windows at Crowfoot General Paints and baffle residents in the area.

James Cormier-Chisholm says he's never heard anything like it before.

"Didn't quite sound like thunder, usually with thunder you have a big boom and then a crescendo fading away," he says. "This was one big sharp boom!"

It wasn't an explosion, meteorite, sonic boom or oil and gas work as many had speculated.

Comment: How do they know it wasn't an overhead meteor explosion?

It's called a frost quake and it happens when it's cold for a long period of time and ice gets brittle and cracks under pressure.

Comment: Sez who?

U of C geophysicist David Eaton says Tuesday's noise was most likely the result of a frost quake but one that happened below ground.

"Frost quakes don't pose any hazard to people or property but they can be quite alarming when you hear how loud the sound it is."

Comment: Oh yeh, since when?

The U of C's closest seismic monitor was offline when the boom happened but it likely is too far away to have registered the sound even if it was on.