A geologist says the largest earthquake ever recorded in Alberta was probably due to natural causes.
Rebecca Salvage of the University of Calgary says the 5.6-magnitude quake that rattled windows and shook homes near Peace River in northwest Alberta was likely too deep to have been caused any other way.
Energy extraction processes such as fracking have contributed to earthquakes in other parts of the province.
Salvage says the earthquake, which was preceded by two smaller quakes and followed by several aftershocks, occurred about six kilometres underground.
She says it is probably related to seismic events originating in the Rocky Mountains.
RCMP report no injuries from the event, although those who lived through it say it came on with the sound of a freight train, rattling their homes and their nerves.
