On Sunday 8 July 2012, slightly before 8.15 pm local time (slightly before 11.15 pm, GMT), an Earthquake struck in eastern Labrador, roughly 146 km south of Happy Valley, according to the United States Geological Survey, who measured the quake as 4.4 on the Richter Scale at a depth of 18 km. An Earthquake of this size is highly unlikely to have caused any damage or casualties, but would have been felt as severe shaking by anybody in the area.
The location of the 8 July 2012 quake. USGS.
Earthquakes in Labrador are extremely rare, making the cause of such quakes hard to determine. This is largest quake in the area since 1962. Eastern Canada is a long way from any active plate margins, the nearest being the Mid Atlantic Rift Zone, which runs through Iceland far to the east, and the subductive zone along the west coast of North America, far to the west.
There are, however, a number of areas of tectonic stress in eastern Canada, one of which, the Lower St. Lawrence Seismic Zone, runs beneath the St Lawrence River, roughly 200 km southeast of the epicenter of the 8 July quake. This is hard to study directly, but seismic studies, which are based upon monitoring the way waves of energy from known quakes travel through the rocks below the region, enabling scientists to build a three dimensional image of the geological structure beneath the river in a similar way to sonar, suggest that this is caused by the reactivation of an ancient rift zone associated with the opening of the Iapetus Ocean in the Late Proterozoic to Early Paleozoic (i.e. roughly 500 million years ago).
Information from witnesses who felt quakes is extremely useful to scientists studying seismic activity. If you felt this Earthquake you can report it to Natural Resources Canada here.
See also Oklahoma shaken by Earthquake on Christmas Day, The dangers of a modern Laki style eruption in Iceland, Earthquake off the coast of Vancouver Island, Quebec Earthquake, 27 August 2011 and Earthquakes on Sciency Thoughts YouTube.
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