Mont-Saint-Hilaire, along the Richelieu River.An earthquake ranked with an initial magnitude of 4.5 shook the Montreal area just after midnight, causing some alarm. The quake lasted for only about 10 seconds, and was centered east of Montreal, about 9 kms north-northwest of
Earthquakes of this magnitude don't happen often in the area, but they aren't unheard-of. Just last Thursday, there was a magnitude 2.5 earthquake at just before 7 p.m. EDT that was centered about 5 km north of Huntingdon, Quebec.
No damage was reported for either quake, as anything of a magnitude of less than 5 is very unlikely to cause any structural damage to buildings. On the Richter scale of earthquake magnitude, any quake of magnitude 2.0 to 3.9 is considered 'minor" and anything from 4.0 to 4.9 is considered "light".
"Based on the size of the earthquake, I wouldn't expect there would be any. It is possible it's big enough (to) have shaken objects off tables or it's possible there's a little bit of damage." says seismologist Allison Bent, with the Natural Resources Canada, in an interview with The Star.
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Montreal is part of the Western Quebec Seismic Zone (WQSZ), which stretches along the Ottawa Valley from Montreal to Temiscaming and also includes Eastern Ontario and the Laurentian Mountains. As the map at the above link shows, hundreds of earthquakes have been recorded in the area, stretching back before the year 1900, but most have been weak, and may not have even been noticed by anyone without a seismometer.
Three events stand out in the record, though.
The most significant earthquake in the Montreal area — but not the whole WQSZ —happened on September 16th, 1732. It measured a 'moderate' 5.9 on the Richter scale, lasted between two and three minutes, according to accounts from the time, and ended up damaging over 300 houses.
On November 1st, 1932, a magnitude 6.1 ('strong') earthquake shook the Temiscamingue region, along the Quebec - Ontario Border, about 115 kms north of North Bay. The quake was felt as far west as Thunder Bay, Chicago to the southwest, Washington, D.C. to the south, and Boston and Fredericton to the southeast and east and aftershocks from the quake were felt for months. This was the most powerful quake in the zone.
The most recent significant quake was on September 5th, 1944, when a 'moderate' magnitude 5.8 earthquake was felt in the Cornwall area. People in Sudbury, New York City, Boston and all the way west to Cincinnati felt the tremors from this one, and it caused significant damage to the area, with over 2000 chimneys reported damaged.
Unlike the west coast, experiencing major quakes is very unlikely on the east side of North America, because the ground is much more stable.
The edges of the North American tectonic plate run up the west coast of the continent, out to cover Siberia, and around to cut Iceland in half, then down the mid-Atlantic ridge, across Haiti and Cuba and through the southern tip of Mexico. It is these areas, along the plate edges, that are more likely to experience very strong earthquakes — above magnitude 7.0 — but the further away you are from the edges of the plate, the less likely it is that you'll experience these major earthquakes.
The reason for this is the stability of the rock towards the interior of the plate, as opposed to the more 'pliable' rock of mountain-forming regions like the west coast of North America. However, this stability also means that the vibrations from any earthquakes that do happen will be felt further away.