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Earthquake zones in Eastern Canada
Background on earthquakes in eastern Canada
The continual shifting of large segments of the earth’s crust, called tectonic plates, causes more than 97% of the world’s earthquakes. Eastern Canada is located in a stable continental region within the North American Plate and, as a consequence, has a relatively low rate of earthquake activity. Nevertheless, large and damaging earthquakes have occurred here in the past and will inevitably occur in the future.
Rate of Activity
Each year, approximately 450 earthquakes occur in eastern Canada. Of this number, perhaps four will exceed magnitude 4, thirty will exceed magnitude 3, and about twenty-five events will be reported felt. A decade will, on average, include three events greater than magnitude 5. A magnitude 3 event is sufficiently strong to be felt in the immediate area, and a magnitude 5 event is generally the threshold of damage. The seismograph network of Earthquakes Canada can detect all events exceeding magnitude 3 in eastern Canada and all events magnitude 2.5 or greater in densely populated areas.
Causes
The causes of earthquakes in eastern Canada are not well understood. Unlike plate boundary regions where the rate and size of seismic activity is directly correlated with plate interaction, eastern Canada is part of the stable interior of the North American Plate. Seismic activity in areas like these seems to be related to the regional stress fields, with the earthquakes concentrated in regions of crustal weakness.
Although earthquakes can and do occur throughout most of eastern Canada, years of instrumental recordings have identified certain clusters of earthquake activity. In these clusters, earthquakes occur at depths varying from surface to 30 km (the deepest mine in Canada is 2 km deep).
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