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The Ottawa-Gatineau region is located far from active tectonic plate boundaries, the usual source of earthquakes, but it does have a seismic history. Within this region, the Earth's crust is being compressed. Once the accumulated stress exceeds the strength of the crust, it is released by slippage along reactivated faults of the Ottawa-Bonnechere graben. Although this area has a moderate risk of a damaging earthquake, a devastating earthquake is unlikely.
Magnitude (Richter scale), or size, reflects the amount of fault movement at the source of an earthquake. However, because the strength of shaking generally decreases with distance from the epicentre, what we feel and the amount of damage differ from place to place. Intensity is a measure of shaking at a specific place and ranges from I to XII (modified Mercalli scale). For any earthquake there will be one magnitude and many intensities.
Ottawa-Gatineau was shaken into the year 2000 by a magnitude 5.2 earthquake centred at Kipawa, north of North Bay, about 300 km from Ottawa. In Ottawa, this event had a felt intensity of III.
By evaluating the local history of earthquakes and the local geology, seismologists can produce maps predicting maximum ground motion or intensity for a region. Seismological data are used to set our national building codes that specify the engineering design requirements for earthquake-resistant buildings.
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