Poster of the Ontario-Quebec border region, Canada Earthquake of 23 June 2010 - Magnitude 5.0

Tectonic Summary

The June 23, 2010 Ontario-Quebec border region earthquake occurred at 1:42 pm local (eastern) time about 60 km (38 miles) north of Ottawa, Ontario, Canada's capital city. The preliminary estimate of magnitude (M) is 5.0, at a depth of roughly 19 km (12 miles). These estimates may change as more data becomes available.

This earthquake occurred near the southern edge of the Western Quebec Seismic Zone. Earthquakes within this zone are mostly small. They tend to cluster in a wide area that is slightly elongated northwest-southeast. Historically, earthquakes in the Western Quebec Seismic Zone have caused damage roughly once a decade. Three or four smaller events each year are felt in the region but are generally too small to cause damage. The largest earthquakes known in this part of Canada occurred in 1935 (M6.1), about 250 km (150 miles) to the northwest of todays event, and in 1732 (M6.2), about 150 km (100 miles) to the east. The 1732 earthquake caused significant damage in Montreal.

Earthquakes of the size of todays event are uncommon east of the Rockies, but many have occurred since the arrival of European settlers three centuries ago. In eastern North America and geologically similar regions worldwide, M5.0 to M5.5 earthquakes typically cause light to moderate damage out to a few tens of kilometers (miles) from the epicenter, depending on the number of people and type of buildings near the epicenter. Typically these earthquakes are felt hundreds of kilometers (miles) away. Earthquakes of this size and depth are unlikely to rupture the Earth's surface, although exceptions are known.

The main faults near this earthquake zone trend northwest. These faults form the Ottawa graben and were most active several hundred million years ago. Some of the faults of the graben have been reactivated one or more times since then. The initial focal mechanism of todays earthquake suggests reverse faulting on a fault trending southeast-northwest. However, the size and depth of this earthquake make it uncertain whether the causative fault can be identified.

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