Quebec earthquake of 20 October 1870

Background. The earthquake occurred in the Canadian province of Quebec on 20 October 1870. Eastern Canada experiences relatively infrequent earthquakes due to its distance from active plate boundaries, but the Charlevoix Seismic Zone is its most active part. This region has recorded five earthquakes of estimated magnitude 6 or greater since historical records began.

Magnitude Estimates. The magnitude of the 1870 event is subject to varying estimates. Geological Survey catalogs assign a moment magnitude of 6.6 Mw. However, researchers such as Ebel calculated an intensity magnitude between 5.5 and 6.0, with 5.8 considered the best estimate. The Modified Mercalli intensity rating was X (Extreme).

Geographic Context. Quebec City is the capital city of the Canadian province of Quebec. The earthquake occurred within this province. While the legacy data associates the event with Quebec City, the supplied passages identify the event as the 1870 Charlevoix earthquake, noting its occurrence in the province generally.