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The 'Saint Lawrence rift system' is a seismically active zone paralleling the Saint Lawrence River. The rift system trends east-northeast and extends more than 1000 km along the Saint Lawrence valley from the Ottawa - Montreal area. Within the system fault reactivation is believed to occur along late Proterozoic to early Paleozoic normal faults related to the opening of the Iapetus Ocean.^[1]
Two significant historically active seismic zones occur along this system associated with northwest trending intersecting graben structures. The Charlevoix region has been the location of at least five magnitude six or larger earthquakes over the last 350 years. At the Lower St Lawrence zone the largest recorded earthquakes are about magnitude five. Seismic studies indicate a crustal compression across the Saint Lawrence valley of about 0.5 mm per year.^[2]
The earthquakes of the Charlevoix zone are thought to be related to the re-activation of ancient fault structures by the Charlevoix impact event.^[3]

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References

1. Saint Lawrence Rift System Retrieved on 2007-06-20
2. Mazzotti, S.; Henton, J.; Adams, J., ''Crustal strain rates and seismic hazard from seismicity and GPS measurements along the St Lawrence Valley, Quebec'', American Geophysical Union, Spring Meeting 2004, abstract #S14A-02 http://adsabs.harvard.edu/abs/2004AGUSM.S14A..02M
3. F. ANGLIN and G. BUCHBINDER, ''Microseismicity in the mid-St. Lawrence Valley Charlevoix zone, Québec'', Bulletin of the Seismological Society of America; October 1981; v. 71; no. 5; p. 1553-1560 http://bssa.geoscienceworld.org/cgi/content/abstract/71/5/1553 (abstract)