| Résumé | (disponible en anglais seulement)
In terms of significant earthquakes, all has been quiet across Canada during the past few months. In this column, I highlight another one of Canada's
interesting historic earthquakes. This one occurred in a part of Canada where we generally don't see earthquakes - especially earthquakes large enough to cause damage. In 1909, a M~5.3 earthquake struck the Saskatchewan-Montana border region on May
15th, a Saturday night, at 10:15 p.m. local time. This rare, Prairie earthquake was felt across Saskatchewan, Alberta, Manitoba, parts of Ontario, Minnesota, Montana, North Dakota, South Dakota, and Wyoming - an area of more than 1.5 million km3. The
closest Canadian communities include Estevan and Regina, SK (180-190 km) and shaking was felt at Lethbridge, AB (550 km), Prince Albert, SK (490 km), Winnipeg, MB (610 km) and even as far as St. Paul, Minnesota (1000 km). There were no reports of
structural damage, but some windows were broken, items were knocked from shelves, and many people were extremely frightened and ran from buildings (even as far away as Winnipeg). For many decades, both the magnitude of this earthquake and its
location were not well known. A detailed study published in 2011 used two instrumental recordings from Europe, as well as a re-evaluation of felt intensities and modern seismicity to determine a preferred magnitude of M5.3 (M5-5.7 at a 95% confidence
level) and a location of 48.81° N, 105.38° W (just south of the Saskatchewan-Montana border). This location places the earthquake within a 300-km-long northeast-southwest trending band of low-level seismicity, suggesting a region of higher seismic
hazard. You can find additional information on this earthquake here: https://www.pressreader.com/canada/regina-leader-post/20080526/281500746994174 This earthquake serves as a reminder that rare, potentially damaging (and certainly frightening)
earthquakes can, and do, strike even in those parts of Canada that we don't generally associate with earthquakes. Lessons learned from rare earthquakes such as this one, have been incorporated into our seismic hazard models and National Building
codes - but we still have much to learn. |