Earthquakes in Canada Maurice Lamontagne, Ph.D., ing. Geological - - PowerPoint PPT Presentation

• Dr. Maurice Lamontagne

Earthquakes in Canada

Maurice Lamontagne, Ph.D., ing. Geological Survey of Canada Natural Resources Canada

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• Dr. Maurice Lamontagne

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What is an Earthquake?

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• Dr. Maurice Lamontagne

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Movement on a fault plane causes vibrations…

The larger the area on which there is slip (rupture) – the larger the magnitude of the earthquake; – the longer the duration

• f rupture/ the more

intense the vibrations/ the longer shaking lasts…

Earthquake Magnitude (M)

• Depends on the size of the reactivated fault surface;
• Large subduction­related earthquakes can exceed M8, almost all

M8+ earthquakes occur at plate boundaries;

• Earthquakes below M2.5 may not be felt and can be only detected by

nearby seismographs.

• For M4+, ground vibrations can be felt over large areas;
• If near the epicentre, M5 is the minimum magnitude to make light
• bjects fall, M5.5 can cause some damage to masonry;

In eastern Canada:

• Largest event was M7.0 (1663 Charlevoix earthquake, magnitude is

estimated from historical records);

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Almost all earthquakes are weaker than M5, which is below the threshold that might cause damage to engineered facilities.

• Dr. Maurice Lamontagne

• Dr. Maurice Lamontagne

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Global Seismicity over 20 years: concentrated at plate boundaries

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Mw 6.0 Mw ≥ 7.7

• Dr. Maurice Lamontagne

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Major earthquakes are related to movements at Plate Boundaries

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Three types of Plate Boundaries

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• Dr. Maurice Lamontagne

Tectonic Context of Canada’s West Coast

Convergence

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• Dr. Maurice Lamontagne

NRCan Seismograph Network detects earthquakes in Canada High density of stations in eastern Canada

Canadian National Earthquake Catalogue

• Authoritative inventory of earthquake location, magnitude,

depth, etc;

• Based on written historical accounts and instrument records;
• NRCan seismograph network can detect all earthquakes greater

than M3.0 anywhere in Canadian territory;

• Near some populated areas, the denser station network allows us

to detect earthquakes as small as M1.0;

• If the earthquake can be felt, we can record and measure it.

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• Dr. Maurice Lamontagne

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Significant earthquakes

• f Canada
• Dr. Maurice Lamontagne

Record of M6+ earthquakes in Canada and smaller events that were notable

1949 1700 1663, 1925 1929

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Earthquakes in eastern Canada

• Earthquakes that can be felt in eastern Canada are rare;
• They occur mainly in well­defined zones, characterized by many tens of

small (<M3) earthquakes annually;

• Most earthquakes that have caused any damage have occurred in known

seismically active zones;

• Most earthquakes occur at depths between 5 and 25 km, and represent

reactivation of old faults deep in the Precambrian Basement;

• Only one earthquake is known to have ever caused a surface fault rupture

(Ungava);

• Faults mapped at the surface are not necessarily seismically active;
• The Canadian National Earthquake Catalogue and our knowledge are the

basis for Seismic Hazard Maps.

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• Dr. Maurice Lamontagne

Earthquake Distribution of Eastern Canada

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Canadian Earthquakes knO'Hl to hive caused $OITl' damage

• Magnitude 4.5 to 8.6
• MagnlbJde 3.0 to 4.5

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• Dr. Maurice Lamontagne

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Seismic Hazard Map Historical seismicity + Geological Model

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Estimate of shaking that new buildings are required to withstand (under the National Building Code of Canada)

Toronto Montreal Québec Ottawa

Increasing Hazard

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Map of all M5 and greater earthquakes

recorded in the region

(Jan. 1900 -Mar 2011)

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Magnitude

* 5.0 - 5.9

6.0 ­ 6.9

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Natural Resources Ressources naturelles

• Dr. Maurice Lamontagne

C, aIlada

Canada Canada

Conclusions

• Large earthquakes (M8+) are expected near plate boundaries such as subduction

zones;

• Eastern Canada is an "intraplate” environment, well away from plate boundaries;
• Generally low­level of earthquakes in eastern Canada, but some well­defined zones

are recognized as being more active (i.e. Charlevoix);

• Historically, most eastern Canada earthquakes occur in these well­defined zones,

but have produced only minor damage;

• The region around Lake Ontario is one of low­ to moderate seismicity, earthquakes

in the Canadian Shield are even more rare;

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• Historical observations and more recent continuous records of earthquake activity

are used to develop seismic hazard maps that define the seismic provisions of the National Building Code.

• Dr. Maurice Lamontagne