Created by Michelle Vokaty and Ashten Sawitsky

The 1870 Charlevoix Seismic Zone Earthquake

Overview • Tectonic setting• Canadian/Quebec/CSZ Earthquakes• Charlevoix Seismic zone and location• Geology• Sediment control• Mercalli Scale• Relationship of Magnitudes• Historic, type, causes and effects of CSZ

Earthquakes

Major Earthquakes in Canada

Earthquakes in the Quebec Region

Charlevoix Local Seismograph Network

Charlevoix Seismic Zone (CSZ)• 100 km from downstream Quebec

City• Most seismically active region in

Eastern Canada, defined by over 2000 local earthquakes between 1978 and 1997

• Detectors record over 200 quakes a year

• Dominated by earthquakes along and in between the Iapetan faults (or otherwise known as the St.Lawrence Paleo-rift faults)

• Most activity occurs along the St. Lawrence valley

Historic Causes of CZS Quakes

• Four major events that are the cause for these earthquakes

• Grenvillian collision (110-900 Ma)• Rifting due to opening of the Iapetus Ocean

(700Ma)• Then the reactivation of these faults when Iapetus

stared closing during Taconian Orogeny (450 Ma)• Finally, the Devonian Meteor impact (350 Ma)• One controversial theory: Conditions such as high

pore fluid pressure and/or low coefficient of friction must exist that do not exceed the maximum crustal stress differences

Location of 1870EQ in Seismic Zone

• Quebec city is rated 6th for earthquake risk and 1st or 2nd for damage

• Strong earthquakes with epicenter distances between 0-80km

Geology of Zone• Four main geological assemblages

1. The Precambrian shield of Grenvillian age with charnockite-mangerite assembleges, metasediments, anorthosite intrusives and local gabbro dykes within the fault zones

2. Ordivician St. Lawrence platform- predominantly limestones

3. Appalachian nappes- Cambrian sedimentary rocks (sandstones, mudstones) which is thrust over the previous two

4. Quaternary deposits- usually glacial till and marine clays and valleys filled with multi-interglacial sedimentary sequences

Sediment controls• Sand, clay, unconsolidated

manmade sediment• Thickness of 5-30m• Thick deposits

– Long period–More shaking–Most damage

• Rivers affect the area 1950– Spring and Fall

Modified mercalli scale

• 12 increasing levels of intensity

• Imperceptible shaking to catastrophic destruction

• Arbitrary ranking based on observed effects

• Effects experience at the place

• Higher numbers=structural damage, lower number=felt by ppl

Rate vs. Magnitude

Types of Earthquakes• High quality records used to

study focal mechanisms, earthquake clusters and crustal velocities

• Earthquakes occur within the Precambrian lithology’s

• Upper to mid-crustal thrust strike-slip events

• No conclusive reasons/pattern for earthquakes

Earthquakes in history

• 1663– M7, epicenter in CSZ,

landslides• 1791– M6, Felt in Quebec City

• 1860– M6, epicenter in CSZ

• 1870– M6.5, felt in Quebec City

• 1925– M6.2, epicenter in CSZ,

damage in Lower Town• 1988– M5.9, MMI = V-VII

Factors of earthquakes

• Earthquake source (magnitude, focal depth, epicenter distance

• Characteristics of inhabited area (distribution of inhabited areas, characteristic of building stock, thickness and properties of underlying material

• Most damage in deep unconsolidated sediment (lower part of town)– Natural deposits and

manmade fills are thickest

• Saint-Roch and Champlain wards effected

• Short epicenter distance=more damage

1870 Geological/Economic Effects• Caused geysers of water and sand • Possibly relates to a sand volcano in Gouffre River Valley• Only 1989 M 6.3 caused surface faulting, • some say some offshore surface faulting could have

occurred, although hard to see/record during that time-recent seismic data report negative results

• Few indirect casualties such as heart attacks, but more structural damage

• Possible geological effect is liquefaction

THANK YOU!

Bibliography

• John E. Ebel, M. D. (2013). Assessing the Location and Magnitude of the 20 October 1870 Charlevoix, Quebec, Earthquake. Seismological Society of America, 588-594.

• Lamontagne, M. (2002). An Overview of Some Significant Eastern Canadian Earthquakes and Their Impacts on the Geological Environment, Buildings and the Public . Natural Hazards , 55067.

• Lamontagne, M. (2008). Earthquakes in Eastern Canada: A Threat that can be Mitigated. Natural Resources Canada, 13-23.

• Lamontagne, M. (2009). Description and Analysis of the Earthquake Damage in the Quebec City Region between 1608-2008. Natural Resources Canada, 514-524.

• Lamontange, M. (1999). Rheological and Geological Constraints on the Earthquake Distribution in the Charlevoix Seismic Zone, Quebec, Canada. Natural Resourses Canada.

• Lamontange, M. (2008). Casualties Directly Caused by an Earthquake in Canada: First Contemporaneous Written Accounts from the M 6.5 Charlevoix, Quebec, Earthquake of 20 October 1870. Seismological Society of America, 1602-1606.