Saint Lawrence rift system
Encyclopedia
The Saint Lawrence rift system is a seismically
active zone paralleling the Saint Lawrence River
. The rift
system trends northeast and southwest and forms a half-graben
that links the Ottawa-Bonnechere
and the Saguenay
grabens. The rift system 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
.
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 earthquake
s over the last 350 years, including the 1925 Charlevoix-Kamouraska earthquake
. At the Lower St Lawrence zone the largest recorded earthquakes are about magnitude five. Seismic studies indicate a crustal convergence across the Saint Lawrence valley of about 0.5 mm per year.
The earthquakes of the Charlevoix Seismic Zone
are thought to be related to the re-activation of ancient fault structures by the Charlevoix impact event
.
St.Lawrence rift system quakes
Seismology
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...
active zone paralleling the Saint Lawrence River
Saint Lawrence River
The Saint Lawrence is a large river flowing approximately from southwest to northeast in the middle latitudes of North America, connecting the Great Lakes with the Atlantic Ocean. It is the primary drainage conveyor of the Great Lakes Basin...
. The rift
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
system trends northeast and southwest and forms a half-graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
that links the Ottawa-Bonnechere
Ottawa-Bonnechere Graben
The Ottawa-Bonnechere Graben , with its branch the Timiskaming Graben, is an ancient rift valley in the Canadian Shield of Northeastern Ontario and Quebec, Canada. This rift valley was formed when the Earth's crust moved downward about a kilometre between two major fault zones known as the Mattawa...
and the Saguenay
Saguenay Graben
The Saguenay Graben is a rift valley or graben in the geological Grenville Province of southern Quebec, Canada. It is an elongated flat-bottomed basin long and wide, bounded by normal faults running parallel to its length....
grabens. The rift system extends more than 1000 km along the Saint Lawrence valley from the Ottawa
Ottawa
Ottawa is the capital of Canada, the second largest city in the Province of Ontario, and the fourth largest city in the country. The city is located on the south bank of the Ottawa River in the eastern portion of Southern Ontario...
- Montreal
Montreal
Montreal is a city in Canada. It is the largest city in the province of Quebec, the second-largest city in Canada and the seventh largest in North America...
area. Within the system, fault reactivation is believed to occur along late Proterozoic
Proterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
to early Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
normal faults related to the opening of the Iapetus Ocean
Iapetus Ocean
The Iapetus Ocean was an ocean that existed in the Neoproterozoic and Paleozoic eras of the geologic timescale . The Iapetus Ocean was situated in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalonia...
.
Two significant historically active seismic zones occur along this system associated with northwest trending intersecting graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
structures. The Charlevoix
Charlevoix
The Charlevoix region, located in Quebec, includes parts of the north shore of the Saint Lawrence River and the Laurentian Mountains region of the Canadian Shield...
region has been the location of at least five magnitude six or larger earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s over the last 350 years, including the 1925 Charlevoix-Kamouraska earthquake
1925 Charlevoix-Kamouraska earthquake
The 1925 Charlevoix–Kamouraska earthquake was a major earthquake that struck the entire northeastern part of North America on February 2, 1925, reaching 6.2 on the moment magnitude scale....
. At the Lower St Lawrence zone the largest recorded earthquakes are about magnitude five. Seismic studies indicate a crustal convergence across the Saint Lawrence valley of about 0.5 mm per year.
The earthquakes of the Charlevoix Seismic Zone
Charlevoix Seismic Zone
The Charlevoix Seismic Zone is a seismically active area in the Charlevoix region of northeastern Quebec, Canada. It is also known as the Charlevoix-Kamouraska Seismic Zone because earthquakes occur in Kamouraska Country where the land expression of the seismic zone is separated by the Saint...
are thought to be related to the re-activation of ancient fault structures by the Charlevoix impact event
Charlevoix crater
The Charlevoix crater is a large eroded meteorite impact crater in the Charlevoix region of Quebec, Canada. Only part of the crater is exposed at the surface, the rest being covered by the Saint Lawrence River. The original crater is estimated to have been in diameter and the age is estimated to...
.
See also
St.Lawrence rift system quakes
- 1944 Cornwall-Massena earthquake1944 Cornwall-Massena earthquakeThe 1944 Cornwall-Massena earthquake occurred on Tuesday, September 5, 1944, at roughly 12:40am EST in Massena, New York. It was registered as a magnitude 5.8 on the Richter scale and was felt for a great distance. This area is part of the Saint Lawrence River Valley and the seismically active...
- 1925 Charlevoix–Kamouraska earthquake