Earthquakes along the West Coast and the Cascadia Subduction Zone

Past Earthquakes along the West Coast

In the past 70 years alone, over 100 M=5 earthquakes have hit the west coast.

Examples of large scale earthquakes: M = 9.0: Cascadia, 1700M = 7.0: Vancouver Island, 1918M = 7.3: Vancouver Island, 1946M = 8.1: Queen Charlotte Islands, 1949M = 7.4: Washington State, 1972

The M9 Cascadia Earthquake

At 9PM on January 26, 1700, the undersea Cascadia fault ruptured along a 1000 km length.

Collapsed houses due to shaking and landslides.

According to geological records, other earthquakes such as this one have occurred in the past, and have been repeated at irregular intervals over hundreds of years.

Recent Activity (Canada)

Earthquakes in Canada in the past 30 days

• Most along west coast

• No magnitude 5 or greater

Recent Activity

Earthquakes in Canada in the past 5 years

• The west coast has been the most active region in Canada

• Magnitude greater than 6 only along the west coast

Earthquakes occur in three regions:

• Along faults in the offshore region

• Within the subducting ocean plate

• Within the continental crust

Tectonic Plates off the West Coast of British Columbia

• Explorer Plate

• Juan de Fuca Plate: 2-5cm/yrCascadia Subduction Zone

• Gorda Plate: 1.8cm/yr

SUBDUCTING PLATES:

Cascadia Subduction Zone

• The Juan de Fuca plate is sliding beneath the continent, but does not move smoothly.

• The plate is currently locked and is building up strain in the earth’s crust.

• This may cause of a much larger earthquake when the plates snap loose.

Geological evidence indicates that large earthquakes, such as the one that may be coming, have hit the west coast every 300 to 800 years

Evidence of Strain Build-Up

• Relative motions of points on the surface of the earth are measured using GPS.• Points on the outer region move at over 10 mm/yr.• Points on the inner region move at half this rate. • The outer region is being compressed and strain is building up within the earth.

• It is expected that the accumulated strain will be completely released and the outer coast of Vancouver Island will move about 5 meters S-W. 

Thank you

References

Natural Resources Canada - www.nrcan.gc.ca Earthquakes in British Columbia -

http://www.crew.org/british-columbia.php Juan de Fuca Plate -

http://en.wikipedia.org/wiki/Juan_de_Fuca_Plate Cascadia Subduction Zone Volcanism in British

Columbia - http://www.emporia.edu/earthsci/student/geller2/cascadia.html#Plate