Download Earthquakes along the West Coast and

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, 1700
M = 7.0: Vancouver Island, 1918
M = 7.3: Vancouver Island, 1946
M = 8.1: Queen Charlotte Islands, 1949
M = 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
Tectonic Plates off the West Coast of British Columbia
Earthquakes
occur in three
regions:
• Along faults in the
offshore region
• Within the subducting
ocean plate
• Within the continental
crust
SUBDUCTING
PLATES:
• Explorer Plate
• Juan de Fuca
Plate: 2-5cm/yr
Cascadia Subduction
Zone
• Gorda Plate:
1.8cm/yr
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