The experts say it is a just a matter of time before the next major seismic event occurs in the Cascadia Subduction Zone off Vancouver Island.
The Cascadia Subduction Zone is a very long sloping fault that stretches from mid-Vancouver Island to Northern California. It separates the Juan de Fuca and North America plates. New ocean floor is being created offshore of Washington and Oregon. As more material wells up along the ocean ridge, the ocean floor is pushed toward and beneath the continent. The Cascadia Subduction Zone is where the two plates meet. Source pnsn.org
Researchers know exactly when the last major quake struck off our coast; January 26th, 1700.
‘The 1700 Cascadia earthquake was a magnitude 8.7 to 9.2 megathrust earthquake that occurred in the Cascadia subduction zone in 1700. The earthquake involved the Juan de Fuca Plate underlying the Pacific Ocean, from mid-Vancouver Island in British Columbia, Canada, south along the Pacific Northwest coast as far as northern California, USA. The length of the fault rupture was about 1,000 kilometers (620 miles) with an average slip of 20 meters (22 yards)’ source http://www.iris.edu/hq/retm
Earthquake seismologist John Cassidy says earthquakes around the world serve as reminders about the importance of being prepared.
Geological evidence indicates that great earthquakes may have occurred at least seven times in the last 3,500 years, suggesting a return time of 400 to 600 years.
The subduction of the Juan de Fuca plate beneath North America changes markedly along the length of the subduction zone, notably in the angle of subduction, distribution of earthquakes, volcanism, geologic and seismic structure of the upper plate, and regional horizontal stress. To investigate these characteristics, we conducted detailed density modeling experiments of the crust and mantle along two transects across the Cascadia subduction zone. One crosses Vancouver Island and the Canadian margin, and the other crosses the margin of central Oregon. Both density models were constructed independently to a depth of approximately 50 km. We gathered all possible geologic, geophysical, and borehole data to constrain the density calculations. The final densities for the Oregon and Vancouver lithosphere models were obtained from gravity inversions.
Our results confirm that the downgoing slab of the Cascadia subduction zone dips significantly steeper beneath Oregon than beneath Vancouver Island, lending support to the idea that the Juan de Fuca plate is segmented from north to south. In addition, our gravity models indicate that the mantle wedge beneath western Oregon (i.e., below the western Cascades) is lighter than the mantle beneath the Canadian continental crust. This low density agrees with the low mantle velocities observed in the mantle and the present day extensional regime of the Pacific Northwest… Full story HERE
Danger Zone of Cascadia Subduction zone.
Could the West coast be subjected SOON to a massive earthquake?
As explained by University of Washington Seismologist William Steele, this is a model of what an earthquake along the Cascadia fault line might look like. In the future technology may be available that can give us an early warning.
OregonLive.com – March 19, 2011: Oregon Coast Must Prepare For Repeat Of The Great Cascadia Earthquake of 1700 (Links)
Timescolonist.com – March 19, 2011: Victoria Subject to Two Kinds of Catastrophic Earthquakes
USnews.com – March 15, 2011: Pacific NorthWest Faces Nearly Indentical Risk to Japanese Quake