HOW BIG ARE CASCADIA SUBDUCTION ZONE QUAKES?
Great Subduction Zone earthquakes are the largest earthquakes in the world, and can exceed magnitude 9.0. Earthquake size is porportional to fault area, and 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. Because of the very large fault area, the Cascadia Subduction Zone could produce a very large earthquake, magnitude 9.0 or greater, if rupture occurred over its whole area. HOW OFTEN ARE CASCADIA SUBDUCTION ZONE QUAKES? The last known great earthquake in the northwest was in January, 1700, just over 300 years ago. 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.
