"... Megathrusts' are the world's largest earthquakes, and happen in a 'subduction zone', a region where one of the earth's tectonic plates is thrust under another. The last one involving Cascadia was estimated at magnitude 9 on the Richter scale, according to Natural Resources Canada.

The Juan de Fuca plate is being forced under the North America plate along the Cascadia fault and, as large parts of the plates are locked together, stress is being built up until an eventual breakage causes a massive earthquake..." (Daily Mail)

The March 11 earthquake and tsunami in Japan was likely the result of a megathrust earthquake. This type of earthquake, were it to occur on the Cascadia fault line could result in a tsunami hitting the west coast of the U.S. rivaling the one that hit Japan.

The Cascadia fault line

Geologists fear that the long dormant Cascadia fault line that stretches from Vancouver to northern California, inactive for more than 300 years, could be overdue for activity. They give a 45% chance for an 8.0 magnitude quake within the next 50 years and a 15% chance for a magnitude 9.0 or greater.

Studies being conducted at the Active Tectonics and Seafloor Mapping Lab at Oregon State University seem to indicate that pressure on the plates is building. We will continue to monitor for any new developments.