Disaster zone? A huge 'megathrust' earthquake could spark a tsunami and devastate the U.S. northwest if the Juan de Fuca plate is forced further under the North America plate on the Cascadia fault line

The huge March 11 earthquake that sparked the tsunami off the coast of Japan may have been a ‘megathrust’ quake and now researchers fear the Cascadia fault line 50 miles off the U.S. coast could rupture and cause a quake and subsequent tsunami.

The average time along that fault between massive quakes above magnitude 8 is 240 years, said The Times, and the last 'megaquake' was just over 300 years ago.

'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.

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