Seattle, Vancouver and Portland are at risk of a MEGAQUAKE: Risk revealed in first detailed map of Pacific Northwest fault line

Tuesday, November 3, 2015
By Paul Martin

Movement of Juan de Fuca plate is connected to the flow of the mantle
But part of the mantle beneath a small piece plate is moving separately
A similar pattern is seen in Pacific Northwest megaquakes, study finds
Researchers believe a killer quake in this area is now 72 years overdue

By ELLIE ZOLFAGHARIFARD
DAILYMAIL.COM
2 November 2015

Seattle, Portland and Vancouver are at risk of being hit by a megaquake, scientists have warned.

Researchers believe a killer quake along Cascadi – a fault line which runs from Cape Mendocino, California, to Vancouver Island – is 72 years overdue.

The ‘Big One’ will hit when Juan de Fuca, a 700-mile chunk of the Pacific Ocean, slides under Canada and America.

Now, scientists have a better idea of how this will happen after creating the first ever detailed map of the mantle under the tectonic plate.

The map shows the movement of the famous Juan de Fuca plate is connected to the flow of the mantle 100 miles (150 km) underground.

‘This is the first time we’ve been able to map out the flow of mantle across an entire plate, so as to understand plate tectonics on a grand scale,’ said Richard Allen, a professor at the University of California, Berkeley.

The major surprise, Allen said, is that the mantle beneath a small piece of the Juan de Fuca plate is moving differently from the rest of the plate, creating a divide in the subduction zone.

A similar pattern is seen in Pacific Northwest megaquakes, which don’t always break along the entire 600 miles (1,000-kilometer) length, producing magnitude 9 or greater events.

The Juan de Fuca plate offshore of Oregon, Washington and British Columbia is small – about the size of California.

It is around 40 miles (70km) thick but ‘big enough to generate magnitude 9 earthquakes’ as it’s placed under the continental North American plate, Allen said.

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