ROCK THE COAST

The west coast of the US has seen a flurry of activity in the last seven days, with 11 offshore quakes on on the Juan de Fuca tectonic plate, which forms part of the Cascadia subduction

A CLUSTER of earthquakes off the California coast might mean 'the Big One' could strike at anytime, devastating the West Coast of the USA, it has emerged.

'The Big One' refers to a large scale earthquake on the Cascadia Subduction, which could rip through California and the west coast of the USA in mere minutes and cause a tsunami.

Seismologists have said a large magnitude earthquake on the offshore fault could trigger a 9.0 magnitude earthquake and an accompanying tsunami.

The recent cluster of earthquakes ranging from 2.8 to 5.6 magnitudes occurred six miles underwater, 126 miles from the west coast on the Juan de Fuca tectonic plate which is part of the Cascadia subduction zone, that runs from Northern California to British Columbia.

Don Blakeman, a geophysicist at the National Earthquake Information Center, told Oregon Live the magnitudes haven't yet been serious, adding that quakes of this calibre occur fairly often off the coast.

Though the largest quake with a magnitude of 5.6 magnitude happened shortly before 8am on Tuesday morning and qualified as a moderate earthquake, the impacts would be more significant if it had occurred on land rather than 10km under the sea, Blakeman said.

While the United States Geological Survey (USGS) has not issued a warning over the recent shakes, stating that they do no pose a risk of a tsunami, in 2016 it was reported that if Cascadia were to have a large-scale quake, the resulting tsunami would kill more than 11,000 and injure more than 26,000 people, the Federal Emergency Management Agency warned.

Chris Goldfinger, a professor of geophysics at Oregon State University told CNN: "Cascadia can make an earthquake almost 30 times more energetic than the San Andreas to start with, and then it generates a tsunami at the same time, which the side-by-side motion of the San Andreas can't do."

Describing what would happen if during a quake, he said: "In this case, three minutes is an eternity. It is a very, very long time… We'll lose a lot of bridges. We'll lose our highway routes. The coast will probably be closed by down bridges or landslides or both."

But he warned there is no way of predicting Cascadia's next "big one".

"I wish there were, but, no, there isn't. We can't look forward and say we are due or overdue really."

Cascadia's last quake was on January 26, 1700 with an estimated moment magnitude of 8.7–9.2, and involved the Juan de Fuca Plate from mid-Vancouver Island, south along the Pacific Northwest coast as far as northern California.

The length of the fault rupture was approximately 620 miles and caused a tsunami which struck the coast of Japan.