An underwater fault line in the Pacific could trigger a megaquake along the US west coast, putting 10,000 lives in danger.
The Cascadia Subduction Zone runs for almost 600 miles along the coasts of California, Oregon and Washington in the US and British Colombia in Canada.
Now, scientists have mapped the region in new and stunning detail – revealing it is even more dangerous than previously thought.
Instead of being one continuous break, the fault is split into four segments. Thismeans the faults could rupture independently of one another, or all together at once – and due to differences in types of rocks and other seismic characteristics, some lines could be more dangerous than others.
The team, from Columbia Climate School’s Lamont-Doherty Earth Observatory, says this means it has the potential to cause an earthquake of magnitude 9 or more, making it as big as ever seen on the planet.
Such an underwater earthquake could trigger tsunamis more than 30 metres high, kill more than 10,000 people and cause more than $80 billion in damage.
In the wake of the quake, survivors would also have to battle infections from injuries and diseases such as tetanus from disturbed soil and rubble, and cholera from contaminated water supplies.
Co-author Professor Harold Tobin said: ‘We have the potential for earthquakes and tsunamis as large as the biggest ones we’ve experienced on the planet.’
Speaking to NBC, he added: ‘Cascadia seems capable of generating a magnitude 9 or a little smaller or a little bigger.’
The researchers mapped fault during a 41-day research trip in which a vessel trailed miles-long cable along the fault to listen to the seafloor and map an image of the subduction zone.
Study leader Dr Suzanne Carbotte, a marine seismologist at the observatory, told NBC: ‘We had models for what the fault zone looked like, but they were based on no data for much of the margin, and little bits of data and old quality data.
‘It’s kind of like you had Coke bottles over your eyes, and they’ve been removed, and you’ve got the proper prescription. Now you can see where the fault zone is.
‘And not surprisingly, the fault surface is way more complex than the picture we had before.’
The researchers believe that the most dangerous segment appears to stretch from off the coast of southern Vancouver Islands through to Washington state. They say this part is potentially the most dangerous section as the fault line is quite smooth.
When tectonic plates are relatively rough, and feature oceanic faults and seamounts, pieces of the plate could be eroded and may limit the quake’s size.
But when the segment is quite smooth, it is more likely to erupt at once, which makes it potentially the most dangerous section.
While the study, published in the journal Science Advances, cannot predict when Cascadia will unleash a quake, the authors note it is believed to give way to big quakes roughly every 500 years. The last one occurred in 1700, and caused a tsunami which struck the west coast of North America and the coast of Japan.
A similar fault zone off the coast of Japan erupted in 2011, creating a magnitude 9 quake that caused a devastating tsunami to strike the country, killing nearly 20,000 people.
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