New Cascadia fault line study finds most dangerous segment sits near Vancouver Island

New Cascadia fault line study finds most dangerous segment sits near Vancouver Island
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A new American-led study has found the most dangerous segment of the entire Cascadia Subduction Zone sits on the southern part of Vancouver Island.

New mapping in a recently published study in Science Advance, found that the subduction zone is made up of at least four segments, each one divided by its depth and dip.

The one that’s catching the greatest attention is the segment between southern Vancouver Island and the border of Oregon. According to researchers, the segment has a smooth and flat surface compared to the other segments with a rougher surface.

“It has the highest destructive potential because of its particular geometry. It’s a very flat segment and we think it’s also smoother than the other segments,” said Suzanne Carbotte, a marine geophysicist at Columbia University and lead author of the study.

The flat and smooth segment poses the greatest risk of destruction because of its potential to slip down the seafloor the furthest, causing massive tsunamis.

“One of the strongest correlations is with the dip of the downgoing plate, with the dip of the megathrust surface. The finding is that these very flat regions…the largest earthquakes are happening at these very flat regions,” said Carbotte.

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This is a new area of research that seismologists had very little understanding of previously. Using sound-mapping technology, researchers created a more complex and detailed mapping of the fault line, which uncovered the textures of the different segments.

“These models are really important for understanding the potential for tsunami generation and where you might see where the largest waves being initiated,” said earthquake seismologist John Cassidy.

Some of Cassidy’s colleagues at Natural Resources Canada were a part of the data-gathering portion of the study, in which they used large Ocean Bottom Seismographs (OBS) to help create the map.

Dozens of OBSs were dropped to the seafloor at different locations along the subduction zone for about a year before resurfacing.

“Understanding how the structure varies along the margin can help us identify areas that you might expect most slip, strongest shaking,” said Cassidy.

This latest research helps groups that analyze tsunamis better understand the potential destruction and how far the effects of earthquakes could be felt.

“They run models where they initiate an earthquake rupture in one region and they see how far it propagates based on their starting parameters,” said Carbotte.

The federal government launched RiskProfilier, a website that helps visualize the effects a large megaquake could have on each community.

Data on the website shows that if a 9.0 magnitude earthquake erupted off the coast of Vancouver Island, it would be felt in northern communities near Fort Nelson, with an estimated $38 billion in damages.

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