Cascadia Subduction Zone study reveals area at particular risk for massive quake
PORTLAND, Ore. (KOIN) – A new study mapping the Cascadia Subduction Zone is giving scientists clues about the state of the fault line as the Pacific Northwest awaits a potentially catastrophic earthquake.
To map the 700-mile zone, stretching from Northern California to Vancouver Island, researchers took a 235-foot ship off the Oregon, Washington, and British Columbia coasts during the summer of 2021, as first reported by The Washington Post.
“We really didn’t have a good picture of where the fault zone was,” said Suzanne Carbotte — Heezen Lamonte research professor at Columbia University and lead author of the study.
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Other fault lines have small earthquakes “going off all the time” which help researchers map those zones; however, the Cascadia Subduction Zone is “very quiet,” making it difficult to define, Carbotte told KOIN 6 News.
Researchers wanted to map the zone to locate where the fault is between the down-going Juan de Fuca plate and the overriding North America plate.
“This is the fault that generates the very large earthquakes that have happened in the past at Cascadia, and we anticipate in the future, and the portion of the fault that generates the large earthquakes is located offshore,” Carbotte explained.
During the study — which was published June 7 in the journal Science Advances — researchers towed a hydrophone streamer from the ship to emit sounds that would echo from the seafloor and the megathrust fault and were picked up by 1,200 microphone-like tools.
Researchers took a ship off the coasts of Oregon, Washington, and British Columbia over the summer of 2021 to map the Cascadia Subduction Zone – discovering one plate near Washington is smoother and more likely a hotspot for earthquakes (Courtesy Madeleine Lucas, University of Washington.) Researchers mapped the Cascadia Subduction Zone over the summer of 2021 by using a hydrophone streamer to emit sounds to echo from the seafloor that were picked up by microphone-like tools to get a better understanding of the fault line (Courtesy Madeleine Lucas, University of Washington.) Researchers mapped the Cascadia Subduction Zone over the summer of 2021 by using a hydrophone streamer to emit sounds to echo from the seafloor that were picked up by microphone-like tools to get a better understanding of the fault line (Courtesy Madeleine Lucas, University of Washington.)
Researchers then used the sounds, and various algorithms, to create images of the fault line and its density that look similar to an X-ray or sonogram, Carbotte said. The researchers were then able to create a map of the zone.
Researchers found that the Cascadia zone is “much more complex” than previously thought. According to Carbotte, the fault surface is segmented with “different geometries.”
“The geometry of the fault plane and how it segmented is very important for the kinds of earthquakes that that we can anticipate and for the shaking that arises, also, of course, the tsunami hazard,” Carbotte said.
Researchers also found that a segment of the zone is “markedly flatter and smoother” from Southern Vancouver Island through Washington state, posing a higher risk for major quakes.
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“Based on other studies of global subduction zones, we know these are the conditions that appear to be associated with the largest earthquakes. So, the flatness and smoothness of the megathrust in this region means that the fault plane likely also continues onshore further than the segments to the south. And that has important implications for the shaking hazard populations that are living in the region,” Carbotte said.
While there is still an “enormous amount to learn” about Cascadia, Carbotte said offshore studies are important because that’s where the massive earthquakes are generated.
Cascadia earthquakes are expected every 300-500 years, with the last 9.0 earthquake hitting the region 324 years ago, spanning Northern California to British Columbia.
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The quake triggered a tsunami that traveled to Japan and created a “ghost forest” on the Oregon coast.
University of Oregon Seismologist Diego Melgar previously told KOIN 6 News that modern quakes like the 9.1 magnitude earthquake in Indonesia in 2004 and the magnitude 9 earthquake in Japan in 2011 tell scientists what to expect when “the big one” strikes in the Cascadia Subduction Zone.
“We’re looking at big tsunamis, lots of strong shaking, and the shaking goes on for a really long time. That’s something that’s really different about these events. Yes, it’s strong shaking, it can last minutes. So, imagine not being able to stand for three, four, five minutes and imagine the forces that our buildings, and bridges, and dams have to put up with in order to weather that event,” Melgar said.
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