Riya Sharma, Andrew Miller / oregonlive.com (TNS)
Just off the Pacific Northwest coast amid record-breaking heat in 2021, researchers braved oddly cold, stormy seas to study another threat to the region — earthquakes and tsunamis. The team of about 50 remained onboard the 235-foot vessel for 41 continuous days.
Their findings — leading to a study released Friday in the journal Science Advances — shed new light on earthquakes. With this new, mostly unexplored data, researchers will be better equipped to model earthquakes and tsunamis — and prepare the Pacific Northwest for the eventual “big one.”
Tectonic plates fragment the Earth’s crust in a delicate dance of collision and separation. In the Northwest, the smaller Juan de Fuca plate is sliding under the North American plate along a roughly 600-mile-long subduction zone. Eventually, researchers say the Juan de Fuca plate may entirely submerge under the North American plate.
The Juan de Fuca plate’s collision has over time given rise to the mountain ranges and volcanoes defining the Northwest. But when tension builds at the collision, the crust can suddenly snap — causing earthquakes and tsunamis. In 1700, a 9.0 quake struck the region, causing immense destruction and a tsunami that reached Japan.
Scientists can’t predict when earthquakes will happen, but they can try to better understand the dynamics surrounding them. This increased understanding can help inform policymakers making building codes, or modelers who map out potential earthquake scenarios.
So the team of scientists set out to make one of the most comprehensive maps of an underwater subduction zone to-date.
Study co-author Suzanne Carbotte said their ship would regularly emit pulses of sound, which would then hit the ocean floor. The sound would then bounce back and a series of microphones on a 9-mile-long cable would collect the sound — allowing researchers to map the ocean floor’s topography and features under the surface.
But Carbotte, a marine geophysicist and professor at Columbia University, said that the team faced several challenges in the data acquisition process. Crab pots damaged the scientists’ equipment — and at one point, the specialized cable broke off the ship entirely. The cable, equipped with GPS and airbags, eventually floated to the surface where the scientists recovered it.
After they returned from the ocean, researchers dove into the data and pored over preliminary conclusions.
In their initial findings, they confirmed the existence of horizontal faults cutting through the subduction zone, splitting it into segments, Carbotte said. Depending on how many segments are involved in an earthquake, the earthquake’s strength can vary.
Another major result: the geometry of the Juan de Fuca plate that runs along the state of Washington to Vancouver Island is unexpectedly “smooth.” Carbotte said the area’s relative flatness means that when tension builds up, it builds up over a larger area. This can make snaps of that tension more powerful.
“We could have a very, very destructive earthquake from just that Washington segment,” she said.
However, Carbotte said that this improved data on the geometries and features of the subduction zone will help earthquake modelers, who will be able to map scenarios in much more detail.
The Cascadia subduction zone is distinct from others because of the variability in its geometry — flat in places like around Washington, while steeper in other areas, said Lydia Staisch, a Portland-based research geologist for the United States Geological Survey. She also noted the presence of sediment along the fault that can impact earthquake characteristics.
“What the researchers have been able to do with this is show, with pretty good confidence, an improved understanding of what the Cascadia subduction zone plate geometry is,” Staisch said. The dataset will be powerful for understanding how earthquakes change along the subduction zone and through time, she said.
Staisch said that this dataset can lead to a host of different directions for future research.
Though the severity and timing are impossible to predict, a large earthquake would devastate the Northwest. Many buildings in the region are not up to code and coastal communities are unprepared for tsunamis, said Bill Steele, an outreach director with the Pacific Northwest Seismic Network.
“We’re poorly prepared; we still have some older structures that aren’t going to do well in the shaking,” he said.
“Hopefully it won’t happen for 100 years or so,” he added.
There is some progress, Steele said. Some coastal communities are constructing vertical evacuation structures for tsunamis. Construction is also improving. But he said earthquake and tsunami-proofing is happening slowly.
The Oregonian/OregonLive has a map of Portland metro buildings by the building codes they were constructed under, and a map of unreinforced masonry buildings — which are vulnerable in earthquakes.
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