BEND, Ore. — A massive earthquake along the Cascadia Subduction Zone—already long overdue—could dramatically reshape the Pacific Northwest coastline, according to a new study published in the Proceedings of the National Academy of Sciences. And when combined with projected sea level rise from climate change, the long-term impacts could be catastrophic for coastal communities from Northern California to Washington State.
Researchers from Virginia Tech, the University of North Carolina, the University of Oregon, and the U.S. Geological Survey have modeled what might happen if “The Big One,” a magnitude 8.0 to 9.0 earthquake, were to strike around the year 2100. By then, global sea levels are expected to have risen by approximately three feet due to melting ice sheets.
The study found that such a quake could cause coastal land to subside by as much as 6.6 feet, effectively pushing entire towns and ecosystems into tidal zones almost overnight. That combination of sinking land and rising seas would leave more than 17,000 people living on newly formed floodplains—twice the number at risk today.
“The earthquake is something you can’t prevent—it’s going to happen,” said Dr. Andrea Hawkes, a co-author of the study and professor of earth and ocean sciences at the University of North Carolina Wilmington. “But we can make better decisions about where and how we build in these vulnerable coastal zones.”
In towns like Seaside, Oregon, and Aberdeen, Washington—already on the front lines of climate impacts—the findings add urgency to planning efforts. The modeling shows that three times as many buildings and critical infrastructure such as hospitals, airports, and utilities would be exposed to chronic flooding following such a seismic event.
The researchers point to historical precedents to emphasize the risks. The 1960 Great Chilean Earthquake, the strongest ever recorded, caused coastal land to drop by over eight feet, transforming pine forests and farmlands into tidal marshes. Similarly, the 1964 Alaska earthquake forced several communities to permanently relocate after land subsidence led to constant inundation by tides.
What makes the Cascadia scenario especially concerning is that these dramatic landscape shifts could happen within a matter of minutes.
“One of the best ways to think about it is: you could be walking your dog through a coastal forest, and after the quake, that same spot is underwater,” Hawkes said.
The authors stress that the study is not intended to spark panic, but to inform better long-term planning. Some communities are already taking steps to adapt, moving schools, clinics, and public services to higher ground. But the study suggests these efforts may fall short if they don’t also account for potential subsidence caused by an earthquake.
“It would be a shame if you missed it by a few meters because you didn’t factor in what the land is going to do during a quake,” Hawkes added.
With climate change and geological forces converging, the research underscores the need for a more dynamic approach to coastal resilience in the Pacific Northwest—one that looks not just at the next storm or decade, but at the next century.
