According to a new study led by Virginia Tech geoscientist Tina Dura, there is a 15% chance of a magnitude 8.0 or stronger earthquake occurring along the CSZ within the next 50 years.
Research warns of catastrophic impacts
Their computer simulations suggest a worst-case scenario could produce waves as high as 1,000 feet (305 metres).
The study also found that coastal land could sink by as much as 6.5 feet (2 metres) during the quake, allowing seawater to flood much farther inland. This would place millions of residents in cities such as Seattle, Portland, and towns in Northern California at immediate risk.
Roads, power lines, hospitals, and other critical infrastructure would likely be destroyed.
Scientists stress that while such an event cannot be prevented, preparation can save lives. They urge governments and communities to build stronger early-warning systems, create clear evacuation routes, and strengthen essential infrastructure like hospitals and emergency shelters.
Researchers concluded that proactive steps today — such as planning for rapid evacuations, fortifying coastal buildings, and training communities — could greatly reduce the devastation from a future Cascadia mega tsunami.
What is a mega tsunami?
A mega tsunami is a very rare but extremely dangerous type of tsunami.
Unlike ordinary tsunamis, which usually reach heights of 10 to 100 feet (3.04 to 30.4 metres), a mega tsunami can send waves hundreds or even thousands of feet high crashing onto land.
These waves are powerful enough to wipe out entire towns within minutes.
US scientists now warn that the Pacific Northwest — the region stretching from Northern California to Vancouver Island — is at risk of such an event because of the Cascadia Subduction Zone (CSZ).
The Cascadia Subduction Zone – a geological time bomb
The CSZ is a fault line running about 600 miles (956km) along the Pacific Coast. Here, the Juan de Fuca tectonic plate is slowly sliding beneath the North American plate in a process called “subduction.”
Day to day, this movement is invisible, but stress is quietly building underground. When that stress finally releases, scientists say it could trigger a massive earthquake of magnitude 8.0 or higher.
This would not only shake the ground violently but also force the ocean floor to lurch upward or downward, displacing water and creating a mega tsunami.
The last time this fault ruptured was on 26 January 1700. Evidence shows that quake sent a tsunami across the Pacific Ocean, striking Japan with what locals described as an “orphan wave” — a wave that arrived without an earthquake in their region.
Scientists estimate such megaquakes happen every 400–600 years, meaning the clock is ticking for Cascadia.
Areas most at risk
The regions identified as most vulnerable are southern Washington, northern Oregon, and northern California.
Low-lying areas here could face permanent flooding, especially when combined with sea level rise caused by climate change.
While states like Alaska and Hawaii also face tsunami risks due to their own seismic activity, their distance from the Cascadia Subduction Zone means they are not as directly threatened by this specific fault line.