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A mega tsunami could strike the US with little warning: Understanding Cascadia, the danger zones, and how to get ready
Waiting. Biding its time. The Cascadia Subduction Zone, a sleeping giant beneath the Pacific Northwest, has remained eerily quiet for over 300 years. But when it finally awakens, it won't just be a powerful earthquake that hits the coastline.
A towering tsunami, land collapse, and flooding on a historic scale may soon follow.
What is the Cascadia Subduction Zone?
The Cascadia Subduction Zone is a massive fault line running from northern California through Oregon and Washington, and all the way to British Columbia. It's where the oceanic Juan de Fuca Plate is slowly slipping beneath the North American Plate. But the plates don't glide smoothly — they get stuck. That strain builds for centuries until it finally breaks loose in a massive earthquake.
The last major quake hit on January 26, 1700. Based on geological records, it likely had a magnitude between 8.7 and 9.2. That kind of power could strike again. According to the US National Seismic Hazard Model, there's now a 15% chance of a magnitude 8.0 or greater event within the next 50 years.
Areas at risk
When the rupture finally happens, it won't just cause violent shaking and a deadly tsunami. According to a new study published in the Proceedings of the National Academy of Sciences, coastal land across 24 estuaries from southern Washington to northern California could suddenly sink by up to 2.67 meters (8.76 feet).
As per reports, these high risk areas include Washington, Oregon, Northern California, Alaska and Hawaii.
"We talk about climate-driven sea level rise, which is occurring at three to four millimetres a year, and that does eventually add up," said Prof Tina Dura, the study's lead author, in an interview with
BBC Science Focus
. "But here we'll have two metres of sea level rise in minutes. Why aren't we talking about that more?"
That sinking, or subsidence, would permanently change the coastline.
Flood zones would dramatically expand — by as much as 300 km² (115 square miles) today. Areas from southern Washington to northern California could see permanent land drops, especially in low lying estuaries. This sinking land would make flooding worse and more widespread- even long after the tsunami has receded.
The Long-term fallout
Beyond the quake and tsunami, recovery efforts would be hampered by the new geography. Roads and emergency services may end up underwater.
Saltwater could poison farmland. Wetlands that once helped block storm surges could vanish.
A 2022 FEMA planning exercise estimated 5,800 deaths from the quake and another 8,000 from the tsunami. Over 618,000 buildings, including more than 2,000 schools and 100 key facilities, could be damaged or destroyed. The total projected economic impact? $134 billion.
Infrastructure now at risk includes:
5 airports
18 emergency facilities (schools, hospitals, fire stations)
8 wastewater treatment plants
1 electric substation
57 contaminant sources (gas stations, chemical plants, etc.)
Aftershocks that never stop
The study warns that even if the quake struck decades from now, its effects could be magnified by climate change.
By 2100, global sea levels are expected to rise another 60 cm (2 feet). In Cascadia, rising land has masked some of that rise — but when the quake hits and the land sinks, the sea will seem to rise instantly.
The study also estimates that if the quake happens in 2100, floodplains could triple compared to today, expanding by up to 370 km² (145 sq miles).
How can people prepare themselves?
There are no easy answers. Cascadia is a unique problem faced by seismologists as it is so quiet. No one can predict the exact date or time it can wreak havoc. In case of an emergency, there are a few things that residents near the coast need to remember to ensure their safety
Identifying and relocating vulnerable infrastructure
Educating the public on risks
Prepare an emergency kit, as the infrastructure will be destroyed
Practice and update your emergency plan every 6 months.
Write down emergency numbers; give copies to all family members.
