A new study published in the Proceedings of the National Academy of Sciences warns that a massive earthquake along the Cascadia Subduction Zone could cause devastating destruction across the U.S. West Coast, with implications for both human safety and environmental resilience. Stretching from British Columbia to Northern California, the fault line has a 15% chance of producing a magnitude 8.0 or greater earthquake within the next 50 years—a likelihood that doubles over a 75-year timeframe.
Researchers emphasize that such an event could cause sections of coastal land to subside by more than six feet almost instantly, dramatically reshaping the landscape and intensifying flood risks. Unlike gradual, climate-driven sea-level rise, tectonic subsidence occurs in moments but can leave long-term impacts lasting decades or even centuries.
Communities in southern Washington, northern Oregon, and northern California are expected to suffer the most severe consequences. The last major Cascadia quake, in 1700, caused a six-foot sea level jump and triggered a tsunami that reached Japan. Today, experts warn that a similar event could result in over 30,000 deaths, damage to more than 170,000 structures, and economic losses exceeding $81 billion.
The study encourages coastal municipalities to incorporate seismic and sea-level predictions into urban planning, emphasizing the increasing risk of “compound hazards”—when earthquakes and climate-driven sea-level rise converge to create layered threats to infrastructure, ecosystems, and communities.
Historical events underscore the gravity of this risk. The 1960 earthquake in Chile caused 2.5 meters of coastal subsidence, permanently submerging farmland and forests and transforming entire regions into marshland. The 1964 Alaska earthquake resulted in over two meters of land sinking, forcing the relocation of towns and the reconstruction of critical infrastructure. A 2022 study also found that an 8.0 magnitude Cascadia quake could generate a tsunami over 200 feet (61 meters) high—devastating coastlines already battered by ground shaking.
“Preparing for these compound hazards can minimize long-term damage, ensure resilient communities, and protect critical coastal ecosystems from permanent degradation,” the authors concluded. “Our findings aim to support decision-makers and coastal residents in the Cascadia Subduction Zone—and globally—as they brace for the combined challenges of seismic activity and climate-driven changes.”
