The geological record shows the area is due for a major earthquake, which would likely be followed by a massive tsunami.
Now, a new study has confirmed the region just off the coast of Washington has the ingredients for a megaquake.
The Cascadia Subduction Zone last experienced a large earthquake in the 1700s – and, it's thought to generate a major event roughly every 200 to 530 years.
While it's impossible to pinpoint the exact timing, experts have long warned the region could soon see another major quake.
In the study, led by a team at the University of Texas at Austin, researchers found that such a quake may be more likely to strike off the coast of Washington and northern Oregon than regions further south along the subduction zone.
Seismic data and sediment samples found that sediments are tightly packed on the plate off the northern sites.
There, little water sits in the pore spaces between the grains, leaving the plates more prone to the build-up of stress.