Just 50 miles off the Pacific Northwest coast is an earthquake hot spot that threatens to unleash on Seattle, Portland, Ore., and Vancouver, British Columbia, the kind of damage that has shattered Chile.

The fault has been dormant for more than 300 years, but when it awakens - today or decades from now - the consequences could be devastating.

Recent computer simulations of a hypothetical magnitude-9 quake found that shaking could last two to five minutes - strong enough to potentially cause poorly constructed buildings from British Columbia to Northern California to collapse and severely damage highways and bridges.

Such a quake also would send powerful tsunami waves rushing to shore in minutes. While big cities such as Portland and Seattle would be protected from severe flooding, low-lying seaside communities may not be as lucky.