Since then, geologists have discovered more than two dozen faults across Washington.

...to something 2,000 times more powerful , a potential magnitude 9.0 quake that would shake for up to five minutes: Projected M 9.0 Cascadia quake 2 915,000 displaced people 14,600 deaths $81 billion in damage

It went from something like a magnitude 6.8 quake that shakes for up to 40 seconds... M 6.8 Nisqually quake in 2001 1 125 displaced people 1 death $2 billion in damage

By the early 1990s, Washington state officials knew the full scope of the Northwest's earthquake menace.

Today, about 5.4 million people in Washington live in the zone endangered by a magnitude 9.0 Cascadia megaquake, an increase of 1.6 million since 1990, according to a Seattle Times analysis. 3

Yet Washington lags nearly all other quake-prone states in policies to reduce the risk, with, for example, no seismic-safety laws for schools, hospitals and other vulnerable buildings, according to a policy analysis this year.

Magnitude 9.0 earthquakes strike the Northwest about every five centuries. But some were only 200 years apart – and it's been 316 years since the last one.

The Big One will shake the entire Pacific Northwest for four to five minutes, longer than the five biggest quakes in Washington's recorded history combined. Communities will lose power and remain dark for weeks. Some 14,600 people could perish in Washington and Oregon, according to the Federal Emergency Management Agency.

It's likely to be one of the worst disasters the United States has ever faced.

And it isn't the worst earthquake that threatens Seattle. The Northwest's biggest city lies above a different fault that could wreak more havoc locally than The Big One.

The number of people endangered by a magnitude 7.2 Seattle fault quake has increased by 1.2 million since 1990.