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Forget the crustal faults running through Portland. By far the biggest hazard facing Portland and surrounding communities is a Cascadia Megathrust Subduction Zone Earthquake (magnitude 9+). A subduction zone megathrust earthquake is far more powerful than most earthquakes we hear about, and Cascadia is among the largest of this breed. The next big Cascadia earthquake is likely to rank no less than fourth in the list of largest earthquakes in recorded history. But that's only part of the story.

Cascadia earthquakes devastate a vast region: from southern Canada to northern California, from the Pacific Ocean to the Cascade Mountains (approximately 84,000 square miles). Rarely do earthquakes have a 700 mile long epicenter. The December 26, 2004 Sumatra earthquake (which caused the Indian Ocean tsunami) was one. Its subduction zone is nearly a twin of Cascadia, and it is the only other subduction zone known to slip all at once, like Cascadia. That earthquake actually caused a measurable wobble in the earth's rotation and altered the earth’s gravitational field! We heard very little about the earthquake itself because it occurred away from a large, heavily-populated land mass. That will not be the case for Cascadia. The smaller scale, yet nonetheless devastating 2011 Sendai (Honshu), Japan earthquake and tsunami is a good preview of what to expect along the Oregon and Washington coastline from a Cascadia Megathrust Subduction Zone earthquake. And while inland cities may be spared a tsunami, they will still be rattled by a M9+ "great" quake lasting up to five minutes. There have only been a couple earthquakes in recorded history with a moment magnitude which may rival or exceed Cascadia, but for the total amount of energy released, Cascadia and Sumatra are unrivaled, massive events.

We are being lulled into a false sense of security when we are told that many of our buildings and bridges are being upgraded for a major earthquake. A "major" earthquake is defined as M7.0–7.9. A "great" earthquake is anything ≥ M8. Portland's seismic codes only anticipate a M7.0 quake. A Cascadia M9+ will be over 1,000 times more energetic than our seismic codes anticipate. Only Japan and Chile try to address such massive earthquakes in their seismic codes. See Portland’s Feeble Seismic Codes for more information.

While we face a variety of threats, such as terrorism, accidents, and natural disasters, if you’re prepared for Cascadia, you’re prepared for almost any kind of disaster. And there is no doubt that Cascadia is coming. The only question is when? The more we learn about Cascadia, the higher the probability becomes. Chris Goldfinger of OSU, who has studied Cascadia extensively, now says he expects a great quake before 2060. We are already past the 300 year cluster average between major events, and have exceeded 75% of the quiet periods between quakes in Cascadia's history.

This web-book is a living document. Our initial focus is Cascadia (as that is our worst-case scenario); in time we may include information on a wider range of hazards.