When Will The Northwest's Big Earthquake Be?

The Northwest is due for a very, very big earthquake, but no one knows exactly when it will happen. The New Yorker published an article in this week's issue featuring a lesser-known fault line — the Cascadia subduction zone — that seismologists believe will produce a devastating earthquake from northern California up to Canada. The pressing question now is, when will the Northwest's big earthquake happen? The scary part is that scientists aren't really sure, and their predictions are vague. Since it's been a few years since middle school geology class, here's a breakdown of the Cascadia subduction zone's problem. The fault runs from Northern California to Vancouver, and the continental plates are currently wedged up against each other.

According to The New Yorker, there is a backstop, or immovable mass, in the center of North America, which will rebound like a spring at some point. When that happens, there are two possibilities: either only the southern part of the Cascadia subduction zone will give way, producing an earthquake between 8 and 8.6 on the Richter scale, or the entire zone will give way at once, causing a quake with a magnitude between 8.7 and 9.2. Either earthquake would be huge, and both would be incredibly destructive to the Northwest.

Oregon State University marine geologist Chris Goldfinger predicts that there's a one in three chance that the smaller of the two potential earthquakes will take place in the next 50 years, but that's the closest prediction we have right now. The Cascadia subduction zone's last mega-quake was in 1700, and many seismic experts think it's overdue for another. But no one knows exactly when it will strike.

The Northwest needs to be prepared, because the predicted quake and subsequent tsunami will devastate the whole region. The New Yorker says:

By the time the shaking has ceased and the tsunami has receded, the region will be unrecognizable. Kenneth Murphy, who directs FEMA’s Region X, the division responsible for Oregon, Washington, Idaho, and Alaska, says, "Our operating assumption is that everything west of Interstate 5 will be toast.”

Although there's no precise estimate for when it will happen, 50 years is within many of our lifetimes, and isn't so far off that it can be ignored. The longer the Cascadia subduction zone goes without a major earthquake, the more the odds increase that it will happen soon. Hopefully, as it approaches, scientists will be able to make a more specific prediction, so that the Northeast won't be totally caught off-guard.