Timeline of ‘the big one’ for the Portland area

Last month the Portland Mercury did some research to develop a timeline of what might occur in Portland if the ‘big one’ hit. That is, the predicted 8+ magnitude earthquake that could occur at the Cascadia Subduction zone off the Oregon/Washington coast. It asks the tough questions like what would happen to utilities, what buildings might collapse, and how the roads and bridges might fare. The timeline also looks at what sort of response people can expect, including from the American Red Cross.

While graphic, it serves as a wake-up call to how we can best prepare. It can be easy to forget one little detail that can throw any plans into disarray, like what if your plan requires electricity or access to the other side of the river? What if you aren’t at home? April is Earthquake Preparedness Month, making it a great time to think about your preparedness plan.

Another serious issue that is possible here and was brought to the attention of the city of Seattle this week is that of the potential power of aftershocks. While the initial quake would be well off the coast at the subduction zone, the shifting of ground can cause shallow and powerful quakes located in the valley. This was unfortunately seen just over a year ago in Christchurch, New Zealand. An initial 7.1 quake occurred six months earlier, 25 miles away and 6 miles deep. While causing an estimated $4.8 billion dollars in damage, it didn’t compare to the 6.3 magnitude aftershock that was only 6 miles away and 3 miles deep. Although weaker, the shallow aftershock is believed to have cost $20 billion dollars in damage.

Thomas James, Portland Mercury