Washington and Oregon: It's Worse Than We Thought

A Major Earthquake in the Pacific Northwest Looks Even Likelier

A team of researchers led by Chris Goldfinger, a geologist at Oregon State University, has found evidence that at least 43 major earthquakes have occurred in the last 10,000 years. That number is slightly larger than previously estimated, which means that—over the long time period—it significantly alters the likelihood of any one event occurring.

In terms of sheer numbers, previous reports estimated that Washington state would have a major quake every 500 years on average. Goldfinger’s team now shows them to occur about every 430 years. And northern Oregon, which used to receive a quake about every 430 years, instead faces one every 350 years.

This means that there is about a 20 percent chance that northern Oregon—a region that includes Portland and Astoria—will be hit by a magnitude-8.0-or-higher quake in the next 50 years. (Previously, the area was estimated to have about a 12 percent chance of facing such a quake.) Washington state has between a 14 and 17 percent chance of facing a big one, up from an 8 to 14 percent chance.

These numbers still pale in comparison to earthquake risks to the south. For instance, the San Francisco Bay area has a 50 percent chance of experiencing a magnitude-7.0 earthquake in the next 30 years. Los Angeles faces a 93 percent chance. But scientists expect a major rupture in Cascadia would be much more powerful than one of these Californian quakes.

The apparent spacing between the major Cascadia earthquakes declined on average, make the current risk slightly larger. And even though the risk isn't terribly high, the consequences of a Cascadia earthquake is so great that the time to start getting ready was 10 years ago.