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Earthquake Record Shakes Up Pacific Northwest Predictions

The study delves into the past of the Cascadia Subduction Zone, a tectonic boundary that stretches more than 700 miles (1,100 kilometers) from Northern California to Vancouver Island. The exhaustive, 170-page report from a team at Oregon State University (OSU) offers ample evidence that 19 or 20 magnitude-9.0 earthquakes have ripped along the fault over the last 10,000 years. 

"That is a remarkable record that goes back a long time," said geophysicist Craig Weaver, the Pacific Northwest coordinator for the U.S. Geological Survey's Earthquake Hazards Program, who was not associated with the research.  

Weaver said that it's been known since the late 1980s that the Cascadia Subduction Zone can rupture its entire length all at once, producing magnitude-9.0 quakes — the same magnitude as Japan's devastating March 2011 earthquake — along a fault that is even closer to shore. Yet the new report shows it has done so repeatedly, about every 500 years. 

The last magnitude-9.0 earthquake hit in January 1700, and sent a deadly tsunami across the Pacific Ocean to Japan. That event has been well-documented both historically and geologically.