Cascadia's last major quake occurred in 1700—some 316 years ago. And according to new evidence, they happen more often than we thought.
Researchers at Oregon State, working with Camosun College in British Columbia and Instituto Andaluz de Ciencias de la Tierra in Spain, have found that the average time between massive Cascadia Subduction Zone earthquakes is 50 to 100 years less than previous estimates.
The Cascadia Subduction Zone is divided into several sections. Previous studies found that major quakes occurred between Newport and Coos Bay, OR every 400 to 500 years. The new estimate is 350 years. The frequency of quakes for the northern section stretching from Astoria to Vancouver was reduced from 500-540 years to 430 years.
That means the likelihood of another catastrophic quake within the next 50 years is slightly higher. For the central and northern Oregon section, the chance of a major earthquake in the next half century is now 15 to 20 percent (up from 14 to 17 percent) and for the Washington and beyond section from 10 to 17 percent (up from 8 to 14 percent).
According to the OSU press release, the new study was based on much more comprehensive evidence than was previously available: 195 core samples retrieved from along the coast. Using those samples, researchers identified 43 major earthquakes along the Cascadia Subduction Zone over the last 10,000 years.
“We believed these earthquakes were possible when the hypothesis was first developed in the late 1980s," says OSU's Chris Goldfinger in a press release. "Now we have a great deal more certainty that the general concern about earthquakes caused by the Cascadia Subduction Zone is scientifically valid, and we also have more precise information about the earthquake frequency and behavior of the subduction zone.”
Read Oregon State's full report here.