Oregon Coast Scientist: Quakes More Frequent in Pacific NW Waters

Published 08/06/2016 at 4:01 PM PDT
By Oregon Coast Beach Connection staff

(Newport, Oregon) – New evidence is pointing to more frequent earthquakes along the Cascadia Subduction Zone than previously thought, and an increased chance the big one expected to hit the Oregon coast will come sooner.

The new findings come from scientists working out of Camosun College in British Columbia and Instituto Andaluz de Ciencias de la Tierra in Spain, as well as Oregon State University and its Hatfield Marine Science Center in Newport. The data was published this week in Marine Geology, showing measurements from 195 core samples that contained the leftovers from undersea landslides caused by submarine quakes. Previous research has usually only come up with around a dozen such samples.

Chris Goldfinger, a professor in the College of Earth, Ocean and Atmospheric Sciences at OSU, was one of those who worked on the project and is considered one of the world's leaders on the subject of offshore quakes.

“These new results are based on much better data than has been available before, and reinforce our confidence in findings regarding the potential for major earthquakes on the Cascadia Subduction Zone,” Goldfinger said. “However, with more detailed data we have also changed somewhat our projections for the average recurrence interval of earthquakes on the subduction zone, especially the northern parts. The frequency, although not the intensity, of earthquakes there appears to be somewhat higher than we previously estimated.”

There are technically four different segments of the Cascadia Subduction Zone as it runs from northern California to British Columbia. The subduction zone has yielded some 43 major quakes in the past 10,000 years. If the entire faultline is involved it can create a magnitude 9.1 earthquake.

It’s been known for some time, and still believed to be accurate, that the southern portions of the subduction zone south of Newport, Oregon, tend to rupture more frequently. Other segments are showing different sides now.

Most ominously for the northern half of the Oregon coast and the Washington coast, the section of faultlines closest to those areas appears to rupture more frequently than previously believed. Goldfinger and others in the past had estimated this area erupts every 400 to 500 years, but they now say the average is more like 350 years.

The last such earthquake of the zone occurred in 1700, some 316 years ago. This is the section of Cascadia Subduction Zone that is also closest to Portland and Seattle.

Goldfinger said the new data increases the chances of the big one hitting in the next 50 years. Of the part of the zone off the central and northern Oregon coast, the chance of an event during that period has been changed to 15-20 percent instead of 14-17 percent. For the northern section off Washington and British Columbia, the chance for such an event is increased from 8-14 percent to 10-17 percent. More of the Oregon coast below:

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