Northern Parts of Cascadia Subduction Zone More Prone to Rupture Than Previously Thought

A new study from Oregon State University revealed that the northern sections of the Cascadia Subduction Zone have more frequent massive earthquakes than what was previously thought, which could potentially affect major population centers such as Portland, Tacoma, Seattle and Vancouver, B.C.

The study, published in the journal Marine Geology, suggests that the chance of a massive earthquake occurring in the area within the next 50 years is also higher than previously estimated.

For the study, researchers from Oregon State University, Camosun College in British Columbia and Instituto Andaluz de Ciencias de la Tierra in Spain analyzed measurements from 195 core samples containing submarine landslide deposits caused by subduction zone earthquakes.

"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," explained Chris Goldfinger, a professor in the College of Earth, Ocean and Atmospheric Sciences at OSU, in a statement. "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."

Based on their analysis, the researchers discovered that the section of the zone from Newport to Astoria, Oregon ruptures every 350 years, reduced from the previous estimate of every 400 to 500 years. At the same time, the rupture for the section of the zone from Astoria to Vancouver Island is also reduced to 430 years, from 500 to 530 years.

Furthermore, their analysis also showed that the chance of earthquake in the next 50 years in the northern region of the subduction zone has increased to 15 to 20 percent from 14 to 17 percent. Also, the chance of a massive earthquake in the northernmost region of the zone has increased to 10 to 17 percent from 8 to 14 percent.

For the past 10,000 years, there have been 43 major earthquakes in the Cascadia Subduction Zone. Earthquakes can occur on the entire zone at once only at some sections. However, an earthquake that has the entire zone involved could produce a magnitude 9.1 at the Richter's scale.