Researchers say earthquake risk looms large for southern Oregon coast

A comprehensive analysis by researchers at Oregon State University (OSU) suggests the southern Oregon coast, not so far from Vancouver Island, may be vulnerable to earthquake sometime in the next five decades.

OSU researchers reached that conclusion, based on recurrence frequency, after completing the analysis of the Cascadia Subduction Zone off the Pacific Northwest coast. They say there is a 40% chance of a major earthquake – one that could approach the intensity of the Tohoku quake in Japan last year – in the Coos Bay, Oregon region during the next 50 years.

“The southern margin of Cascadia has a much higher recurrence level for major earthquakes than the northern end and, frankly, it is overdue for a rupture,” Chris Goldfinger, lead author and a professor in OSU’s College of Earth, Ocean and Atmospheric Sciences, says in a statement. That does not preclude the possibility of an earthquake along the northern half, from Newport, Oregon to Vancouver Island, Goldfinger continues.

“But major earthquakes tend to strike more frequently along the southern end – every 240 years or so – and it has been longer than that since it last happened,” Goldfinger adds. “The probability for an earthquake on the southern part of the fault is more than double that of the northern end.”

The Cascadia Subduction Zone is a region off the Northwest coast where the Juan de Fuca tectonic plate is being subducted beneath the continent. Cascadia is now known to be at least partially segmented.

This segmentation is reflected in the region’s earthquake history, Goldfinger suggests. “Over the past 10,000 years, there have been 19 earthquakes that extended along most of the margin, stretching from southern Vancouver Island to the Oregon-California border,” he says. “These would typically be of a magnitude from about 8.7 to 9.2 – really huge earthquakes.”

“We’ve also determined that there have been 22 additional earthquakes that involved just the southern end of the fault,” Goldfinger says. These are believed to have been “very large earthquakes that if they happened today could have a devastating impact.”