Study reveals potential for devastating West Coast earthquakes to strike simultaneously

PORTLAND, Ore. (KOIN) — Oregonians have long known that a major earthquake could devastate the region in the next 50 years, but a new study suggests the impact could have implications for the entire country.

Researchers suspect that when the large Cascadia earthquake does occur, it could coincide with another quake along the northern San Andreas fault, according to a new study from Oregon State University.

“We’re used to hearing the ‘Big One’ – Cascadia – being this catastrophic huge thing,” said Chris Goldfinger, a marine geologist at Oregon State University and lead author of the study. “It turns out it’s not the worst-case scenario.”

Instead, the worst-case scenario could be two major West Coast faults synchronizing, overwhelming emergency resources at the same time.

“We could expect that an earthquake on one of the faults alone would draw down the resources of the whole country to respond to it,” Goldfinger said. “And if they both went off together, then you’ve got potentially San Francisco. Portland, Seattle and Vancouver all in an emergency situation in a compressed timeframe.”

Researchers drilled for sediment samples in the deep sea off the coast of Oregon and northern California, representing 3,100 years of geologic history. They analyzed the layers, which are deposited by underwater landslides and often triggered by earthquakes. When they compared samples from both faults, they found similarities in timing and structure, suggesting seismic synchronicity between the faults.

There have been three instances in the last 1,500 years where researchers believe that ruptures between the Cascadia subduction zone and the northern San Andreas fault were minutes or hours apart, Goldfinger said. The findings have significant implications for hazard planning.

In September, Oregon Governor Tina Kotek signed an executive order directing the creation of a plan to ensure new buildings over 10,000 feet high are built in line with seismic safety standards.

The last major Cascadia earthquake was 9.0 in magnitude and shook the entire Pacific Northwest, from the coast of Northern California to British Columbia, in the year 1700. The earthquakes typically occur every 300 to 500 years, so scientists expect the next one soon.