Anyone who lives on the coast of the Pacific Northwest is likely aware of the Cascadia Subduction Zone fault, which stretches from northern California to British Columbia.

The likelihood of when that fault will rupture, resulting in a tsunami, is one thing scientists called “hazard geologists” study.

Ian Madin is a senior scientist and earthquake hazard geologist for the Oregon Department of Geology and Mineral Industries. In an interview with The Gazette on Tuesday, Madin said there is “fairly well-established” data on the chance of an earthquake rupturing the Cascadia Subduction Zone fault for different parts of the coast of Oregon.

He said the likelihood of the “big one,” a magnitude 9 earthquake that affects the entire length of the Cascadia Subduction Zone, is 12% sometime in the next 50 years. That would affect the entire Pacific Northwest.

“There are more-frequent earthquakes on the southern coast from Coos Bay to northern California - smaller earthquakes of 8 to 8.5,” he said. So if an earthquake occurred at the fault line near Brookings, it would be “very damaging in Brookings, very little damage in Portland.”

However, if a magnitude 9 rupture of the entire Cascadia Subduction Zone fault happened, “everyone gets some damage,” he said.

The likelihood of a magnitude 8 to 9 earthquake adjacent to Brookings over the next 50 years is 37%, he said. That means there is a “68% chance that it won’t happen, 2-1 more likely it won’t happen.”

Adjacent - meaning near Cannon Beach - the likelihood of a “major damaging earthquake and a big tsunami” is 15% to 20%, he said.  These numbers are “approximate, because we haven’t done calculations specifically for Cannon Beach.

“People shouldn’t be terrified that (an earthquake) is inevitable,” he added. “It’s not overdue, it’s not a bus” and doesn’t run on a schedule. But the consequences could be “bad enough” that people should prepare.

“If we haven’t made any preparations, it will damage everyone’s life permanently,” he said. “If we are prepared” and fix infrastructure such as water, power, transportation and sewer treatment, “it will be a manageable disaster.”


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