10 Earthquakes Rumble off the Oregon Coast in Pacific Ocean

While the earthquakes were off the Oregon Coast, they weren't in the Cascadia Subduction Zone, where a plate is slipping under the North American plate of the Earth's crust, and where experts say pressure’s building.

by Dylan Darling, The Register-Guard, Eugene, Ore. / June 25, 2019

(TNS) — A cluster of earthquakes shook this weekend, a couple hundred miles off the Oregon Coast and about six miles below the floor of the Pacific Ocean.

There were 10 earthquakes in all, each of magnitude 3.1 or more — the greatest of the temblors registered magnitude 5.4. They struck less than 10 minutes apart around 6 a.m. Saturday, according to U.S. Geological Survey data. The earthquake cluster was due west of Florence by about 200 miles.

Although the earthquakes were off the Oregon Coast, they weren't in the Cascadia Subduction Zone, where the Juan de Fuca plate is slipping under the North American plate of the Earth's crust. Experts say that pressure building in the zone likely will someday release, causing a massive earthquake — upward of magnitude 9 — along the 600-mile-long fault between Vancouver Island in Canada and Northern California.

The recent earthquake cluster occurred farther out at sea, in an area called the Blanco Fracture Zone, said Evelyn Roeloffs, spokesperson at the USGS' Cascade Volcanic Observatory in Vancouver, Wash. There, plates are sliding next to each other and where they rub regularly generates earthquakes.

"Those faults that are between the oceanic plates and farther offshore are quite a bit more seismically active than the subduction zone," she said.

It's the expected huge magnitude and proximity to populated areas along the West Coast that has earthquake experts on high alert about the Cascadia Subduction Zone earthquake. Experts say that there's a 25% to 40% chance of a magnitude 8 to 9 Cascadia earthquake in the next half century.

Oregon, California and Washington are racing to improve a network of sensors around the West Coast called ShakeAlert, to better warn of a major earthquake. University of Oregon researchers have teamed up with counterparts at the University of Washington, University of California, Berkeley, and the California Institute of Technology, as well as USGS officials on the project. Once fully operational, the system would send an alert to citizens if a distant earthquake is detected. Even less than a minute's warning of a major earthquake could give people time to take cover, close off a bridge or emergency vehicles to prepare.

The state's goal is to get its portion of the system up and running by 2023. To do so, Gov. Kate Brown included $12 million for the ShakeAlert system in her proposed 2019-2020 budget. But with Senate Republicans evading the legislative session, any decision of whether to approve said funding is on hold until they return.

ShakeAlert's funding is wrapped into House Bill 5005, which allocates general obligation bonds to community colleges and universities. The bill would give $12,255,000 to UO. A work session for the bill scheduled for Monday was cancelled due to Republicans' absence and rescheduled for Tuesday at 10 a.m. The bill is currently in the Joint Subcommittee on Capital Construction, which includes two Republican senators: Sen. Fred Girod, R-Stayton who is the committee's co-chair, and Sen. Chuck Thomsen, R-Hood River.

The recent cluster of earthquakes in the Blanco Fracture Zone are outside of the ShakeAlert network, so the rumbling didn't trigger an early warning, said Leland O'Driscoll, UO ShakeAlert project manager and a seismic field technician. "There's never been a correlation between Blanco Fracture Zone activity and Cascadia Subduction Zone activity," he said.

Separate from the cluster, a magnitude 5.5 earthquake shook shortly before 9 p.m. Saturday closer to the coast near Eureka, Calif., and in the ShakeAlert network. O'Driscoll said the relatively minor temblor served as a good test of ShakeAlert system in California, creating about a 35-second warning for people living in cities about 150 miles away.

While not connected to the Cascadia Subduction Zone, the recent earthquakes in the Blanco Fracture Zone serve as a reminder that the West Coast is earthquake country.

"It's just another reminder that things are active and we really have to be thinking about the earthquakes in our future that actually could do some damage," Roeloffs said.

Follow Dylan Darling on Twitter @DylanJDarling. Email dd@registerguard.com.

———

©2019 The Register-Guard (Eugene, Ore.)

Visit The Register-Guard (Eugene, Ore.) at www.registerguard.com

Distributed by Tribune Content Agency, LLC.

Platforms & Programs