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More than 40 earthquakes strike Oregon's coast in 24 hour-period

5 months 2 weeks 3 days ago Wednesday, December 08 2021 Dec 8, 2021 December 08, 2021 8:44 AM December 08, 2021 in News
Source: CNN
Generic image of Oregon's coast

More than 40 earthquakes occurred in a 24-hour period off the coast of Oregon, Tuesday, according to CNN

The earthquakes ranged from a magnitude of 3.5 to 5.8 and were all clustered between 200-250 miles west of Newport, OR.

The fault line responsible for the quakes is the Blanco Fracture Zone, which Oregon State University lists as even more active than California's infamous San Andreas Fault.

The Blanco Fracture Zone has reportedly produced more than 1,500 quakes of magnitude 4.0 or greater since the 1970s.

During this week's series of quakes, at least nine of the tremors reached a magnitude 5.0 to 5.8, with the majority occurring at a shallow depth of only 10 km.

This number of magnitude 5.0 or greater quakes in the region triples the annual average (three 5.0+ quakes per year) since 1980, according to the USGS database.

The activity has heightened the concern level for some, but Harold Tobin, Director of the Pacific Northwest Seismic Network at the University of Washington, says the surprising number of quakes may not be a cause for serious concern.

"Blanco Fracture zone quakes are strike-slip (lateral motions of the crustal blocks on either side, rather than up-down displacement), so it is very unlikely for them to pose a tsunami threat, even if a bigger quake happened, like a magnitude 7.0 for example," Tobin told CNN. 

He added that worries of the smaller quakes serving as forecasts of the approaching "big one" may be groundless, saying, "There's quite a lot of distance from these quakes to the Cascadia Subduction Zone. Our best current understanding of how stress transfers through the crust (and mantle) would suggest that these events don't change stress on the subduction zone appreciably."

Tobin concluded that the remarkable number of magnitude 5.5+ quakes in a short period of time is seismologically interesting, but not inherently alarming.

CNN notes that a similar series of quakes occurred earlier this year near the Salton Sea in Southern California.

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