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Swarm of earthquakes jolts seabed off the U.S. West Coast

Friday, December 10th 2021, 1:42 pm - Seismologists have measured more than 90 earthquakes off the coast of Oregon since Wednesday.

A swarm of earthquakes rattled the seabed off the U.S. West Coast this week, causing quite the ruckus in an area that’s used to the occasional rumble. The tremors struck along an active fault line situated off the Oregon coast. However, some good news is that seismologists don’t expect this earthquake swarm to trigger tsunamis or larger earthquakes closer to land.

A series of earthquakes began shaking several hundred kilometres off the Oregon coast during the predawn hours on Wednesday, December 7. The temblors came fast and furious; the United States Geological Survey (USGS) recorded dozens of earthquakes over the next 24 hours, including eight that measured 5.5-magnitude or stronger.

Approximately 90 earthquakes have been recorded in the area since Wednesday morning.

The earthquakes occurred along the Blanco Fracture Zone, an active fault zone between the Pacific Plate and the Juan de Fuca Plate. The two plates slide past one another across this region, causing earthquakes as they move.


This week’s earthquake swarm isn’t the first dense cluster of earthquakes along the Blanco Fracture Zone. Several clusters of small earthquakes have occurred here over the past 30 years. A notable swarm in the same area in 2008 featured more than 600 small tremors in just a couple of weeks.

The USGS said in its tectonic summary for the event that tsunamis are “very unlikely” as a result of this earthquake swarm.

“The main tsunami threat for the Pacific Northwest is the Cascadia subduction zone” that’s several hundred kilometres away from the Blanco Fracture Zone and hasn’t been affected by this earthquake swarm, the summary said.

Experts at the USGS added that it’s unknown how long the earthquake swarm will last. The swarm “can continue for days to weeks, or it can stop suddenly any time,” according to the agency.

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