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Over 40 earthquakes off the Pacific Northwest coast raises fears of a quake causing possible Tsunami

More than 40 earthquakes erupted along one of North America’s most active fault lines beginning on Tuesday morning in the waters off the coast of Oregon and continuing into Wednesday, sparking fears of a tsunami among residents in the Pacific Northwest.

The swarm of earthquakes ranged from a magnitude 3.5 to 5.8, and occurred about 200 to 250 miles west of Newport, a city on Oregon’s central coast, in an area called the Blanco Fracture Zone – which is more active than California‘s notorious San Andrea Fault.

The Blanco Fracture Zone has produced over 1,500 earthquakes of 4.0 magnitude or greater since the 1970s, according to Oregon State University. 

‘If you had asked me yesterday where on Earth would be most likely to produce a bunch of magnitude 5.0+ quakes in a single day, this would have been high on my list,’ Harold Tobin, Director of the Pacific Northwest Seismic Network at the University of Washington, told CNN

The National Weather Service tweeted about the massive seismic activity, while adding that there was no tsunami risk due to such little water being displaced

Pictured: the plate systems along the Pacific Ocean, where the Blanco Fracture Zone had over 40 earthquakes in 24 hours

Pictured: the plate systems along the Pacific Ocean, where the Blanco Fracture Zone had over 40 earthquakes in 24 hours

The swarm of earthquakes, none of which were detected on land, ranged from a magnitude 3.5 to 5.8, all occurred about 200 to 250 miles west of Newport, a city in Oregon's central coast

The swarm of earthquakes, none of which were detected on land, ranged from a magnitude 3.5 to 5.8, all occurred about 200 to 250 miles west of Newport, a city in Oregon’s central coast

Pictured: Harold Tobin, Director of the Pacific Northwest Seismic Network at the University of Washington

Pictured: Harold Tobin, Director of the Pacific Northwest Seismic Network at the University of Washington

At least nine tremors hit a magnitude of 5.0 to 5.8, the majority of which took place at shallow depths. 

According to the USGS database, the amount of 5.0 or more magnitude earthquakes amounts to three times the annual average, or three 5.0+ quakes per year, since 1980.  

However, the US National Tsunami Warning Center reports that none of the 40-plus earthquakes from this week have caused a tsunami alert, according to CNN. 

The National Weather Service also tweeted about the massive seismic activity, adding that there was no tsunami risk due to little water being displaced.

The heightened seismic activity in the area has prompted concern among residents of the Pacific Northwest regardless, with the region having already set the record for the largest earthquakes in the continental US with a magnitude of 8.7–9.2 on January 26, 1700.  

The National Weather Service PTWC helps to monitor tsunamis in the region through the National Tsunami Warning Center

The National Weather Service PTWC helps to monitor tsunamis in the region through the National Tsunami Warning Center

Pictured: the major subduction zones in the Pacific Northwest, where the extremely active Blanca and Cascadia Subduction Zones are located

Pictured: the major subduction zones in the Pacific Northwest, where the extremely active Blanca and Cascadia Subduction Zones are located 

That megathrust quake happened on the nearby Cascadia Subduction Zone, and caused a tsunami strong enough to hit both the West Coast of North America as well as the coast of Japan. 

The neighboring Cascadia Subduction Zone includes the Juan de Fuca plate, which dives underneath the North American plate, and can trigger catastrophic tsunamis as well as extremely destructive shaking. 

While the Blanco Fracture Zone responsible for this week’s swarm of quakes is one of the most active in North America, it has rarely caused deadly or destructive earthquakes. 

The Blanco fault sits about 275 miles west of Oregon and roughly 200 miles further west of the Cascadia Subduction Zone, which stretches from northern Vancouver Island in Canada to Northern California. 

‘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 the network. 

Pictured: Pacific Northwest Seismic Network - Recent Earthquakes, showing a cluster of earthquakes that occurred on Tuesday and Wednesday off the coast of Oregon

Pictured: Pacific Northwest Seismic Network – Recent Earthquakes, showing a cluster of earthquakes that occurred on Tuesday and Wednesday off the coast of Oregon

Seismologist Dr. Lucy Jones told CNN that since 1980, there have been over 133 earthquakes of magnitude 5 or higher on the Blanco Fracture Zone, none of which have ever caused destruction on land.

‘Today’s quakes can be thought of as something like a main-shock and a swarm of aftershocks, the one distinction being that in this case, there’s not a lot of magnitude difference among them,’ Tobin added. 

Meanwhile, Tobin tried to assuage fears that this week’s quakes could cause the next ‘big one.’  

‘There’s quite a lot of distance from these quakes to the Cascadia Subduction Zone,’ Tobin said. 

‘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.’


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