Swarm of more than 40 earthquakes in 24 hours on the Blanco Fracture Zone off the Pacific Northwest coast raises fears of a significant quake that could cause a tsunami

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  • More than 40 earthquakes off Pacific Northwest coast raise potential tsunami threat
  • The earthquake, each of magnitude 3.5 to 5.8, struck about 200 to 250 miles west of Newport, a city on Oregon’s central coast.
  • Earthquakes of magnitude 5.0 or greater are three times more frequent than the annual average
  • The US National Tsunami Warning Center reports that none of this week’s more than 40 earthquakes carried a tsunami warning
  • A magnitude 8.7–9.2 earthquake struck the region on January 26, 1700, the largest known earthquake in continental American history.
  • That earthquake occurred in the nearby Cascadia Subduction Zone, and caused a tsunami that affected both the West Coast and the coast of Japan.

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More than 40 earthquakes struck along one of North America’s most active fault lines, which began in the waters off the coast of Oregon on Tuesday morning and continued through Wednesday, raising tsunami fears among residents in the Pacific Northwest.

The quake was between a magnitude of 3.5 and 5.8, and occurred about 200 to 250 miles west of Newport, a city on the central coast of Oregon, in an area called the Blanco Fracture Zone—which runs off California’s infamous San Andrea Fault. is more active.

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According to Oregon State University, the Blanco Fracture Zone has generated more than 1,500 earthquakes of magnitude 4.0 or greater since the 1970s.

‘If you had asked me yesterday what Earth is most likely to produce a bunch of magnitude 5.0+ in a single day,’ said Harold Tobin, director of the Pacific Northwest Seismic Network, it would be high on my list. University of Washington told CNN,

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The National Weather Service tweeted about the large-scale seismic activity, while saying there was no tsunami threat with so little water being displaced.

Image: Plate system along the Pacific Ocean, where more than 40 earthquakes occurred in 24 hours in the Blanco fracture zone

Image: Plate system along the Pacific Ocean, where more than 40 earthquakes occurred in 24 hours in the Blanco fracture zone

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

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

Image: Harold Tobin, director of the Pacific Northwest Seismic Network at the University of Washington

Image: Harold Tobin, director of the Pacific Northwest Seismic Network at the University of Washington

At least nine aftershocks came in at magnitudes 5.0 to 5.8, most of them at shallow depths.

According to USGS DatabaseThe magnitude of earthquakes with magnitude 5.0 or greater is three times the annual average, or three 5.0+ earthquakes per year, since 1980.

However, the US National Tsunami Warning Center reports that none of this week’s more than 40 earthquakes carried a tsunami warning, according to CNN.

The National Weather Service also tweeted about the massive seismic activity, saying there was no tsunami threat as little water was displaced.

The increased seismic activity in the region has caused concern among residents of the Pacific Northwest, even though the region already holds the record for the largest earthquake in the continental US on January 26, 1700 with a magnitude of 8.7–9.2 .

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

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

Image: Major subduction zones in the Pacific Northwest, where the extremely active Blanca and Cascadia subduction zones are located

Image: Major subduction zones in the Pacific Northwest, where the extremely active Blanca and Cascadia subduction zones are located

That megathrust earthquake occurred over the nearby Cascadia subduction zone, and caused a tsunami that could affect 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 beneath the North American Plate, and can trigger devastating tsunamis as well as extremely destructive aftershocks.

While the Blanco fracture zone responsible for this week’s swarm of earthquakes is one of the most active in North America, it has rarely caused fatal or devastating earthquakes.

The Blanco Fault is located approximately 275 miles west of Oregon and about 200 miles further west of the Cascadia Subduction Zone, which extends from North Vancouver Island to Northern California in Canada.

‘Blanco fracture zone earthquakes are strike-slip (lateral movement of crustal blocks on either side rather than up-and-down displacement), so they are very unlikely to pose a tsunami risk even if a major earthquake has occurred, such as for example for magnitude 7.0,’ Tobin told the network.

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

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

Seismologist Dr. Lucy Jones told CNN that since 1980, there have been more than 133 earthquakes of magnitude 5 or greater at the Blanco fracture zone, none of which have ever caused land destruction.

“Today’s earthquakes can be thought of as a main tremor and a swarm of aftershocks, with one difference being that in this case, there is not much difference between them,” Tobin said.

Meanwhile, Tobin tried to allay fears that this week’s quake could lead to the next ‘major quake’.

Tobin said, ‘There is a considerable distance from these earthquakes to the Cascadia subduction zone.

‘Our best current understanding of how stress is transferred through the crust (and mantle) would suggest that these events do not appreciably change the stress on the subduction zone.’

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