A swarm of more than 40 earthquakes in the last 24 hours is causing a stir in the northwestern United States

(CNN) – One of North America’s most active faults came to life Tuesday after a swarm of more than 40 earthquakes, magnitudes between 3.5 and 5.8 degrees, rocked the Oregon coast, drawing the attention and concern of millions of people. people in the region.

The series of earthquakes, which began Tuesday morning and continued on Wednesday, clustered between 200 and 25 miles west of the coastal city of Newport, Oregon, far enough away not to be detected on land, but given the seismic history of the area, is creating quite a stir.

“If I had been asked yesterday where on Earth a group of earthquakes of magnitude greater than 5.0 would be most likely to occur in a single day, this would have been the first on my list,” Harold Tobin told CNN, director of the Pacific Northwest Seismic Network at the University of Washington.

The fault responsible for the earthquakes is the White Fracture Zone. According to an analysis by Oregon State University, it is more active than the infamous San Andreas Fault in California, and has produced more than 1,500 earthquakes of magnitude 4.0 or greater since the 1970s.

Not all earthquakes are the same

The most impressive of the earthquakes This week is that the swarm included at least 9 tremors of magnitudes between 5.0 and 5.8, most of which have occurred at a depth of only 10 km.

The number of earthquakes of magnitude 5.0 or higher in the region is three times the annual average (three earthquakes of 5.0 or more per year) since 1980, according to the United States Geological Survey database (USGS).

Fortunately, according to the US National Tsunami Warning Center, none of the earthquakes this week has caused a tsunami warning.

However, the activity has raised the level of concern for some, as the region is among the areas most prone to earthquakes of North America and has already produced one of the major earthquakes in the continental United States on January 26, 1700. The earthquake occurred in the neighboring Cascadia Subduction Zone, an interplate fault much closer to land, where the Juan de Fuca plate dips below the North American plate. This fault can not only unleash devastating tsunamis, but also destructive shocks.

This is not necessarily a precursor to the so-called “Great Earthquake”

Although the epicenter of this week’s earthquake swarm, the White Fracture Zone, is among the most seismically active in North America, it rarely causes destructive earthquakes.

The fault is about 442 kilometers west of the Oregon coast and about 322 kilometers west of the Cascadia Subduction Zone, where the most destructive earthquakes in the Northwest have historically occurred.

“The Blanco fracture zone earthquakes are landslide (lateral movements of the blocks of the earth’s crust on both sides, rather than up-and-down movements), so it is highly unlikely that they pose a tsunami threat Even if there were a bigger earthquake, like a magnitude 7.0, for example, “Tobin told CNN.

There has been a ‘swarm’ of earthquakes off the Oregon coast this evening; the strongest reaching 5.8!

Such swarms are common. Thankfully, they mostly occur far from shore along strike-slip faults.

This means there is NO tsunami risk because little water is displaced! pic.twitter.com/8reA3m3rL0

– NWS Eureka (@NWSEureka) December 8, 2021

According to seismologist Lucy Jones, more than 133 earthquakes of magnitude 5 or greater have occurred in the White Fracture Zone since 1980 and have never been followed by anything on the ground.

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

Although this week’s earthquakes raised concerns that the so-called “big one” may be close, Tobin said that is not necessarily the case.

“There is quite a distance between these earthquakes and the Cascadia subduction zone,” Tobin explained. “Our current best understanding of how stress is transferred through the crust (and mantle) would suggest that these events do not change the stress in the subduction zone appreciably.”

Tobin pointed out that although we have had a remarkable number of earthquakes of magnitude greater than 5.5 in a short period of time, it is not inherently alarming, but rather interesting from a seismological point of view.

A similar swarm of earthquakes, though not of this week’s magnitude, struck earlier this year near the Salton Sea in southern California.