Posted by Stephanie Pappas on December 21

There is nothing to be wary of about the Oregon earthquake swarm.

In the past two days, more than 50 earthquakes have occurred on the seafloor off the coast of Oregon. But scientists say that the risk of earthquake swarms threatening land life or property is very low. 

According to data from the US Geological Survey, as of noon on Wednesday (December 8), there were 55 earthquakes, most of which were between 4.0 and 5.5 in magnitude, with the largest one reaching 5.8. They occur in an area called the Blanco Fault Zone, where moderate-scale earthquakes often occur. 

Blanco’s proximity to the Cascadia subduction zone leads to fears that earthquakes in the Blanco fault zone will put pressure on the Cascadia fault. These faults can produce very large earthquakes in coastal areas of Oregon and Washington. But seismologists say this is not a threat. 

"These earthquakes are far away from the Cascadia subduction zone," Harold Tobin, director of the Pacific Northwest Seismological Network at the University of Washington, told CNN. "Our current best understanding of how pressure is transmitted through the crust (and mantle) shows that these events will not significantly change the pressure in the subduction zone."

The Blanco fault zone is about 200 miles (322 kilometers) from the Cascadia subduction zone. In Cascadia, the Juan de Fuca plate dived under the North American plate. This diving sport is called subduction, and it produces large, devastating earthquakes. The up and down movement of the crust in the subduction zone can also produce dangerous tsunamis. 

But Blanco is a gentler and gentler fault zone. It is located where the Juan de Fuca plate and the Pacific plate rub against each other. It is a transition fault zone, also called a strike-slip boundary. As the name suggests, this means that the plates slide over each other with almost no up and down movement. According to a 2019 blog post by Scientific American, although strike-slip faults (such as the San Andreas fault) can cause dangerous earthquakes, the lack of vertical motion on the fault means that the risk of a tsunami caused by the Blanco earthquake is very low. .

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According to the post, the crust of the Blanco fault zone is also relatively young and warm compared to the more brittle continental crust found on faults like San Andreas. In smaller events, the younger, warmer crust is more likely to rupture, and seismic waves do not travel as far as the colder, older crust. The fault zone is far enough away from the shore that even the waves of a large earthquake from the Blanco fault zone cannot reach the land. 

For all these reasons, scientists were not shocked by the earthquake swarm this week. 

"In the past 20 years alone, Blanco has experienced 91 earthquakes of magnitude 5.0 or greater," Tobin wrote on Twitter. "This kind of thing happens often!" 

Originally published on Live Science.

Stephanie Pappas is a contributor to Live Science, covering topics from earth sciences to archaeology to human brains and behavior. She used to be a senior writer for Live Science, but is now a freelancer in Denver, Colorado, and regularly contributes to the monthly magazines Scientific American and Monitor of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz. 

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