One of the most active geographic faults in North America came to life this Tuesday (7) after more than 40 earthquakes – ranging from magnitude 3.5 to 5.8 – were recorded on the Oregon coast, which drew attention and concern of millions.
The series of aftershocks, which began on Tuesday morning (7) and continued through Wednesday (8), were all detected between 400 and 500 kilometers west of the coastal town of Newport, too far away for residents to feel, but enough to alert experts.
“If you had asked me yesterday where on Earth would be most likely to produce a bunch of magnitude 5.0+ earthquakes in a single day, here would be one of the most likely answers,” Harold Tobin, director of the Pacific Northwest Seismic Network at the University of Washington , I told CNN.
The responsible geological fault is the Blanco Fracture Zone. According to an Oregon State University analysis, it is more active than the infamous San Andreas Fault located in California, having produced more than 1,500 earthquakes of magnitude 4.0 or greater since the 1970s.
Most impressively, at least nine tremors this week have reached a magnitude above 5.0 on the Richter scale, with most occurring at a shallow depth of just 10 km.
Fortunately, according to the US National Tsunami Alert Center, none of this week’s earthquakes triggered an alert at sea.
However, the activity has raised the level of concern for some, as the region is among the most earthquake-prone areas in North America and already produced one of the largest in the continental United States as of January 1700.
Forerunner of something bigger?
While this week’s epicenter, the Blanco Fracture Zone, is among the most seismically active in North America, it rarely leads to destructive earthquakes.
“The earthquakes in this zone are caused by lateral movements of the tectonic plates on both sides, rather than up and down shifting, so they are very unlikely to pose a tsunami threat,” 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
While this week’s earthquakes have raised concerns that “something bigger” might be close at hand, Tobin said that isn’t necessarily the case.
He pointed out that while we have had a remarkable number of magnitude 5.5+ earthquakes in a short period of time, it is not inherently alarming but rather seismologically interesting.
Reference: CNN Brasil