“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 fault line responsible for the quakes is the Blanco Fracture Zone. According to an analysis by Oregon State University, it is more active than the infamous San Andreas Fault in California, having produced more than 1,500 quakes of magnitude 4.0 or greater since the 1970s.
This is not necessarily a precursor for the so-called ‘big one’
Though the epicenter of this week’s swarm of quakes, the Blanco Fracture Zone, is among the most seismically active in North America, it rarely leads to destructive quakes.
The fault is some 275 miles west of the Oregon coastline and about 200 miles west of the Cascadia Subduction Zone, where the largest and most destructive Northwest quakes have historically taken place.
“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 CNN.
“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 said.
Though this week’s quakes have raised the concerns the so-called “big one” could be near, Tobin assured it is not necessarily the case.
“There’s quite a lot of distance from these quakes to the Cascadia Subduction Zone,” Tobin explained. “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.”
He pointed out, although we have had a remarkable number of magnitude 5.5+ quakes in a short period of time, it is not inherently alarming but rather seismologically interesting.