Source: Strange Sounds

Just to confirm!

The earthquakes (now 51 from which 12 are >M5.0 in the last 24 hours) currently hitting off the coast of Oregon are NOT on the Cascadia Subduction Zone (blue line on the map below).

strong earthquake swarm off Oregon on December 7-8 2021
Another map of the strong earthquake swarm off Oregon on December 7-8 2021. Cascadia subduction zone in blue.

The swarm is taking place on the Blanco Fracture zone, a transform Fault, located at the Juan De Fuca plate as shown in the illustration below.

blanco fault line juan de Fuca Plate
Blanco fault line earthquake swarm along the Juan de Fuca Plate on December 7-8 2021

Quakes of this size and larger near the Blanco Fracture Zone are not uncommon and do not have a history of provoking larger earthquakes. A M6.3 struck nearby in 2003. Along the same fracture zone but closer to land, there was a M6.3 in 2019, a M6.2 in 2018, a M6.0 in 2012, a M6.3 in 2008, a M6.1 in 2000, a M6.3 in 1994, a M6.5 in 1985, and a M6.2 in 1981.

So what’s up with all these quakes?

The Juan de Fuca plate is made up of three semi-independent segments the Juan de Fuca, the Gorda segment and Explorer segment off the Canadian coast (look at the above picture).

The Cascadia trench marks the subduction zone of all three segments and is less than 100 miles from the coastline. Although it is the largest of the three segments, the Juan de Fuca segment is less than 275 miles wide measured from spreading ridge to subduction zone. The three segments subduct beneath North American Plate at different rates. The Explorer segment may no longer be subducting.

Cascadia Subduction Zone and Cascades volcanoes
Cascadia Subduction Zone and Cascade volcanoes

The average rate of convergence between the Juan de Fuca segment and the North American Plate over the past 5 million years is between 9.8 and 13.8 feet per 100 years and the direction is about 49 degree east of north, which implies oblique subduction.

Cascadia subduction rates
Cascadia subduction rates

Stresses from the neighboring North American Plate (right side of the blue line) and Pacific Plate (left side of Juan de Fuca plate) cause frequent earthquakes in the interior of this plate, including the 1980 Eureka earthquake (also known as the Gorda Basin event) that generated a M7.3 earthquake on Nov 8, 1980.

So what’s the connection?

Subduction of the Juan de Fuca plate causes melting and magma generation in the mantle, which rises to the surface that created the Cascade volcanoes. This powerful earthquake swarm could possibly make the volcanoes in that region active again.

If you are interested about the geology and the actual volcanic and seismic risks in the Cascadia region, you should watch the movie below:

As you may have now understood it, Yellowstone is a distraction! The Big One is Cascadia!

Be ready; get prepared! [Facebook]

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