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4.4 Earthquake off Oregon Coast, Foreshock?

March 26, 2011, by Ken Jorgustin

magnitude-4.4-earthquake-25-march-2011
credit: base images: GoogleEarth, IRIS
credit: overlay: MSB

I found this latest earthquake to be interesting, 100 miles off the coast of California / Oregon, a magnitude 4.4.

The magnitude is of no particular interest, however it’s location is, at least to me… Given the recent very large earthquakes that have been shaking at the Pacific tectonic plate boundaries during the past year or so, the remaining ‘untouched’ region so far has been the west coast U.S (untouched – meaning a large earthquake).

While looking at the location of the past 5,000 earthquakes in the region shown in the map above, it is interesting that the recent magnitude 4.4 earthquake occurred in an area by itself, with no other apparent history of quakes there. In itself this is not alarming, but given the specific region with it’s very high concentration of historical earthquakes pulling and tugging at the Pacific plate boundary, the specific location of yesterday’s quake is exactly between two very active zones.

Could it be a precursor or fore-shock of the next big Pacific plate earthquake? Or is it just another anomaly. No one knows of course, but it did peak my curiosity.

The region is complicated in that on the left there is the Pacific plate, which is actually pulling away from the coast there. Towards the right, just off the coast of Oregon and northern California lies the Cascadia Subduction Zone, where the piece in-between itself and the Pacific plate (the Juan de Fuca plate) is actually diving down underneath the North American plate to the right.

This subduction zone is capable of producing magnitude 9+ earthquakes, and it’s historical timetable is due for another one.

Got your earthquake kit ready?



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