Blanco Fracture Zone Earthquakes!

This morning we had three earthquakes related to the Blanco fracture zone, a transform (shear) plate boundary. These earthquakes occurred quite a bit north of the bathymetric expression of the BFZ (though the M 5.8 is actually plotting closer to the BFZ this morning), similar to the seismicity earlier this year to the southeast of today’s swarm. Here is a post regarding the seismicity along the BFZ in April 2015.

Here is a map showing these earthquakes, with moment tensors plotted for the M 5.8 and M 5.5 earthquakes. I include an inset map showing the plate configuration based upon the Nelson et al. (2004) and Chaytor et al. (2004) papers (I modified it). I also include a cross section of the subduction zone, as it is configured in-between earthquakes (interseismic) and during earthquakes (coseismic), modified from Plafker (1972).


Here is a version of the CSZ map alone (Chaytor et al., 2004; Nelson et al., 2004).

Here is a version of the CSZ cross section alone (Plafker, 1972).

Here is a map showing the BFZ seismicity from April 2015.

Category(s): cascadia, Chemeketa Community College, education, geology, HSU, humboldt, plate tectonics, strike-slip, subduction, Transform

4 Responses to Blanco Fracture Zone Earthquakes!

  1. From the look of the plate movement, it looks to have more of a chance of affecting the Mendocino area with more quakes than Oregon? (Wishful thinking?)

    • these small earthquakes probably do not affect the megathrust, individually. over time, they do… as plate convergence adds up.

      the stress changes along the fault from nearby earthquakes is very small compared to the stress required for the subduction zone fault to slip. plus, these earthquakes are at a great distance for them, at their magnitude, to affect the megathrust.

      it is possible, that if the megathrust were just about ready to go, that these smaller earthquakes could affect it (but only if they were much much closer and the subduction zone were to go off sometime in the next “year or so” anyways). rest peacefully with your “go kit” ready to use… ;-)

    • Thank you for splainin to the nonscience types! I appreciate how quickly you post info.
      I have food, water and camping gear near the door and tend to keep my gas tank full. Hopefully that’s a good enough “go kit” I don’t want to ever need to use… I’m betting peeps west of me will have it worse..

    • yeah, you are far enough east that you will probably be fine! (power may be out…). sounds like a good go kit!

8 Responses in other blogs/articles

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