I am a writer, not a scientist of any kind. I live in the SW AZ desert (USA), so we get earthquakes from time to time. I grew up in southern CA, right next to the San Andreas fault, so I have a cursory "high school geology" understanding of tectonic plates and earthquake forces. (The schools made sure we understood what was going on and how to prepare for The Big One.)

In doing some more research for a writing project, I came across some web sites that showed the progressive subduction of the Farallon plate (for instance: https://pubs.usgs.gov/gip/dynamic/Farallon.html). I'd never known about that one! These show that all that remains is the Juan de Fuca plate at the north end, and the Rivera and Cocos plates at the south.

So now I'm wondering what has happened to the middle? One web site (and I'm sorry I can't find the link right now) suggested it "folded" and was pushed edge-downward toward the center core. Other sources seem to suggest it broke apart and the remnants fused with the North American plate.

Al of this is in concert with the idea of "the next big one" on the West Coast, where over a hundred years of pent-up friction suddenly releases and the North American and Pacific plates move up to 20 feet. (Common theories bantered about, based on about 2 inches of movement per year, but unable to move that much for over a hundred years. Feel free to correct, please!!)

If the Farallon plate was still solid underneath the NA plate, would it also push the Juan de Fuca, Rivera, and Cocos plates as well? If the three remnant plates are indeed separate and now caught in between the two larger plates moving opposite directions, would they shear apart? Or just individually subduct more (which in itself would be quite a violent movement)?

If the answers are too complex and what I really need is a better basic understanding of the dynamics of plate movements, I would appreciate any resources you can point me towards.

(One terminology question: I keep seeing references to a fault causing earthquakes. It's actually the other way around, isn't it? Plate movement causes earthquakes, which creates faults in the crust up where we are?)

Thank you!!

  • $\begingroup$ "...was still solid..." - Common misconception. Earth's mantle is overwhelmingly solid. There is very little magma down there. $\endgroup$
    – Gimelist
    Mar 24 '21 at 12:38

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