reply to post by PuterMan
This matter of Japan's major subduction zones versus the CSZ is one I've been wondering over increasingly during the past year. Okay, the past 11
months, since Japan's big one on March 11.
Does Japan-region activity impact the CSZ, and if so, in what way? Because the first problem is that while we can assume that whatever happens with
Japan has to influence the CSZ and perhaps other regions, that's all it is: an assumption. I think it's a fair one, if we allow plate tectonic theory
is more-or-less correct in the concept that plates subduct because of pressure on the opposite edge due to lateral pressure from spread at the ridges.
While I don't think the theory is the be-all and end-all it's at least something to be going along with for now, so, like most, I'm happy to accept
that assumption as valid. Okay, so we have plates being pushed laterally in both directions from expansion points at ridges. When a subducting plate
on one of the opposite sides from the ridge lets go, what's the effect on the plate on the other side and its own subducting edge?
Now I'm going to think out loud. I hope you all can follow the ummm... the following...
If the plates on both sides of the ridge are under stress, then does the pressure on them increase (from ridge expansion) at roughly the same rate?
From the point of view of action and reaction, it's not unreasonable that it does. Granted, we could present arguments to the contrary, but for the
sake of the discussion let's say that it is so: the pressure from the ridge is applied equally.
In that case, the periodic failures (ruptures) along each plate's subducting edge occur at intervals largely determined by those other influences
However, when a subduction zone lets go and much of the stress along that boundary is relieved in a huge quake, could it be that as the plate is now
de-stressed (so to speak), then a greater proportion of the energy from the expanding ridge gets transferred to that plate. I'm thinking of the "path
of least resistance" concept, which is commonly observed in nature. Yes, some energy is still going into the other plate, but as it's already under
greater stress than the one that just let go, it gets less of it.
I know there are holes in this line of reasoning but I'm just putting it out there.
Now, to take the opposite tack. What if the release of stress on one side of the ridge actually "unbalances" the ridge itself? The ridge is
(apparently) a key to the whole energy-transfer system, after all. Could it be that releasing stress from one side of the ridge allows the ridge to
open more, hence allowing greater energy release than had been occurring on average for years or centuries prior? In that
case, even if the
still-stressed plate gets a lesser "share" of the energy transferred from the ridge, the ridge's total energy release is now greater (as it has opened
more) and so it could be putting more energy into the stressed ridge than it did before the other
ridge let go.
If this latter scenario is possibly correct, then we ought to see some kind of increase of quake activity along the stressed plate's subduction
And just by the way, the USGS maps for the PNW now show ten offshore quakes in the CSZ during the past seven days, and three of them are right along
the subduction boudary (purple line on the USGS maps). They took their sweet time adding them but they are there now.
And Puterman: yes, I prefer those graphs as you have them in your newest post. It matters not if they're longer. No problem with needing to scroll
edit on 10/2/12 by JustMike because: O tempores, o mores, o typos!