Saturday, December 8, 2012

Big and Little Japan earthquakes: equal but opposite

I just did this in g+ communities, but I'll do it here, since you can do a better layout.  I can't see switching a blog to g+ yet, mainly because of the formatting.

So, we have the fault-plane solution of the big earthquake.

These are lower-hemisphere projections, which means the lower slab hammered down, and all those seismic stations in the white section got a positive compressive pulse.

Now the recent M7.3

Total surprise!  Same fault plane but all the stations got the opposite pulse.  Shows it is a true aftershock of the M9, perhaps with a bit of snap-back of the upper hanging wall.

I only looked at this because the M7.3 was on the cusp of the curve that starts the next segment to Tokyo.  Sometimes these earthquakes are more bizarre because of mixed stresses.  The recent M8 at Sumatra was one such.  Anyway, the upshot is that I can't make dark inferences about the next segment, and I doubt that any stresses carry through the oceanic crust, so we can't even say that the Tokyo segment is closer to failure.  Studies have shown that these segments are very uncoupled.

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