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Re: [OM] Anchorage Earthquake

Subject: Re: [OM] Anchorage Earthquake
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Thu, 27 Dec 2018 14:27:39 -0900
> Same sentiments here.  I guess, at some point, the aftershocks become a
> part of daily life.

They really are settling down. The first couple of weeks had
noticeable aftershocks every hour or two. The first couple of days it
was really wild as they were quite strong and loud. Now, almost all
are below 3.0 which is rarely felt and easily ignored. But we are
still getting a few bigger ones after days of relative quiet. And the
type of motion really is more important than the rating. If it's a
bump, you'll probably not feel it if sitting on the couch, but a side
motion will get your attention even if it's much weaker. The dishes in
the cupboard will tell you which it is. The bumps make them jump, the
side-to-side will make them slide back and forth.

In another couple of weeks, it should be pretty much over except for
the occasional bump or rattle. It really doesn't take long for them to
stabilize. A couple months is usually about it. However, there is
always the chance that it will keep moving for a while longer, but at
some point it just merges in with the background noise of other faults
wiggling away. And there are MANY of them in this area. However, it's
the Aleutian Megathrust that will be the next regional ELE when it
tops the 9.4 of 1964.

And this one is likely not a historical fault, but the result of a new
stress crack that formed across this specific slab. There are two
other known cracks in this area and this one is right between them and
a result of the fact that this slab is getting pushed from one side
and it isn't able to rotate freely.

This earthquake/fault is so close to the city that the motion is
entirely different depending on our orientation to the epicenter of
the aftershock. Some of them are nearly below your feet and will cause
the jolt, where others are to the side which gives a different motion.
Five miles makes a world of difference. Also, local soil conditions
and other geological formations are causing different motions.

AG
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