Muzzy (and previously Puterman), you pretty much nailed it. As far as what the general belief amongst the geologists at PNSN think. They believe it
is coming from the base of the Winthrop glacier, which is on the North side of the Volcano.
So here's the scoop:
The last 'event' happened back in June/May of 2010 and lasted for about three weeks. It created over 4,500 low-frequency events, or what they call
'muliplets'. These occured near the summit of Mount Rainier on the Winthrop Glacier (about a km above Camp Shurman), and most events whithin each
multiplet happened at regular intervals.
So to better explain these multiplets, I have obtained a graph of the current 'event'.....which is demonstrating all the same characteristics (so far)
as the event back in 2010. It appears to be in the same area, though some of the quakes (at least to me) seem to be migrating a bit:
Each circle represents an earthquake, each line is essentially the same quake happening in the same place over and over again.
And this is what some of them look like up close:
Rainier has the largest amount of glacial ice than any other mountain in the US. It is unique. That it is an active volcano posing the greatest
threat in the US also makes it unique. Obviously, the mountain is continuously studied in an effort to make sure it isn't showing any signs of
eruption, but also to try and look for any changes or possible signs of future eruption. There aren't a whole lot of other volcanos to compare it to.
The only two known to exhibit similar behavior was Mount Baker and the one that erupted last year in iceland. (the one I can't pronounce....
Because of the behavior of these quakes and the low frequency there has been a lot of study put into it make sure it ISN'T harmonic tremor. They do
NOT believe it is. Using all the equipment, studies and techniques known to them (PNSN), their summation of the event in 2010 is that it was a
repeated basal-slip of the Winthrop glacier and possibly other glaciers. It may be weather-related but they have not been able to confirm that so the
other theories is the spring thaw or hydrothermal activity. Again, they DO NOT KNOW for sure. It is speculation based on scientific knowledge.
Since this event (so far) seems to be a similar one, they also feel it is originating from a stick-slip motion (ice grinding over rock). They are
constantly trying to rule out volcanic activity vs. glacial, but obviously it is not easy. They use (mainly) the three stations at the top
(RCS/RCM/STAR) and then the next three further out to help determine the size/type and origin of the events. It is very difficult to get a good
location since the events are so small (-1 to 0.5) and it is traveling through a whole lotta ice.
What I know is that this series started on the 28th, got much stronger on the 30th and has created hundreds (if not thousands by now) quakes. They
are VERY small and at a low frequency. They seem to be coming from the Winthrop glacier and at this point, the geologists at the PNSN are attributing
it to the stick-slip motion of the Glacier but are watching it closely.
If you have any questions, I will try and get them answered.
Of note, it seems to have calmed down in the last 24 hrs. This also happened back in 2010....a period of lessening that then picked up again for
another week, so don't be surprised if that happens.
My general take on this is that it is pretty darn cool to get to be studying this somewhat unknown process at the same time as the geologists. Based
on what I have read, it seems very likely it is originating from the glacier. My biggest question right now is why. If it is hydrothermal, that may
be the more interesting aspect of this, rather than the quakes. That this recent series is happening in January may point their research more in that
general direction, but we HAVE had a warmer season than normal, so the 'spring thaw' theory may be relevant.
ETA: I am sorry that I can't link refrences. This info is coming from a paper that is not yet published so for obvious reasons, I can't share it
here, but have permission to talk about what I have learned.
edit on 3-1-2012 by westcoast because: (no reason given)