Today around 13:00 or 14:00 UTC (not sure exactly when) there was a possible minor harmonic tremor at Grímsfjall volcano. But earlier today I did write about the fast rise that is happening at Grímsfjall according to GPS data. It seems that things might get interesting soon if the current trend continues as it has for the past few weeks.
I do not believe that this is weather interference that I am currently seeing.
Possible harmonic tremor pulse seen at Grímsvötn SIL station on 2.October 2010. Image from IMO web site
Text updated at 16:25 UTC 2. October 2010.
It would surely help if tremor data was smoothed or averaged (like RSAM charts USGS uses for some volcanos). Anyway, it looks like we’re likely going to see some action soon from Grímsfjall volcano.
Keep up the good work Jón!
Yet another question, Jón: Harmonic tremors are expected to go on till the moment of the eruption, or we must still wait for more earthquakes, counting from now?
Renato Rio, The harmonic tremor will go up before the eruption. It happened in 2004 and I saved that image somewhere on my computer.
However, this pulse might also mean that a glacier flood has started. So this pulse might not necessary be magma related. But if that is the case, things might get interesting soon.
Other stations around Vatnajökull show an increase in the red 0.5-1 Hz band with no correspondingly sharp rise in the green (1-2Hz) or blue (2-4Hz), i.e. there is a divergence between the red on the one hand and green+blue on the other. At Grímsfjall, the rise is across all three bands. Is this in line with what you’d expect to see Jón?
Henrik, Other stations around Vatnajökull are just showing weather related changes in the 0.5 – 1Hz bands. The pulse does not reach those stations, it is that small in fact.
You always say that, Jón! Care to explain? (Please?)
Henrik, Weather is a big factor on those sensors. It is just the way it is. But when something happens weather noise gets lost in the tremors from volcanoes or earthquakes quickly. That is how you can tell when something is going on or not.
Iceland has now gone almost 13 hours without a single quake registered at IMO, unusual.
Perhaps its the quiet before the storm
I noticed the lack of earthquakes … not even a teeny one! Last one was 0512…. surely they have had some or maybe they haven’t paid the electricity bill
@renee: Or, as Lurking pointed out on the other day: “someone stumbled into the cables”.
Thanks for info re harmonic tremors I see pages of these squiggly lines but didn’t understand what they meant
Earthquake at Krýsuvik. Cables repaired.
i’d love to know more about recognizing harmonic tremor.
http://en.wikipedia.org/wiki/File:Four-types-seismograms.gif
and with a tiny amount of experience of watching the seismograms at Redoubt i realize they are very difficult to pick out of the background noise esp. with many earthquakes. And i suspect they may differ slightly from volcano to volcano.
So here’s the question, Jon, do You suspect harmonic tremor where all three color lines raise together and spend a minut time in the elevated area?
Really enjoying this blog, btw………
Best!motsfo
@motsfo: please note that’s a very misleading chart. It does not contain errors per se, but have a look at the horizontal scale. You don’t see helicorders/webicorders with that expanded scale on the web.
This is what you would see with a “normal” (what you can usually see on USGS helicorder charts posted on the web) scale:
http://img827.imageshack.us/img827/7387/fourtypesseismogramscor.png
Well, not exactly, but you get the idea.
@motsfo, It is the change in the chart that tells me that this is a harmonic tremor rather then weather. Weather for instance does not change the chart exactly like this. But harmonic tremors do.
Currently there is a new tremor starting. This might be related to water movement, rather then magma. If this is water we will know in several hours time.
Well if its water i guess there is magma heating the glacier right?
If this is water, then this means a glacier flood is on its way down Vatnajökull. But until it is confirmed we are just guessing on what the data actually is telling us.
Dynamic links don’t retain the moment at the time of capture.
Thus for reference:
Grímsfjall SIL Sept 14 2010
Grímsfjall SIL Oct 3 2010
On September 14th, a storm struck Southern Iceland and all stations showed a dramatic increase in tremor. That said, the tremor plots do look different.