Posted on by Jón Frímann

Background noise compared to a eruption and other events

Here are few examples of how the tremor plots looks like if anything important is going on in Iceland.


Normal quiet tremor plot. Few earthquakes create spikes on it. But besides that everything is quiet. Copyright of this pictures belongs to Icelandic Met Office.


This is from the Grímsfjall volcano eruption in May 2011. On this tremor plot it can be clearly seen how much noise a eruption actually makes. The background noise just goes away soon as there is something going on. Copyright of this pictures belongs to Icelandic Met Office.


This is Skrokkalda SIL stastion on 12 July 2011. It can clearly be seen where the harmonic tremor goes above the background noise. Copyright of this pictures belongs to Icelandic Met Office.

It is quite clear. Besides earthquakes and some harmonic tremors that are different then this signals that I have shown here. Unless you see this on Icelandic Met Office tremor plot you can be sure that it is quiet in Iceland. Volcano eruptions make a lot of noise when they are ongoing, even the small eruptions make some noise that can be detected by the SIL network in Iceland.

Note: I might update this blog post on later date and put in more examples about the difference between background noise and a eruption.

109 Replies to “Background noise compared to a eruption and other events”

  1. Thank you, Jon. A very useful post to refer back to as we speculate about activity at Askja, Hekla, Katla and anywhere else that grabs our attention! 🙂

    1. In what unity is strain measured actually? The graph reads strain counts per minute, but what the heck is a strain count? I have never been able to really get a grip on this strain stuff hehe. 🙂

      1. It follows exactly the same pattern as the other transient we have had during the last year. It is just much more powerfull.
        It is much clearer if you look at this graph.
        http://hraun.vedur.is/ja/strain/str_corr/index.html

        When the more vigorous transients happen the system makes a series of resets to find the correct level of power to show, that is why it looks as an error.
        When in doubt, wait 30 minutes and check the long term and it clears up a bit what is happening.

  4. Micron. It is a quartz-rod being stretched and being pressed together.

    That is the measurement units for the borhole-thensla plot.

    The other one is in nanometres.

    1. Okay that seems logic to me, but still, whats the strain count?
      By the way, Carl, remember we saw these strain transients like a year ago on the old strain plot!

      1. Yes we did, I have them all saved, had them on automatic tracker when I was gone. This is more then ten times larger than anything the last year.
        We had one “normal” abortion yesterday. There where 56 of them a year ago within a period of two weeks. Then 7 sinse then, and now two within a day.

  5. Bloody teasing volcano, nothing on tremor, no quake, just a massive transient… She is just one big tease testing her new brew or something.
    It is closing in on actually being able to rip something open, but it wont be at the same spot as the last eruption, that much is clear. But she will most likely not do more tonight if she follows the pattern.

    1. How do you figure this future eruption would be any different from the previous ones?

  6. I think it will be to the northeast side of the volcano.
    There is an inferred dyke towards Burfell that has been inflating the last two years. Seems logical since the transients are all driven with Burfell as the oposite agent to the others. It was another borehole that was the agent the last time around.
    I do not know, and I think I will try to not speculate to much.

  7. Jón, thank you for this post. It’s very good and informative.
    Another type of event in Iceland is an ice quake which is caused by the glaciers cracking or moving. Jón did cover this before on http://icelandgeology.net/?p=513 but I am not sure how these will appear on the tremor plots. I think it is hard or impossible to detect or tell the difference in a normal earthquake unless you have the more detailed graphs.

    Another thing to remember when looking at earthquake spikes. These devices are very sensitive, and can pick up large events from a long distance away. I remember a M6 near Jan Mayen that did show up on the tremor plots. Also the M8.8 from Chile in 2010 or M9.0 from Japan this year and even the aftershocks in those events showed up clearly on the charts. I remember quite distinctively, when the Japan quake happened I had the tremor plot for Grímsfjall open and saw a big spike on it. I thought some eruption was about to happen, until I realized that every single tremor plot for Iceland had a same or similar spike on it.

    1. If you mean those few small quakes very near Hellisheiði geothermal plant, my guess would be they are related to pumping or other work going on there. We saw these before in February of this year. They look very similar in size and depth to what I remember from then, but I don’t have all the data in front of me to compare.

  9. A question that may be daft – but I would like the answer to if someone could provide it please. On the tremor graphs we have the 3 different colours for the Hz frequencies of tremors, against a vertical scale of ? units?

    Whatever the answer might be (I have previously assumed this is roughly equivalent to energetics or ‘volume’ of the tremors) what can be surmised about what is going on at Askja? The scale of tremors here is not far off from that generated by the grimsfall eruption, as well as producing persistent odd pattern anomalies similar to those seen for some days following the grimsfall eruption. Whilst this pattern was seen at numerous stations across iceland initially, it is only at Askja that these ‘patterns’ have persisted.

    Any theories anyone?

    1. Actually the scale is just a “measuring stick” as far as i know. It could just as easily been measured in amount of hamburgers. But that would not be professional. 😉
      Its just to get a look at the scale of tremors. Since the scale is -1000 up to 8000 on all the charts it has to be a standard used by the IMO. Otherwise if the numbers actually represented something it would have been different scales depending on where in Iceland the SIL station was located.

      1. And regarding the Askja chart. Noticed that roughly around lunchtime each day the noise goes up? I bet there is some reoccurring manmade noise at those times. Such as traffic (people hurrying to get something to eat) and so on.

        The latest spike though is probably caused by some other event. Carl had a theory regarding degassing in the lake or something similar. I will probably stick to my theory of a small magma intrusion though. 😉

      2. I left the degassing theory, the duration was to long.
        I think it was water seeping down into the ground. I think there should have been more low frequencies involved if it had been magma intrusion.
        But I think that at this time everyones guess is as good as the other. 🙂

  10. Thank you Jon. A very useful comparison.
    @ Carl
    I am not sure of the location of Burfell. I have looked on my favourite map that I use for locating places mentioned in this Blog . However, when searching it needs precise text including Icelandic letters I don’t have on my keyboard! So most of the time I have to copy and paste. Unfortunately “Burfell” has not been found I am guessing it is a small ridge or spur… somewhere. Please can you point me in the right direction?
    http://atlas.lmi.is/kortasja_en/

    1. Diana —
      Well for starters it overlooks Hekla. If you look at the bottom of the Hekla cam it says “Hekla séð frá Búrfelli” which I assume means “Hekla seen from Burfell”. So it is the home of the Icelandic Dalek.

      1. Also, what I got out of the very sad Google translation of the information under the webcam image is that Burfell is a 700 meter high mountain, and Hekla is 12 km south-east of Burfell. For some reason Giggle translates Burfell as “harnessed”. I’m sure that Carl can clarify this, he works cleverly with Icelandic.

      3. So the link didnt work. Paste these coordinates in to Google maps instead and you will get it.

        64.086944,-19.827778

      4. Thank You Denise- Marie
        I entered Búrfelli with no result. Then Búrfell and got 104 results!
        I found it, a hill North east of Hekla. You can even see the track… I looked hard but I think the Dalek must have gone walkabout!

        @ Daniel_Swe I thank you also for your help.
        It is interesting as many of our Northern England place names have Norse roots from the many Norse people who settled here. We call the Hills in Cumbria “Fells” and of course there are lots of water “Falls”. So I can hazard a guess at some Icelandic words. My Youngest Step son has moved to Norway with our grandson so I have picked up a little Norwegian. The Icelandic language is a very old Norse language I have been told.
        I find these language links fascinating.

    5. Diana, there are several mountains called Burfell in Iceland. In fact, in Iceland there is often one name for more than one mountain.

      Burfell is a mountain, 10km northwest of Hekla, see in google earth.
      There is also another quite large mountain, 20km northeast of Hengill, and 60km west of Hekla, called Burfell, an extinct volcano just north of the dormant Grimsnes volcano, the smallest active volcano in Iceland.

  11. @Jon. I hope you are feeling better today.
    I read somewhere recently that before anyone can think “Eruption” The professionals all look at ( Inflation +Strain + Tremor) then consider the possibilities.
    I have taken to this procedure as far as I can on line.
    I therefore do not get all excited at every quake spike as I did when I first started lurking on Jon’s Blog.
    However I do question anything unusual such as the huge spike at Askja yesterday, simply because I want to find out “WHY?”
    I am just naturally very nosey(forvitinn) !!

    1. And the activity continues at Askja, nothing major, but a small quake, and some tremoring that probably are cars, and some other proper spikes.
      But as said before, nothing pointing to an eruption or some such in the nearby future.

    1. Interestingly there have been a series of quakes at 1.1km depth. under or near Myrdalsjokull. The most recent quake at that depth is
      Tuesday
      16.08.2011 07:46:41 63.898 -19.024 1.1 km 1.5 90.02 10.4 km S of Landmannalaugar
      There was one there yesterday in the same area
      Monday
      15.08.2011 23:20:06 63.911 -19.024 1.1 km 2.0 90.04 9.0 km SSE of Landmannalaugar
      + a series at that depth under Myrdalsjokull

      Not much to make a big thing about but would I be right in suspecting that at 1.1 Km there may be some intrusion happening maybe in a fault running North North East to South South West…. ish?
      I am trying to practice some of the lessons I am learning on here! 🙂

      1. The interesting part is that up until now the quakes has been centered around 3-4 spots. Godabunga, just south of Hábunga, and just within the southern rim of the Katla caldera. Now there is even a spot on the north east rim of the caldera.

        Of course there has been some solitary tremors in other places within the caldera but main focal points have been these 4 places.

        I wonder what this could mean. Are there several intrusions which might cause a large fissure eruption which will spread in a Y shaped fissure (lines between the spots)?
        Several smaller vents opening up?
        A new calderaforming event in the future?
        The latter would not be good of course since the eruption would be quite large if the caldera roof were to collapse into itself.

        But as I see it it is a worrysome pattern since the spots are spread out and the intrusions would indicate alot of movement simultaneously beneath Katla.

      2. And the worst of all which I forgot..A flank eruption on the southern end of myrdalsjökull.

        caveat, Im not a pro at this. Just a rank amateur with wild guesses. 😉

      3. Look at Sigrúns Austmannabunga plot and things will get clearer.
        But this is the plot of all plots to understand the movements in Katla. Notice the small movement in all other stations during July. And then compare to the zumba-moves of Austmannabunga. Those moves are rocking the boat of everything inside the caldera.
        So there are only 3 “hotspots” at Katla. Godabunga cryptodome as usuall, Austmannabunga (likeliest to cause an eruption), and the south point of interest.
        http://strokkur.raunvis.hi.is/~sigrun/katlajul.png

        I wrote a piece a couple of Jón-posts ago about how I think Katla will erupt when she is ready.

    2. Well the quakes at Torfajökull does not have a high enough quality to it to be sure they are actually there. The location might (and probably will) be changed. And it would probably be placed beneath Katla.

      1. ROFL !Well my brilliant piece of theorising has been booted well out of the window as all the depths have now been qualified!! That will teach me to wait before opening my mouth and showing my rank amateurism to the world!
        @Daniel I still think that you are right as regards to” Jon’s interesting Spot” on the southern edge of Myrdalsjokull. Something may happen there .
        At least I am sure my posts cause a smile and a chuckle and brighten the day for the experts 🙂

      3. Well the location changed. Not to Katla as i first thought. The depth on the other hand is very shallow. And for a volcano that hasnt had an eruption since the 15th century that is very shallow.

        My money is on icy action. 😉

    3. Sooner or later it will wake up again.
      There has been some small quake activity, and a bit of tremoring now and then.
      But this volcano has been dormant for so long that we would see a hell of activity before an eruption.

      1. Yes 600 years of dormacy would need a bit of fracturing below in order to let magma escape. Earthquakes like the ones we are seeing now would probably need half a century or longer in order to clear paths. I would expect it to stay quiet for a long long time yet. Unless there are whoppers of quakes like mag 5´s or so. 😉

      2. I’m very much inclined to agree with you, especially about the timescale. However, from analysis of the Laacher See eruption it would appear that under certain conditions, an eruption could start within days (or even hours) after an intrusion so I’d like to hedge my bet if it’s okay? 😉

  13. Morten: your plot shows something similar as tidal effects.

    Jon: the tremor plots are also used to predict oncoming eruptions. That is something you do not go into, do you know more about typical signs in this respect?

    1. To predict an eruption is almost possible. All the volcanologists can do is to interpret all data they can find such as tremors, GPS readings, ground deformation, gas levels and so on.

      The tremor charts which are availible on the icelandic IMO website is basically raw realtime data. It shows what is happening now and as such can not be used to make any accurate prediction. As was seen in the picture Jón posted on the Grimsfjall eruption this year the tremors were even in a downtrend just before the eruption started. So in this case the tremorcharts in the months before could give a hint that there was something brewing but it can never say when it is going to erupt.

      A good example is the current situation with Katla. The tremor charts show spikes sometimes and they show that something is moving down below. However based on only tremor the eruption could be within a week or just as easily be in one years time. This is where all other information comes in to play. And even with all information its still a guessing game..Even for the trained professionals.

    2. They just use tremor plots too see what is going on. On the terms of predicting a eruption they often see it because of earthquakes or increased tremors that do come from a volcano just before a eruption.

      But that is just sometimes.

  14. A typo..of course.

    I meant to write “To predict an eruption is almost IMpossible” ..

    1. To predict the exact day, yes. But it is possible to predict that a volcano might prepare for an eruption, if you have proper data (meaning tremor, inflation data and seismic data).

      1. There is a splendid volcano to prove this point.
        Hekla 2000 was spotted to the minute. First the GPS-trending gave off signs that gave the probably year, the seismic moment count gave the half of the year, other signs as water disapearing gave the month, then came the initial quake and a warning that actually gave the minute of the eruption start. It is so far the best predicted eruption in history. Which is weird since this is probably the hardest volcano to predict.
        In 2005 they started the year clock again, according to GPS it was filled to the brim, seismic moment was ready. But we are still waiting. Same rate of filling, seismic combined moment is off the chart, water has come and gone, filling of an inferred dyke towards Burfell/Isakot with GPS going up in that area. And now we have this borehole transients since a year.
        Still nog eruption… Point is, they missed by six (6) years this time (and counting).
        I still think they will not miss to give the proper warnings in time, Icelandic volcanologists are world-champions at what they do, but still it made them a bit less cocky, probably for the better. 🙂

      3. Well yes. My point was that a tremorchart alone can not be used to predict an eruption. There are many factors involved and the tremors show that something is on the move.

        Sorry if i was unclear. 🙂

  16. I know it is a regular occurrence for quakes to be upgraded or downgraded on the IMO site but… I honestly can’t remember, has the most recent quake at Katla just been upgraded?

    Sorry about that sometimes I think I’m going mad! 😛

  18. I used my day to go through almost everything ever written on Hekla, poured over anything from InSAR to GPS-measurments and quantified it all, and then I put it all into Mathematica to do a computer modell for a probabilistics analyzis. I do after all like weird statistical math. The modell is heavy into path-integers, not montecarlo-modelling. And then I set my poor computer to chuggin’ unchuggable numbers.
    It was all made as a time-series started from 2000 eruptions end and onwards and set to give a percentage of a time periods whit the highest probabillity of eruption, all was then offset to a historics vectored-database.
    Barring that my computer modell is not flawed, the data inputs are correct, and withstanding that we do not know all we need about the volcano, here goes my physicist wet-dream mathematical conjecture of a prediction.

    Hekla will have an eruption between december 2011 and maj 2012 with the highest likelihood in march, it will be between VEI-2 and VEI-4 with the higher probabillity for the higher number. The statistical certainty is 0,86 +/-0,05.
    Thing is that the probabillity number has increased for every year since 2006, last year the probabillity was 0,72 +/-0,03, combined up the likelihood of an eruption before today is 0,97+/-0,03.
    So in a way you could say that all my fancy math is saying is that the volcano allready had an eruption, but forgot to tell us.

    I also got out a probabillity for how it will behave.
    Summit eruption, fissure eruption along the fissure trend, explosive eruption, radial flanking eruption trending to north-west. Probabillity for this is 0,52+/-0,07

    So, the forecast of nude dancing infront of the Dalek is not good.

    I will eat my hat before a webcam on Iceland if I am wrong. 🙂

    2. Quick everyone, let’s combine to give Carl a nice Mexican Sombrero ahead of that day!

      3. I made a barbute with a grill infront a few years ago to use instead of my black sallet with grill (aka Dark Helmet).
        We live for the Sword, we die by the Sword.

      4. Now I am hoping you are wrong. Just the thought of seeing you eat a hat infront of an icelandic webcam is just too alluring. 😀

    3. So, putting it out with another words: You’re just predicting another typical Hekla eruption, one-sigma within the familiar interval…

      I’ll make a “better” one: Hekla will erupt within one year, and it’s explosive, larger than typical (i.e. VEI4-VEI5), and it ends with major lava flows covering over 1 km3 of land.

      If I fail, I’ll … shut up and go home.

      1. Yepp, I am boring, I know… ;(

        On the other hand, why not a VEI-6 that creates the Cameron-tephra ontop of Drowning Street, ending with a silicic explosion as a 10 km3 caldera is created causing the first and only VEI-8 on Iceland. As a result of this cataclysm Ryan air starts to charge for the air we breath onboard, the Icelanders launch a new Caldera-beer.

      2. I forgot to answer…
        Hard to predict something that the numbers do not give any substance too…

        Nope, you have to eat your hat too if you fail 🙂

      4. Be careful, people living in vicinity of Hekla, like me, don’t want that. If an eruption happens in Hekla, I wish that it is at the very most VEI4 and running for a short-while.

        Carl, when do you think Katla, Askja, Hamarinn and Bardarbunga would erupt, using your model?

      5. The numbers gives a probability peak at strong 3 to a strong 4. There is only a nince percent probabillity of it becoming a 5, and even then a week one.

        The model I used is only applicable for volcanos who are very well known with an abundance of hard numbers like Hekla. I would say there are few volcanos that is this well-known. But, she is still very mysterious.
        Second thing, Hekla is pretty much unique, so my modell would not work well with let’s say Etna.
        There is no known runnups of Katla, Hamarinn/Bardarbunga as far as I know, and Askja is very neglected as Icelandic volcanos go. It is after all in the middle of nowhere so it does not affect a lot of people.
        So, sorry, I would have to make much less exact and totally different modell for Katla and Bardarbunga, and yet another for Askja. I need numbers for my equations, and there are quite simply to few. I could probably though do it for Grimsvötn and Eyja with a bit of certainty, but the modell would still need to be different.
        But Grimsvötn is easy to predict, just look at the combined seismic effect, when it reaches the by now well known threshold it will erupt. No magic there 🙂

      6. And still, the combined moment could not predict the strength of the eruption. I believe here the accumulated inflation was a better “predictor”.

        I have an impression that for Hekla we have already exceeded both. Inflation being more important as Hekla’s chamber is very deep. The deeper chamber the stronger forces are needed (for an equal inflation, if compared e.g. to Grimsfjäll). Hence I expect a larger than typical eruption for Hekla.

        I know this is simplistic, but I think we do not have anything significantly more reliable yet. I could throw in some Bayesian statistics, but I do not like it as “an educated hunch” gives often way better results. Jon is a good example of it.

  19. Something is happening to the far of the north in MAR.
    The two first quakes probably the same.
    Tuesday
    16.08.2011 14:46:44 68.147 -17.083 5.3 km 3.0 43.08 129.9 km NNE of Kolbeinsey
    Tuesday
    16.08.2011 14:42:29 66.606 -16.789 29.0 km 2.7 33.58 37.0 km NNW of Kópasker
    Tuesday
    16.08.2011 07:51:37 71.055 -17.289 5.8 km 3.6 38.77 437.6 km N of Kolbeinsey

      1. Yes thats probably it. Didnt look at the time. 🙂

        Speaking of regular noise intervals. I have been wondering what may be the cause of the regularity at ALF SIL station. It seems most of the noise is beeing picked up from the southern part of myrdalsjökull. It is the closest station to the “new” spot south of Hábunga.

        I know there was some discussions earlier about this but was it ever laid to rest?

        http://hraun.vedur.is/ja/oroi/alf.gif

        The spikes always comes with a few hours interval and looking at the tremor chart they all have the same magnitude. Now that HAS to be man made but what may cause it with such a regularity?

      2. That is a really good question actually. I do not know what is around, but it looks like some sort of 24/7 industrial operation.
        I guess one of our Icelandic friends know the obvious answer that eludes us.

      7. Ehm..A scheduled train passing by was my next thought but then i realized that there are probably no trains in iceland. Everyone seem to travel by air or behemoth 4×4´s 😉

  22. Tuesday
    16.08.2011 16:03:35 65.708 -16.802 3.4 km 1.3 99.0 2.1 km WSW of Kröfluvirkjun
    Tuesday
    16.08.2011 14:42:29 66.606 -16.789 29.0 km 2.7 33.58 37.0 km NNW of Kópasker

  23. Carl, using your model, when do you think Katla and Hamarinn might erupt?

    I also agree with you, we are not very distant from an eruption of Hekla. Most likely happening as a fissure extending northwards, and larger than the one in 2000.

    1. I posted the answer up in the thread.

      All the numbers point to it being about a lot bigger, and with radial fissure running towards north-west. Probably with more lava than the last time.

    1. Here we go, it was near Grindavik, a 3.7:
      2011-08-16 22:14:18,7 63,850 -22,397 2,5 3,7 90,05 2,6 km ENE of Grindavík

      Strange enough that we didn’t feel it here in Reykjavik, since we already felt weaker quakes from that area.

  29. Magnitude

    ML 3.7

    Region

    ICELAND REGION

    Date time

    2011-08-16 22:14:18.7 UTC

    Location

    63.85 N ; 22.40 W

    Depth

    2 km

    Distances

    40 km SW Reykjavík (pop 113,906 ; local time 22:14:18.7 2011-08-16)
    32 km SW Hafnarfjörður (pop 22,289 ; local time 22:14:18.7 2011-08-16)
    2 km E Grindavík (pop 2,539 ; local time 22:14:18.7 2011-08-16)

  32. I felt it in Reykjavik, Living in Breiðholt. it was like someone angry slammed the front door 🙂

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