Posted on by Jón Frímann

Earthquake swarm on the TFZ

There is currently a earthquake swarm taking place on the TFZ. This earthquake swarm appears to be rather small at the moment. The largest earthquake so far has been a ML3.2 according to the automatic earthquake list on Icelandic Met Office earthquake list.

There is no volcano activity connected to this earthquake swarm, as there are no volcanoes in this area off the coast of Iceland but there are volcanoes in part of what is considered part of TFZ. This area has its earthquakes from a slip faults. But they move in both north-east to north-west, but also in south-north direction in some cases.


The Tjörnes Fracture Zone. Copyright of this picture belongs to it’s owner. Picture found here.

Here is the latest earthquake image from Icelandic Met Office about this earthquake swarm.


Copyright of this picture belongs to Icelandic Met Office.

It is impossible to know how this earthquake swarm behaves. It is also known for the TFZ area that one earthquake swarm can start a new earthquake swarm nearby if a large enough earthquake happens. This happens sometimes, but not always. It is not a common thing to take place in the TFZ from what I remember about activity in TFZ.

I am going to update this blog post if this earthquake activity becomes something larger then it already is, or if a large earthquakes takes place in the TFZ.

108 Replies to “Earthquake swarm on the TFZ”

  2. Following Jon’s link, I found this VERY interesting page: http://www.raunvis.hi.is/~geirf/seg/seg-ind.htm

    Check the map on residual magnetic field at http://www.raunvis.hi.is/~geirf/seg/SVID.GIF for locations of the known volcanoes.

    Calderas of Katla, Hekla, Bardarbunga, Grimsfjäll, Hamarinn, Askja, and many others are clearly blue spots, many surrounded with red rims. But the locations for Eyjafjöll, Kverkfjöll, Öraefafjöll, Krafla, and others are markedly red, if compared to those listed before. Also Eldgja and Laki fissures lie in the “red zone”.

    Is this due to the magma types involved, or what does it tell of the respective volcanoes?

    1. Interesting indeed. Since this is a residual magnetic field map I wouldnt be surprised at all if it is as you say. Different types of magmas contains different types of minerals or the characteristics of the minerals are different.

      The red fields almost looks like where the deposit of tephra ended up after its erution. And since some of these volcanoes are fissures and not calderas they are not visible as blue spots.

    2. Yes it is. We also use the same kind of method, based on the magnetic caracteristic of different rock-types or of the caracteristics of the interstitial water, when we have to prospect or map regions for specific needs.
      Another example is reproducing the orientation of earth’s magnetic field through it’s history. The magnetic minerals in the magma align with the magnetic field, and in correlation with dating methods You can see when the field had wich direction.

  3. Whilst everything is Quiet, I have been wondering for over a Year now what that object is on the Hekla Webcam!
    Does anyone know? It Looks like a Dalek, with a dome & ..a Window? Is it a Bin? It it a piece of Equipment? Or a Hutt maybe?!

    And I’ve also noticed an elongated upright Yellow Rod appear on the Katla Cam! In Fact, has someone moved the pan to the left a bit? 😀

    1. Yes, the Katla cam was panned slightly left yesterday afternoon. 🙂

      And, I have no idea what hat thing is on the Hekla Webcam, I too thought it was a Dalek! But I think It perhaps detects seismic activity? 🙂

      Sam

    2. The Dalek is working with telecommunications 🙂

      It is written on the page. Here it is in translation to english.

      “Burféll is an about 700 meters high mountain. At the top of the mountain Fjarski has put telecommunications facilities, RUV got permission to bring a camera directed at the volcano Hekla, which is 12 km. south-east of Burféll. Hekla is nearly 1500 m. high and usually erupts at intervals of decades. Probably in the near future Hekla will erupt, as well as the big sister, Katla. Hekla erupted last 26th February 2000.
      Safety Committee RUV did the installation of the Burféll camera in collaboration with Civil Defence, LV, and fiber-optic Fjarski Reykjavik suplying connection to the system.”

      Boring as Daleks go… 🙂

      2. I probably should have put a warning on the translation…
        I am not Icelandic, and I am not a certified translator, so there might be errors there.
        And it is of course Búrfell, not Burféll… 😉

    1. I upped a little bit on every recorder following from Kolbinsey Ridge via SISZ up to TFZ. It started yesterday after a 2,0 quake close to Selfoss at VOGS and then started slowly migrating to the north. But it was so little (except at VOGS) that I felt I was conjecturing.
      VOGS with the interesting pre-quake spike, second spike started when the small quake hit.
      http://hraun.vedur.is/ja/oroi/vos.gif

      So my guess is tectonic stress, not anything to do with Hekla… But on the other hand all it takes is one beer and she vomits…

      1. Tectonic stress… The you could see the stress wave propagating (read: passing) in the Hella strain meter data.

  5. Then I would like to know what that white thing is which crosses the webcam at Katla (left side) a view times a day? 😉

  6. I love this blog. Was in Iceland recently seeing everything for myself, including hiking up to the new fissure / craters between Katla and eyjafjoll. What a sight!
    Keep up the good work.

  7. A Dalek working with Telecommunications! That’s something I never thought I’d hear!

    Thanks for explaining that for me! 😀

    I Wonder why they Panned the Camera to the left… I Think it may be a sign that they are expecting Katla to erupt on it’s South side somewhere maybe? I Wonder if she really IS going to erupt in the Near future. Or if she will from now just produce small sub-glacial eruptions.

    I Keep hearing “Overdue”, “Magma movement” & “Bulging Ground Stresses” etc. And yet Katla her beloved self seems to be doing what she has always done – Sleeping with the occasional turning in her sleep!
    If Katla were going to Erupt Violently, & give us all a display we’ve been waiting for, there would be much more activity. Much MUCH more.

    It’s like waiting for a time bomb to explode!
    I have this Crazy Idea that if she is So dangerous, It’s better to all Evacuate the Island, & then Drop something Sharp & Heavy from high in the Air onto the Icecap & Relieve the pressure! Yes, it would probably cause an eruption! :-b
    But the only difference is they would all be prepared!

    Jon! Keep an eye out for any Giant Long Sharp Icicles! >_<

  9. I seem to have noticed a pattern (well, sort of…) There appears to be an earthquake at the ‘area of interest’ on the Myrdalsjokull glacier, followed by an earthquakes either in the caldera or of to the left, followed by yet another quake in the ‘area of interest’, and the pattern will constantly repeat itself.

    Dont know if this is true or me just ‘desperate to find a pattern!’ 😉

    2. I noticed it too.

      I am guessing it’s just due to weather conditions since the wind is making noise on Jon’s helicorder for the past few hours.

    3. I do not think it is wind that is showing on the graphs and Jons Helicorder. There is something else going on. Distinct spikes and quakes are visible, and the rumble is growing all around, visible as far away as Vestmannaeyar.
      But, I am awaiting Jóns comment since he can see details we cannot on his eminently placed helicorder.

  11. Another quake at Katla, this time a 1.7 around one of the ‘areas of interest’. 🙂

    1. It can be seen clearly at Hekla tremor data, but only on the low frequency data. Does this mean that it was magmatic? How about Jon’s helicorder data?

  12. Wednesday
    10.08.2011 16:14:45 63.645 -19.323 1.1 km 1.7 90.01 3.6 km W of Goðabunga

  15. The Katla webcam vas moved by me slightly to the left because I wanted to look at some interesting clouds 🙂

    I work for RUV and have access to both cams.

    Sorry to overexcite you 🙂

    2. Ah, the Icelandic camera-god has spoken 🙂

      Thanks for the explanation.
      Now I just remembered the nude guy walking around for half an hour infront of the Thorolsfell-camera during Eyjafjallajökull. I guess that would have been more interesting if it hadn’t been on a very cold and rainy day… Lets just say the cold ruined it for the ladies… 😉

      1. Are you serious? There really WAS a naked guy? I thought geo Loco was joking!……
        Is it an ancient Icelandic custom?
        OK! OK! So who’s going to volunteer for this when Katla erupts?

      2. Yes, there was a naked guy. But believe me, you wouldn’t have been happy. First of all he wasn’t exactly a looker, and the cold was so severe that day that he was pretty much not even PG-rated.
        As a guy I preferred the (in this circle) famous woman in a bathing suit two days later. (My lips are forever sealed).

        I volonteer for the Hekla eruption, but I will not be naked. I will be dressed like Dr Who in reference to the Dalek mentioned above.

      4. I guess that in an Icelandic winter then the use of a Dr Who long scarf would be an advantage in hiding imperfections. There again I guess when Helka erupts it will certainly warm things up!

  16. Regarding the noise on Jons helicorders. This seems to be weather induced and the “spiky” sections seems to be man made or something. Looks very different from when there was volcanic activity in the past. Additionally the windinformation on the page also indicates wind over 7m/s and on top of that the wind is northerly. This could affect noise from the coast as waves come in.

    And the reason they panned the camera to the left could be that there might be some concern about the area just south of Hábunga.

  17. There was some car traffic + human traffic on the geophone at Hekla today. But only for the short while.

    I did record the ML1.7 at Goðabunga. It was a low frequency earthquake that normally happens in this area.

  18. And here is the ever present longterm tremor energy level for Godabunga. Yes it is rising, but it is still very low, even comparing with the last few days…
    http://hraun.vedur.is/ja/Katla/god_trem.gif

    Still long way to go for Katla I think.

    Back to TFZ:
    The pattern of how the quakes move around is interesting. The tectonic ones are of course just tectonics, but there have been a few around pretty much all of the known aquatic volcnos to the east of TFZ. I know, they always have quakes, but it is still a bit interesting. Must be large stress there for the quakes to jump around like that, the area is rather large after all…

    1. Sam, a few tips on the quakes in question.

      1. Very shallow quakes are almost always due to ice fracturing in the glacier, they are always very shallow of course. The reason for them almost always showing up at 1.1km depth is that it is the dummy depth for the too shallow quakes to record properly by the SIL-stations, weird bug in the system.
      2. If Katla goes she will roar off a bunch of plus 3s first, perhaps up towards heavy 4s. And there will be a lot of them. Think waves of them hitting with 10-100 an hour, all of them above 2.0.
      3. They will start deep and move upwards as the magma fractures the rocks and builds conduits. That is why I look at the quakes deeper than 4 km. They will most likely start down at the MOHO.
      4. The tremor levels will be between 100 to a 1000 times higher then they are now. And the tremor will skyrocket and explode quite literally off the chart within minutes, not slowly build up.
      5. And the ground deformation (GPS) will have been moving like crazy for days or weeks before as the new magma gushes into the vast magma reservoirs that are hidden under this truly staggering volcano.

      I do not know if you where around when Eyja bopped, or recently when Grimsvötn erupted, but if you where, think like this… Expect energy levels 10 times larger then Grimsvötn this year, or 100 times what Eyjafjallajökull did.
      Believe me, you will notice things not seen in a Iceland for almost a hundred years, and it would still not be a truly vast eruption from Katla.
      For the rest, Eyja VEI-4, Grimsvötn presumed as a VEI-5 and I am comparing this to Katlas last eruption that was a VEI-6. I know that it could be something as low as a VEI-4 judging from the list of former eruption, but VEI-4s are almost as rare as Eldgja-style eruptions from Katla… It is a big mother after all…

      1. Got to correct you on some points here:
        -Grimsvotn 2011 was by far not a VEI5
        -Katla’s latest eruption was VEI5
        -Most of Katla’s eruption have been either VEI3 or VEI4 with only a several VEI5 eruptions.
        -Katla has a very shallow magma chamber, so these earthquakes are most probably NOT due to ice fracturing.
        -Earthquakes do not necessarily have to start deep before an eruption. The feeding from the moho is often done long before the actual eruption. For example; Grimsvotn’s latest eruptions hardly saw any earthquake deeper than 4km.
        -GPS does not necessarily have to go crazy. The pressure has been building up for ages, the inflation is already present. It’s just the cork that has to pop.

        Summary:
        Katla(‘s eruptions) really isn’t(aren’t) really thát impressive. The eruptive force and erupted volume might be more than what we’ve seen at Grimsvötn or Eyja, but it could just as well be a smaller eruption with a nice and steady VEI3 as result. The only thing really impressive will be the glacial flood, since the ice covering Katla is much thicker than it was during any other recent Icelandic eruption.

      2. And a short recorection…
        Grimsvötn was as far as I know ejecting enough to be counted as a VEI-5, although the big wigs are still debating how to count it.

        This is a general comment on old VEI calculations with a lot of unknowns. Either you try to do them with a lot of guesses like at the Global Volcanism Program (and then you count low) or you just go by the ejecta volume. I prefer ejecta volume due to the expedience of it normally being easiier to calculate with a reasonable amount of exactitude.
        If you go with ejecta you get a week 6 for the 1918 eruption. Also the black-and white pics I’ve seen seems to support it. I might though be wrong, but I think not by much.
        I like ejecta volume in the forms of ash and tephra to calculate old VEIs.

        As a comparison I used the standard modell of calculating VEI numbers on old eruptions and applied it a year ago on Pinatubo and got a weak VEI-5.

        But if you go by the list at Global, yes then you are correct. Lets just say that this is one of the moments where I based on my skill in physics and science theory have doubts for good reasons on the APPLICATION of a standard modell. Or more to the point, overextension of low-grade data to fit a modell not made for what it is used for… 🙂
        Here I will argue the rest.
        Yes, the chamber is shallow, but the 1,1 IS the dummy value. You should know that. And as far as I, or you, know this is ice-fracturing. It is very common this time of year.
        Progression of quakes from the deep. Grimsvötn has open conduits most likely all the time, this is a volcano that has been dormant since 1918 probably. So, it will most likely erupt following the pattern of Eyjafjallajökull where there was an almost perfect progression upwards of the quakes.
        You know as well as I do that most volcanos hyperinflate shortly before erupting. I know as well as you that Katla has inflated for many many years, but it will still hyperinflate, the same as Eyja, and the same as Grimsvötn did.
        Yes, you are right, it might be a small eruption. But I do not think it will be this time. But I wont write why now. I will get back to it though.
        Pieter, have you seen the images of the 1918 eruption? I have, and I almost pooped my pants the first time I did. Impressive does not even cover it.

        Pieter, I make a bet, if Katla erupts and it does not behave like I said before the actual eruption starts, than I will gladly eat my hat.
        I will hereby also go on record saying that I will eat my hat if Katla erupts before Hekla.

      4. As you know ejecta volume is just one of the 3 criteria VEI is based on. Without one of these 3 (ejecta volume, plume height, explosive power) the VEI rating can not be granted to an eruption. In this case, the plume did not reacht 25km. About the ejected volume I have yet found nothing but I do believe that might get close to the VEI5 requirement but I’m not sure it really ‘made it’. The last, explosive power, was certainly immense. But lacking the plume, it can not never ever be classified as a VEI5.
        You can classify an eruption without plume height, but you can not give it a VEI-rating.

        Pinatubo was VEI6, with the exception of the small uncertainty for the ejected volume. It is indeed balancing on the edge.

        I did indeed know that 1.1km is the dummy depth. But could as well be regular earthquakes. Ice fracturing earthquakes often are localized at 0.1km depth.
        The deep progression has already been there. I’ve observed many many earthquakes with >15km depth in the central caldera this year. I’m not saying it wouldn’t happen, just that is not necessary.

        Hyperinflation at Grimsvötn? From the graphs I’ve seen this was not the case
        http://hraun.vedur.is/ja/vatnajokulsvoktun/gps_faersla.html
        Yes, some spikes before, but they happen all the time, even in the early and middle stages of the build-up. In Eyja’s case it was indeed present. But that’s what I was pointing out. It could happen, but it does not have to.
        My point: We do not have any clue how Katla is going to behave simply because we haven’t seen her act live yet.
        Oh and I agree, I’ll gladly eat my hat too if Katla erupts before Hekla.
        Hekla is one nasty unpredictable momma!

      5. @Pieter:
        Now you have found my entire point. Volcanologists do assign VEI numbers without knowing 2 out of 3 criteria. My entire point is that VEI numbers are dubious at best, and totally ludicrous when assigned to old eruptions. In many of the VEI assigned eruptions in Iceland nobody even saw them happen. And still they have given those eruptions VEI numbers.
        Katla 1918 have a VEI of 4.
        Let us now go through the numbers together.
        It ejected more than one cubic kilometre of tephra and ash. That puts it into a solid 5 on ejecta. On the picture I have taken from a steamer out in the ocean and with the known size of objects it is easy to use trigonomy to calculate the plume height. The picture was taken shortly after eruption start so it was probably at its peak. Height on the picture is 35km. Once again a 5.
        Then we have explosivity. Well ash got deposited as far away as the faroes. 5 or 6.

        Now I cheated above, I had info the volcanologist probably didn’t have. I have the fortune of having the picture and the notes from the captain. So I could probably say that it was a heavy five or a very low six and be fairly correct about it. The “scientist” at GVP sat the values from ejecta only and disregarded the rest you know. So, for once I am going to say that it is more likely my number is correct.
        Check GVP for old eruptions and you will see a lot of weird results regarding GVP on the old Icelandic eruption.

        Oh yes, and I have good reasons to think Hekla will be bad this time. It has had the same rate of lift since the 2000 eruption, in 2005 it was at the same level, and now it has risen to more than twice the level, and other growth factors are also at double. Ie, there are more than twice the amount of Magma down there, more like 3-4 times. It has also swollen in new places indicating that it will have a flanking eruption in a new place.
        I would say it is about 1 day away from an eruption, but that day seems to start over and over again…
        I usually think I am a brave man, I would gladly dance zumba on top of Katla. I have sailed through a hurricane, and soforth. But nothing on the planet could get me to climb Hekla. Ever.

      6. Thanks for the information Carl, however I am aware of the proceeding of a volcanic eruption, but thanks anyways! 🙂

        Having said that, there has just been a tiny earthquake nevertheless, but a depth of 5.0km. 😀

      7. Seeing the black and white photos of Katla 1918, compared to the eruption of Grimsvotn this year, bears no comparison. Grimsvotn had a way bigger and larger ash cloud, compared to what we see in Katla pics from 1918. Those seems to be very similar to last year eruption of Eyjafjallajokull. Yes, having experienced both Eyjafjallajokull and Grimsvotn in Iceland, I must say Grimsvotn eruption was way way bigger.

      8. Hello Irpsit!
        Have you seen the one taken from the ocean? It gave a good view and made it possible to mathematically set the height of the ash column. It was big…

        People have a tendency to forget that Grimsvötn blew out more junk in the first hours than Eyja did in the entire eruption. I think the reason is that the ash was “harmless” that make people think it was smaller.
        The VEI-5 designation for Grimsvötn was actually set by the IMO as a provisional designation. But I have not seen a definite designation yet.

      9. Eyja eruption in my opinion was one of the most overestimated events in the last years. By the media, not by scientists of course. Big proof of how vulnerable our occidental society has become. 2 days without easyjet and we behave as it was the end of times. Like a probability 1/100 per year earthquake in Japan (wild estimation, not looked up) with a tsunami of the same kind, and because we were stupid enough to put a nuclear plant at the bad place we make it merely “biblical”. Many seem to completely lack the ability to “classify” natural events…

      10. @Carl: The numbers I read for the eruption estimate around 650 mio cubicmeters of erupted material for Grimsvötn 2011. This would be a solid VEI 4.

      11. I give Eyja one thing though, it was very educational, and in its own way beautifull.

        The tsunami was pretty bad, but not biblical. As long as we live at coastlines that are prone for natural hazards people will get killed on a big scale now and then. But I will not go into my opinion of nuclear power-plants. I have already resigned from the board of Europes largest power-company due to them… I will just start venting more steam out of my ears than a steam-turbine. I will just say that I am on very good and informed grounds very much against them.

        In my view, biblical proportions come out of the amount of people hit. Grimsvötn this year killed no one as far as I know. If it had been Vesuvio blowing that hard hundreds of thousands would have been killed. The hardest hurricane ever hit an empty spot of the pacific and none died… Katrina hit New Orleans, if it had been the pacific hurricane nothing would have survived.

        People not force makes biblical in the end.

      13. 70% of population on this planet lives “on or near the coast”. Additionally, another 70% lives in areas that are prone to earthquakes. Combined, at least half of the human population lives in areas prone to tsunamis.

        You’ll get what you ordered…

  21. Maybe its my Imagination running away with me but does Katla look more raised today on the webcam?

    1. Stoobie:
      If you look upwards to my answer to Sam you will see what I wrote about what you could expect before an eruption.
      But one thing we will never see is a raised Katla on the webcam… 😉

      The camera is moved again… that is all.

      1. Yeah, I had read your response. I didn’t think it was going to Erupt, just that it looked a little higher up! 🙂 I check the webcam regularly,I prefer the new positioning makes things a little easier to make out.
        I wish I knew more about the tremor plots and stuff though, I have been fascinated with Iceland since Eyja went up!

  22. I am going to post about Katla volcano later tonight. But before that I am going to post a little more on how donations help me.

    That won’t be a long blog post. It is the details I forgot in the last blog post (http://icelandgeology.net/?p=1265) about the same subject.

    Note: Comment has been updated! At 19:29 UTC.

  24. I’m joking quite often, but there many times might be some truth behind it… 🙂
    But how hot might You be? If I wasn’t married I might want to go in front of that cam just to give You the show of the year…
    Your so incredibly fresh. Thanks for many laughs in a short time since I read You.

    1. @GeoLoco . Oh My! I am now Blushing! But a little humour in this serious world is no bad thing. A smile costs nothing but it’s effect can be worth more than money can buy.

      1. We take so heavy decisions every day. One mistake and lifes can change, or lots of money are spent on wrong efforts, miss a detail in Your analysis and live with the fact that the consequences can be death. If you can’t find a way to keep cool and objective, You won’t stand it ’till retirement. Humor, respectful one, is a very nice way. Reading “fresh” people also helps keeping open for efficient thinking. Fantastic people here.

  26. @Geo:
    Seems like you slipped down from the conversation 😉
    It was about fifty people seeing the nudedude when it happened.
    I leave the hot or not judgement to the ladies discretion.
    Show of the year? Hm, now I am thinking the return of Pink Floyd or something 😉

    How about we dress in pink fullbody woollens and dance Polka while chanting Cold arse? That might disgust more people than nudity 🙂

    1. I’m in. Let’s raise funds for the flight and the arctic truck rental. But if the ladies Katla or hekla go off at the same time, we go for the full monty in front of this scenery – then run very, very fast… 🙂

      1. I have my flight-ticket already and access to the truck…

        I am not married so I do not need to run that fast… I have been to Iceland and I would not dream of running from the ladies there, being nude or not 🙂

      2. I thought of running from the blowing volcanoes in the background. My lady knows that nothing helps when I’m in Iceland. Once there, You need some kind of army to get me off this nicest spot on earth. Was there twice and if they needed a hazard / risk management specialized geologist, I’d probably go – if they were ready to pay me in Swiss francs, of course… 🙂

      3. Problems in this world… It is harder nowadays to get a currency one trusts. I take swiss francs and swedish/norwegian kronor. Definitly not dollars, even if paid in advance. Euros I change emediatly.
        Oddly enough, nowadays ISK are fairly good. Strange world…

        You are the lucky one, where on earth did you find a wife who lets you run naked infront of a cam with a barfing volcano in the background? And most importantly, does she have a sister?

        🙂

      4. Didn’t say she let’s me – just that she knows there’s nothing one could do against it… 🙂
        No, but a cousin. But I’ll be honest to You, none of the same deal. I’d tend to recommend Diana, but I think I remember she’s already married. I’ll watch the market in the next days and tell You if something interesting shows up… 🙂

      5. You do that, or I move to Iceland now that I have all the time in the world at my disposal.
        An entire country filled with beautifull female volcanologists and sheep flying in the storms… *sighing*

  27. Can someone explain to me about the red, green and blue? 😛 really trying to learn about volcanoes here, but it’s kinda hard when i’m sitting in norway, and only reading about them..

    1. I guess you are refering to the tremor charts?
      It is the frequencies, with red being 0,5-1 hertz (vibrations) per second, green 1-2 and blue 3-4 hertz.
      A volcano puts out all three of them. But the higher frequencies can also be noise in various forms like cars and stuff. Therefore one can sometimes check any increase in tremors if it is noise or not due to lack of increase in the red low frequency.
      Another thing is that it takes more energy to produce lower frequencies. Think here about a stereo. For every octave down you go towards the base, the amount of energy needed increases to create the same amount of decibels.
      So, if red, green and blue all go up with red more then the others, it might be significant for a volcano. If it is mainly blue it is probably wind or wave-noise.
      Hard to answer it all, wave theory is a large field…

  28. Ok, so basically the red one have to go up too, not just the blue one? For some reason I thought it was opposite:P but I understand. Can you also explain to me in a way that I will understand about harmonic tremor? I’m on my phone here, so it takes some time for me to write back to you:P

    1. Please know that I am a physicist, not a volcanologist. Yes, my field is wave propagation theory (with a big slab of particle physics), but volcanowhise I am a noob.
      But if I have it correctly harmonic tremor is the noise produced as magma moves in the conduits in a volcano.

      All of them jump up when a volcano increases in activity. Here is a link showing the 2000 eruption of Hekla, not the brutal jump up in all frequencies, no build up just one big jump:
      http://hraun.vedur.is/ja/hekluvoktun/hau20000226.gif

      1. But you have one big advantage: You come from science. Having this background means that you are used to ask questions, discuss stuff. And most important: You learned how to acquire new knowledge.

      2. Actually it sometimes feels like am constantly trying to use the slightly wrong tool for the job… Like using a spanner instead of screwdriver to turn a screw…
        Be that as it may, I am fast at reading and have a knack for finding where science is not so good… 🙂

      3. You know, answering is not difficult for science, once you have the question. Asking the right questions first is mandatory for the correct answer. If you do not know the question, you can throw away your answers as they are only useless guesses!

  29. And what about now for example? With katla? The red one seems to be on the way up, and the blue on it’s way down?!

    1. It is more ocean-wave activity south of Iceland. It is just a background noise however. As a tremor from a eruption is many times higher then a background noise from the nearby area.

  30. Someone earlier wrote about volcanos that does not have a lot of quakes or tremors infront of an eruption.
    Hekla is the mother of that type. Here is the borehole strainmeter readout for the 2000 eruption. Only four small quakes in total, and only one was before the eruption. And no advance tremoring either.
    Yes it is the worlds best predicted eruption, they hit it to the second actually. But the prediction was made less than an hour in advance. In 2005 they predicted an eruption within 6 months, we are still waiting for that one, it is still building.

    Heres the readout. Scary in a way:
    http://hraun.vedur.is/ja/hekluvoktun/strain_rate_1500.png

    1. A couple of questions about the Borehole Strain that you link to, probably simple to answer once you know the answer, but here goes…

      Is a borehole just like the ones in the Antarctic that the scientists take away to measure the atmosphere over past centuries? If so, I assume that they leave a measuring device in the hole in this instance?

      Bur, Hel and Sto have the unfortunate coincidence of being red, green and blue, the same as on the tremor charts. Looking at the tremor charts versus the Borehole one, I can’t imagine that it is any more than coincidence, so what are Bur, Hel and Sto?

      As ever, thanks in advance!

      1. Not simple at all actually…
        You use a strainmeter to measure velocities that are far below the hertz range. The technologies involved vary a lot.
        Either you take a thin rod and insert it into a borehole and glue it to the bottom and attach it to a device measuring how much pull or push the rod is suffering as the hole elongates or shrinks. You can also use an argon laser to measure the length of the hole. A third tecknique is to fill the hole with a fluid and measure the volumechanges of the hole, this is my favourite for two reasons. 1, it is almost totally free from atmospheric pressure changes, and 2 it is measuring the volume and not the length which gives greater accuracy.
        In the case of Hekla as far as I know they are using type 1, but with quartz rods instead of steel rods.
        A simple version would be to seal the top and measure changes in air-pressure, but that is more likely to show errors due to atmospheric conditions.
        This answer is a bit simplified though.

        Regarding the colourcoding I guess you are refering to this chart?
        http://hraun.vedur.is/ja/hekla/borholu_thensla.html

        It is a rendering showing 2 different locations and three measurment devices for borehole strain. That is then coupled against a seismic tremor intensity chart. It is a bit confusing sinse they use the same colours for the strainmeters as the tremor… I think they should use different colours… But…

      3. Ha! That Wiki article gives me headache to look at, never mind trying to read it!

        Yes, that kind of plot, but I was referring in particular to the earlier one that you posted of Hekla’s eruption:
        http://hraun.vedur.is/ja/hekluvoktun/strain_rate_1500.png

        I’d guess that the three measuring devices are Bur, Hel and Sto. I’m not even going to ask why the eruption at Hekla triggered only Bur and not all three of them. I’m not sure that I’ll like the answer. It might involve Physics and while I love this blog, I only have the capacity to learn so much about volcanoes and volcano monitoring! 😉

        Thanks, Carl!

      4. Cathy, this time I have to defer to the volcanologists I think. I heard an answer once, that it was only that area of the volcano that was affected during that eruption.
        Jón knows that one far better than me.
        You are right about it being BUR, STO and HEL.

    2. @Carl: Hello! TYVM for that link and information. I always wondered why that chart was so le Strange!!

      1. Thank!
        I had misplaced that on my new computer!

        It is wonderfull and shows in depth why transients are so dangerous. Transients are when the curves go in two different directions like that.
        Hekla had a period in Janury when it had more than 50 hard transients (not as hard as the one in your graph of course) that I then saw as aborted eruptions. They came after a 2,5 quake. I still shudder at that period. After that quiet…

  32. hey! Thanks for that Carl. I have been waiting for such an explanation. I knew what I was looking for and at, but couldn’t describe it so well. This is an explanation not a description. This makes it far more clear.
    I am afraid I was afraid of Physics at school and I tended to panic. However when physics is in relation to something concrete such as measurements of strain in a volcano or pressures inside pants my interest outweighs my fear of not understanding. Therefore I can manage to understand….. just a little more!

    1. And once more reading You might be my most sexual moment of the day. I’m looking forward to seeing the reactions to a Carl Le Strange post about thermodynamics…
      A little more serious, I always found it interesting to see that considerations here were strongly based on physics, altough the behaviour of volcanic systems is also highly depending on what is going on from a chemical point of view. It’s a shame my knowledge of details of the different magma-compositions in Iceland is so poor, and I just can’t steel the time to work on that in this phase of my life… Maybe one of You clever guys know more and pick’s this point up. Magma isn’t magma, and it changes whilst it makes it’s way up to the surface, and during the time it is “stocked”, and when pressure and temperature conditions change. This can have weird effects that would be extremely hard to interprete in tremor or other charts.

    1. It is in the area of Upptyppingar. That area had a magma injection few years ago. It is still ongoing, but at slower rate at the moment.

      What happens with all that magma that is down there is a question that is still being debated. This magma might not go anywhere, or we might get a eruption there in about 10 years time (or longer) time. There is no good way to know for sure at the moment.

  36. Now there has started a earthquake swarm in north part of TFZ. It seems that TFZ is getting more active now, but it has been rather quiet during large part of the year 2011.

    1. Could you explain something about the Kolbeinsy Ridge and the TFZ? Because according to the Google Earth location of the KR, these and the previous earthquakes were occuring at the KR and not the TFZ.

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