Earthquake swarm deep on the Reykjanes Ridge

During the night a earthquake swarm started deep on the Reykjanes Ridge. This earthquake swarm is currently at distance of 730 to 735 km SW of Reykjavík. So it is clear that nobody is going to feel this earthquake swarm out in the deep ocean.

From this distance it is impossible to know if this is just a earthquake swarm or a volcano event. This distance also makes it close to impossible for the SIL network to locate this earthquakes with any details. But EMSC and USGS should show the largest earthquakes as they happen on the Reykjanes Ridge.

The largest earthquakes are appearing on my Hekla geophone, but just barely. Due to this large distance only long period seismometers are going to record those earthquakes properly.

77 Replies to “Earthquake swarm deep on the Reykjanes Ridge”

  1. Monday 05.09.2011 09:04:34 64.458 -17.410 5.9 km 1.8 49.41 8.8 km NW of Grímsfjall

    Isn’t that the position of Grimsvötn?

      1. Broomstick anyone from where i can take a bite? Wrong copy’n’paste. Here’s the correct one:

        Mánudagur 05.09.2011 09:04:38 64,606 -17,181 16,5 km 1,1 99,0 16,9 km ASA af Bárðarbungu

  2. We should expect a new wave of quakes all over the country, if the pattern is repeated.

  3. Well ! That has woken us up at the start of a new week!
    Thanks you Jon et Al for the heads up about this.

    I wait with anticipation. I wonder if it will kick start one of the Ladies?
    Also thank Jarin for this nice little picture posted on the previous Post.

    Will it be possible for scientists to tell if this is just tectonic earthquakes or if a volcano is involved? How will they find out?

  4. What would have to happen in Katla to make the Icelandic goverment evacuate? Do they not do that before an eruption starts?

      1. They cannot just evacuate the people every time a volcano is restless. People live there, have their jobs. The volcano is most likely (I would say 90-95% changes) will not erupt just yet, because it needs to it will most likely give stronger signs when it is just a few days from an eruption.

        Weeks before before the eruption we should see several quakes up to 3.0 and 4.0 happening, becoming more frequent with time, and inflation climbing faster upwards. This has not happened yet, but it has happened to some degree before Eyjafjallajokull eruption.

        Hours before the eruption, there should be volcanic tremor as well as more significant earthquakes. This is likely probably with a 95-99% likelihood. The authorities are going to wait for the stage described first and then alert the population to be ready. When volcanic tremor starts, then helicopters will be evacuating people. This is what I think it will happen. This is for the towns of Vík (400) and Skógar (200) and some farms too. The Westman Islands should be aware that it can receive a big ash cloud and even a tsunami due to the big flood entering the nearby ocean.

        So, concerning the necessary warning signs stated, we should be at least a few weeks from an eruption of Katla, if not later. It is not going to happen tomorrow or in next week. That is very unlikely. But eruptions in Katla usually happen in late summer and autumn, so it is interesting to keep a look.

        With Hekla, there are no warning signs only until 30-90 min beforehand. So, this means, climbing the mountain and walking near its base is not recommended presently by authorities since a Hekla eruption is expected. There are only summer houses around and a camping. When the first quakes start, SMS are sent to the people there to evacuate. But if you have a car, this should not be a problem, because even summer houses are mostly not very close to its bottom. Because Hekla is ready and gives so little warning, Hekla could erupt even tonight or could erupt only in 200 years (the eruption pattern might change).

      2. “So, this means, climbing the mountain and walking near its base is not recommended presently by authorities since a Hekla eruption is expected.”
        And still you climbed it? Hehe, you are a nutcase 🙂

  5. OK, now it gets confusing. I am pretty sure that the mentioned EQ was shown farther south than it shows up right now.

    1. That posting was supposed to be a re to ‘The other lurker’ – i’d better shut up now…

      1. Sorry, should have had some more coffee this morning before writing, Grímsfjöll is of course in Vatnajökull, don’t know how I read that as Hestfjöll – going to have a sight test this afternoon (true). Hope I will not keep on doing mistakes like that again

  6. I’m getting confused. I see a 4.6 EQ on the USGS website for this morning on the Reykjanes Ridge but nothing on IMO for that time or magnitude on IMO’s maps of epicentres (although the termor graphs do show that something has affected most sites symptomatic of a largish earthquake in or near Iceland).

    Just washed my windows so hope that Katla does not errupt for a bit.

    1. As Jón wrote, this quakes happened some 700km away from Iceland. Since the IMO doesn’t cover this area, its no wonder, that you don’t see it there.

    1. If it’s something small, like in Hekla, then it’s some interesting for me, you, and many other Icelanders and tourists.

      But if you wish something large to happen, like Katla or Bardarbunga, then it’s a foolish wish, because it will ruin your travel plans and the only thing you will see is an ash cloud, and from distance, not mentioning all the impact in Iceland and the globe.

  7. Hi All.
    Dumb question but if big enough earthquake happened on Reykjanes ridge could it cause a tusanami which would effect west uk?

    1. I think this is very unlikely. I don’t think earthquakes in the Mid Atlantic ridge can be much more than 6.5. Maybe a 7.0, but it would be rare. So, tsunamis would be rare and if happen small. But a major landslide could happen underwater, like it happened once near Norway, and this could cause a major tsunami. But this is very rare and doesn’t have to be linked with tectonic activity.

      But there is a place that can cause a big tsunami to strike the UK. (I am not talking about the Canary Islands landslide scenario, which is very rare) I am talking about something that happens about every 300-500 years, which are 8.0 to 9.0 earthquakes to the southwest of Portugal (a subduction zone) and this always causes big tsunamis that strike the entire coast of Europe. It has happened last in 1755, and there were other documented events before.

      1. I have read that the SW of the UK , Cornwall and Devon got a 2/4 meter tsunami from the 1755. Put that up to a mag 9 and 10meters is not out of the question.
        I walked some of the coast near by my house with a geologist on a guided walk 20 years ago, there was a 5000 year(+-500 year) gravel and smashed oak tree deposit 15 meters up a cliff, he showed me and the group I was with. He said a great flood did this, (then we thought storm/rain/tide!) now we know the flood was likely a tsunami, in all probability from the same fault as the 1755 Lisbon EQ.

      2. The thing is that not the size of the earthquake but the vertical motion creates a tsunami. You can have a M9.0 earthquake at a transformal fault and wouldn’t create anything. It’s the vertical displacement which creates a sudden shift water mass.

      3. The tsunami in 1755 was caused by an earthquake estimated to be 8.5 to 9.2 in Richter scale. Actually, researchers think there was 3 powerful earthquakes, within a few minutes. The event lasted 6 minutes with two small intervals.

        The location is still discussed, but it was somewhere SW of Portugal. The displacement was 12m along a 200km fault. The tremor was felt as far away as Finland. The tsunami was estimated to be up to 20m in Lisbon, and 3m in UK. It should have been at least as big as the last Japan tsunami.

      4. Thank you Pieter, I am glad you pointed this out, I forgot about the vertical displacement or other, slip displacement.

    2. I wouldn’t worry too much about it – tsunamis are very rare in the UK.

      The only one I know of is one is believed to have occured in the Bristol Channel in 1607. See for some details on the research. Possible causes of the flooding / tsunami “include a landslide off the continental shelf between Ireland and Cornwall, or an earthquake along an active fault system in the sea south of Ireland. This fault system has apparently experienced an earthquake greater than magnitude 4 on the Richter scale within the last 20 years, so the chance of a bigger tsunami earthquake is a possibility. ”

      There may also have been one on the East coast from a land slippage across the North Sea in the Nordics(?).

    1. And here is another UK flood thought to have been a Tsunami…
      It caused havoc up the Bristol Channel.

      Lizzy as Pieter says it’s not the size of the earthquake that is the worry is is the water displacement.
      A sideways movement will not displace as much water as a sudden drop or up thrust of the sea bed.

      Lizzy Life is for living. Worry, if you must, about the things we CAN change, and start with those things and people close to you . Meanwhile wonder and enjoy the magnificence and beauty of nature ……. but do not copy Irpsit and sit pondering about these things on the top of Mount Hekla! 🙂
      Tsunamis have affected the UK coastline when part of the edge of the continental shelf, which is like sort of underwater cliffs or steep slopes, has a big “avalanche”. The rock face or slope slides down and away and pushes the water into an upward moving wave.

      Please don’t worry about these natural happenings.

    1. Fönix says:
      September 5, 2011 at 18:52

      “There will be a Tsunami when Katla erupts, but it is unlikely to cause any damage outside of Iceland.”

      Only in a river or if part of the coastal shelf lets go, otherwise… no.

      1. I believe large glacial floods have the ability to create tsunami-like waves. They behave somewhat like a massive landslide or displacement.

      2. But they cause no significant tsunamis. The 1918 flood changed the coast line by about 5km to the south. That was it.

      3. I suppose it depends on the size of the eruption and where the flood comes down, if a large part of the glacier is melted in a few hours and hits the ocean, it is bound to make a big splash.
        The size of the wave might also depend on the ocean floor near the coast, it may change the wave into a Tsunami that could be dangerous to ships and boats in a large area.

        The last Katla eruption was relatively small according to what she can do, but according to history she usually has small eruptions after Eyjafjallajökull eruptions.

  8. That is nice, the eruption ash/gas vapour cloud created Crepuscular rays. That is a good picture, I bet the original was stunning even in monochrome.

  9. Hurray, a new swarm at Katla. I’m getting used to it, almost like it’s nothing special.

    1. This earthquake swarm looks like a dike intrusion. Given the small area the earthquakes are happening on.

      More on this later on. But I am going to monitor the progress for the next few hours.

      1. This is “only” 2-3 times more. And it has been rising quick in the last few days with a relative small number of quakes.

      2. @IMO
        Thank you for fixing the plot!

        @The rest:
        They fixed it after I predicted that it was a holliday over-look and that they would fix the plot as soon as we started talking about it in here… 🙂
        Guys, it did not simply jump like crazy, it had been standing still for 2 months, but now they have recalced it up to today, so it is 2 months worth of quakeing added. But it is still impressive.

  10. Hi all

    I’ve been following this blog for a year now! And I gotta say a huge thanks to Jon and the rest of you for enabling a total volcano novice to follow the Katla activity with a surprising degree of understanding! BUT I am hoping one of you will dierect me to a site which will enable me to further develop my knowledge – (I was an arts student!) I struggle with the ‘terminology’ – not only do I fail to observe Harmonic tremors – I don’t know their significance for example! And what the heck is ‘inflation’?


    1. Suzie:
      inflation=swelling of the surface caused by magma intrusion from beneath.
      Harmonic tremors = low frequency earthquakes which create seismic waves of a very typical pattern, usually associated to magma or other fluids running in a pipe or a volcanic conduit. They are a strong indicator of volcanic activity.
      Wikipedia has much better depictions for these phenomena, and I would trust it rather then my poorer explanation. 🙂


      Some other terms can be found there as well.

      Basically, harmonic tremors are indicative of magma on the move. Either as a dike intrusion or sill emplacement. The magma move up cracks and pathways, filling voids made from the earthquakes, which release stress. This stress can be either tectonic or volcanic. Tectonic if from the movement (or, attempted movement) of the earth’s various plates. Volcanic quakes occur as magma pushes it’s way some where. (and usually have a coincidental harmonic tremor or one happening soon after)

      It’s not available (that I can find) for Icelandic quakes, but the focal mechanism is also handy for visualizing what has occurred in a quake. Those are the “beach balls” that you see in some of the USGS technical data on quakes.

      Another type of seismic activity that was first noted in a South American volcano, is a waveform called a “tornillo” (screw shaped, hence the name). This also indicates magma on the move. I’ve only seen one volcano outside of S America that had what I suspect were tornillos, and that was Redoubt in Alaska.

      Another seismic feature is called “wagging,” this you would see in a full-on eruption as the magma bounces off the spongy magma along the walls of the conduit. This became a apparent in a paper that was released earlier this year.

      Most of us here are also novices about volcanoes, and we digest information as we get it.

      Hope that helps.

    3. If there is anything you do not understand you should just ask! That’s how most of us have learned here. For your questions:
      Harmonic tremor appears as a result of magma movements. The waves that are captured by seismometers have a distinct pattern which is indeed somewhat hard to recognize, but Jon made a great post about this. (

      Uplift or inflation happens when a magma chamber fills up. Because of magma inflow in the chamber, the chamber’s volume expands and therefor the overlaying ground swells. This is not as extreme as it may sound, but very precise GPS stations can record this very well. It is a very good indicator that there is pressure in the magma chamber and thus a very good chance of an impending eruption.
      An example of ground uplift at Grimsvotn volcano preceding this year’s eruption:

      A little more explanation to this plot:
      You can clearly see how in the vertical direction (which is the bottom graph) the ground ‘rises’ untill it reaches the breaking point. This marks the start of the eruption, after that most of the pressure is gone, and the ground subsides/deflates again.
      You can also see that in the other directions (East-West, 1st graph and North-South, 2nd graph) there is a clear change. This is also a result of an expanding magma chamber. Just imaging blowing a balloon, if you draw a spot on the side of the balloon, it will both move up and sidewards as you blow. This is exactly what happens to the GPS station located on the flanks of the volcano. It moves away from the volcano, which in this case is the south-east direction.

    4. Bollocks, I had a feeling that while writing the reply, someone else had answered before me! Oh well. 😀

  11. Interesting swarm. All quakes packed in a small area.
    Definitely Katla is cooking something in there…
    As for the Portugal tsunami, it was a very important event, caused by an earthquake that was felt all over Europe, damaging houses in Switzerland, and bringing birth to the science of seismology, and also influenced many of the philosophers of the time.
    Probably it was a mega thrust quake that took place at Azores-Cape Saint Vincent ridge.
    Giant waves hit, not only Lisbon, entering Tagus river (where they had increased in size), but also Morocco and the southern coasts of England and Ireland.

  12. This picture reminds us that even if the biggest volcanoes blow up and cause lots of problems, the sunshine isn’t far away 🙂

  13. Isn’t thee a harmonic component for the present swarm?
    I think I can see it in some nearby stations.

  14. I think there is going to be an eruption within the next 12 months. Judging by the exponential growth of cumulative seismic release. And I think there is even a great change that the eruption will happen at the end of this year or early next year, probably between November and February. What do you guys think? It is just a large inflation that is missing, but maybe Katla already inflated for decades

  15. I think the graph Chris pointed out is very interesting. As I can see this year has already exceeded any other records of cumulative seismic moment. Even the 1999 and following seismic crisis is nothing compared to what has happened. This ofcourse with the exception of Godabunga tremors which were way higher after 1999.

    1. If the rock is more solid under Katla, would this mean less inflation than in a region of more ductile crust, like under Hekla or Laki?

      This also explains why we see much more earthquakes but little inflation. If so, this is once more reason why we will see a lot of earthquakes before an eruption of Katla, but not so much inflation. This stands for my reasoning of why we are really becoming quite close to a Katla eruption, probably within months.

      What to expect of Katla within the next months:
      With Eyjafjallajokull we saw 2.5 months with earthquake activity more or less like we are observing now with Katla, with many swarms in scale of 1 or 2, with the largest earthquakes around 3.0. I think this is the stage we are now, it might last the same with Katla or it might last longer. This could gives an estimation in how large and long would be the eruption.

      A couple of weeks before the eruption, a 3cm displacement was observed in the glacier. I expect also at least one sudden significant displacement in the stations around Katla. When this happens, we could be within a month of eruption. We have been observing minor changes and a few days ago, almost a displacement like that. We will see lots of earthquakes happening close to surface just a couple of days before, and then tremor a few hours before the eruption starts. With Eyjafjallajokull, the major earthquake before the big eruption was a 3.6. I think with Katla this might be in the 4-5 scale, but it could only happen also only shortly before the eruption.

  16. There was a 6.6 earthquake about 70km northwest of Toba lake. Considering that the lake caldera is 80km long, this is quite close to the rim of the volcano. But the earthquake was very deep.

    1. You could become worried but… since the VEI8 eruption there has been other smaller scale eruptions, so even it the earthquake would be close to surface, it could mean something small.

  17. There is a growing harmonic tremor in Katla volcano this moment. I am going to make a blog post about it in few moments time.

    It can now be seen properly on SIL stations around Katla volcano.

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