Posted on by Jón Frímann

Earthquake activity in Bárðarbunga and Grímsfjall volcanoes

Yesterday (17-March-2016) an earthquake swarm took place in Bárðarbunga volcano. This is a weekly cycle at the moment in Bárðarbunga volcano so older readers are used to seeing and read about it already. This started in September 2015 (for the new readers) after the eruption in Holuhraun ended in February 2015. This activity suggest that magma has started to flow into the magma chamber in Bárðarbunga volcano again at faster speeds than before the eruption in Holuhraun. The exact rate is difficult to know, since the magma that started the eruption in Holhraun had been building up in Bárðarbunga volcano since 1970-ish and part of that time earthquake recording was poor or did not exist in Iceland or parts of it until 1995 when the SIL network was created by Veðurstofa Íslands.

160318_0000
The earthquake activity in Bárðarbunga and Grímsfjall volcanoes. Copyright of this image belongs to Iceland Met Office.

The largest earthquake this week had the magnitude of 3,4 while other earthquakes that took place had smaller magnitude. The second largest earthquake had the magnitude of 2,8. Other earthquakes where smaller in magnitude. It is also interesting that part of the earthquake swarm aligned it self along north-south fault in the eastern part of the caldera. That is a new feature, either a weakness is forming at this location or something else is up. This area has around 300 – 500 meter thick glacier on top of it and an eruption at this location would be extremely bad. The glacier flood from eruption at this location would mostly go down Jökulsá á fjöllum glacier river. Other flood locations can’t be ruled out (I’m not an expert on glacier floods and I do have limited knowledge of the landscape under the glacier).

Grímsfjall volcano

It has been five years since Grímsfjall volcano erupted in a largest eruption in 140 years for Grímsfjall volcano. Over the past few weeks there has been a slight increase in earthquake in Grímsfjall volcano. At the moment this doesn’t mean an eruption is imminent, the thing however about eruptions in Grímsfjall volcano is that they happen suddenly and without warning. Normally eruption happens in Grímsfjall volcano every 3 – 5 years on average, sometimes its shorter and sometimes its longer between eruptions.

Notice on Böðvarshólar geophone station

For the longest time now I’ve been having 3G connection issues with Böðvarshólar geophone station. The problems include poor signal, little bandwidth. The poor signal leaks into my recording of earthquakes, making them bad and extremely noisy and that makes them less usable for me. I am going to attempt to improve this situation but if that fails I will have to turn the station down. Since the cost of getting a good antenna for this location is too high and the solution takes too long to implement anyway. I will post a notice if I take down the Böðvarshólar geophone station. If it happens, it is going to happen before I move to Denmark.

Article updated on 18-March-2016 at 13:31 UTC. Minor spelling error fixes.

11 Replies to “Earthquake activity in Bárðarbunga and Grímsfjall volcanoes”

  1. Just thought I would post this…it is from a Barda Facebook page I follow…

    ‎Debra Jones‎ to Addicted to Bardarbunga
    7 March at 13:15 ·
    finally an explanation of the ‘slips’ we have been seeing, thanks to George for his perseverance in getting to the bottom of it. This was posted on Bardar FB this afternoon by George Holt:
    “Slip” Information Alert!
    I have received some replies from various IMO departments to my questions about alerts (“slips”) that do not show on eq list, and also about eq’s that do not show on alerts, here is one of the replies –
    We are presently experiencing two problems with the alert maps – and with your questions you basically pointed on both of them:
    – The apparent “large” events that show up on all or many stations are due to short data gaps that occur in data transmission or data storing. These gaps are rarely longer than a second, but they occasionally cause false alerts. You can however easily distinguish from a real and a false event, as the peak ground velocity (PGV, center map) should decline with the epicentral distance. That means it should be red close to the event and then fade out with distance. False events are just randomly coloured over the whole country.
    – The other way round, i.e. large events in our earthquake list that do not appear in alert maps is more tricky.
    There seems to be a timing issue in the program. Real events are often completely mislocated by the automatic locator in alert maps and often have completely wrong magnitudes due to that false location. If the results are too far off and the program cannot associate station detections of the same event with each other, that particular event can easily be missing in the automatic list.
    It is always safest to use our manually checked earthquake lists. The one for past 48 hours on our webpage shows a quality factor. Values between 30 and 91 stand for the quality of automatic detections (the higher the better), the value 99 means that the event has been checked. The coloured dots on our map further get a tiny black circle around them (no circle means unchecked, circle means checked, but that is hardly visible).
    Further, check our weekly event lists: http://hraun.vedur.is/ja/viku/2016/vika_08/index.html#mark
    (“Skjálftalisti” means event list, “Fyrri vika” previous week, “Næsta vika” next week)
    These lists are updated at least once per day around 16:30 UTC, sometimes more often. In general, we manually check all automatic detections in the SIL system in 24/7 shifts. We further go through all alert maps to check for events that were overseen by the SIL detector (which runs completely independent from alert maps). In case of a match, we create an event with a crude initial location, check the data for wave onsets and then locate the event correctly. The alert time and the actual source time of the event can differ by +/- 30 seconds, in extreme cases up to a minute, due to the timing issue described above.
    Sorry we are not delivering more accurate automatic detections in alert maps at the moment. We hope we can fix that in the future, all a question of manpower.

    Skjlftavirkni viku 8, 2016
    Vi skju og Herubrei mldust um 70 skjlftar, s strsti af str 1.2 ann 24.2. kl 14:47. Tveir smskjlftar mldust suvestanverum Langjkull.
    HRAUN.VEDUR.IS

    1. I don’t use the alert map, since I consider it somewhat unreliable at times. I also just check the reviewed results when I’m looking at what is going on in the volcanoes.

  2. I have to ask. If magma was flowing into Bardarbunga’s magma chamber, wouldn’t there be inflation shown on the gps stations around it? I’m asking because from what I can see, their hasn’t been any.

    1. This inflow is happening at more depth than 15 km. Making it hard to detect with any certainty. What is seen at the upper layers of the crust is just a symptom of that inflow of magma. Since some of it reaches the upper layers, resulting in pressure change that start earthquake swarms.

    1. I don’t have exact magnitude but it did appear poorly on my geophone in Böðvarshólar. So it might have the magnitude of 2,7 – 3,2.

      1. Seems quite different from the other ones as it lasted quite long on the plots.

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