Posted on by Jón Frímann

Large earthquake swarm in Krísuvík volcano

After four days of continues earthquake activity it appears that Krísuvík volcano has stepped up it’s activity by a order of magnitude. Since midnight there have been over 400 earthquakes in Krísuvík volcano. The activity is continuing when this is written and does not show any signs of slowing down at this moment. Geologist in Iceland are expecting more earthquakes in this area over the next hours and even earthquakes that are larger then ML3.0 in size.

The largest earthquakes where ML3.3 and ML3.7 in size. This is automatic size by the SIL system. The depth of the earthquakes was 4.7 km and 1.1 km according to the automatic SIL system. Due to high number of earthquakes the SIL system is putting earthquakes down all around the Reykjanes Peninsula. While there might be some earthquakes there, the number is not nearly as high as can be seen on the map. The earthquakes can be located by there low quality number.

Given the location and how this earthquake swarm is behaving it is my opinion that this is due to a magma is pushing up the crust in this area. But it remains a question of this is going to start a eruption or not. But the chances are growing for as long as this earthquake pattern holds up in Krísuvík volcano. If a eruption starts in Krísuvík volcano it is going to one of Hawaii type eruption, unless it is under water then it is going to be explosive for as long there is water getting into the crater. Last time there was a eruption in this area a 25 km long eruption fissure did form.

For now however all that can be done is to wait and see what happens. This earthquake swarm is going to continue for the next few hours and even days. The largest earthquakes can be seen on my geophone sensors here.



Map of the earthquake swarm in Krísuvík at 15:00 UTC. Picture is from Icelandic Met Office web page. Copyright belongs to them.

Icelandic news about this earthquake. Use Google translate at own risk.

Búist við áframhaldandi virkni (Rúv.is)
Engin merki um gosóróa (Rúv.is)
Heldur rólegra síðasta hálftímann (Vísir.is)
Jarðskjálftinn var 4 stig að stærð – 200 skjálftar frá miðnætti (Vísir.is)
Jarðskjálfti í Reykjavík (Vísir.is, 09:13 UTC)
Hætta á fleiri skjálftum (mbl.is)
Skjálftinn var nær höfuðborgarsvæðinu (mbl.is, 11:00 UTC)
Jarðskjálfti í Reykjavík (mbl.is, 09:07 UTC)
Skjálftinn líklega 4 stig (mbl.is)
Kort af skjálftanum (mbl.is)
Dregið hefur úr skjálftahrinunni (Vísir.is)
Tveir snarpir jarðskjálftar 24 km SSV af Reykjavík (DV.is)

Note: Check time stamps of the news articles.

Blog post updated at 14:50 CET on the 27.02.2011.
Blog post updated at 16:14 CET on the 27.02.2011.

144 Replies to “Large earthquake swarm in Krísuvík volcano”

  1. Very very exciting times. This has to be the largest swarm since the Eyjafjallajokull eruption last year. My feelings say that an eruption is nearly inevitable, but who knows. We’ll see. 🙂

    1. You do not know me but a very good friend has friends and family in Iceland near where the earthquake happened. The phone lines went dead in the last hour can you tell me where we can get the latest news? and how bad was it?
      was anyone hurt? Thank you so much. Monica Sharf

  2. If an eruption happen, how much time we will have to wait. This volcano can be comparable with eyjafjallajokull eruption?

    1. I do not know. This volcano last erupted in around the year 1340. But this would not be like Eyjafjallajökull eruption. This would be more like a Hawaii style eruption as I mention in this blog post.

      So no danger to air traffic.

    2. No one knows what it will take to start an eruption. When it starts the eruption will probably less explosive then the Eyjafjalljokull eruption, but more effusive. (more lava pouring out)

      By the way; Jon, a 25km fissure? Are you sure? This would’ve reached the present-day suburbs Reykjavik.

      1. If it will have more lava flows, we can think it will be more easy an eruption to start or not? Lava will have much less viscosity, so maby more easy to start an eruption?

      2. I think what’s of more importance is the pressure from beneath and how rigid/strong the crust is.

      3. Yes i agree, but that particular volcano is a lot of time building pressure and acumulating magma.

  3. Exciting indeed, but before anyone gets too excited – If you go back to the weekly records, you’ll see that swarms as intense as this preceeded the Eyjafjallajökull eruption by 11 years and there have been many similar “earthquake storms” in other Icelandic volcanoes over the past two decades of decent monitoring, but no eruptions.

    What makes Krísuvík especially interesting is the inferred evidence from deep cracks and a disappearing lake that magma may encounter water at a depth of 1 – 2 kms (guesstimate) and there may be quite sizeable phreatic explosions. Another possibility is that there is enough mush left over from the 14th century, mush that would have fractioned towards an andesitic-dacitic composition, that could be revitalised by the ongoing basaltic intrusion. However, I’m with Jón in that the by far most likely type of eruption – IF there will be one – is a hawaiian, albeit one with an initial surtseyan period.

    1. Actually the focus is quite close to Kleifarvatn, but on the other side of a mountain chain. If a possible eruption would come up there, Kleifarvatn would not be touched. See here: http://maps.google.com/maps?q=63.931,+-22.034+(Jar%C3%B0skj%C3%A1lfti+5,1+km+NNA+af+Kr%C3%BDsuv%C3%ADk+klukkan+09:05:59,5+af+st%C3%A6r%C3%B0inni+3,7,+g%C3%A6%C3%B0i:+90,06.+d%C3%BDpi+4,7)&hl=en&ie=UTF8&t=h&sll=65.689953,-15.897217&sspn=2.185284,6.811523&ll=63.932621,-22.026987&spn=0.027872,0.087461&z=14&iwloc=A

  4. Well this is getting exciting again. Very similar to the excitement with the first swarms at Eyjafjallajökull. Have the volcanologists confirmed whether this is an intrusion yet?

    Henrik, I think you are right that fractionation is unlikely here . Why I can’t tell you (just me speaking our of my derrière again) but something about this ridge being too young and that is more or less a surface expression of the MOR i.e. the crust here (I imagine) is nothing like as thick as under eastern Iceland…. all just wild postulation to distract me from my dayjob and hoping for correction from someone with more knowledge..

  6. Its very interesting to watch all this activity.

    One question, most tremor graphs in Reykjanes peninsula region show the tremor “jump” of 24/02 but Nylenda station http://hraun.vedur.is/ja/oroi/nyl.gif is the onle where the graph of the high frequence jumped above the lower frequences.

    Is this in any case significant or how could that be explained?

  7. huh? looks like my first comment got eaten.. oh well. what the heck. back to work and popcorn for me.. nevertheless exciting developments!

  8. Well I’m ready for it this time- wireless broadband up and running.
    Lurking’s plots a very much appreciated.

  9. I may have missed this explanation but… Why do you think if there is an eruption it will be a Hawaiian type ?

    1. I would guess that geologists have been surveying the area for some time now. The rock and the old lavafields tell a very accurate story. If they have found large widespread areas of old lava it would suggest that the eruption was effusive. And another indicator would be the composition of the rock itself. For example if there is a lack of pumice it would indicate that the magma was without gas which makes an eruption more explosive.

      According to http://www.volcano.si.edu/world/volcano.cfm?vnum=1701-03= the past has produced crater rows and that all these are shield volcanoes which proves that it has been hawaiian type eruptions in the past.

      If the composition of magma has changed during this dormant period from a more fluid to more viscous magma I have no idea. I will let Jon answer that one. 🙂

      1. Craters row 50 km long, Hawaiian style eruption ..

        Uhm, why is this ‘supposed’ to be especially different from Laki ? The name and location are different but the spreading rift is similar.

      2. Magmatic composition, lava volumes.
        The Laki eruption had a volume of 1.5 x 10^10 m3
        The last Krysuvik eruption had a volume of 1 x 10^7 m3
        This is about 1000 times more lava, imagine.
        Also the Laki eruption-magma was of another composition and included a lot of toxic gasses.

      3. For Iceland, I’m not sure that looking back to the history is a reliable indicator of the future.

        The place is like a volcanic adventure theme park. So much is happening and evolving, that the map of Iceland looks as if it is one developmental trend layered atop an earlier alternative.

        How can a person know that what transpires is the repeat of of something old or the start of something new?

        There is a sizable element of the unexpected. Looking back can mislead as well as inform.

      4. @Raving, That’s no argument. Ofcourse we can’t predict an eruption in detail. Volcanism and earthquakes are still a big mystery, but using what we know this eruption won’t cause as much harm as the Laki eruption. Ofcourse, unexpected things can happen but that’s complete randomness.

        If we think this way, for example, a fissure could open up beneath Reykjavik and swallow all of it inhabitants, then there could be a supervolcano beneath New York. This won’t happen and is not the case. But yes, we can never be 100% sure.

        History is not a reliable indicator, but it’s all we have.

      5. Pieter says: at 21:58

        @Raving, That’s no argument. …

        But that’s the problem with arguments. Rational arguments are believable and compelling. They appear to be better than nothing and are thus reassuring. That assurance misleads.

        Whenever science does get it wrong, it invariably turns around with the clarity of hindsight and proclaims, the science wasn’t wrong … the problem was misconstrued.

        Muttered nonsense can be discounted.
        Muttered rationality is more stifling and dangerous.

        🙂

      6. @Raving I’m not saying there is no possibility, it’s just that it’s irrelevant to discuss these things because it add’s nothing but chaos to the discussion. What you’re actually doing is throwing away thousands of years of science and rules made my men. I think it’s very interesting to go beyond and think about alternative explanations rather than present day sciene, but that’s not relevant to this discussion of what kind of eruption this could turn into.

      7. It is very central to science, that you ask the right question! If your question is misformulated and/or inaccurate, your answer will be, too. That’s how science progresses! Think about history of science, e.g. ether, black body radiation, etc.

        I think Raving nailed it correctly by saying: “Looking back can mislead as well as inform.“

    2. So in the 1300’s there was a fissure eruption in the same location and that is why this eruption will be Hawaiian. I guess that makes sense but leaves a lot of uncertainty in my book.

      2. No, all of the historic eruptions in this volcanic system (and also in all adjacent volcanic systems) have been like this. The surface expression is also evidence for fissure-lava-emitting eruptions. (no single central cone, no single mountain, long ridges, surrounded by lavafields)

  12. Magnitude ML 3.4
    Region ICELAND REGION
    Date time 2011-02-27 17:25:21.8 UTC
    Location 63.92 N ; 22.03 W
    Depth 2 km
    Distances 25 km S Reykjavík (pop 113,906 ; local time 17:25:21.8 2011-02-27)
    16 km S Hafnarfjörður (pop 22,289 ; local time 17:25:21.8 2011-02-27)

  13. Actually we had three quakes: 3,4 and 3,1 almost at the same time, and a 4,1 2 minutes later:
    2011-02-27 17:27:36,3 63,928 -22,034 1,1 4,1 90,07 4,8 km NNE of Krýsuvík
    2011-02-27 17:25:22,1 63,934 -22,036 7,5 3,1 90,05 5,4 km NNE of Krýsuvík
    2011-02-27 17:25:21,8 63,920 -22,030 1,6 3,4 90,07 4,0 km NNE of Krýsuvík

  14. Sunday
    27.02.2011 17:27:36 63.928 -22.034 1.1 km 4.1 90.07 4.8 km NNE of Krýsuvík
    Sunday
    27.02.2011 17:25:21 63.920 -22.030 1.6 km 3.4 90.07 4.0 km NNE of Krýsuvík
    They are very shallow…

  17. It appears that Icelandic Met Office system is getting blocked by the high number of earthquakes. So if the list stops updating it does not mean that the earthquake swarm is over.

  18. Yes, the website seems to be slow and hanging. But once the site comes up, the tables seem to be updated.

  19. If the activity was indeed tectonic wouldnt there be fewer quakes but larger? Or maybe one massive quake? If I look at it soberly it seems the tremors are magma intrusions as there are so many quakes.

    or am I wrong?

    1. I don’t think there would be any difference in view of the earthquakes. So I think it is close to impossible to know if the earthquake swarm is tectonic or by magma.

      But given the fact that magma is on the move in the Krísuvík volcano. I am going to assume that this a magma related earthquake swarm, not tectonic. But if I am correct on that is a question that I am only get answered later.

  21. Tremor charts from both RNE and NYL..have similar patterns..with the 2-4 hz (blue) graph rising above the lower frequencies. Does this pattern have any meaning..other than swarms of quakes? I think this might have already been asked, but with both showing this pattern, its interesting.

  22. Looking at Jón’s helicorders/geophones/seismometers it looks as if all quakes are tectonic – at least according to the turorials on EBT and here. Now, how’s this for a hypothesis?

    Widening cracks lets water seep even deeper to where it’s very close to, but not in direct contact with magma, ie very hot rocks. The result is a large number of subterranean phreatic explosions when water flashes into steam, which would explain the wide variation in size and location. Hm, where’s Lurking when you need a large-scale 3D image of this quake storm?

    1. Interesting theory. However looking at the “trend” at IMO website the quakes run abit from the NE to SW. Just as the Krisuvik crater row is located with a bigger concentration on the SW end of the rift.

      And considering the recent inflation in the area that would suggest a magma intrusion.

      But I guess we will all see what will happen soon enough.

      1. I hope when things get really interesting, one of the Icelandic webcam service providers might relocate one of their cameras into the vicinity. The online community would certainly welcome it!

    2. It is not a volcano per se. as of yet and nothing spectacular to be seen today when geologists went there today (evening radio news ). They are expecting tremors following the quake at 17.28 (4,1R) (made it’s presence known in Reykjavik by a sound wave prior to the thud).

  25. Okay… latest set. Evidently this thing wants to make some noise.

    So far, the main group of quakes seem to be lining up on a plane. Pretty much what you would expect in a pre-faulted environment prone to fissure rows and linear cracks.

    View North

    http://i55.tinypic.com/smy1xd.png

    View East

    http://i53.tinypic.com/2ewprwg.png

    As for a moving quake focus… that could possibly indicate magma on the move… it’s not there. No specific trend either way. That doesn’t mean you have to have a trend… just that nothing definitive shows up in the plot. There has been an upswing in the average depth in last few hours (towards the surface), but that could just be indicative of the upper layers responding to the larger quakes.

    http://i56.tinypic.com/6ypmaw.png

  26. Good afternoon, fellows.
    EMSC shows the two big ones.
    Lurking is probably taking a nap, from being awake through the night as I did. 🙂

  27. This is the last paragraph from Visir news posted by Jón from the links above.
    Could anyone do a better job than Giggle having this translated for us?
    It doesn’t make sense to me.
    What, the last eruption endured for 500 years?
    Thanks.
    “Hún segir að mörg eldfjöll séu á svæðinu en síðast gaus þar fyrir mörg hundruð árum.
    „Það var gostímabil þarna frá 800 til 1300, þannig þetta er ekki eins og Hekla eða þannig,” segir Sigþrúður.”

    1. The last eruption phase in this area ended about 800 years ago. But last eruption was in the year 1340 they think.

      There are several volcanoes on the Reykjanes.

    1. Yes it seems to pick up in events/minute.

      What is your take on Henriks theory of water getting in contact with hot rocks due to tectonic release?

  29. And… a perspective view from the SW looking to the NE. This is the one that looks really interesting. Just remember that these are all occurring in that diamond shaped area that has seen previous quakes… so it doesn’t really mean anything. (such as feeder pipes converging on an area)

    http://i51.tinypic.com/2sabbep.png

    What is going on is still up in the air, and I’m in the Henrik camp with regards to “tectonic” in nature. BUT, this area is not a Mk-1 mod 0 volcano. It’s a fissure structure/row on the MAR. Most activity, volcanic or other wise, would be driven by plates moving apart and magma accretion up into the opening left behind. Basically that means you wouldn’t necessarily need a high pressure reservoir busting it’s way to the surface. It could just open up and seep. Sure you would get the resulting interactions as it made the final trip to the surface and interacted with water, but the mechanics of a normal volcano might not be expected… if it does anything at all.

    MEDIA CAVEAT: I am not a volcanologist, seismologist, geologist, biotechnologist, hedge fund manager, or investment banker. Any attempt to attribute my verbiage as an “expert opinion” is shear lunacy. If you want an experts opinion, call one. Talk to them. Run my scenario past them and see if they agree, if they do, feel free to use it in your article. If not, you are an idiot for not doing due diligence.

  30. Does this stuff frighten those of you who live in Reykjavik or do Icelanders not think much of events like this?

  31. I have to remind you that in a run-up to a fissure eruption, there will occur tectonic earthquakes. Unlike stratovolcanoes with a traditional cone and mountain and conduits already in place, these eruption have to create a path themselves. My thought would be that this should ofcourse be accompanied by a larger-longer lasting earthquake swarm than we’ve seen before Eyjafjallajökull. There simply is a much greater seismic moment needed to create a pathway up to the surface.

    I kinda agree with Lurking, but in a sense that pushing magma is creating these ‘volcano-tectonic’ earthquakes in order to form itself a path up.
    More info about different kinds of volcanic earthquakes:
    http://www.pbs.org/wgbh/nova/volcano/seis_flash.html

  32. Has anyone any idea what the water level is doing in Kleifarvatn? Is it stable, or is it decreasing? That might add a piece to the jigsaw puzzle.

    1. Not mentioned today, 2 divers were diving at Kleifarvatn this morning, when the quake happened, reported being “shaken” (not stirred ok, that was a J. Bond joke if anyone missed it).

      BTW. OT
      Can anyone remember when tremors were at the most (ie. number) before Eyjafjallajökull eruption ? A year before or 2 ?

      1. About one or two weeks (5 march 2010) before the Fimmvorduhals eruption (20 march 2010) earthquakes started to pick up with about 200 quakes per day which slowed down a bit the last week before the eruption.

      5. @Pieter: The interesting thing is, that almost all quakes are minimum of strength 1. There are only very small numbers of smaller ones, but large number of 2+, which have been quite rare in earlier swarms. And this makes me really curious.

      6. @Chris, this is probably due to the overflow of data coming in the system, in which smaller earthquakes are not recognized at first hand but might manually be added later. They do occur, but get lost in the big mess. 😀

  33. Just for some reference, during the last Krisuvik eruption in the Trolladyngja system the eruption emitted 0.22 x 36km of Lava Flow.

  34. I agree with the tectonic-volcanic theory too.
    Or else how would we explain the other earthquakes taking place simultaneously in places such as Þjórsárbrú, Hvolsvöllur (Eyjafjöll), Hvalstöð, Skjaldbreið and Húsafell (Langjökull)?
    The MAR seems to be spreading apart in a more “visible” way. No wonder Kolbeinsy is seeing earthquakes too.
    But why this concentrated “weakness” at Krýsuvík?

    1. These quakes are ghosts in most cases. In other cases they might be tiny stress points which came loose after the large earthquakes. The magma pushing occurs on a much smaller scale than you are thinking. It’s just this single bobble of magma pushing itself up beneath Krisuvik. In order to make it’s way it has to move some mass, which stresses, fractures and create earthquakes. Together with that I think there is a large portion of these quakes which truly are magmatic earthquakes in the sense that they origin from magma-movement, and not magmatic-pressure.

      1. I didn’t mean the fissure would have THAT extension, I only meant that, if effusion occurs, it will be locally, where there is this weakness.
        But I don’t think we will hear much of harmonic tremors in this case, because magma will not flow through a conduit.

      2. It will not flow through one sinlge conduit (probably, could be the case, small shield volcanoes are sometimes created in these areas), but probably through a lot small conduits on a plane. So harmonic tremors will be there, yes.

    2. The other earthquakes is just noise in the SIL system. It happens always when there this big type of earthquake swarm. You will notice that the earthquakes in that locations have really poor quality.

      Big earthquake swarm = a lot of noise in the SIL system and a lot of false earthquakes.

      1. Well, the noise follows a pattern, doesn’t it? they are “echoed” along the fault, aren’t they?

  35. Jón, do you have a detailed picture of the large quake(s) that happened today. They were perfectly visible on your h’corder.

    1. @Pieter, I do not have it at the moment. As my earthquake computer is not properly internet connected and I plan to get the earthquakes when the swarm is over. When ever that might be.

      I just see what you are seeing at the moment on the online plots.

  36. For the record: the last M3.0 is a fake quake or will be downgraded bigtime, it didn’t appear as large as it should on Jon’s helicorder so it’s either a smaller quake or a ghost.

  37. The swarm seems to take a southern trend. Wouldnt that contradict the “tectonic” theory? My meaning is that if it is tectonic the spread of the swarm would be larger and not focused on a single corridor as shown in the picture below.

    http://i53.tinypic.com/2qalbx3.jpg

    1. The line at the east is a false one. Wrong location by the IMO software. The earthquakes are actually taking place west of Kleifarvatn lake. Close to where the ML3.0 earthquake did happen.

  38. Biggest earthquakes during the last 48 hours
    Size Time Quality Location
    4.1 27 Feb 17:27:36 90.1 4.8 km NNE of Krýsuvík
    3.7 27 Feb 09:05:59 90.1 5.1 km NNE of Krýsuvík
    3.6 27 Feb 08:20:25 57.5 40.8 km ESE of Eldeyjarboði
    3.4 27 Feb 17:25:21 90.1 4.0 km NNE of Krýsuvík
    3.3 27 Feb 09:49:03 90.0 5.7 km NE of Krýsuvík
    3.0 27 Feb 20:04:07 90.0 4.1 km WSW of Fagradalsfjall (You mean this one?)

      1. This is the list provided by the IMO, outside the automated table, and the quality is 90. Hasn’t it been reviewed?
        And it was located in a farther spot from Jón’s helicorders.
        But let us wait and see.

      2. That’s true, but I doubt that this location was correct. But indeed, wait and see. 🙂

  39. @Daniel_swe February 27, 2011 at 21:40

    No, this is in pretty good alignment with the existing faulting. Remember that there was a paper recently that indicated that the plane of the sprugur and faults tend to rotate to a different alignment with depth.

    As for side by side fault corridors, that also fits with existing mechanisms. Just look at the region of South Iceland and note the alignment of the actual sprugur. (surface expression of faults.. aka “cracks”)

  40. @ Peter Cobbold!

    Great to see you again Peter! Glad you still have your eye on these things. And quite the map you linked to there. 2o-22 km is not really that thick at all. OTOH, it wasn’t that much thicker at Eyafjallajökull either. The biggest difference I guess is simply the historic record. For whatever reason, the eastern volcanic zone is capable of storing magma chambers long enough for crystal fractionation to occur and hence the volcanoes there are capable of erupting more felsic magma. Here right on the ridge I’d be surprised to see anything other than lava fountaining (you live and learn though so I’m not putting my very amateur finger in the fire).

    @ Lurking and others who weren’t around here in the day:
    Re the earthquake swarms: at Eyjaf there was a marked periodicity in the onset and duration of the swarms (Peter is the man to ask here). What they didn’t show (at least to us) was a clear physical progression up through the crust.. well they did, but it was kind of obscured. What it generally looked like (to me) was that a surge of magma rose from depth (I think bolus was the term used by Peter) and charged up the pressure in the entire magma system resulting in a swarm of earthquakes more or less simultaneously at a range of different depths. Towards the end I thought I could discern a vague trend indicative of a pressure wave rising up through the system during each particular swarm, but it was pretty vague. What I’m saying is that you are unlikely to see the quakes happening only at the top of the system as it fingers its way through the crust. On the contrary, it’s more like a tree with branches sprouting out at all levels.

    Lurking you might have more luck to identify such a progression this time through with your mapping skills. For sure, over time the swarms slowly got more top heavy as the magma rose to the surface and I think most of us knew that an eruption was imminent in the last few days/hours which was pretty exciting to say the least.

  41. My question here: since no one is really sure if there is an eruption or even a larger quake coming up, are there any precautions being taken?
    I mean, a plan or something?
    Even though it could be just some “oozing” magma, or merely an intense swarm, I fear that in such a populated area a larger event could damage roads and other structures.

    1. I was wondering about that too, since this area is also highly popular among hikers, and there is a geothermal feature nearby.

      1. In one of the reports listed by Jón, I think I read a remote note about it, but I was too sleepy to remember.

      2. Hehe well get your rest because this might go on for some time and you gotta be awake when (if) the fireworks start!

    1. This would be because of the swarm I think. But this looks interesting anyway. I wonder what is up. But I am no expert in reading straimeters far from it.

  43. Bruce
    I been lurking too…
    Would be happier about a bolus (diapir more correctly) if we saw EQs extending up from the crust-mantle boundary at 20km ( yes, agree that’s shallow). Unlike Eyjaf we’ve not seen those here. But maybe some time in the past- years/decades? Is there historical depth data thats easy to access manually
    Peter

    1. I think that if that has been the case, it happened in the future already. With Eyjaf the earthquake depth was also between 10km and 0km.

    3. Peter. Good point though I have my doubts about the 2o km figure. This is no doubt the rough thickness of the crust east and west of the ridge but right on the mid-ocean ridge I think we might be looking at a completely different scenario. I wouldn’t be surprised if locally the crust was indeed only 7km thick in such a setting. In fact crustal thickness might have very little relevance when you are sitting astride a spreading center like this.
      Let’s wait and see if the experts think this is magmatic or simply tectonic (another distinction that probably gets kind of vague around a spreading center as magma movement and tectonic shifts are so closely intertwined). The sheer frequency makes me suspect that magma is on the move, but then what do I know.

      1. The tectonic/volcanic question remains yes. I’ve been looking at historical tectonical earthquake swarms of this magnitude. And what I’ve noticed is that in most of these cases you either have a sudden mainshock and lot’s of aftershocks, or a build-up to a climax in which the largest shocks occur, and a bunch of weaker aftershocks. In this case the larger and smaller earthquakes are all scrambled and there is no pattern.

      2. the tectonics of a spreading center are indeed kind of interesting. I guess you’d normally expect a graben to form with slip faults on its boundaries as the lid of the graben slowly sinks down as a result of extension. In this case you probably would get a main shock / aftershock sequence happening (though I haven’t really seen this pattern much in the Taupo Volcanic Zone – the only place where I do follow the seismographs, and also frequented by eq swarms.)
        But what happens in the case of an intrusion? Does this create compression quakes in an extensional setting? hmm.. Does anyone have access to the beachballs for these events? Would be kind of interesting to see what’s going on.

      3. No… I can’t even find a station that I can scarf traces out of. IRIS isn’t very helpful in locating stations unless you know what network the thing in a member of.

        I know that there is one station in the network up in Reykjavik but I can’t remember it’s ID to save my arse. Sure, it’s almost 30 km away, but we should be able to dig up the spectrum for the quakes if they registered.

      1. Nice one! thumbs-up

        @ Jon, interesting how you say a lot of the other quakes are system-generated noise. This gif looks so similar to the swarms at Eyjafjallajökull. The sudden phase change and spread of quakes 10 to 20 km around the main focus… are these noise? It is notable that they are not followng any set fault line like you’d expect for a purely tectonic movement.

      4. @David
        Your gif: great way to follow events.
        How about a mega-gif going back to 1995- to sort out days when we should seek depth data?
        Peter

  45. Silly question perhaps, but is there ever pressure waves created below the earth’s crust from big earthquakes elsewhere in the world, which propergate as a wave round the earth under the crust taking several days then play havoc with places where the crust is particularly thin?

    1. That is probably not a realistic scenario. Wave do travel across the earth but they lose their strenght considerably. Ofcourse even small things could give the final push for fractures which are under a lot of stress, but this has not been proven and is called the ‘butterfly effect’.
      http://en.wikipedia.org/wiki/Butterfly_effect

      1. Thanks, and how about changes in the weight of water on the crust when abnormal tides occur? Can they have any influence?

      2. I don’t know, there are theories about influences on earthquakes and volcanoes from these kind of things but none of them have been proven I believe.

  46. The swarm seems to have calmed down a bit. But I’m being carefull with what I say because it could pick up any minute, but for now I’m off to bed. G’night!

  47. @ David L – Good graphic. I second the thumbs up.

    —

    Re: Waves.

    I’ve pondered this before. While there is a tidal effect on the Earth from the Sun/Moon, the relative strength is far to small to show up in any long term plot of the data. In other words, if its there, I can’t dig it out. Other possible sources are large events in other parts of the world setting up a wave. Unless it’s the scale of the Bandar Ace event, I doubt seriously if you would see anything. The only reason that I would entertain something of that level, is because it actually shrunk the planet enough to show up in the rotation. Given that, you now have the problem of how to get the energy/wave from one point to another. The athenosphere/mantle is an ultra thick mass that doesn’t flow very well… think warm tar. While it can exhibit a wave… it dampens out pretty fast and doesn’t propagate well. If my analogy is correct, I don’t think a wave is in the basket of “possible causes.”

    Since I have been fiddling with this stuff, I have done enough reading to know that one of the vexing problems of plate tectonics, is just how much push a flowing mantle can give to a plate that is merrily bobbing along on the surface. After buckets of coffee and bottles of aspirin, the answer is “we aren’t really sure.”

    “Slab Pull” has generally been accepted as the dominant mechanism in the operation of the mid ocean ridges, so the big question as to a cause should be on the other ends of the affected plates. Just remember that this is on geologic time scales.

    Okay.. back to the present.

    This is my most recent plot, still no indication of something moving around down there, be it magma or a wayward Graboid™

    http://i54.tinypic.com/35naipc.png

    And, going back to the trend plot from a day or so ago… before the swarm went into overdrive, if there is anything down there, and if the trend is tracking it, we should see some sort of manifestation around the 16th.

    http://i52.tinypic.com/i376th.png

    Again, all media caveats apply, “carpe canum” all that neat stuff.

      1. When I see these gaps, I think immediately in external forces like tides or other kinds of influence.
        Swarms come in waves, and they seem to spread along the whole rifting system, in a different scale.
        If we had a way to connect “slab pulling” to increase in rifting… I know, it happens in Geological scales, but swarms and eruptions don’t.
        That’s why I think your graph is so telling (black magic?).

    3. “we should see some sort of manifestation around the 16th.”

      Unless the rock type changes as the surface is approached, or the degree to which the rock is fractured changes, that is.

  48. It is a pity that we don’t have data from swarms occurring in the MAR (or other rifting areas) in detail, as we have from Iceland’s.
    I think they occur with a frequency greater than we think, but they only come to our knowledge when the earthquakes are above 4.5 magnitudes, as recently happened at the Aden gulf or at the Azores.
    It would be great to see a plot comparing Iceland to other rifting zones.
    And what do we know about effusive events in the MAR?
    Recently there were many submarine vents discovered in the Atlantic, but such places have no monitoring to see what caused them to happen.
    So, what is left to us, is wait and see.

  49. I’ve quickly done a rough trawl for Krisuvik EQs for every week since 1995, using data here:
    http://ijsland-enzo.nl/ijsland/actueel_aardbeving.asp
    Very few EQs – a handful – at Krisuvik were at depths of 8-10km. On 24-05-2009 ther was a 2mag at 15.7km, but “one swallow does not a…..”.
    On weeks with some activity EQs were around 7km or shallower.
    The most active weeks were:
    18-12-95
    26-04-98
    16-08-98
    11/18 and 25 -06-2000
    11/21 -07-2004
    24/31-05-2009
    04-07 to 08-08- 2010
    29-08-2010
    26-09-2010
    10-10-2010
    29-10-2010
    ( hover on map for depths)

    What jumps of the map is the linear EQ focus trending SW-NE 10-20km south of Krisuvik, presumably illuminating the spreading centre of MAR. Krisuvik is off-centre.
    So I dont see evidence for EQ activity progressing upwards with time: its not like Eyjaf.
    Someone else can do pre-1995 analysis, RSI setting in..

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