Posted on by Jón Frímann

A minor earthquake swarm in Krýsuvík volcano

At 20:41 UTC (28. March 2011) a minor earthquake swarm did start in Krýsuvík volcano. This earthquake swarm is small and no earthquake has gone over the size ML2.0. All the earthquakes recorded so far have rather poor quality in the SIL system and therefore it is not possible to say for sure what the the depth of this earthquakes is. But the assumed depth of the earthquakes in this earthquake swarm is around 5 km.

It remains to be seen if this earthquake swarm grows larger or not. But so far it remains small in both number of earthquakes and size.

21 Replies to “A minor earthquake swarm in Krýsuvík volcano”

  1. There is also a very minor swarm at Grimsvotn. Hmm….

    Before the last eruption in 2004, there was also a minor swarm, in the 2 weeks before.

  2. And another minor quake 20km SW of Hekla. That area, that nearly had no earthquakes in 2010, now had 5 quakes just in the last month.

    Hekla, Grimsvotn, Katla. Who wants to bet which volcano goes first?

    1. Please, the earhtquakes west of Hekla are NOT related to the volcano at ALL.

    2. Hekla is very likely, NOT going to give you a warning.

      It’s not a conventional volcano… at least in my opinion.

      This is a plot of the earthquakes that were going on in timeframe of it’s last eruption. Note the circled quakes. Those are the ones associated with the Hekla eruption. The rest of them are associated with the cracks and faulting in the area… notice how many of them have a lean to the left aspect, falling along the prevailing fault structures. (the plot view is looking North)

      http://i52.tinypic.com/j17cd2.png

      Now, in that batch of circled quakes, here is a magnitude vs time… notice how much time elapsed from the start of quake activity, until it actually erupted. That’s about an hour and a half. Not only was it quick, but in all likely hood, if you were standing on top of Hekla at the time, you might have had 20 minutes warning from the time you noticed the quakes, until it broke the surface.

      http://i55.tinypic.com/30m5w7k.png

      As for Katla… it has made no indications, quake wise, that it is even thinking about erupting.

      Grimsvotn? Yeah, it’s ready, but no one knows how it’s going to do its thing. It’s like watching a gopher hole. You could sit there all day and nothing shows up.

  4. @Lurking,

    Is it possible to calculate the magnitude of an earthquake, if you know the spectrum, and crack length and/or depth?

    1. The Mo can be determined from the fault area and shear modulus, and from that you can get to a magnitude. Fault area is (natch) length x height. I don’t have a way of determining that, and I don’t have a good way of figuring out the shear modulus. The modulus is what hangs me up in replicating the Grímsvötn cumulative Mo plots for other areas. My versions, though close, are far enough off to keep me from posting them.

      The spectrum can be used in magnitude calculations, but that is outside my ability. I’ve seen it mentioned in some literature.

  5. I see lately on a regular basis light earthquakes left of Katla (look like it is in the neighbourhood of Fímmvörduhals). It’s only small, this time MW1.4 at 1.0 km depth.
    Does anyone has an idea on these quakes?

    Henk Weijerstrass

  6. Yes, I know that earthquakes to west of Hekla are part of the SISZ and not the volcano. I know that, but I can see several signs of an approaching eruption (while knowing that Hekla is particularly unpredictable, showing nearly no warning)

    Even if both Hekla and SISZ are unrelated, sometimes there seems to be a connection between Hekla and earthquakes at SISZ (before or after an eruption), as you can see at http://icelandgeology.net/?category_name=hekla. But this is not clear at all.

    Also in past months, we not only saw some earthquakes, like a 2.5 in December close to Hekla (see posts at link) as well as the streams coming from the volcano drying up (another possible sign, but not very well studied).

    Yet another sign are recent changes in nanostrain meters at Hella (which were observed 2 years before the 2000 eruption). But, as you all have said, Hekla generally gives no warning, she likes to surprise you.

    1. Well… somewhat. But most of that shown in the slides is karst topology in a sedimentary setting. A bit different than layers of tephra and magma.

  8. In reference to the recent tremor anomaly at Grimsvötn, this is what I read about the Gjàlp eruption in 1996:

    “The seismic swarm continued throughout 30 September, with increasing intensity. Hundreds of earthquakes were recorded each day, including over 10 events larger than M 3. The earthquakes were located in the N part of Bardarbunga and migrated towards Grímsvötn. They were accompanied by high-frequency (>3 Hz) continuous tremor of the same type as was frequently observed during intrusive activity within the Krafla volcanic system during 1975-84.”

    http://www.volcano.si.edu/world/volcano.cfm?vnum=1703-01=&volpage=var#bgvn_2109

    1. Nice.

      Anybody happen to know the equation for the resonant frequency of a rock or rock mass? I have an idea.

      1. It depends on the geometry. There is no “general equation for bulk rock”.

      2. Ehh.. figured as much.

        After posting the above I realized that there is no participating seismic station near Vatnajökull that I can get a waveform from. I was gonna squeeze it though a pretty tight bandpass filter to see what popped out.

    1. I wouldn’t describe this as a swarm, but the frequency of the earthquakes is increasing yes, which is very interesting.

  10. Grimsvotn does not generally gives much warning. Just some major earthquakes a few days before (1996) or some small swarm about 1-2 weeks before (1998 and 2004). But swarms also occur once in a while, without any eruption.

    Let’s see

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