Posted on by Jón Frímann

Quiet time continues in Iceland

The quiet times that have been ongoing in Iceland for the past few weeks continue. It has been been my experience over the past few years that when this type of long quiet happens. Usually there is a medium to large event that follows it. Sometimes it is volcanic. But in most cases it is a medium (Mb5.0+) sized earthquake that follows it.

But while the quiet time continues I am going to write a short story and publish it on Amazon as a e-book. More on that when I set-up a special blog about my story publishing.

44 Replies to “Quiet time continues in Iceland”

      1. First of all, I really like your site.
        I am curious.
        Are there really any connections between long quiet times and a sudden “big” event happening afterwards that we can explain with scientific explanations ? I mean, is there a bigger probability of an lets say Mb4.0+ happening rather then not if there have been alot of medium quakes?

      2. @Jón also, this is rather obvious. It’s either quiet or there is something going on. So silence can only be broken by sound huh. 😀

      3. Some quiet times just end with a increase in earthquake swarms. But the quiet time ending with a a lot of earthquake activity is also common.

        The time frame in this is unpredictable far as I can tell.

  4. Mainly because I can… An FFT of the data from my last plot. An FFT (Fast Fourier Transform) is handy for looking for time sensitive characteristics in your data. If you do a plot combining a lot of frequencies all mixed together, an FFT will let you dig those frequencies out of the rather messy waveform.

    From this it seems as if there is not a very a time dependant characteristic to Icelandic quakes. Something like an effect from the tides or the moon would stick out like a sore thumb. Mostly, it’s a pretty gentle curve with some minor bumps in power at various intervals.

    I’m not overly proficient at reading these things, but there are people who visit here that are… well, most likely they are.

    For one, I have no idea what that deep null at the one day mark is. It could be an artifact of when the seismo network gets turned on or off… (either now or at some time in the past), or it could be a manifestation of quake events occurring in groups of less than a day. Dunno.

    http://i55.tinypic.com/2z4e8lz.png

    1. LurkDood, one day, can you schedule a GoTo Meeting inservice for all of us on how to do these plots. Seriously, that would be fascinating. Hell, you could even charge for it 🙂 I’m in.

      Now, onto more exciting news. CA/NV is hoppin. Something is definately brewing near Hawthorne, NV. There was even an article on Drudge. Also, 3 tandem 3.0’s on the San Jacinto Fault, and of course, the LSF is like a hornets nest. Is all of this going to pass into obscuritiy, probably, but watching beats having to watch what my wife forces me to watch. Baking with Stars or is it Dancing with the Stars and Bakers from Hell…i dunno.

      2. Turns out my brother knows one of the authors of the article on the Walker Lane PDF and is going to get this thoughts on it and report back. I’ll circle back here and let you know. Today was a very active day over there with numerous quakes over 3.0 all centralized like your plot shows.

      3. As for the plots, mostly its due to a career in rummaging through data. This led to becoming a bit proficient in using Excel. Then, when Excels graphs would no longer do, switching over to a dedicated graphing program that has quite a large number of features and algorithms that you can squeeze the data through.

        The “knack” part of it is remembering enough Analytic Geometry and Calculus to make sense of it. The stats stuff is a learn as I go thing.

        About the FFT. When I run the FFT on the day count, it complains about the spacing of the data. In order to get a data set that it can digest, I run an “equal interval” function and use the linear interpolation set for 0.25 days. I feel that this gives me enough resolution for what I’m doing. After the FFT run, I switch to a LogX LogY graph in order to find the curve (sometimes it gets stuck out in never never land). At that point, the X-axis is in “hertz” mode.. or “cycles per an interval.” I then add a really small value to all of the Xs. In this case 0.00000000000001. Thats so that the program doesn’t crash due to dividing by zero. Then I run 1/x on all of the X values. This puts it back into a mode that gives me the output in days per cycle.

        The rest of it is just recognizing where the peaks are at. In my case, having 30+ years in electronics (20 of it in dealing with RF circuits), I am quite familiar with modulation envelopes, beat frequencies and frequency domain based data.

        The overall shape is Gaussian noise, you just look for where the noise peaks and how well defined (or not) they are.

        Okay.. the obligatory example. Be careful, my lack of knowledge and skill may show through.

        This is a waveform.

        http://i52.tinypic.com/rkzy80.png

        It’s not any particular waveform, other than some number sequences that I was able to generate in Excel plus some noise from random numbers.

        There are three sine waves that were added together, along with the noise. It’s visually apparent that there is some periodicity to the waveform.

        Lets look at the FFT for it.

        http://i55.tinypic.com/w7ju5h.png

        I have labeled the predominate peaks, and cheated a bit by labeling a knuckle that I know is important.

        From the FFT, you can see that 4.95, 7.78, 9.90, 14.85, and 24.74 are important spectral peaks that warrant being looked at.

        Now… what frequencies did I use?

        5, 8, 10 and two random numbers.

        Five stands out pretty clearly as the 4.95 peak, Eight is less so, almost being totally obscured. (it’s the knuckle I was talking about). Ten, being a multiple of Five stands out just as strongly at 9.90. In this case, 5 is a base frequency.

        So where did 14.85 come from and why does it stick out? 5 + 10 = 15. The same thing with 24.74. 5+8+10 =23.

        Other peaks that you could look for in this graph are 3 (8-5), 2 (10-8), 18 (10+8), 13 (8+5) etc…

        And that’s not going into the combinations of the different combinations.

        Essentially, it’s a manifestation of the hetrodyne effect. (sum the difference and the two originals) In a real world environment this is the source of most radio noise and spurious signals. Just be aware that as you continue this pattern through the various combinations, the power level starts to drop off.

        And that is essentially what an FFT gives you… a spectral plot of the “energy” in the combined waveform.

        On the Iceland FFT quake plot, you see that Gaussian noise signal. In my example plot you don’t see that. It’s just a couple of random number functions that sort of approximates white noise. It’s responsible for those peaks not exactly matching the entered frequencies.

        What else can you do with an FFT? Well, ran against a seismic waveform, you can see where most of the power of the quake was at. You see something like this in the tremor signals, but they use filtering to extract the different components of an almost continual signal.

        Dunno if this helps… or confuses. I’m not an “engineer,” I’m a “technician.” So, I have a technician’s understanding of things. Not to knock engineers, but their focus is usually on design and how it works (or used to work). A technician’s focus is on making the thing work… no matter what.

      4. Note… the “technician’s focus” has been known to blow stuff up.. which is why basic fire fighting knowledge is handy.

      6. No.. not at all.

        You just have to achieve a Zenlike state and become one with your inner geek.

      7. Back on that geek thing and the chastisement from Jack (deserved, I should have noted that).

        Here is geek for you. I spent about 5 hours rummaging around under my upper intake manifold fiddling around with the #6 fuel injector, realized that Def Leppard was on the radio and noted how 30+ years hadn’t changed much. The only difference was that I wasn’t 19 any more. Now, 2 shots of Jim Beam and three beers later, my %#@$% taxes are done.

        I need an eruption. Bad. I have to plot something.

      8. Things might seem like they haven’t changed much, but due to the insidious nature of change, we don’t grasp the scope of the evolution, just what our conscious filter perceives.

        As far as change goes, I see huge changes in the world and no one can dispute this. I fear we are headed again into a very bad storm and the end of this year and a little beyond will definately cause people to take notice of the change. Just my opinion.

    2. Well, Lurking…

      Your original plot was “quakes per day”, so the sampling frequency (using an analogy from CD audio) is once a day. When you do an FFT on that, anything seen below 2 days (the Nyqvist frequency!) is just artefacts of data processing. You just can’t talk anything about happenings at noon, if you take the sample always at midnight!

      So, what’s left is very likely a power distribution (which is very common in nature). Plot it again in frequency scale, so you’ll see what I mean.

      1. I appreciate that.

        I was pretty sure that it was some sort of artifact… it stuck out there far too prominently.

  5. Seems like the earthquake activity in Krysuvik area is picking up again a little.. Quakes are at the usual depth of 5km..

    Sander

  6. Jon, Good luck with the short story.

    I would strongly recommend that you consider writing a book that is essentially a tourist guide aimed at visitors to Iceland who have only a little knowledge of volcanoes or volcanism, to inform and guide them when viewing the volcanoes of iceland; their is lots of scope to write something interesting and informative that ties up their history and prognosis with icelandic history and folklore, which could it make it entertaining and informative. Such a book could then be sold both here on the blog, and via ebook directories… if would fund you better! Its also what you know, and know well.

    1. Thanks. But I think that I am no good at writing tourist books. Plus, pictures for those books would cost me a lot of money.

      There is also a great deal of books far better then I can write in this field. Here is one of them.

  7. I have been checking the tremors on the Island Met Office page almost daily for a year now. Lately quite some look really odd. http://hraun.vedur.is/ja/oroi/allarsort.html
    Can someone explain to me whats going on?.
    Some of the hm odd looking tremors are:
    Aska
    Flatley
    Godabunga
    Grimmsfjall
    Grindavik
    Krokotovotn
    Nylenda
    Reykajanes
    ski and skr
    Vatnfjell
    and Westmanaeyar

    I am not saying something is going on, i am just saying all those graphs look different to what they did a month ago.

  8. The blue line tremor is relates to weather disturbance. Since the weather is often windy and stormy in Iceland, as I can personally experience, those disturbances happen when bad weather occurs. Its also in places where the winds are stronger in Iceland, such as near sea (Westman Islands, Flatey, Reykjanes) and glacier places. That’s my opinion only.

  11. One quake pretty close to Hekla, which is also visible on Jóns Helicorder.
    17.04.2011 19:28:56 64.008 -19.900 10.8 km 1.3 90.01 11.3 km SSW of Búrfellsstöð
    Jón: Is this magmatic or tectonic?

    1. This earthquake was tectonic in nature. But it happened inside Hekla volcano. So what is too be expected is a big question.

      I forgot to press the send button earlier on what I did write about this earthquake. Darn it.

  12. A earthquake with the size of ML1.3 with the depth of 10.8 km. This earthquake took place at 19:28 UTC and was inside the Hekla volcano. But at the edge of the defined volcano system.

    I find this earthquake quite interesting.

  13. Why would this earthquake be any different from all the others that occur at near this faulting system that belongs to the SISZ?

      2. This is on the edge of the SISZ, but just outside it. But it appears that this earthquake is just barely inside Hekla volcano system.

        But you can expect the fault systems in this are to be aligned with SISZ, even if they actually belongs to Hekla volcano.

  15. There appears to be a small increase in earthquakes in the volcano named Kverkfjöll. The number of earthquakes have been increasing in that volcano over the past five years or so.

    1. Seems like all volcano systems under Vatnajokull had their earthquake in the past 24 hours 😛 Except Esjufoll

      Sander

  16. What is the large low-frequency spike that appears on a lot of tremor charts?

      1. I highly doubt that the M5.1 could have caused this, so I’ll go with the Kermadec one. Amazing that even an earthquake at exact the opposite of the world can cause this spike.

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