Images of El Hierros magmatic system

Image: GeoLurking, rights reserved. Basic triangulation, how to find a spot or a station

First, my qualifications. None. I have been a fan of geophysical processes and phenomena for the last 35 years. More so if you count the time spent hanging out in the archeological part of the library.

Image: GeoLurking, rights reserved. Margin of error from one station within one standard deviation

When an earthquake occurs, the energy from that quake travels directly to the seismic station. Granted, there is more to it than that, and it actually takes a curved path through the earth depending on the density of the material (refraction), but for our purposes it’s a direct path.

When an earthquake appears in a seismic catalogue, you are given the latitude and longitude of the epicenter, and the depth. The addition of depth turns that position report into a hypocenter, because it locates the quake in three dimensions. In the more detailed phase portion of the reports, you can obtain the arrival times of the quakes. Take the difference in arrival times for each station with respect to the event time, and you have how long it took for the quake’s energy to reach the station. Knowing the distance from the station to the quake, and you can work out the speed of that seismic wave.

Image: GeoLurking, rights reserved. The P-wave

This presents a problem if you don’t realize what you are looking at. The distance from the station to the quake, is usually seen as surface distance if you use a map. This is not the actual path that the wave took. Remember, it takes a direct path. How do you find it?

Geologists, and geological organizations, think in terms of central angle when discussing seismic events. This is the angular distance as measured from the center of the earth that describes the arc length on the surface between two points. I’ve mentioned AK135 before, in it you can find the expected arrival times for the various phases based on our current model of the Earth’s structure. All of its data is listed by the central angle. It is used to assist in identifying what each individual squiggle in a seismic trace represents. (Based on the path that particular portion of the wave took)

Image: GeoLurking, rights reserved. The S-wave

For the simplistic technique employed here, AK135 and the more advanced concepts aren’t really needed… as long as we remember that this is a simplified approach, and prone to error.

Treating the orientation of the seismic station and the quake as being two points on a slice of a sphere, the problem reduces to being a series of calculations on a circle. You have the chord, which is point from the seismic station to a point equidistant from the quake on the other side of the quake. That chord will have a height which is the distance from it to the part directly below the epicenter. Calculate that and you can then find the parts of a right triangle when you determine the depth of the quake in relation to the midpoint of the chord. Find the hypotenuse and you have the direct patch distance to the quake. If your eyes have glassed over by now, don’t sweat it. It took me three days to get the spreadsheet formulas down. Sometimes you just have to get up and walk away for a while.

Image: GeoLurking, all rights reserved. P and S wave paths

Now that we have the direct path distance, we can calculate the actual P-wave and S-wave speeds. We can do something with that.

Before we do, I want to point out (yet again) that this IS NOT seismic tomography. That involves far more than our simple juggling of the geometry and data.

Image: GeoLurking, rights reserved. Preliminary image

P-waves are compression waves, much like sounds are a compression waves. The molecules move toward and away from the direction of travel. S-waves are transverse waves, they move side to side with respect to the direction of travel. The density of the medium that the waves travel through affects the speed of propagation, or how fast the waves moves. S-waves cannot travel through a pure liquid as S-waves.

When the rock density goes up, the difference in the speed betweed P and S waves grows smaller. With lower rock density, the speed difference grows larger.

Image: GeoLurking, rights reserved.

About the Plots

I’m not going to interpret what the plots mean. I’ll leave that to Carl and the others. But I will tell you what they are (it took me a few days to figure this one out). They are a plot of the speed field of quakes in a particular area. The quadratic surface interpolates the regions between the individual quakes, and shows you what a quake originating there should look like if one occurred there… based on the speed of the ones that did occur.

Like I said, it’s not tomography, but failing that, it’s about as good a representation of what is going down there that we can obtain as non geologists, based on available data.

Image: GeoLurking, rights reserved.

Since quakes occur over a period of time, these plots are a summary of what was observed over that period of time. In other words, they have very poor temporal resolution. Keep that in mind.

Other aspects of the plots show what would be expected from rising pockets of magma… compression of the overlying material, and a subsequent decrease in the speed difference of P and S waves.

Image: GeoLurking, rights reserved.

The unnerving part of these plots, and why I was apprehensive about releasing them, is that they dovetail well with anecdotal information about the dynamics in play.

Image: GeoLurking, rights reserved. The original image that started the discussion. Here we can see what might be a magma chamber, and the feeder tube that goes down into the deep. Location of the inferred magma chamber is below Tanganasoga volcano.

Again, my standard caveat: I am not a geologist and am not trained in that field. I could be very wrong in my methods. Take it with questioning view, which is sane way to look at it.


Afterword: Peer review

In science when you wish to publish something new, you send the paper in and then a review-board reads it through, and either it pass and becomes published (often after revisions), or not.

Since this is something that can affect a lot of peoples lives the author wanted the post checked. So, here is how the peer review was done.

First I picked a part the reasoning, and then I looked if I would get the same result. I also went through  the physics of it to see that it checked out.

Then the paper was sent to an engineer in the oil industry that works with tomography on a daily basis. And he found it to be correct.

After that I started to think about what other ways one could “see” what the author had found. So I deduced that the quakes that are smaller then 2M are just hiding the real action. So I tricked KarenZ and Ursula into plotting that, and guess what, the same structures showed up again. For those who follow the comments in here, those plots are there to be viewed.

I guess there are more ways we could have checked it, but in the end, I wished to publish this before the volcano became demented with old age.



490 thoughts on “Images of El Hierros magmatic system

  1. I allow myself getting on with the thinking about a phrase that would be ours and still quoted by future generations.
    When penguins walk across the yard,
    the winter will be very hard.

  2. Carl, the only way to learn to drive a car like that is from a racing driver on a track. There is so much power and handling that otherwise goes to waste….

    Me in an earlier life. I could get in, but I doubt that I could get out of the cockpit these days!

      • I never made F1 lol!

        Most of my cars end up with the odd crunch here and there. 😉

        Just Formula Ford, and just local for a short time (I live between Donington Park and Mallory Park tracks). I like to change my life on a regular basis. I’ve also been a coal miner, had a business repairing cameras (35mm mainly), been a climber, a sailor (maybe not much longer:( ) and had 2 divorces – so far! 😉

        • carl, no way – you wont do that. The throttle goes both ways.
          Once you’ve power-slid the tail out,briefly, once or twice on a track – in safety – you’ll know where the limits are. And you wont get up there on public roads – you dont come across as a hooligan on here.

        • Problem is that I do not really like cars… I bought the car because I wanted a swedish car, and Saab is dutch and Volvo chinese… So it kind of got out of hand. 😦

        • I have to confess to being a petrol head. Not a modern image – but old enthusiasms die hard. I had a project in mind to ‘dual fuel’ my old supercharged TR, then the E85 fuel was taken off sale. So much for DIY engineering for both power and economy…

  3. I can now reveal that I am the answer to British Stealth attacks. Here I am being trained last year. I am about to take control of the power base. A very large Kite. The metal buggy can slip under the enemies’ surveillance. Kites could be the answer to taking good photos of the centre of Bob’s Jacuzzie. I am not volunteering.
    PS Yes! my legs very rarely see the sun these days!

    • Cool! Never tried that….

      I’ve seen sailing video taken from from a camera attatched to a kite flown from the boat, might try that one day.

      • Rofl! Mr Pirelli eat yer heart out! How about we run a competition for the 2012 Volcano Cafe Calender? Any subject ,male, female,animal, vegetable or mineral as long as it is loosely connected to the subject of volcanoes. Only 2 rules
        1) The photo must be of or taken by the person submitting the photo.
        2) Anything goes!

        • I’m up for it! lol

          Rock included for possible volcanic qualification. The rock behind me was one I sat on earlier……

        • Kenpea,, You shouldn’t say things like that, coffee and Keyboards don’t mix well.
          A little tip, if you spit coffee on them turn upside down immediately. Usually works, although i am on my second keyboard this year.

    • Love it!!! Mind you it looks as though you are about to head out to sea on the wings of a strong easterly. Your presence here assures me this was not actually the case.

  4. Look at la Restinga webcam now. The middle one shows a lot of material floating on the sea but the lower one has just started showing what looks like a new jacuzzi, can anyone else see it?
    A white pastch to the left of the picture and close to the edge. Wasn’t there half an hour ago. Wonder if it is a new vent?

    • Was going to check, but I can’t, because it’s just happily buffering, buffering, buffering….
      If you see something cool, would you mind taking a screenshot and putting it up on tinypic, please?

  5. Under EU law any picture produced by any state or EU funded agency is common property. That also goes for all their data.

  6. What in the name of all Hork is this???

    SARMIENTO DE GAMBOA (The Ship) is a dredger built in 2006, 71 meters long and weighing 850 tons.
    If I combine that with Dianas new mound of dirt I get the horrible feeling that they have decided to try to fill in poor little Bob. Unlikely to succeed, and if the do succeed it would be to ask for a disaster… I hope I am dead wrong here.

  7. A very belated Great Plots to GeoLurking. Apologies for the delay, I have been getting my head round the maths (slow because it is a long time since I did maths) and trying it out on a few quakes myself. The maths I can now cope with, but manually extracting EQ phase data from IGN’s text files is not for the faint-hearted.

    GeoLurking deserves several medals for the effort he is putting in on this.

    @GeoLurking: on the very small sample of EQs I looked at, I noticed that a few for CHIE did not have arrival times for the P waves. Is this because the P wave data is lost in the harmonic tremor?

    • Now I see why the PS time difference was not plotted for each eq and displayed clour coded in a 3D swarm. Hence the use of the quadratic surface etc that I found so confusing?
      Manual extraction – could we all work together and do all the eqs as a ‘distributed processing’ project? Scoop IGN- with its own data!!

      • I thought about trying to do it electronically but the download time was taking too long, indicating that it might be using too much IGN server time. So I aborted the download as I did not want to be held responsible for slowing down IGN’s servers. Multiple users on the site would have a similar effect.

        So great idea but neither IGN nor the people on El Hierro would thank us if we stopped them from analysing critical EQ data.

        Unless of course Carl or Lurking have a better way of getting hold of the data?

  8. hey,
    I’m following this and jon’s blog a while, very informative!
    I saw a video on youtube which i found interesting.

    I know it has to do with steam and pressure but the actual fhysics behind it i don’t know.
    p.s the one who uploadded this video has also very spectacular videos about lavaflows,
    see the right side on the youtube movie (my fav is etna)

  9. If you go back to ER page (Armand) you will find a clickable link to the boat – a new oceanographic research vessel, 2004, crammed with all sorts of equipment. The dredger must be some other boat of the same name.

  10. Can anyone confirm if this is true?
    In heavy snow storms cattle put their noses into the wind and walk till they get to an obstruction they can shelter behind. Sheep on the other hand put their behinds to the wind and walk until they get to an obstruction where they get buried.

      • In Iceland in the winter time, it’s possible that sheep get buried in snowfilled ditches, this happens every year. They seem to seek out the shelter of ditches in the storm (not a lot of trees in Iceland), and when the snow comes, it can bury them.

        In the northwest of Iceland, near Hólmavík (Westfjords), there is a museum specialised in sheep breeding. On their webpage, they are talking about different kinds of danger for sheep (rollur in Icelandic – pron. rodler], among others that they would die in the snow (= fönn – Í óveðrum á haustin er alltaf hætta á að kindur fenni.).

        Could be an interesting excursion to go to this museum, it’s a beautiful region there, too.
        I know the museum well, when I went there first, some years ago, the explanations were just in Icelandic. Being a guide, I talked to the people there about it, that it would mean additionnel income to have also guests from foreign countries. They first thought, it would perhaps not be very interesting for them, but I insisted – it is, as we here know best.:) And last time I was there, they had also explanations in English.

        By the way, there is another interesting museum at Hólmavík, the museum of sorcery, because the inhabitants of the Westfjords esp. in the Middle Ages and till the 17th century were known for their witchcraft.

        • Anyone who has ever owned sheep must know that they have an inbuilt death wish! … and where one goes the others follow.

        • @ Woomf. That is why they have a sheep called a Jacob sheep. This sheep is used to lead the sheep that are to be killed into the slaughter house. The Jacob calmly walks in and the other sheep follow without panic. A sad fact but true.

  11. Bubbling now showing on the top screen of this site.
    I also saw what I thought was a sailing boat on the lower cam but it disappeared as I watched so I wonder if it was a spuot of water. Too hard to see at that distance and the middle close up cam is just constantly trying to connect.
    Really sorry bit I don’t know how to take a screen shot. Kids haven’t taught me that.

    • Hi Una Canaria, thanks for the link, my son has just come in and says a bit later he will show me how to do it and write it down for me. I am not very good at following written instructions and find it much easier when shown how to do it. I blame being older but I mustn’t let my brain seize up for lack of use. I need a lot of practice though so hope for lots more action on the cams.

    • Una,
      Presione ‘imp pant’. es la clave de 4 º de la parte superior derecha del teclado.
      entonces se puede pegar a una página en blanco de Word de Microsoft, si no tiene una programa del ‘paint’

      • translation (ish)

        press on ‘Print Screen’ it’s a button probably at the top right of your keyboard

        you can then paste that screenshot into a blank word document if you don’t have the ‘paint’ program

        the paint program lets you save it as a few different file formats – it you want the biggest file with the most info save it as whatever file name you pick.bmp, but thats usually not the best choice i’d suggest you pick filename.PNG as that stores the data more efficiently without trashing the image (which jpg sometimes does)

        incidentally if you’re more PC literate and want a decent free equivalent to photoshop I’d suggest getting as that seems to do prettymuch everything photoshop/illustrator does and it’s free

  12. Ref carbon fibre ship building.

    Not a new technology. Carbon fibre is one of the strongest yet flexible construction materials known to man.

    Wr used to call it “wood”.

  13. ok, first person to see a mermaid on the webcam wins a sheep.
    Scratch that.
    First person to see a sheep on the webcam wins a mermaid..
    that’s not right either, dang it..

    • Ursula… Even I think that 3500£ is a bit steep for a piece of software 😉
      Could you register us as a University so we get that Free Teaching Software price?

    • I know it’s pricey. 😦
      I just said this could probably what my voxler can’t…
      And unfortunately my university is not on the list (and we don’t actually have geology dept here, so no dice, sorry).

      • Where are the clever people when you need them ?

        ok well it appears to have started with a series of 12 bangs in 4 minutes, then been followed by 20+ bangs spaced out at regular 2 minute intervals

        they seem too regular to be anything natural but perhaps it’s a particular size chamber that fills in 2 minutes and empties – a bit like a geyser ?

        • Clever people? Where?

          Buut seriously, Sissel nailed it down below.
          “Drumbeats” are associated with increasing pressuge against plug in a volcano. Now I wish we knew where that plug is… It is a sign of an eruption coming closer.
          Could one of our clever Plotters Plot a Plot of the Plug?

        • Re: plotting: this started at about 16:20.
          Since then, IGN Hierro boletin lists three (only) earthquakes:
          1) 2011/11/29 16:19:23.24 27.6160 -18.0755 3.70 2.70 28 2.10 3.3 1.60 0 8 8 0.40 283.0 1115502 SW EL PINAR.IHI
          2) 2011/11/29 16:22:29.24 27.6536 -18.0758 4.60 3.10 8 3.80 3.3 1.40 0 8 8 0.29 255.0 1115503 SW EL PINAR.IHI
          3) 2011/11/29 17:16:15.46 27.7655 -18.0631 37.30 6.90 164 21.70 7.1 2.20 0 5 5 0.18 209.0 1115509 W FRONTERA.IHI

          So, nothing much to plot…
          Although since 1&2 are close apart, this is probably Bob (see location):

        • Bruce, it may not be the plug – it is just only three earthquake points published until now (so the only thing I can plot)…

      • Thanks to Sissel and you Carl I have learnt something else new today and when I can drag my son from computer games I will know how to publish a screen grab. Two things in one day! Overwhelming. 😉

    • Here is som information on “drumbeats” in Mount St. Helens:

      “The current eruption of Washington State’s Mount St. Helens, which began about two years ago, has been marked by a series of weak, shallow earthquakes, or “drumbeats,” that occur every couple of minutes, a new study says.

      The “slip/stick” motion of the rocky “plug” being pushed out of the volcano is causing those rhythmic quakes, according to scientists from the Cascades Volcano Observatory in Vancouver, Washington (Washington State map).”

    • It could be for this reason:to make a study of the earth’s crust, ship Sarmiento de Gamboa has to launch seismic waves that are reflected in the seismographs. Is this not the way to make a “scan” the crust of the Hierro?

  14. @ Geolurking
    A stonkingly good blog, sorry I;m a bit late reading here, however…!!

    Anyone fancy a ‘health and safety’ moment?


    • And not a safety rope to be seen. Argh, I fell out of bed the other night and nearly lost my nerve to ‘get back up there again’. 😉 This has made me scared to sleep now.

        • The French used to shout “Guardez l’eau” when emptying water into the street. The English used a corruption of it, Guardy Loo, when they emptied their chamber pots into the street. Wonder what these blokes shout when they need a toilet break. 😳

  15. just an outlandish idea. but if the two nests of seismic activity indicate two distinct locations of melt that hasn’t yet interconnected, then perhaps this drumming is a sign of them interconnecting… resonance patterns getting set up or something, at least this would tie in with the location of the last quake.

        • is the ship in motion – is the aircannon irregular in it’s function, are some of the quakes real ones mixing the signal or is this really volcanic – I think it needs a plot showing where they are centred and then someone to dig out that ship movement link – and see if they tally up.

        • No they are still there although fainter. I am afraid I don’t buy the ships sending out seismic waves theory unless someone can show me the ship is still in the area. I would still go for natural tremor rythme. But then I am just an old granny. 😉 I do still have an inquiring , if sceptic, mind though.

        • or perhaps it’s easier ? for someone to ask the ship if they are making rythmic pulses that are picked up on the seismographs

        • @Newby – Plaudits for the sceptical attitude 🙂

          currently I’m leaning away from the aircannon toward actual volcanic – as I think I can see it detected on other stations – and I’m guessing the ship would not be capable of generating such powerful bangs.

          but I’m not a volcanologist and I don’t know diddly squat about it 🙂

  16. Looks like a volcano sized version of “water hammer” that you get when there is air trapped in your water system at home.
    Gas in the system?

    I know more about home water systems than volcanos….. 😉

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