Carl le Strange:

This is the best article so far on the Banda Aceh quakes. So I decided to Reblog it.

Originally posted on lithics:

Earlier I posted an info bulletin about this morning’s Banda Aceh earthquake.  Rather than muddle it with more and more stuff, I thought it might be better to include this update as a separate post, as it is more of a discussion than a news piece in any case.

The truth is that this earthquake is properly strange.

The part of the Indian Ocean in which this earthquake occurred has two very different types of geologic structure very close to each other; there is the Ninetyeast ridge – a volcanically produced range,  and a destructive margin subducting the Indian plate eastwards under the Pacific margin. It is important to note (in the context of this earthquake at least) that the sea floor under the Ninetyeast ridge was originally produced by standard constructive margin seafloor spreading.

These two structures are shown quite nicely in this image taken from GeoMapApp, with…

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119 thoughts on “

  1. Great find, Carl (or I think it was Renato in the last thread, thanks both).
    Meanwhile, strainmeters in Hekla are showing another (external?) earthquake this morning:
    http://hraun.vedur.is/ja/hekla/thensla_burfell.html

    And another thing, today is my moving day, so after I leave this place later in the afternoon, I’ll be without proper internet access for a while (not sure how quickly I can get internet in my new place). So have fun and see you in a few days (I hope).

    • Ah just saw that I duplicated the comment above. :-)
      Blame it on general moving scatterbrainedness and lack of coffee (better go and make another cup right now)!

    • It was Renato who had fished it out from Eriks, where Sherine had posted it.
      To give it a precise legend :)

      Good luck with the moving, your new job and everything!
      See you soon!

  2. these EQ happenend around the Equator, with the axis changing and the bulge of the EQ changing, could the plates seperate? there are now 40 EQ between 10-30km dept, listed in two distinct lines, like a zip

    • The plates that are separating are always separating at quakes belonging to separation.
      The earths plates are always moving about. Nothing new or exceptional in that.

    • Isn’t Etna a bit to frisky now?
      It is not much more than a week between the paroxysms now… If this continues she will soon (a year or so) have pretty much continous eruptions.
      But I might be terribly wrong here.

  3. Thank you for the re-blog above.

    Read somewhere that geologists are puzzled about the fact that the strike-slip EQs were so large (i.e. greater than 8.0)? Is that because previously observed ones have been smaller? Or is it because of assumptions in the modelling for strike-slip faults?

  4. Geologically, culturally, or in general political area?
    1. Geologically it is not a part of the Scandian mountain, nor the scandian Sub-plate. We are actually being pushed to them, and slghtly upwards, each year.
    2. Culturally they belong to the Scandinavians, they just have a really different language. They are also Nordic, and part of the Baltics. Biggest difference being depressed, imbrabeable, and pretty much unbeatable. Oh, and the knifes ;) Actually Fins are awesome, but never tell ‘em.
    3. Politically they are Scandinavians. Actually they where one country up untill 1809 when we lost them our brothers due to a stupendously stupid King.

    • Culturally, the Finns are Finno-Ugrians and quite different from us Indo-Europeans. Their origin stretches back eastwards along the permafrost boundary to a point of origin east of Lake Baikal. Germanic, Slavonic and Latin peoples have far more in common with Indians than with Finns or Hungarians. :mrgreen:

      • The Finns of today have the same culture as we other Europeans. And a lot of the Slavonic and a lot of the Germans also have traces of Mongolean or other Asian blood. If you think about all the Mongolean and Tartaran raids into Middle Europe in the Middle Ages and so …
        A lot of German people today eg. have and had broad cheekbones and small eyes (and I don’t talk about people from recent immigrant origine here). I don’t understand why this should be an issue… :?

        • Issue? Sorry Inge, you’ve lost me. I haven’t got a clue to what you mean by issue here? :confused:

      • henrilerevenant says:

        “…Germanic, Slavonic and Latin peoples have far more in common with Indians than with Finns or Hungarians…”

        What kind of Indians? Indian Indians or American Indians?

        I am from the only family that I know of, that has had a full on feud with itself. It seems that one half of the family had a European Great Grandmother, the other half had a Choctaw Great Grandmother.

        They didn’t get along so well.

  5. While the “Strombolian explosion” reported during the night were not a paroxysm, one has started an hour or so ago as confirmed by both tremor and thermal imagery from the revitalised INGV site.

    • Sorry, lost a word or two – “seems to”. I should have said “one seems to have started an hour or so ago as confirmed by both tremor and thermal imagery from the revitalised INGV site.”

    • If you take a look at the tremor plot, you’ll see the peak from yesterday’s Indonesian eqs almost bang on 24 hours ahead of today’s apparent paroxysm. Coincidental? While I believe so it will be fun to hear expert opinion and speculation on the subject.

  6. Good day.
    The re-blog was very conformational, (Thanks for reposting it Dragon) on the idea that was bouncing around yesterday re: the peculiarity and the forces/vectors involved around the Ninetyeast ridge,
    ”Scientists do not agree on a direct relation in between earthquakes (even very powerful earthquakes) and volcano activity.” (Earthquake report/Armand Vervaeck)
    Yep, I understand, difficult to put money where mouth is on this one. No-one want’s to be a doom-monger, or in the position of being shot as the messenger. Interesting that El Hierro 26.10km 1.30mblg you mention KarenZ, reminds me of a deep cough, or rather a huhgmph if you get my idea.
    What is going on in the Gulf of California? 28.N -113.W
    2012-04-12 10:26:55.0 10 5.0 , 2012-04-12 08:54:48.0 30 4.5
    2012-04-12 07:57:32.8 10 4.2, 2012-04-12 07:15:48.0 10 6.9
    2012-04-12 07:06:01.0 10 6.0, 2012-04-12 06:48:38.0 10 4.6
    2012-04-09 21:37:09.0 15 4.2 ( http://www.emsc-csem.org/Earthquake/Map/zoom.php?key=84&typ=NAM#2 ) The 30 km at 08:54:48 stands out oddly.
    Sounds as if the planet was struck like a bell, for want of a better phrase, whilst Alaska had a round of applause from the sidelines. ! Keep safe all.

    • Interesting foot note: The ”2012/04/08 14:03:43.5 51.401 1.663 5 1.9 19KM EAST OF MARGATE (courtesy of BGS.ac.uk)” that was posted April 10, 2012 at 16:38 on ”Why the VEI… ?” has now been removed from BGS. Political correctness or just a ghost?

  7. Is the Ninety East Ridge really a former spreading center? I always thought it was the ‘tail’ of the Kerguelen hotspot. An extinct hotspot trail does not have any ‘inactive’ faults, which makes this theory pretty implausible.

  8. Thursday April 12 2012, 13:02:28 UTC 15 minutes ago Sicily, Italy 2.1 8.0 CSEM-EMSC Feed Detail
    Thursday April 12 2012, 12:57:10 UTC 21 minutes ago Sicily, Italy 2.9 5.0 CSEM-EMSC Feed

  9. Does anyone have a link to a decent, accurate map of plate tectonics? It seems all the ones I’m finding are inconsistent with each other.

  10. I don’t recall how large the set was that originally got me tracking “stress waves” up the Gulf of California. M 6.2 isn’t an itty bitty quake.

    If I was correct in my line of reasoning then… there should be another bit of activity within a month or so, about 150 to 250 km further to the north along that system. It would keep doing this until it gets to the area of Yuha-Wells… then whatever happens, happens. At that point it turns into a gravel pit and you can’t really state what it’s going to do. The area is well fractured and many possible ways to dissipate/absorb the energy.

  11. Question to all you seasoned/regular Etna watchers: is it my imagination or is this paroxysm XXL size?

      • There are some very rapid “flows” coming down the flank – I hesitate to call them pyroclastic. Could be lahar? Very white (steam) and certainly not lava (it doesn’t flow that quick)

        • Without exaggerating too much… That “flow” dropped half the height of the summit in something less than 4 mins

        • There was snow on the slopes below the new SE crater. What you see is lava spatter/flows reaching and melting that snow, turning it to steam. No sign of either pyroclastic flows or lahars (which I doubt occur at Etna).

      • VAAC Toulouse has it but no forcast maps yet issued. Seems rather large to me,
        INFO SOURCE: INGV CATANIA, WEBCAM
        AVIATION COLOUR CODE: NIL
        ERUPTION DETAILS: SIGNIFICANT ASH CLOUD OBSERVED AT 1053Z
        OBS VA DTG: 20120412/1053Z
        OBS VA CLD: ASH NOT IDENTIFIABLE FM SATELLITE DATA.
        WINDS SFC/FL100 W 25KT.
        Last sentance is winds at Flight Level 100 (10,000 ft “standard at 1013 Hp / ISA”) are from West at 25 knots (12 m/s)

    • I think Boris is going to hate taking that well earned vacation.
      It is the largest I have ever seen.

      • He should have left his camera set up so his daughter Ida could have taken some photos.

        • Hey, it is Boris daughter, I bet she is photographing, if she is not with daddy in Germany.

    • Saw some big ones sometime around 2000-2002 (I forget exactly when but I remember coming home from either my GCSE or A Level exams and going straight on the computer to watch them)…… and I think this one might be bigger. Impressive.

  12. Hell, am I looking at Etnatubo here or what.
    when did Etna last cough up a 5 km ash column?
    Wonder if this will be the first paroxysm that get a DIE-number attached to it.
    Judging from column height and an estimate of 100 tons per second of ash it should be a DIE-2.

      • Once SHE blows, Mt Etna’s best like today’s are going to seem no more than a polite cough.

      • All I saw was snow being melted and turned into steam, Carl. There were three “plumes” counting from the top: 1) Eruption column, dark grey, 2) weak plume over lava flow, brownish grey, and 3) strong water vapour plume, white.

        • Yepp I know, and I have pic of 1 faltering and running downhill. There is also some melting done there, and that gave white steam, but you can see the difference.

          • I should clarify here, there was a lavaflow exactly as Henrik says, it is just that when the ash column failed it took the same road down.

  13. And there it was over by the looks of it, the entire shebang stoped and the ash column droped down.

  14. Take a look at cam 2 (Etna Guide/Etna Trekking) and tell me what you see please.

  15. Etna Trek 2 Looks like wisp of steam or smoke venting from the lower right side of the slope and drifting across and up?

  16. Henri, Carl,
    Both pyroclastic and lava flows. And also a lahars generated by both. Boris has explained that in other occasions. And huge phoenix clouds from the PFs!

    • Andy, I like it! It sounds as though Boris is moving away from earlier comments about PF flows forming during these events. Though Etna has had true PFs in the past during other eruptive phases. I remember asking him precisely this question some years ago.

  17. Boris comment:
    “Boris Behncke That’s the thing we used to call “pyroclastic flows” lately, although we are beginning to understand they are not typical pyroclastic flows (that is, dry and hot) – these are very wet and less hot (though presumably still deadly) and probably at their base they are rather lahars (mudflows). These phenomena have never been accurately described in the scientific literature until 2011, and seem to be pretty common during high-rate lava effusion from snow- or glacier-covered basaltic or basaltic-andesitic volcanoes (e.g., Llaima, Kliuchevskoi …)”

    • OK, I claim copyright on “pyrohydroclastic flow” ;-)

      Good stuff Etna – first time I’ve caught a start-to-finish live. I’m impressed!

    • I say “pyro-avalance” (Blend of heavy-ash-laden-gases, hitting snow, turning it into steam, the added water content makes it more fluid and increasing downhill speed, when water dries out it settles as ash-sholes.) ????

  18. New post with the failing ash column. I guess it is what Boris commented on. A heated ash column with a lot of steam in it that can not sustain its wait as it crashes down.

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