6 comments on “Kunlun Volcanic Group, China

  1. Hi

    Here is an exploratory plot for Mayotte earthquake sequence (sorry a little late as I had some issues with Python).

    You can see the quakes from May to November from the Catalog recently released by the BRGM (thanks guys and gals by the way !).

    The color of the dots go from blue (older) to red (younger)

    https://doi.org/10.18144/372c5809-3d30-440c-b44a-1c89385f176a

    There seems to be 3 clusters and 2 different depths. Of course the precision is low as there is limited instrumentation on site for the time being.

    I’ll redo something more elaborate later.

    Thanks Agimarc for this new and unknown to me volcanic field ! Another discovery

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    • Thanks a lot dfm, I thought you would come up with this as soon as you were ready 🙂

      I wonder why they have no more different depths. The 20 km in July seem to be (halfways) real, since ESCM has some of those as well. Additionally, ESCM have quite a few of different depths, some at 2 km, 14-16 and 30 km. Well, perhaps those are also not very accurate. ESCM have also 5 new quakes in December, between M4 and M5, while the BRGM catalog is not being updated.

      What I don’t quite understand is why it seems such a big problem to get several more seismic sensors installed very quickly. The thing has been going on for eight months now, and it seems to be an important case – for the residents of Mayotte as well as for French scientific research. It is not as if France is a poor country, they would have the means of putting a lot of new equipment where it is needed. But they still speak of limited instrumentation and being unable to determine smaller quakes. What do you think?

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      • Ah, I just saw that BRGM posted a table of December quakes in their situation updates of 18/12 and one quake on 29/12. Still without depths, though, and only >M4 😦

        And, they DO have the smaller EQs as well, they just don’t publish them:

        “The last fortnight was very active and stronger than the previous fortnight with 99 earthquakes of magnitude greater than 3.5 averaging 5 per day. 8 earthquakes have a magnitude greater than 4.0, of which 1 detected by the USGS, but we also count 23 earthquakes with a magnitude slightly lower than this threshold (around 3.8-3.9).
        [table of 8 EQs]
        For the event of December 6, 2018, it is actually 2 equivalent earthquakes, 7-8 seconds apart. Low magnitude activity (<3.5) is important with several earthquakes per hour. 228 earthquakes were located over the period. If the localization becomes rather difficult because of the density and the mixture of the phases, it is always the zone towards 35-40 km of distance of Mamoudzou which is the most active.
        Note the change in the typology of some earthquakes (low Frequency with S waves difficult to point and longer durations)."

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        • Yes you are right on many points. I have also wondered why it took so long for the french scientists :
          1 – to get there (no guys from france for several months)
          2- to install some instrumentation (there is a raspishake added I think)

          My analysis is :
          – there was probably some guy responsible (geologically speaking) on the island. Getting there is not cheap and all the agencies have budget restrictions, even if France is not poor ( but did you see the yellow vests movement? All is not going well at the moment)
          – Mayotte – it’s complicated- it is the youngest french department (only for a few years). It is also by far the poorest, even compared to the overseas (Réunion + West indies). The immigration from the Comores is a big problem (but an old story)
          – the quakes have not posed too many problems at first, then some were felt by the population (some panic, some people sleeping outdoors) and that changed the authorities perspective.
          – there was no immediate danger (and maybe the authorities did not want to draw attention on the quakes fearing stress in the population)

          As for the catalog it is the FIRST time something has been made public. You have to know that the earthquake/volcano guys at first were from the CEA (Commissary to Atomic energy – like Tazieff) – probably linked to the nuclear test detection. They probably have kept some reflexive secrecy.

          I’ll dig a bit around the USGS data, but their instruments are far away so precision is bad. French data gives only 2 standard depths 10 and 20km.

          Cheers

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  2. Hi

    Here is a new version of the visualization of the BRGM earthquake catalog data.

    3D timelaspe of Mayotte earthquake sequence from May to November 2018.
    Mayotte island is on the left.
    First view is from the top, then from the east and finally a 360 rotation of all events
    The first 2 parts are an event by event sequence, the latest event being a bigger red dot.
    Event color changes according to its rank in the list with blue event being older and red events being younger.
    Dot size is proportionnal to event magnitude.
    The date and magnitude of the event is in the title bar
    Bathymetry data from NOAA and SHOM Projet Homonim-http://dx.doi.org/10.17183MNT_MAY100m_HOMONIM_WGS84″

    Sismo data from BRGM
    Bertil D., Roullé A., Lemoine A.,Colombain A; Maisonhaute E., Dectot G. (2018) MAYEQSwarm2018:
    BRGM earthquake catalogue for the Earthquake Swarm located East of Mayotte
    May-November 2018. http://ressource.brgm.fr/data/data/372c5809-3d30-440c-b44a-1c89385f176a
    Done with python 3.7 – Ubuntu 18.04

    There are clearly 3 different clusters with 2 different depths. The latest cluster seems to get nearer the island.

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  3. Hi

    I redid the plots with BRGM data (with a small pause at the end of each sequence) and I added the same plot but with USGS data (this goes up to January 2019).

    On the USGS data plot you see that there are different depths than on the one using French BRGM data. However it is probably due to a lesser precision.

    I have alos used some better bathymetric data from SHOM (french agency, bathymetry)

    plot with BRGM Data

    plot with USGS Data

    Timelapse (event by event) of Mayotte earthquake activity since May 2108
    Dot size is proportional to event magnitude.
    Dot color is according to time, blue oldest and red youngest.
    Current event displayed is a bigger red dot.
    In the title bar you find the day of the event and the magnitude 3D view of Mayotte earthquakes’ location vs time First view is a top, second view is from the the south and finally there is a 360° rotation.
    Mayotte island is on the left.
    Topographic and bathymetric data from SHOM and NOAA Sismo data from USGS or BRGM.
    Made with Python on Ubuntu 18.04

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