• A swarm of 85,000 earthquakes at the Ant

    From ScienceDaily@1:317/3 to All on Wed Apr 13 22:30:46 2022
    A swarm of 85,000 earthquakes at the Antarctic Orca submarine volcano
    In a remote area, a mix of geophysical methods identifies magma transfer
    below the seafloor as the cause

    Date:
    April 13, 2022
    Source:
    GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre
    Summary:
    Volcanoes can be found even off the coast of Antarctica. At the
    deep-sea volcano Orca, which has been inactive for a long time,
    a sequence of more than 85,000 earthquakes was registered in 2020,
    a swarm quake that reached proportions not previously observed
    for this region. The fact that such events can be studied and
    described in great detail even in such remote and therefore
    poorly instrumented areas is now shown by a new study. With the
    combined application of seismological, geodetic and remote sensing
    techniques, they were able to determine how the rapid transfer of
    magma from the Earth's mantle near the crust-mantle boundary to
    almost the surface led to the swarm quake.



    FULL STORY ========================================================================== Volcanoes can be found even off the coast of Antarctica. At the deep-sea volcano Orca, which has been inactive for a long time, a sequence of
    more than 85,000 earthquakes was registered in 2020, a swarm quake that
    reached proportions not previously observed for this region. The fact
    that such events can be studied and described in great detail even in
    such remote and therefore poorly instrumented areas is now shown by the
    study of an international team published in the journal "Communications
    Earth and Environment." Led by Simone Cesca from the German Research
    Centre for Geosciences (GFZ) Potsdam, researchers from Germany, Italy,
    Poland and the United States were involved.

    With the combined application of seismological, geodetic and remote
    sensing techniques, they were able to determine how the rapid transfer
    of magma from the Earth's mantle near the crust-mantle boundary to almost
    the surface led to the swarm quake.


    ==========================================================================
    The Orca volcano between the tip of South America and Antarctica Swarm
    quakes mainly occur in volcanically active regions. The movement of fluids
    in the Earth's crust is therefore suspected as the cause. Orca seamount
    is a large submarine shield volcano with a height of about 900 metres
    above the sea floor and a base diameter of about 11 kilometres. It is
    located in the Bransfield Strait, an ocean channel between the Antarctic Peninsula and the South Shetland Islands, southwest of the southern tip
    of Argentina.

    "In the past, seismicity in this region was moderate. However, in
    August 2020, an intense seismic swarm began there, with more than 85,000 earthquakes within half a year. It represents the largest seismic unrest
    ever recorded there," reports Simone Cesca, scientist in GFZ's Section
    2.1 Earthquake and Volcano Physics and lead author of the now published
    study. At the same time as the swarm, a lateral ground displacement of
    more than ten centimetres and a small uplift of about one centimetre
    was recorded on neighbouring King George Island.

    Challenges of research in a remote area Cesca studied these events with colleagues from the National Institute of Oceanography and Applied
    Geophysics -- OGS and the University of Bologna (Italy), the Polish
    Academy of Sciences, Leibniz University Hannover, the German Aerospace
    Centre (DLR) and the University of Potsdam. The challenge was that
    there are few conventional seismological instruments in the remote area,
    namely only two seismic and two GNSS stations (ground stations of the
    Global Navigation Satellite System which measure ground displacement). In
    order to reconstruct the chronology and development of the unrest and
    to determine its cause, the team therefore additionally analysed data
    from farther seismic stations and data from InSAR satellites, which use
    radar interferometry to measure ground displacements. An important step
    was the modelling of the events with a number of geophysical methods in
    order to interpret the data correctly.



    ========================================================================== Reconstructing the seismic events The researchers backdated the
    start of the unrest to 10 August 2020 and extend the original global
    seismic catalog, containing only 128 earthquakes, to more than 85,000
    events. The swarm peaked with two large earthquakes on 2 October (Mw
    5.9) and 6 November (Mw 6.0) 2020 before subsiding. By February 2021,
    seismic activity had decreased significantly.

    The scientists identify a magma intrusion, the migration of a larger
    volume of magma, as the main cause of the swarm quake, because seismic processes alone cannot explain the observed strong surface deformation
    on King George Island.

    The presence of a volumetric magma intrusion can be confirmed
    independently on the basis of geodetic data.

    Starting from its origin, seismicity first migrated upward and then
    laterally: deeper, clustered earthquakes are interpreted as the response
    to vertical magma propagation from a reservoir in the upper mantle or at
    the crust-mantle boundary, while shallower, crustal earthquakes extend
    NE-SW triggered on top of the laterally growing magma dike, which reaches
    a length of about 20 kilometres.

    The seismicity decreased abruptly by mid November, after about three
    months of sustained activity, in correspondence to the occurrence of
    the largest earthquakes of the series, with a magnitude Mw 6.0. The
    end of the swarm can be explained by the loss of pressure in the magma
    dike, accompanying the slip of a large fault, and could mark the timing
    of a seafloor eruption which, however, could not yet be confirmed by
    other data.

    By modeling GNSS and InSAR data, the scientists estimated that the volume
    of the Bransfield magmatic intrusion is in the range 0.26-0.56 km^3. That
    makes this episode also the largest magmatic unrest ever geophysically monitored in Antarctica.

    Simone Cesca continues: "Our study represents a new successful
    investigation of a seismo-volcanic unrest at a remote location on Earth,
    where the combined application of seismology, geodesy and remote sensing techniques are used to understand earthquake processes and magma transport
    in poorly instrumented areas. This is one of the few cases where we can
    use geophysical tools to observe intrusion of magma from the upper mantle
    or crust-mantle boundary into the shallow crust -- a rapid transfer of
    magma from the mantle to almost the surface that takes only a few days."

    ========================================================================== Story Source: Materials provided by GFZ_GeoForschungsZentrum_Potsdam,_Helmholtz_Centre. Note: Content may
    be edited for style and length.


    ========================================================================== Journal Reference:
    1. Simone Cesca, Monica Sugan, Łukasz Rudzinski, Sanaz Vajedian,
    Peter
    Niemz, Simon Plank, Gesa Petersen, Zhiguo Deng, Eleonora Rivalta,
    Alessandro Vuan, Milton Percy Plasencia Linares, Sebastian Heimann,
    Torsten Dahm. Massive earthquake swarm driven by magmatic intrusion
    at the Bransfield Strait, Antarctica. Communications Earth &
    Environment, 2022; 3 (1) DOI: 10.1038/s43247-022-00418-5 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220413104151.htm

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