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Earth of fire

Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #volcanic activity, #Sismologia

At Anak Krakatau, explosive activity resumed on July 16 marked by 3 eruption earthquakes with an amplitude of 42-50 mm and an earthquake duration of 27-35 seconds.

Anak Krakatau - 16.07.2022 / 22:56 - Sertung / PVMBG / Magma Indonesia webcam - one click to enlarge

Anak Krakatau - 16.07.2022 / 22:56 - Sertung / PVMBG / Magma Indonesia webcam - one click to enlarge

Anak Krakatau - 16.07.2022 / 11:40 p.m. - Sertung / PVMBG / Magma Indonesia webcam - one click to enlarge

Anak Krakatau - 16.07.2022 / 11:40 p.m. - Sertung / PVMBG / Magma Indonesia webcam - one click to enlarge

Anak Krakatau -16.07.2022 / 23:59 WIB- Sertung / PVMBG / Magma Indonesia webcam - one click to enlarge

Anak Krakatau -16.07.2022 / 23:59 WIB- Sertung / PVMBG / Magma Indonesia webcam - one click to enlarge

The PVMBG details two eruptive episodes:

- the first on July 16 at 10:55 p.m. WIB, accompanied by a plume observed at around 1,500 m. above the top; it was recorded on the seismogram with a maximum amplitude amplitude of 50 mm and a duration of 29 seconds.

- the second episode occurred at 23:39 WIB, accompanied by a black plume at 1,500 m. above the summit, drifting northeast. It was recorded on a seismograph with a maximum amplitude of 50 mm and a duration of 35 seconds.

 

The rest of the seismicity of July 16 is marked by :

- 6 blast/emission earthquakes, with an amplitude of 12 to 30 mm and an earthquake duration of 25 to 115 seconds.

- 7 low frequency earthquakes, with an amplitude of 5 to 28 mm and an earthquake duration of 5 to 12 seconds.
- 4 deep volcanic earthquakes, with an amplitude of 21-47 mm, S-P 1.6-3.4 seconds and an earthquake duration of 10-25 seconds.
- 4 periods of continuous tremor with an amplitude of 0.5 to 45 mm, dominating 5 mm.

Anak Krakatau - 17.07.2022 / 08:48 WIB- webcam Sertung / PVMBG / Magma Indonesia - one click to enlarge

Anak Krakatau - 17.07.2022 / 08:48 WIB- webcam Sertung / PVMBG / Magma Indonesia - one click to enlarge

This Sunday July 17, 2022 at 08:47 WIB, a new eruptive episode is observed, with a column of ash observed at ± 2000 m above the summit (± 2157 m above sea level). The column of ash is observed to be gray to black, with a thick intensity, drifting towards the south. This eruption was recorded on a seismograph with a maximum amplitude of 56 mm and a duration of 79 seconds.

The activity level remains at 3 / siaga, with recommendation:
Communities/visitors/tourists/climbers do not approach Mount Anak Krakatau or engage in activities within 5 km of the active crater.

 

Sources: PVMBG, Magma Indonesia

Reykjanes Peninsula / Fagradalsfjall - photo Adventurer of the third planet / 06.08.2021 - one click to enlarge

Reykjanes Peninsula / Fagradalsfjall - photo Adventurer of the third planet / 06.08.2021 - one click to enlarge

A new research paper on the Fagradalsfjall eruption has just been released on Earth and Planetary Science Letters: "Swarm seismicity illuminates stress transfer prior to the 2021 Fagradalsfjall eruption in Iceland". 2021 Fagradalsfjall eruption in Iceland)

The 2021 Fagradalsfjall pre-eruption seismicity study, in the Krýsuvík-Trölladyngja system, traces the processes leading to the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula, southwest Iceland.

Tectonics and seismicity of the Reykjanes Peninsula, with the locations of the 2021 double-difference earthquake swarms (orange dots) and the SIL network background seismicity from 2013 to 2021 (black dots). The green triangles designate the seismic stations of the Reykjanet network; red and black fault lines indicate postglacial volcanic eruptive and opening fissures, respectively; the yellow star is the ML 5.3 main shock; yellow lines show the extent of high temperature geothermal fields on the peninsula (Flóvenz et al., 2022) – Doc. see in source - one click to enlarge

Tectonics and seismicity of the Reykjanes Peninsula, with the locations of the 2021 double-difference earthquake swarms (orange dots) and the SIL network background seismicity from 2013 to 2021 (black dots). The green triangles designate the seismic stations of the Reykjanet network; red and black fault lines indicate postglacial volcanic eruptive and opening fissures, respectively; the yellow star is the ML 5.3 main shock; yellow lines show the extent of high temperature geothermal fields on the peninsula (Flóvenz et al., 2022) – Doc. see in source - one click to enlarge

The highlights of this study:
- The double-difference locations of pre-eruption seismicity at Fagradalsfjall 2021 indicate the activation of two main fault segments.
- The NE-SW seismicity not taken into account in the previous swarms is linked to the movements of magmatic dykes.
- The eruptive fissure coincides with a jump in the rift transformation zone, at the location of the weakening of the crust.
- The Coulomb stress reveals that the main shock is responsible for triggering the swarm and the ensuing eruption.

The full article is to be read following the link in source.

 

Source: Swarm seismicity illuminates stress transfer prior to the 2021 Fagradalsfjall eruption in Iceland, by T. Fischer, P. Hrubcová, A. Salama, J. Doubravová, T. Ágústsdóttir, E.Á. Gudnason, J. Horálek, G.P. Hersir,
Earth and Planetary Science Letters, Volume 594, 2022, 117685, ISSN 0012-821X,
https://doi.org/10.1016/j.epsl.2022.117685.

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