MSGID: 1:317/3 63d4a4f1   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Looking back at the Tonga eruption    
      
     Date:   
         January 27, 2023   
     Source:   
         Hokkaido University   
     Summary:   
         A 'back-projection' technique reveals new details of the volcanic   
         eruption in Tonga that literally shook the world.   
      
      
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   FULL STORY   
   ==========================================================================   
   A new analysis of seismic data recorded after the massively violent   
   eruption of the underwater volcano Hunga Tonga-Hunga Ha'apai, on January   
   15, 2022, has revealed new and useful information on the sequence of   
   events. Kotaro Tarumi and Kazunori Yoshizawa at Hokkaido University   
   discuss their methods and findings in an article in Earth and Planetary   
   Science Letters.   
      
      
   ==========================================================================   
   "We showed that the eruption consisted of two distinct sequences   
   of events, some of which occurred quasi-periodically in the first   
   sequence. It will be worthwhile to investigate the mechanisms involved   
   in such eruption cycles further," says seismologist and geophysicist   
   Yoshizawa.   
      
   The volcano generated seismic, tsunami and atmospheric waves that were   
   recorded worldwide. Recent studies have estimated that it was one of   
   the most energetic eruptions recorded by modern instruments.   
      
   "Eruption episodes are difficult to analyse fully from seismic surface   
   waves, but we have teased out more details using what are called   
   teleseismic-P waves," says PhD student Tarumi. These are seismic waves   
   that have travelled through the planet to locations distant from the   
   eruption site. In this case, the team used seismic data collected from   
   sites as far as at a 93-degree angle around the circumference of the   
   planet.   
      
   The team's "back-projection" analysis successfully detected the locations   
   and timing of multiple explosions, even though P-waves from each eruption   
   overlapped and were masked by other seismic signals and noises.   
      
   The back-projection technique reverses the transmission of seismic   
   signals to reveal details of a potential source that radiated seismic   
   waves. It was originally developed and applied for imaging the source   
   processes of large earthquakes, but is now proving equally applicable   
   to large scale volcanic events.   
      
   The results revealed that the sequence of eruptions occurred in two   
   main parts.   
      
   The first sequence began at 04:02 UTC on January 15, then escalated into   
   major explosions at 04:15 UTC and 200 to 300 seconds after. The entire   
   sequence lasted at least until 04:35 UTC. A second sequence of eruptions   
   began about four hours later and continued from six to seven minutes,   
   including a massive eruption at 08:31. Satellite imagery recorded the   
   resulting dramatic ash cloud from the first eruption sequence, but until   
   now the precise details of the underwater events have remained elusive.   
      
   One interesting finding was that significant explosive eruptions   
   intermittently occurred at 270 to 280 second intervals, a frequency   
   suggesting a resonance effect with the atmosphere and the Earth. "This   
   apparent agreement of the eruption cycle and the atmospheric resonant   
   oscillation with the Earth could be coincidental, but it certainly   
   deserves further exploration," Yoshizawa concludes.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Albert_Einstein # Physics # Optics   
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                   # Natural_Disasters # Volcanoes # Earthquakes   
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   ==========================================================================   
   Story Source: Materials provided by Hokkaido_University. Note: Content   
   may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Kotaro Tarumi, Kazunori Yoshizawa. Eruption sequence of the   
      2022 Hunga   
         Tonga-Hunga Ha'apai explosion from back-projection of teleseismic   
         P waves. Earth and Planetary Science Letters, 2023; 602: 117966   
         DOI: 10.1016/j.epsl.2022.117966   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/01/230127131154.htm   
      
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