MSGID: 1:317/3 64951ff5   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Sinking seamount offers clues to slow motion earthquakes    
      
     Date:   
         June 22, 2023   
     Source:   
         University of Texas at Austin   
     Summary:   
         The first ever 3D seismic imaging of a subducting seamount shows   
         a previously unknown sediment trail in Earth's crust off the coast   
         of New Zealand. Scientists think the sediment patches help release   
         tectonic pressure gradually in slow slip earthquakes instead of   
         violent tremors.   
      
         The findings will help researchers search for similar patterns at   
         other subduction zones like Cascadia in the U.S. Pacific Northwest.   
      
      
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   FULL STORY   
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   Scientists have long puzzled over what happens when seamounts -- mountains   
   and volcanoes on the seafloor -- are pulled into subduction zones. Now,   
   new research from The University of Texas at Austin shows that when   
   seamounts sink, they leave behind a trail of soft sediments. The   
   researchers think the sediment patches help tectonic pressure escape   
   gradually in slow slip earthquakes instead of violent tremors.   
      
   The findings, published June 7, 2023, in the journal Nature Geoscience,   
   can be used to adjust earthquake models and help scientists unravel the   
   mechanisms that drive earthquakes.   
      
   The research was led by Nathan Bangs, a senior research scientist at   
   the University of Texas Institute for Geophysics. In 2018, Bangs led an   
   ocean seismic survey that resulted in the first ever 3D scan of a large   
   subducting seamount. Known as the Pāpaku Seamount, the long extinct   
   volcano lies some three miles under the seafloor inside the Hikurangi   
   subduction zone off the coast of New Zealand.   
      
   Images from the scan show the seamount colliding with the subduction   
   zone and the pattern of stresses, fluids and sediments surrounding   
   it. Previous models suggested sediments are pushed down the subduction   
   zone ahead of the seamount, but the scan revealed something different:   
   a massive sediment trail in Pāpaku's wake.   
      
   In another surprise, the scientists spotted the fading trail of a much   
   larger seamount that had long since sunk beneath New Zealand's North   
   Island.   
      
   According to Bangs, the discovery suggests that sinking seamounts drag   
   down enough water-rich sediment to create conditions in the crust suitable   
   for slow slip earthquakes, at least in New Zealand.   
      
   "That older one seems to be very much linked to an uplifted ridge that's   
   really in the bullseye of where recent slow slip activity has been,"   
   Bangs said.   
      
   "There could be other places like Cascadia (in the U.S. Pacific Northwest)   
   that have subducting seamounts and a lot of sediment, but because the   
   subducting crust there typically has less water than Hikurangi, they may   
   be less likely to have the same kind of shallow slow slip activity."   
   Slow slip earthquakes are slow motion versions of large earthquakes,   
   releasing similar levels of pent-up tectonic energy but in a harmless   
   creeping fashion that can take days or weeks to unfold. Scientists believe   
   that the make-up of the crust is a major factor in how tectonic energy   
   is released, with softer, wetter rocks allowing plates to slip slowly,   
   while drier, brittle rocks store energy until they fail in violent and   
   deadly megaquakes.   
      
   The new findings reveal how those conditions sometimes come about and   
   importantly, said Bangs, tell scientists what to look for at the world's   
   other subduction zones.   
      
   The research and seismic survey were funded by the National Science   
   Foundation and similar scientific agencies in New Zealand, the United   
   Kingdom and Japan.   
      
   The University of Texas Institute for Geophysics is a research unit of   
   the Jackson School of Geosciences.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Earthquakes # Natural_Disasters # Geography # Geology   
             o Fossils_&_Ruins   
                   # Early_Climate # Paleontology   
       * RELATED_TERMS   
             o Earthquake o Geologic_fault o Alpine_Fault o Sedimentary_rock   
             o Crust_(geology) o Mid-ocean_ridge o Paleoclimatology o Volcano   
      
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   Story Source: Materials provided by University_of_Texas_at_Austin. Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Nathan L. Bangs, Julia K. Morgan, Rebecca E. Bell, Shuoshuo Han,   
      Ryuta   
         Arai, Shuichi Kodaira, Andrew C. Gase, Xinming Wu, Richard Davy,   
         Laura Frahm, Hannah L. Tilley, Daniel H. N. Barker, Joel H. Edwards,   
         Harold J.   
      
         Tobin, Tim J. Reston, Stuart A. Henrys, Gregory F. Moore, Dan   
         Bassett, Richard Kellett, Valerie Stucker, Bill Fry. Slow slip   
         along the Hikurangi margin linked to fluid-rich sediments trailing   
         subducting seamounts.   
      
         Nature Geoscience, 2023; 16 (6): 505 DOI: 10.1038/s41561-023-01186-3   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230622120919.htm   
      
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