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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Warm liquid spewing from Oregon seafloor comes from Cascadia fault,   
   could offer clues to earthquake hazards    
      
     Date:   
         April 11, 2023   
     Source:   
         University of Washington   
     Summary:   
         Oceanographers discovered warm, chemically distinct liquid shooting   
         up from the seafloor about 50 miles off Newport. They named the   
         unique underwater spring 'Pythia's Oasis.' Observations suggest   
         the spring is sourced from water 2.5 miles beneath the seafloor at   
         the plate boundary, regulating stress on the offshore subduction   
         zone fault.   
      
      
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   FULL STORY   
   ==========================================================================   
   The field of plate tectonics is not that old, and scientists continue to   
   learn the details of earthquake-producing geologic faults. The Cascadia   
   Subduction Zone -- the eerily quiet offshore fault that threatens to   
   unleash a magnitude- 9 earthquake in the Pacific Northwest -- still   
   holds many mysteries.   
      
      
   ==========================================================================   
   A study led by the University of Washington discovered seeps of warm,   
   chemically distinct liquid shooting up from the seafloor about 50 miles   
   off Newport, Oregon. The paper, published Jan. 25 in Science Advances,   
   describes the unique underwater spring the researchers named Pythia's   
   Oasis. Observations suggest the spring is sourced from water 2.5 miles   
   beneath the seafloor at the plate boundary, regulating stress on the   
   offshore fault.   
      
   The team made the discovery during a weather-related delay for a cruise   
   aboard the RV Thomas G. Thompson. The ship's sonar showed unexpected   
   plumes of bubbles about three-quarters of a mile beneath the ocean's   
   surface. Further exploration using an underwater robot revealed the   
   bubbles were just a minor component of warm, chemically distinct fluid   
   gushing from the seafloor sediment.   
      
   "They explored in that direction and what they saw was not just methane   
   bubbles, but water coming out of the seafloor like a firehose. That's   
   something that I've never seen, and to my knowledge has not been   
   observed before," said co-author Evan Solomon, a UW associate professor   
   of oceanography who studies seafloor geology.   
      
   The feature was discovered by first author Brendan Philip, who did the   
   work as a UW graduate student and now works as a White House policy   
   advisor.   
      
   Observations from later cruises show the fluid leaving the seafloor is   
   9 degrees Celsius (16 degrees Fahrenheit) warmer than the surrounding   
   seawater.   
      
   Calculations suggest the fluid is coming straight from the Cascadia   
   megathrust, where temperatures are an estimated 150 to 250 degrees Celsius   
   (300 to 500 degrees Fahrenheit).   
      
   The new seeps aren't related to geologic activity at the nearby seafloor   
   observatory that the cruise was heading toward, Solomon said. Instead,   
   they occur near vertical faults that crosshatch the massive Cascadia   
   Subduction Zone. These strike-slip faults, where sections of ocean crust   
   and sediment slide past each other, exist because the ocean plate hits   
   the continental plate at an angle, placing stress on the overlying   
   continental plate.   
      
   Loss of fluid from the offshore megathrust interface through these   
   strike-slip faults is important because it lowers the fluid pressure   
   between the sediment particles and hence increases the friction between   
   the oceanic and continental plates.   
      
   "The megathrust fault zone is like an air hockey table," Solomon   
   said. "If the fluid pressure is high, it's like the air is turned on,   
   meaning there's less friction and the two plates can slip. If the fluid   
   pressure is lower, the two plates will lock -- that's when stress can   
   build up."  Fluid released from the fault zone is like leaking lubricant,   
   Solomon said.   
      
   That's bad news for earthquake hazards: Less lubricant means stress can   
   build to create a damaging quake.   
      
   This is the first known site of its kind, Solomon said. Similar fluid   
   seep sites may exist nearby, he added, though they are hard to detect   
   from the ocean's surface. A significant fluid leak off central Oregon   
   could explain why the northern portion of the Cascadia Subduction Zone,   
   off the coast of Washington, is believed to be more strongly locked,   
   or coupled, than the southern section off the coast of Oregon.   
      
   "Pythias Oasis provides a rare window into processes acting deep in   
   the seafloor, and its chemistry suggests this fluid comes from near   
   the plate boundary," said co-author Deborah Kelley, a UW professor of   
   oceanography. "This suggests that the nearby faults regulate fluid   
   pressure and megathrust slip behavior along the central Cascadia   
   Subduction Zone."  Solomon just returned from an expedition to monitor   
   sub-seafloor fluids off the northeast coast of New Zealand. The Hikurangi   
   Subduction Zone is similar to the Cascadia Subduction Zone but generates   
   more frequent, smaller earthquakes that make it easier to study. But   
   it has a different sub-seafloor structure meaning it's unlikely to have   
   fluid seeps like those discovered in the new study, Solomon said.   
      
   The research off Oregon was funded by the National Science   
   Foundation. Other co-authors are Theresa Whorley, who did the work as a UW   
   doctoral student and now works as an environmental consultant in Seattle;   
   Emily Roland, a former UW faculty member now at Western Washington   
   University; Masako Tominaga at Woods Hole Oceanographic Institution;   
   and Anne Tre'hu and Robert Collier at Oregon State University.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Earthquakes # Oceanography # Geology # Natural_Disasters   
                   # Tsunamis # Geography # Atmosphere # Earth_Science   
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             o San_Andreas_Fault o Mid-ocean_ridge o Alpine_Fault o   
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   ==========================================================================   
   Story Source: Materials provided by University_of_Washington. Original   
   written by Hannah Hickey. Note: Content may be edited for style and   
   length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Brendan T. Philip, Evan A. Solomon, Deborah S. Kelley, Anne   
      M. Tre'hu,   
         Theresa L. Whorley, Emily Roland, Masako Tominaga, Robert   
         W. Collier.   
      
         Fluid sources and overpressures within the central Cascadia   
         Subduction Zone revealed by a warm, high-flux seafloor seep. Science   
         Advances, 2023; 9 (4) DOI: 10.1126/sciadv.add6688   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230411105851.htm   
      
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