MSGID: 1:317/3 6273533f   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Major 2020 Alaska quake triggered neighboring 2021 temblor    
      
     Date:   
         May 4, 2022   
     Source:   
         University of Alaska Fairbanks   
     Summary:   
         A study of two powerful earthquakes in adjacent areas off the   
         Alaska Peninsula in 2020 and 2021 shows a connection between the   
         two. It also suggests they may be a part of an 80-year rupture   
         cascade along the fault.   
      
      
      
   FULL STORY   
   ==========================================================================   
   A study of two powerful earthquakes in adjacent areas off the Alaska   
   Peninsula in 2020 and 2021 shows a connection between the two. It also   
   suggests they may be a part of an 80-year rupture cascade along the fault.   
      
      
   ==========================================================================   
   The research was published today by the journal Science Advances in a   
   paper jointly led by University of Alaska Fairbanks Geophysical Institute   
   associate professor Ronni Grapenthin and Michigan State University   
   assistant professor Julie Elliott. UAF postdoctoral researcher Revathy   
   M. Parameswaran is among the four co-authors.   
      
   The researchers also conclude that the two deep earthquakes on the   
   Aleutian- Alaska megathrust fault, where the Pacific plate is sliding   
   beneath the North American plate, may have brought shallow portions of   
   the fault closer to failure.   
      
   They add that their research will help scientists better understand   
   stress transfer and earthquake triggering in the region and in general.   
      
   "One large earthquake increases the stress on the neighboring part of the   
   megathrust fault. This patch then ruptures and increases the stress on   
   the next patch in the fault, like delayed dominos," Grapenthin said. "And   
   that's what we're seeing here."  The first of the two major quakes,   
   known as the Simeonof event, occurred July 21, 2020. It registered at   
   magnitude 7.8, struck near the Shumagin Islands south of the Alaska   
   Peninsula and ruptured westward.   
      
      
      
   ==========================================================================   
   The second quake, the Chignik event, occurred just over one year later   
   on July 28, 2021. It registered at magnitude 8.2, was located south of   
   the Alaska Peninsula and northeast of the Simeonof quake and ruptured   
   eastward.   
      
   The two quakes and their aftershocks occurred in the Shumagin Gap, a spot   
   near the Shumagin Islands in a known band of historical ruptures. That   
   1,900-mile subduction zone, where the Pacific tectonic plate slides under   
   the North American plate, starts at the tip of the Aleutian Islands. It   
   continues along the south side of the islands and the Alaska Peninsula,   
   curves upward across the Kenai Peninsula and encompasses the Anchorage   
   area and Prince William Sound.   
      
   No major earthquakes had been recorded in the Shumagin Gap, a space about   
   100 miles long in the subduction zone, until the 2020 and 2021 quakes.   
      
   "This could be a case study to understand how adjacent earthquake patches   
   could be activated by a significant release of energy that has accumulated   
   through plate motion," Parameswaran said.   
      
   The researchers studied data to assess the impact of the stress changes   
   caused by the 2020 Simeonof quake, particularly as they might relate to   
   the Chignik quake's rupture site.   
      
      
      
   ==========================================================================   
   Modeling the Simeonof quake's stress buildup shows that the Chignik   
   hypocenter, the location inside the earth at which an earthquake rupture   
   begins, is embedded in an area of increased stress change, consistent   
   with what scientists know about how earthquakes are triggered.   
      
   The work also indicated some notable areas of "very high" stress loading   
   of the fault, especially in the shallower regions of the model fault   
   plane. That area didn't rupture during this earthquake, according to   
   the research paper.   
      
   The researchers added that the two earthquakes may be part of an 80-year   
   cascade of large subduction earthquakes along this major plate boundary   
   and that the cascade has now concluded, with the most recent large event   
   prior to the 2020 Simeonof quake being the 1965 magnitude 8.7 earthquake   
   off the Rat Islands in the Aleutian Chain.   
      
   Prior to 1965, five earthquakes of magnitude 8 or greater occurred within   
   30 years from the farthest Aleutian Islands to Southcentral Alaska.   
      
   "In the concept of cascades, the entire Aleutian-Alaska megathrust has   
   now ruptured and released most of the stress that has accumulated since   
   the onset of that most recent cascade," Grapenthin said.   
      
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_Alaska_Fairbanks. Original written by Rod Boyce. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Julie L. Elliott, Ronni Grapenthin, Revathy M. Parameswaran, Zhuohui   
         Xiao, Jeffrey T. Freymueller, Logan Fusso. Cascading   
         rupture of a megathrust. Science Advances, 2022; 8 (18) DOI:   
         10.1126/sciadv.abm4131   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220504144514.htm   
      
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