Grouted sediment slices show signs of earthquake shaking


  • Brian F. Atwater,

    1. U. S. Geological Survey, Department of Earth and Space Sciences, University of Washington , Box 351310, Seattle, Wash. 98195-1310, USA
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  • Diana Baker,

  • Walter A. Barnhardt,

  • Kevin S. Burrell,

  • Marco Cisternas V.,

  • Tsuyoshi Haraguchi,

  • Bretwood Higman,

  • Robert E. Kayen,

  • Diane Minasian,

  • Takashi Nakata,

  • Kenji Satake,

  • Koichi Shimokawa,

  • Keita Takada


Sand and mud from Washington State, sampled with Japanese methods for identifying structure in unconsolidated deposits, have provided new evidence for earthquakes over the past 2000 years at the Cascadia subduction zone. Each sample was collected as a vertical slice, 0.5 m wide and up to 8 m long, in sheetpile driven into wet sand and mud beneath a tidal bank of the Columbia River (Figures 1 and 2). Painted with flexible, hydrophilic grout, the slices yielded full-size peels that reveal bedding and its disruption (Figure 3). Evidence for liquefaction is common, even where it is absent at the ground surface. Especially common are sills that imply lateral escape of water. These findings may affect ground-motion estimates for plate-boundary earthquakes in the northwestern United States and Canada.