The Big One  

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Earthquake Research

Thanks to the support of universities and public agencies, geologists have been able to investigate the mechanisms of earthquakes and learn about their damaging effects.

A Great Detective Story

Like detectives arriving on the scene long after a crime has been committed, geologists look for clues in the landscape in order to understand the past. By the 1980s, geologists were wondering whether there had ever been devastating earthquakes—Big Ones—in the Pacific Northwest. Brian Atwater was one of those geologists. As his research began to uncover clues to the Big One mystery, his discoveries have transformed our understanding of Northwest geology and the risks we face.

Clue One: Ghost forests
Ghost forests—long-dead trees—stand stark along the coasts of Washington and Oregon. Atwater knew that similar stands of trees in Alaska had been killed after the Prince William Sound earthquake of 1964. He realized that the Alaskan quake had caused parts of the forest to drop below sea level. Tidewater had rushed in, drowning the trees. Over time, tidal mud accumulated and the area became a salt marsh and then a coastal meadow. But the dead trees still stood.
Tree drowning
1. Living coastal forest
2. Land level drops, tidewater drowns tree roots
3. Tidal mud accumulates and salt marsh develops

Clue Two: Tsunamis
Atwater wondered whether the Washington and Oregon ghost forests were like Alaska’s drowned forests. He knew that great subduction zone earthquakes usually produce tsunamis—massive waves that travel with jet-like speed across the ocean. Near shore, tsunamis reach towering heights and surge far inland. When Atwater looked at the ghost forests, he found distinctive layers of sand over the soil. This was another clue to the mystery.

Earthquakes cause tsunamis

  1. The coast before an earthquake
  2. Land level changes during an earthquake, tsunami waves generated
  3. Tsunami surges onto shore
  4. Sand deposited over the land


Land layers in an Oregon ghost forest (from top)
Marsh plants today
Tidal mud (gray layer)
Sand deposited by tsunami in year 1700 (light layer)
Old topsoil (very dark layer)
Fire pits with charcoal, used by Native Americans (swellings in the very dark layer)




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