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Spirit tales reveal ancient landslides

July 13, 2005 By Tom Simonite This article courtesy of Nature News.

North American folklore points to dangers for Seattle.

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A study of Native American tales of a two-headed serpent spirit has hinted at the potential impact of a fault that lies directly beneath Seattle.

Researchers have been studying stories from the Salish people of the North American west coast about a'yahos, a spirit associated with shaking of the ground and rushing, muddy water. They say the tales are strongly linked to a quake that occurred in AD 900. By tracing the tales to specific locations, they have found evidence of ancient landslides.

Ruth Ludwin, a researcher at the Pacific Northwest Seismograph Network at the University of Washington in Seattle, thinks another earthquake in the now densely populated area could trigger a similar slide, with potentially disastrous effects. "I don't think people fully appreciate the severity of the landslides," she adds. She also says that such work can help to educate residents about the risks of an earthquake. "I think that the first-person eye-witness accounts are necessary to fully understand the hazards."

Shaken up

Human records do give the event a reality that geological evidence can't ever give.
Brian Atwater
University of Washington
The Seattle fault line, which lies directly beneath that city in Washington state, last produced a major earthquake in AD 900. That earthquake, of estimated magnitude 7.4 on the Richter scale, caused landslides, major ground upheavals and a tsunami in the adjacent Puget Sound. Many Native American settlements were destroyed, although the area was quickly repopulated.

Today, nearly four million people live in the area, but seismologists know relatively little about the last earthquake, or when another might occur.

Ludwin and her colleagues collected stories about a'yahos in an attempt to discover more. They found that a dozen appearances of this spirit occurred at locations close to small faults connected to the larger Seattle fault line, with five appearances occurring on or very close to the main fault.

One story tells of a 'spirit boulder' associated with the appearance of a'yahos on a beach in west Seattle, and Ludwin tracked it down with the help of local Salish people. "If you hadn't heard the stories you would never pick it out," she says. By using a technique called light detection and ranging (LIDAR) to image the ground beneath and around the rock, they found that it lies at the bottom of a landslide near land that is known to have been pushed upwards by the AD 900 earthquake.

Vengeful spirit

At another site in greater Seattle, stories say that a'yahos demolished a cliff side when people disturbed him. LIDAR pictures again found evidence of a large and previously unknown landslide. The researchers report their findings in Seismology Research Letters1.

Ludwin is keen to continue her work, but says she is having difficulty securing funds from the US Geological Survey. "I think they feel it doesn't strictly fall under their mandate," she explains. "It kind of falls somewhere between the humanities and the sciences." She says she will look for alternative sources of funding.

Brian Atwater, a geologist at the University of Washington, says the work is interesting, but that conventional Earth science studies may be more helpful in predicting the impacts of future quakes. "Human records do give the event a reality that geological evidence can't ever give," he says. But he adds that such studies can probably tell us more about anthropology than earthquakes.

References

  1. Ludwin R. S., et al. Seismol. Res. Lett., 76. 431 - 436 (2005).

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