Earlham College | News from Public Affairs

Named by Time as one of the 100 most influential people in 2005, Brian Atwater has spent much of his career studying the likelihood of large earthquakes and tsunamis in the Pacific Northwest.

RICHMOND, Ind. — In the wake of the devastating December 2004 Asian tsunami, many North Americans wondered whether such catastrophes could happen closer to home. Scientists had an answer ready: Yes. Geologist Brian Atwater will explain this on Wednesday, Nov. 14, 2007, during an Earlham College convocation.

Atwater presents "The Orphan Tsunami of 1700 — A Trans-Pacific Detective Story," a fascinating tale that connects a severe Pacific Northwest Coast earthquake with a destructive Japanese coastal tsunami. The convocation begins at 1 p.m. in Carpenter Hall's Goddard Auditorium. The program is free and open to the public.

Two decades ago, Atwater began paddling his canoe among the salt marshes of bays and river mouths on the Pacific coast in Washington. He found telltale signs of seismically shifted land levels and associated tsunamis. These findings, paired with documents from Japan, helped spur precautions against earthquake and tsunami hazards in British Columbia, Washington, Oregon and California.

"Here is a case where geologic hindsight helped build awareness before disaster strikes," says Atwater, a U.S. Geological Survey (USGS) geologist and a research professor at the University of Washington.

Earlham Assistant Professor of Geology Andy Moore, made similar use of geology to forewarn of tsunamis in Washington's Puget Sound. Working with Atwater in 1991, Moore discovered traces of a tsunami that was generated 1,100 years ago during a large earthquake on a fault that runs beneath downtown Seattle. The State of Washington recently published a tsunami inundation map for Seattle that is based on this geologic history.

The story of what has become known as the "orphan tsunami" that Atwater helped expose is a fascinating tale that draws on decades of research in North America and Japan.

Atwater's contribution began in 1986, when, by canoe, he started identifying and tracing geologic evidence for Pacific Northwest earthquakes and tsunamis in far greater detail than had been done previously.

Atwater found the remains of coastal marshes and forest that had been suddenly lowered by three to five feet. In some places he also found that sandy water had rushed far inland across the marshes and forests shortly after they had dropped. He found this combination best explained by an earthquake followed by a tsunami.

"By the early 1990s, geologists had learned that most, if not all, of a Pacific Northwest fault that is about 1,100 kilometers long had broken in the decades close to 1700," Atwater says. "We were unable, however, to say whether that entire length had ruptured at once in a giant earthquake of magnitude 9, or whether it had broken piecemeal in a series of lesser shocks."

In 1996, Japanese tsunami historians linked this North American seismology to a tsunami three centuries ago in Japan. This tsunami came ashore without the warning that the parent earthquake usually provides. It was registered in the writings of samurai, merchants and peasants.

The Japanese researchers used these writings to pinpoint the evening of January 26, 1700, as the exact time the tsunami occurred. This is also the precise time, Atwater says of the Pacific Northwest earthquake and tsunami.

North American tree-ring scientists soon checked this proposed date by measuring, to the year and season, the time of death for earthquake-killed trees in coastal Washington. They learned that the trees had lived through the 1699 growing season but were dead by the start of the 1700 growing season. This finding, says Atwater, leaves little room for doubt that the Pacific Northwest earthquake caused a tsunami that not only attacked the adjacent coast but also crossed the Pacific to Japan.

Earlham's Moore says that Atwater was his adviser at the University of Washington for nine years while completing his master's and doctorate degrees. They subsequently worked together on land-level changes in Hokkaido, Japan, and now continue their association through field studies in Indonesia and Sri Lanka.

"I thought Brian was a perfect fit for the Convocation series here at Earlham," Moore said. "He has very close contact with researchers in Japan, and has lived there for a year. He is interested in sharing the story and showing the hazards and their relevance."

Contact:
Denise Purcell, public affairs assistant
765/983-1323 — E-Mail Denise