of work, geologists and historians finally found evidence of an elusive earthquake,
nearly 300 years after it occurred. The magnitude-9 event that struck the Pacific
Northwest on Jan. 26, 1700, was responsible for a huge tsunami that inundated
the Pacific Northwest from southern British Columbia to northern California,
depositing thin lenses of sand over wetlands. The tsunami itself had been a
secret in the geologic record and hidden in historic records kept over centuries
in Japan, until it was unearthed by Brian Atwater, a geologist with the U.S.
Geological Survey (USGS) in Seattle, Wash., who in April was named one of Time
magazines most influential people of 2005 because of his research.
Brian Atwater has spent nearly two decades investigating the great tsunami that swamped the coastline of the Pacific Northwest and traveled all the way to Japan with devastating effects. Recently named one of Time magazines most influential people of the year, he, with colleagues, will publish The Orphan Tsunami of 1700 this fall. Copyright Helen Lambourne; courtesy of Brian Atwater.
Until Atwater waded into the muddy wetlands of the Pacific Northwest more than two decades ago, no one knew the seismic history of large earthquakes for the region. But through careful radiocarbon dating of drowned trees, fieldwork that documented land shifts and tsunami deposits, and other data collected since the mid-1980s, Atwater and others have collected evidence for quite large earthquakes in the region. Atwater published the first inkling of a very large event that happened around 300 years ago in a 1987 paper in Science, careful not to conclude too much, as he says there were not enough data at the time.
So when Kenji Satake of the Geological Survey of Japan and colleagues published a paper in Nature in 1996, showing evidence that the 1700 Cascadia tsunami reached Japan, Atwater was extraordinarily interested so much so that he started learning Japanese so he could examine the historic evidence firsthand. Learning a new language at an age of nearly 50 is not an easy task, and Japanese is not an easy language for westerners, Satake says. As a traditional, and sometimes stubborn, geologist, he would not be convinced until he examined the data by himself, he says. The data were not coastal geologic sections, but rather Japanese historical documents. A normal person would not step further. Brian, however, was different.
Eventually, Atwater and Satake wrote a proposal together so that Atwater could visit Japan in 1998, to study for about a year. I often joked that Brian did not believe me, so he came to Japan for inspection, Satake says. That work paid off in part with the publication of the 2003 paper in the Journal of Geophysical Research, which used radiocarbon dates of trees drowned immediately after the earthquake, calculated by Atwaters colleague Minze Stuiver.
Reflecting on the path that led him to those discoveries, Atwater, a native of Connecticut, recalls spending summers as a backpacking group leader in the White and Green mountains and the Adirondacks, which led him to combine outdoors with a career. As an undergraduate student working at USGS in Menlo Park, and while working on his Ph.D. at the University of Delaware, he studied the wetlands that ring the San Francisco Bay and the marshes further east in the San Joaquin and Sacramento river deltas.
After switching to the hard rock geology and geomorphology of northeastern Washington, he came back to studying wetlands, moving to Seattle in 1985. Around this time, Atwater heard a talk given by Tom Heaton, a seismologist at USGS at the time who is now at Caltech in Pasadena, Calif. Asked by the Nuclear Regulatory Commission to review studies for the placement of nuclear power plants in Washington, Heaton noticed that there was no sure evidence either way as to whether the region was due for a large seismic shock. But he spoke persuasively about the potential for a great earthquake in the region, which is extraordinarily close to the subduction zone off the Pacific coast, where the Juan de Fuca plate dives under the North American plate, pushing it up and making it bulge.
Atwater says he immediately started to think about what I could do. The bulge of the North American plate was the key, he decided, calculating that at 3 millimeters of uplift a year, 3,000-year-old shorelines would have been pushed up 9 meters (or around 30 feet). So thats what I went looking for, he says. Land-level change is the heart of what Ive been working on. In most places, abrupt changes in land surfaces are the main signal of earthquakes.
Atwater is not enamored with high-tech, Heaton says. His instrument is a canoe and a hand auger, he says, a pipe that takes brute force to drive it into the ground for collecting core samples.
Atwater is adamant that all the researchers he has worked with receive credit for their role in the tsunami and seismological research that has redefined the seismic hazard in the Pacific Northwest. The nearby Cascadia subduction zone had never had an extraordinarily large earthquake recorded with an instrument, and so people had once thought the colliding tectonic plates an anomaly, Satake said, and without Brian, the Pacific Northwest might have been still considered a safe place from great subduction earthquakes.
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