r all those jokes about an earthquake on the San Andreas Fault causing California to slide into the Pacific Ocean? In fact, says Brian F. Atwater, a U.S. Geological Service scientist, here in the Northwest "we have the potential for a much larger earthquake than you can get on the San Andreas."

The fact that we now understand we are living with a serious "seismic hazard," as the scientists call it, can be attributed to research Brian and four other scientists from around the world have done in the past 20 years.

The discoveries that led to our new knowledge that the Northwest likely will experience a quake of the size that occurred in the Indian Ocean in December 2004 -- and the ensuing giant tsunami certain to follow -- reads like a good old-fashioned mystery, with clues in foreign places and microscopic bits of evidence a forensic detective would admire.

Brian is a modest man. "I'm just a mud geologist," he says. Yumei Wang uses more glowing terms. Yumei is the earthquake engineer in Oregon's Department of Geology and Mineral Industries. For the past decade she's led the fight to prepare Oregon's schools and emergency facilities for the severe earthquake scientists now predict.

"Brian's work has been fundamental to our understanding of the seismic hazard," Yumei says. Because Brian worked with other scientists, historians and archeologists and pulled together clues from those disciplines, we now understand "we are in a geologic setting that is one of the most dangerous settings there is in the world," Yumei says.

Evidence indicates a history of magnitude 9 or greater earthquakes on the Cascadia Fault, which runs about 60 miles off the Oregon coast from Northern California to British Columbia. The geological evidence goes back 10,000 years. Sometimes the quakes were 200 years apart, sometimes the wait was longer. The most recent giant quake occurred Jan. 26, 1700.

How can we know that with certainty? After all, there was no recorded history in the Northwest until about 1770. Mapmakers in 1700 left our corner of the world blank.

But if you piece together the evidence, as Brian and other scientists have, it's hard to refute that on that date the earth shook here, and the sea invaded the land. And someday it will happen again.

Native Americans preserved their history mostly in the form of storytelling. In Washington, in 1864, a Makah leader named Billy Balch told of a flood that had occurred in the "not very remote" past, that covered all but the highest land in the Strait of Juan de Fuca, lifting canoes into trees and killing many people. His story was recorded in the diary of a man named James Swan, who noted he saw signs of the flooding.

Geologic study uncovered "ghost forests" in coastal tidal marshes, thousands of tree stumps on land that fell when an earthquake dislodged great chunks of earth on the coast. By counting the rings of great cedar stumps, biologists discovered the trees died when submerged in salt water between August 1699 and May 1700.

The marsh mud revealed more signs. Sheets of sand were layered between marsh mud on top and land beneath that was once the floor of a forest -- a clear sign of a tsunami following a quake.

Archaeologists identified former Native American coastal fishing camps that were abandoned after being overrun by a tsunami.

Clearly, the Northwest had experienced a major earthquake in late 1699 or 1700. But how large was it? What magnitude quake should people expect and prepare for along the Cascadia Fault?

The answer came from Japan, in written records of the "orphan tsunami" of 1700.

The Japanese kept careful written records in 1700. In Japan tsunami and earthquake historians have pored over ancient documents, collecting descriptions of quakes, floods and high tides.

By 1700 the Japanese, who live in an active seismic zone, were used to feeling the earth shake and knew to expect a tsunami soon after. But that year, historians discovered, there'd been a flood not preceded by an earthquake.

In the 1970s and '80s other orphan tsunamis, as they're called, had been explained away by large earthquakes in South America. But there had been no 1700 earthquake off the South American Pacific Coast.

Brian Atwater says a Japanese scientist teaching in America first suggested there might be a connection between the research Brian and others were doing in the Northwest, and Japan's orphan tsunami. Brian packed up his family and moved from Seattle, where's he's based, to Japan for a year to examine historic documents.

They were persuasive and specific. A huge earthquake had occurred somewhere in the Pacific, generating a tsunami that flooded the Japanese coast on Jan. 27, 1700, the very year scientific evidence indicated the Northwest had experienced an earthquake and tsunami.

The orphan tsunami wasn't an orphan anymore.

It was new information, and it changed everything the residents of the Northwest had believed about the kind of earthquake hazard we live with.

Just reaching the conclusion wasn't enough for Brian. He had to make sure people understood what a magnitude 9 or higher earthquake could do to their lives, their homes and their cities.

So he wrote a book, "The Orphan Tsunami of 1700" (University of Washington Press, $24.95 paperback, 133 pages). He began working with government geologists. And he started reaching out to teachers, to create curricula to educate young people.

Because of Brian's work, Yumei says, "we have begun preparing." And Oregon has done a good job getting started.

"Oregon is extraordinary," Brian says. "I don't know of a proactive stance like this in any other state." Voters have approved changes in the state constitution to shore up schools and other facilities to withstand a huge quake. Legislators have funded efforts to create tsunami warning systems and evacuation maps.

When will the earthquake hit? No one can predict. But pressure has been building on the Cascadia fault for 300 years, and within the next few hundred, it's almost certain our ground will shake again.

Thanks to Brian Atwater, we'll be more prepared.

Margie Boule: 503-221-8450, marboule@aol.com