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SEATTLE — When scientists figured out that sea water drowned groves of tall trees up and down the coast of Washington state the same year a tsunami hit Japan, they theorized that a massive earthquake in the Pacific most likely triggered both events. 

Based on Japanese records, scientists were able to pinpoint a date — Jan. 26, 1700 — and estimate that the rupture of a long stretch of sea floor had caused a magnitude 9 quake, which would be the largest known temblor ever to strike what is now the contiguous United States. 

But Ruth Ludwin, a University of Washington geophysics professor, wanted more. There appeared to be no accounts of cataclysmic earth-shaking in the stories and legends of the only North Americans who would have been here to witness the quake — Indians. 

“When you talk about a very large earthquake in 1700, for that to be really convincing to me, I really need to have evidence from people who were there,” Ludwin said. “I was looking for a more comprehensive story.” 

Ludwin began to search obscure volumes of tribal folklore, where she found that, for centuries, Indians from British Columbia’s Vancouver Island to the coast of Northern California had been telling strikingly similar tales of mudslides, of plains that suddenly became oceans and other stories that strongly suggest tribes bore witness to tsunamis like the one in 1700. 

Many of the legends involve a mythic battle between a thunderbird and a whale. 

One tale told by generations of Hoh Indians from the Forks area of Washington’s Olympic Peninsula contains what Ludwin considers the clearest description of a concurrent earthquake and tsunami yet discovered in tribal legend. 

As the story goes, Ludwin wrote in a research paper, “There was a great storm and hail and flashes of lightning in the darkened, blackened sky and a great and crashing ’thunder-noise’ everywhere. ... There were also a great shaking, jumping and trembling of the earth beneath and a rolling up of the great waters.” 

The Makah Indians, whose reservation at Neah Bay sits at the northwest tip of Washington state, also have a version — one that ends with a thunderbird delivering a whale inland to the mouth of a river, giving the giant beast to a tribe that had been starving one winter thousands of years ago. 

Although it’s unclear exactly how long the story has been told, it formed the basis of the tribe’s centuries-old whale hunt and could be linked to one of the seven “megathrust” quakes scientists believe have occurred over the past 3,500 years. 

“I think it’s really interesting that our cultural knowledge can help unravel some of these scientific mysteries,” said Janine Bowechop, director of the Makah Museum. “I feel good that we can share information and then really have a better understanding for both worlds.” 

Many legends contain no time elements. Others that were never written down have been lost entirely, so Ludwin’s work can seem like trying to solve a puzzle with most of the pieces missing. But she insists it’s worth it. 

“The work that I’ve done is not extremely important from a scientific point of view, but it’s important from the point of view of understanding and believing,” Ludwin said. “It’s another piece of the puzzle.” 

The megathrust quake believed to have occurred in 1700 ruptured the Cascadia subduction zone, where two of the tectonic plates that form the Earth’s crust — the Juan de Fuca and the North America plates — overlap. From its northern end, off the western coast of Vancouver Island, the subduction zone stretches about 600 miles south to Cape Mendocino in Northern California, then runs into the San Andreas fault. 

It was the Japanese who first theorized that an enormous earthquake in the Pacific caused what they called their “orphan tsunami,” so named because there was no local temblor that accompanied the torrent of 6-foot-high waves that crashed along 500 miles of coastline. 

When they learned that groves of red cedars and Sitka spruces along Washington’s coast had dropped several feet, drowning in saltwater sometime in the late 1600s or early 1700s, they theorized that one huge quake must have been responsible for both the Japanese tsunami and this state’s “ghost forests.” 

Radiocarbon dating of spruce stumps narrowed the timeline of the tree drownings to somewhere between 1680 and 1720, said Brian Atwater, a U.S. Geological Survey scientist in Seattle. 

That was too large a window, so scientists went back to one of the estuaries where roots of red cedars had survived and could be dated by the rings in the roots. 

At that grove, near the Copalis River in Grays Harbor County, tree-ring dating showed the red cedars died sometime between August 1699 and May 1700. 

“If we had found that those red cedars died in 1697 or 1703, we would say, ’Well, we’re not sure your tsunami came from our earthquake,’ ” Atwater said. “We knew there was an earthquake or a series of earthquakes. The question was how big and exactly when.” 

Although the geological evidence of the 1700 megathrust seemed solid, there were still some skeptics before Ludwin started finding Indian tales that supported the science. 

Tribal folklore, Atwater said, “is important, because people understandably want human evidence as well as physical evidence.”