UW Researcher Confirms 1700 Superquake Study Of Dead Coastal Trees Yields Evidence Of Magnitude-9 Shocker

Studying growth rings in long-dead cedar trees on Washington’s coast has provided further evidence that a gigantic earthquake occurred on Jan. 26, 1700, University of Washington researchers said Wednesday.

“This earthquake really happened,” said David Yamaguchi, a UW tree-ring analyst. Not only did it devastate the coast of Washington, but the quake, possibly magnitude 9 and rivaling some of the strongest earthquakes ever recorded, also caused a tsunami that raked the shores of Japan, Yamaguchi said.

Yamaguchi and Brian Atwater, a UW professor and U.S. Geological Survey researcher, are publishing a report in Thursday’s issue of Nature describing their research.

By reading the annual tree ring patterns in the trunks and roots, the scientists determined the time of death of six Western red-cedar trees found along 60 miles of the Washington coast. They found each of the trees produced its final ring in the 1699 growing season, indicating the trees were dead by the spring of 1700.

The trees were found in the tidal wetlands of the Copalis River, Grays Harbor, Willapa Bay and the Columbia River.

Last year, Japanese scientists reported that a tsunami, or earthquake-caused ocean wave, that hit Japan’s central island of Honshu on Jan. 27, 1700, was probably caused by an earthquake on the Cascadia subduction zone, a 600-mile coastal fault stretching from British Columbia to Northern California.

Based on the size of the tsunami, the Japanese scientists estimated the earthquake at magnitude 9, even though no Cascadia-zone quake of magnitude 5 or above has been recorded by seismologists.

Because of the simultaneous tree deaths, “we can say now pretty firmly that that tsunami came from here,” Yamaguchi told a news conference.

“All of a sudden we have living organisms that died at the same time as that tsunami in Japan,” he said.

The Cascadia subduction zone is an area where plates in the Earth’s crust collide.

Earlier research by Atwater and others indicated a tsunami from the subduction zone would take about 10 hours to reach Japan, so researchers calculated the quake’s time at 9 p.m. on Jan. 26 - consistent with Indian legends that an earthquake occurred on a winter night.

Scientists have disagreed as to whether the entire 600-mile-long Cascadia zone could rupture at once, creating a monster quake, or whether it would fracture in a series of quakes of about magnitude 8 at most - still large, but creating a smaller tsunami and a much smaller area of damaging effects.

Because the trees were spread out along the coast, it adds support to the theory that one massive quake rocked the zone.