M 9.0 - The 1700 Cascadia Earthquake

This earthquake, one of the largest in the history of North America, was found by combining First Nations and Native American oral histories with tree-ring dating and other geological evidence in North America and an “orphan tsunami” in Japan. The location has been assigned to the approximate center of the Cascadia Subduction Zone, based on the conclusion that an event of this size likely ruptured nearly all this 1,100 km zone.¹

The Earthquake and its Effects in Cascadia:
When this earthquake occurred, the Cascadia region of North America (present day Vancouver Island, British Columbia, western Washington and Oregon and Northern California) was pretty much unknown to Europeans², but it was by no means uninhabited. Many groups have oral histories of violent shaking, building damage, sea waves with major flooding, and people killed.

From oral history of the Huu-ay-aht First Nation, people were just going to sleep in the longhouses at Anacla, on Pachena Bay, [present-day Vancouver Island] when the earthquake hit. It shook for more than half a minute, and many of the longhouses sank into the sand [a description of liquefaction]. The tsunami that followed had an estimated wave height of more than 50 ft (15 m) and flooded Anacla and other coastal villages. Only 1 out of more than 600 people in Anacla survived, and in all, seven Huu-ay-aht villages were destroyed. Only the village of Malthsit survived, since it was on high ground about 75 feet (23 m) above Pachena Bay.³

The Cowichan Tribes First Nation, located near present-day Duncan, British Columbia, describe a night-time earthquake that threw down houses and “brought great masses of rock down from the mountains. One village was completely buried beneath a landslide. People could neither stand nor sit for the extreme motion of the earth”.⁴

Several oral accounts describe a great flood on what is known today as the Olympic Peninsula of Washington. Along the coast of what is now southern Oregon, Native American oral history describes a “huge tidal wave [tsunami] when the ocean rose up and huge waves swept and surged across the land. Trees were uprooted and villages were swept away. [People] said they tied their canoes to the top of the trees, and some canoes were torn loose and swept away. After the tidal wave, they found tree tops filled with limbs and trash. The big flood and tidal wave tore up the land and changed the rivers. Nobody knows how many [people] died.”⁴

Archaeological evidence also indicates that some native villages on the British Columbia, Washington, and Oregon coasts were subsided, flooded by tsunamis, and abandoned following this earthquake.⁴

Ghost forests, predominantly composed of western red cedar, a rot-resistant tree, and buried stumps of predominantly less-resistant Sitka spruce, have been found in tidal marshes and estuaries along the coasts of southern Washington, Oregon and northern California. They indicate that the land had subsided and drowned the trees. In places such as Willapa Bay, Washington, dendrochronology (tree ring dating) of many of the trees and stumps indicated that the last growing season was 1699, showing that the trees had died before the start of the growing season in 1700. This shows that the subsidence occurred suddenly, instead of gradually over multiple years.²

In addition, sand sheets coming from the sea and tapering inland indicate that a tsunami arrived shortly after the subsidence occurred and before the land could be covered by tidal mud. In addition, sand-filled cracks in the subsided ground indicate that liquefaction occurred, providing more evidence that the subsidence and cracking was due to shaking from an earthquake.²

The Tsunami in Japan:
People in towns along the Pacific Coast of Japan wrote about destructive waves on the 8th and 9th days of the 12th month of Genroku 12, which is equivalent to January 27 and 28, 1700, in the calendar used today in much of the world. Because no one in Japan felt an earthquake before the waves struck the coast, many writers were reluctant to call the waves a tsunami. An observer at Kuwagasaki called it a tsunami, and the headman at Miho wondered if it was a tsunami, while others referred to the event as high tide or high waves. Based on the damage reports, the maximum wave heights in Japan were estimated to be in the range of 2-5 meters.²

At Kuwagasaki, near Miyako, 13 houses were destroyed by flooding and an additional 20 were destroyed in a subsequent fire. This represented about 10 percent of all the buildings in the town. Houses were also destroyed by flooding at Tsugaruishi, at the south end of Miyako-wan (Miyako Bay). At Otsuchi, about 30 km south of Kuwagasaki, the tsunami damaged 2 buildings, 2 salt kilns and some fields and paddies. Because the waves struck Otsuchi and Kuwagasaki on the same day and hour, this helps to pinpoint the origin time of the earthquake across the Pacific in Cascadia to be about 9 PM local time on January 26.²

At Nakaminato, where sea-going ship cargoes were offloaded onto smaller vessels to travel by river to Edo (now named Tokyo), a ship carrying 28 metric tons of rice could not enter the port due to high waves in the morning of January 28, possibly due to outwash from the tsunami. A storm later that evening drove the ship onto a rocky shore, killing 2 sailors and destroying the cargo.²

At Miho, near Shizuoka, the village headman observed a swift series of tides, and warned villagers to flee to higher ground. The headman was puzzled because although the waves behaved like a tsunami, there had been no earthquake felt in the area. No damage was reported at Miho.²

In the Tanabe area, near Wakayama and about 880 km southwest of Kuwagasaki, the waves destroyed wheat fields and rice paddies, flooded a government storehouse and ascended a moat of Tanabe castle.²

The Connection:
By process of elimination, the timing and wave heights in Japan compared to more recent tsunamis in the Pacific make Cascadia the most likely source of Japan’s “orphan tsunami” of 1700, and the tree ring dates of the ghost forests in Oregon and Washington complete the connection.²

References:
¹Fault slip and seismic moment of the 1700 Cascadia earthquake inferred from Japanese tsunami descriptions, by Kenji Satake, Keilin Wang, and Brian F. Atwater (2003), Journal of Geophysical Research, 108(B11), ESE p. 7-1 to 7-17.

²The Orphan Tsunami of 1700 – Japanese clues to a parent earthquake in North America, 2nd ed., by Brian F. Atwater, Satoko Musumi-Rokkaku, Kenji Satake, Yoshinobu Tsuji, Kazue Ueda, and David K. Yamaguchi, U.S. Geological Survey Professional Paper 1707, University of Washington Press, Seattle: 2015.

³Prepare for next tsunami, says chief, by David Wiwchar, Raven’s Eye (2005), 8(9), p.3, online at https://www.ammsa.com/publications/ravens-eye/prepare-next-tsunami-says-chief, retrieved 18 Mar 2021.

⁴Dating the 1700 Cascadia Earthquake: Great Coastal Earthquakes in Native Stories, by Ruth S. Ludwin, Robert Dennis, Deborah Carver, Alan D. McMillan, Robert Losey, John Clague, Chris Jonientz-Trisler, Janine Bowechop, Jacilee Wray, and Karen James (2005), Seismological Research Letters, 76(2), p. 140-148.

This is one of the World’s Largest Earthquakes (M>=8.0) and is one of the Largest Earthquakes in the United States (M>=7.0)
The USGS has designated this as an event for “This Date in Earthquake History” for Jan 27 (UTC and in Japan, Jan 26 local time in North America) and has designated this as an event for “This Date in U.S. Earthquake History” for Jan 26