On January 26, 1700, at about 9:00 p.m. Pacific Standard Time a gigantic earthquake occurs 60 to 70 miles off the Pacific Northwest coast.

The quake violently shakes the ground for three to five minutes and is felt along the coastal interior of the Pacific Northwest including all counties in present-day Western Washington. A tsunami forms, reaching about 33 feet high along the Washington coast, travels across the Pacific Ocean and hits the east coast of Japan. Japanese sources document this earthquake, which is the earliest documented historical event in the Pacific Northwest. Other evidence includes drowned groves of red cedars and Sitka spruces in the Pacific Northwest. Indian legends corroborate the cataclysmic occurrence.

The earthquake ruptured what is known as the Cascadia subduction zone -- the area of overlap between two of the tectonic plates that make up the earth's surface, the Juan de Fuca plate and the North American plate. The Cascadia subduction zone extends from Vancouver Island, British Columbia (about 49 degrees 30 minutes North Latitude) south to Cape Mendocino in northern California (about 40 degrees North Latitude). The earthquake dropped the entire Pacific Northwest ocean coastline three to six feet. The tsunami, up to 33 feet high, inundated the ocean coast.

This was one of the largest earthquakes the Pacific Northwest has ever had. It compares with two disastrous earthquakes: the March 27, 1964 Alaska earthquake, which measured 9.2 moment magnitude, and the May 21-22, 1960 Chile earthquake, which measured 9.5 moment magnitude.

This is a drawing made as part of the description
of the events on the day of the tsunami.

Four contemporary Japanese sources describe the 6- to 10-foot-high tsunami and five of the towns it inundated along 600 miles of the Honshu Island coast.

"The water also went into the pine trees of Ego. The receding water went out very fast, like a big river. It came in about seven times before 10 a.m. of that day and gradually lost its power…Because the way the tide came in was so unusual, and was in fact unheard of, I advised the villagers to escape to Miho Shrine…It is said that when an earthquake happens, something like large swells result, but there was no earthquake in either the village or nearby."

Initially, investigators believed it was possible that these waves originated from a meteorological origin such as a storm surge. However, the uniform heights of the waves distributed along Japan's coastline indicated that the waves were characteristic of a far-field tsunami meaning they could not have been produced by a storm surge. Furthermore, typhoons cause most storm surges in Japan, and typically occur only from August to October. In fact, on January 27 and 28, 1700 the weather over central Japan was recorded as sunny or cloudy.

The Japanese call the tsunami their "orphan tsunami" because no earthquake felt in Japan accompanied it.

Evidences

Burried tidal marsh or coastal forest soils point to sudden land subsidence of about 1 metre occuring at the same time from Vancouver Island to Northern California.

Changes in tree ring growth from coastal old-growth also suggest a sudden, widespread subsidence and drowning of roots

Sand layers on top of the buried coastal marshes, driven in from offshore bars by the wave of the large tsunami that rushed into the subsided coastal region

Silt turbidite (landslide) layers on the deep sea floor far off the coast from underwater landslides, likely caused by strong seismic shaking

Tsunami evidence

• local sources - marine organisms swept into and preserved in the bottom muds of coastal lakes that are separted from the ocean by land elevations of some 5 m high
   

• distant sources - large tsunami in Japan with no local Japanese earthquake. Modelling this tsunami has revealed that the most recent earthquake for Cascadia was M ~ 9.0 and occured on January 26, 1700, at around 9 p.m
   

• Drowned groves of trees occur in several places in the Pacific Northwest. They have been dated within 30 or 40 years of the known date of the earthquake, which is suggestive but not conclusive. However, carbon dating of the tree rings of a seawater-drowned red cedar near the Copalis River in Grays Harbor County show that the tree died between August 1699 and May 1700, that is, in the same earthquake.
   

• Native Americans witnessed this earth-shattering event. Ruth Ludwin, a University of Washington geophysics professor has searched for Indian legends that could refer to the event. She has found many similar tales of plains becoming oceans, mudslides, and the like.
   

• The Hoh Indians of the Forks area of the Olympic Peninsula tell of an enormous "shaking, jumping and trembling of the earth ..." (The Seattle Times). The Makah who live on Neah Bay at the northwest tip of the continent have a version in which a whale is delivered to the mouth of a river and saves the people who had been starving. This legend forms the basis for the tribe's whale hunt.