January 26, 1700 Cascadia Earthquake

On January 26, 1700, what is now the US Pacific Northwest was shaken by a Magnitude 9.0 earthquake. Oral traditions tell of collapsed houses, from shaking that was so stong that people could not stand. The quake caused many landslides. A tsunami was created that destroyed at least one village. However, since the people living in the area did not have a written language, so what we know of the quake is from sketchy oral tradition and traces left in the geological record. We know from that record that there have been 13 great quakes in the last 6000 years. We know that the tsunami was powerful enough to cause damage in Japan. It was the Japanese records of the tsunami that allows us to pinpoint the time of the quake. We can assume that there was widespread damage both from the quake itself and from the resulting tsunami. The tsunami caused damage in Japan and most likely in many places around the Pacific.

The Cascadia Subduction Zone, where this quake occurred runs from southern British Columbia to Northern California. It represents the eastern edge of the Juan de Fuca tectonic plate, which is being overridden by the North American Plate. As the Atlantic Ocean widens at the mid-Atlantic ridge, North America is being forced westward. The Juan de Fuca Plate is a small remnant of what was once a large plate in between the Pacific Plate and the North American Plate.

As the Juan de Fuca Plate is forced below the North American Plate large earthquakes are generated as strain builds up at the plate boundary, which is released periodically in large earthquakes. This subduction process leads to the largest earthquakes in the world. During this quake the entire subduction zone ruptured. The closest modern equivalent would be the 2004 Sumatra quake and tsunami . Like the Cascadia quake, the Sumatra quake was the result of a long subduction zone rupturing, producing severe shaking and a tsunami. The 2004 was unusually severe due to the geography of the Indian Ocean where it occured and the high population living near the sea. Nonetheless, a repeat of the Cascadia quake would be devastating in an area the now holds a large urban population. A repeat is certain, although we don't know whether it will come tomorrow or in 300 years.

(See the Plate Tectonics page for more information on these processes.)

Here is the USGS Page on the Cascadia Quake .