The Cascadia Subduction Zone and the earthquakes near the fault over the years.
The last huge earthquake, the last really "Big One" to hit the Pacific Northwest Coast, struck around 9 p.m. on Jan. 26, 1700 — 321 years ago.
Called Cascadia, the magnitude 9.0 quake caused the entire Pacific Northwest coastline to suddenly drop 3 to 6 feet and sent a 33-foot high tsunami across the ocean to Japan.
"Japanese sources document this earthquake, which is the earliest documented historical event in Western Washington. Other evidence includes drowned groves of red cedars and Sitka spruces in the Pacific Northwest. Indian legends corroborate the cataclysmic occurrence," according to HistoryLink.
The earthquake ruptured what is known as the Cascadia subduction zone from British Columbia to northern California — 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.
This was one of the largest earthquakes the Pacific Northwest has ever had, according to HistoryLink, and 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.
The Japanese call the tsunami their "orphan tsunami" because they did not feel the earthquake that preceded it.
