The last megathrust earthquake that created an ocean-crossing tsunami was recorded along the 600-mile-long fault of the Cascadia Subduction Zone in the Northwest on January 26 in 1700. Hopefully the next one won’t hit any time soon, but another is due every 300 to 500 years. In fact, on Friday, the Pacific Tsunami Warning Center published a re-enactment of the massive waves in a model animation. Here’s the explanation from the Center’s YouTube page:
By comparing the tree rings of dead trees with those still living they could tell when the last of these great earthquakes struck the region. The trees all died in the winter of 1699-1700 when the coasts of northern California, Oregon, and Washington suddenly dropped 1-2 m (3-6 ft.), flooding them with seawater. That much motion over such a large area requires a very large earthquake to explain it—perhaps as large as 9.2 magnitude, comparable to the Great Alaska Earthquake of 1964.
Such an earthquake would have ruptured the earth along the entire length of the 1000 km (600 mi)-long fault of the Cascadia Subduction Zone and severe shaking could have lasted for 5 minutes or longer. Its tsunami would cross the Pacific Ocean and reach Japan in about 9 hours, so the earthquake must have occurred around 9 o’clock at night in Cascadia on January 26, 1700 (05:00 January 27 UTC). READ MORE