Tree ring records from Oregon coast Douglas firs reveal that there were at least 41 great earthquakes that produced tsunamis between A.D. 900 and A.D. 1700. Most of the tsunamis came from subduction zone megathrust earthquakes on the Cascadia subduction zone.

Tree ring, geological and historical evidence suggest the 1700 Cascadia quake ranks as one of, if not the, most powerful earthquake in the entire seismic history of North America.

The first tsunami waves struck Japan about ten hours after the earthquake, devastating several areas. Then, after traveling 7000 km (4,350 mi) across the Pacific Ocean, it reached North America, where it caused even greater destruction.

The most detailed reports come from Native Americans inhabiting coastal areas from Northern California to British Columbia.

Native legends from numerous tribes describe the ground violently shaking and the ocean suddenly retreating seaward, exposing the ocean floor teeming with marine life, then returning as monster waves that flooded the land. Archaeological, geological, and biological evidence supports the oral traditions.

Japanese fishermen reported seeing dead trees and large amounts of debris floating thousands of kilometers out to sea. The debris field may have been from coastal forests destroyed by the American tsunamis.

This event was probably the largest earthquake to strike North America in the past 2,000 years.

Similar but smaller tsunamis from great earthquakes along other sections of the Pacific Rim struck Japan in the 18th century: the Shōwa Sanriku earthquake in 1896, the Shōwa Sanriku earthquake in 1933, and the Sendai earthquake in 2011.