The megathrust earthquake involved the Juan de Fuca plate from mid-Vancouver Island, south along the Pacific Northwest coast as far as northern California.

[4] The most important clue linking the tsunami in Japan and the earthquake in the Pacific Northwest comes from studies of tree rings (dendrochronology), which show that several "ghost forests" of red cedar trees in Oregon and Washington, killed by lowering of coastal forests into the tidal zone by the earthquake, have outermost growth rings that formed in 1699, the last growing season before the tsunami.

For instance, the Huu-ay-aht legend of a large earthquake and ocean wave devastating their settlements at Pachena Bay places the event on a winter evening shortly after the village's residents had gone to sleep (consistent with the 9pm reconstructed time).

[11] The only other Panchena Bay survivor was a young woman named Anacla aq sop, who happened to be staying that day at Kiix-in, located on the less-tsunami-impacted Barkley Sound.

[13] Ethnographic research has focused on a common regional pattern of art and mythology depicting a great battle between a thunderbird and a whale,[8] as well as cultural signifiers such as earthquake-inspired ritual masks and dances.

[14] The geological record reveals that great earthquakes with moment magnitude 8 or higher occur in the Cascadia subduction zone about every 500 years on average, often accompanied by tsunamis.

[16] Kenneth Murphy, who directs FEMA's Region X, the division responsible for Oregon, Washington, Idaho, and Alaska, stated, "Our operating assumption is that everything west of Interstate 5 will be toast.

[23] The Quileute people secured a land grant from the US government in 2012 to move their settlement inland, both as protection from a future tsunami threat and because of more frequent flooding on the Quillayute River.

[13] The Shoalwater Bay Indian Tribe also sought federal funding to move their community uphill receiving a FEMA PDM grant to build the first vertical evacuation tower on their coast, completed near the Tokeland Marina in 2022.