On March 11 of this year, an earthquake of this magnitude occurred beneath the ocean floor 43 miles east of the Oshika Peninsula of Japan. The quake and resultant tsunami killed over 15,000 people and resulted in an economic cost of over 200 billion US dollars.
On December 26, 2004, a similar type of earthquake occurred just off the west coast of Sumatra in Indonesia. The resultant tsunami killed over 200,000 people around the Indian Ocean and caused tens of billions of dollars in damage.
Similarly large earthquakes have occurred along offshore subduction zones in 1985 in Mexico, 1964 in Alaska, and 1960 in Chile. They're not especially uncommon.
Queule, Chile, before and after the 1960 earthquake and tsunami
Painting of 1854 Hiro Village, Japan tsunami
Pacific Northwest native peoples also had legends of a large earthquake and tsunami (although not specifying a date). Many of the stories are wrapped in stories of battles between mythological creatures like Thunderbird and Whale.
Here's one matter-of-fact account from at 1864 diary entry by James Swan, the first schoolteacher on the Makah reservation at Neah Bay near the Straits of Juan de Fuca...