I live in the area. Most of the city I live in is built about 6-15 meters above sea level. All of it would be wiped out in a smaller event than what this legend is based on.
The 1964 Alaska "Good Friday" earthquake is the second most powerful earthquake in recorded history, estimated to have been stronger than the 1700 Cascadia earthquake.
In 1970 I wandered the ruins of the original city of Valdez. They relocated up the hill. The next morning, sleeping in our homebuilt camper van, there was a rolling 5.9 earthquake right under us. Yikes.
“The seagull and the mackerel”