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In 1700 the area of the Triple Junction up into British Columbia ruptured and set off a 9+ R that did much to alter the landscape from Eureka Ca north. They were able to document the event to the minute by studying data in Japan of the resulting Tsunami. I have seen a core sample from Crescent City showing a one inch layer of setiment from the Anchorage quake and tsunami of 64. The same core sample shows a four inch layer from the 1700 event. Further studies show a 9+ event every 300 years in this area.

Hmmmmm. 1700+300=???

In 1700 the area of the Triple Junction up into British Columbia ruptured and set off a 9+ R.

A few years ago I worked on an environmental impact report in which I had to assess tsunami potential from offshore earthquakes. The event in the Pacific northwest which caused a tsunami, which effects can be measured still, and that was recorded in the coasts of the western Pacific (China, Japan), was a topic of research at the time. I do not recall an estimated magnitude that large for that 1700's event.

The size if the earthquake, in terms of magnitude, does not necessarily relate to the tsunami generated. There is good evidence that a number of large tsunamis have been spawned by submarine landslides on the continental shelf/slope, which sometimes occur hours after the initial shaking event. If you are interested in tsunamis of this type, do a google search on the "Scotch Cap" (not "cape") Lighthouse, formerly located in the Aleutian Islands, which was destroyed by a 100+ ft tsunami.