[Rockhounds] Younger Dryas Impact Hypothesis and Missoula (Spokane) Megafloods

[Dora Smith]

Exactly.   The 1700 Cascadia earthquake, which is the one I recall seeing a documentary about, was caused by an earthquake on the subduction fault. A different kind of earthquake from a different cause, wouldn't cause a catastrophic tsunami.   Only an offshore subduction-type earthquake displaces that kind of water.
Cascadian megafloods caused by earthquakes on the Cascadian subduction zone are expected to occur every few hundred years, from the geological record. So you'd not find evidence of just one megaflood. However, an impact could cause a tsunami as well, depending on where it hit.
I understood the article to say that those earthquakes result from common, ordinary events.  They do not.     What this means is that tsunamis occur often in that region and for more than one region - so we can't use them to disprove that an impact occurred. https://en.wikipedia.org/wiki/1700_Cascadia_earthquake In case you forgot already - or never read before sending.  

 Dora