You could have a thousand 5.0-6.0 quakes and these couldn’t adequately release any built up pressure of a Cascadia Megathrust 9.0. And just because you had a bunch of medium sized 5-6 quakes it doesn’t mean a Megathrust quake is imminent. You have to look at the location and depth as well as other markers before trying to make scientific prediction, and even then its only a prediction( maybe a 50% likelihood at best) far from 70-80% likelihood.