Not necessarily. The seawater can also contain those rare earth minerals with current methods it is just way too expensive to extract those comercially.
If we find a way to improve this technology and make it way cheaper or use it on a bigger scale we could potentially extract those elements from the sea.

And northern japan isn't in a region where earthquakes should surpass a magnitude of 8.5 and yet they famously got hit by a 9.1 in 2011.
The word can't only works until nature shows us that it absolutely can if it comes to the absolute worst case.

But it is true there are probably a lot less deaths in southern california than there are in turkey but it is still going to be a catastrophic event. There will still be thousands of deaths.

Because noone knew of the danger. European settlers arrived in the pacific northwest after the last quake. It has been quiet ever since there was no reason to think there would be any danger.
It took some dead forests, a native american story of disappearing land and tsunami records from japan to realize just how dangerous cascadia really is.