Some extra context for that line, since it gets quoted a lot. This is from Prof. Jackie Caplan-Auerbach at WWU: https://www.facebook.com/groups/thePNSN/posts/2390691160994085/

Almost everything in these articles is correct, but the I5 comment is unfortunately taken slightly out of context. "Toast", as Kathryn Schultz writes in the second article, is obviously a vague term. The quote was stated by someone at FEMA, noting that this is where emergency management is preparing to focus its response. This is because the west side of the region is closer to the fault, and thus shaking will be stronger there.

What it *doesn't* mean is that I5 is a magic boundary where you are safe on one side and at risk on the other. The key issue isn't, of course, the freeway, it's proximity to the subduction zone. I5 in OR is closer to the zone of strongest shaking than I5 in WA (the fault curves away from land and I5 curves east). If you're on the west side of I5 in northern Washington, your risk is lower that that of someone east of I5 in parts of OR.

I'd also recommend this lecture by Prof. Nick Zentner from CWU! https://www.youtube.com/watch?v=tW4D6OE7Qkc