It's only designed to give you enough time to get in a doorway (the most reinforced part of a building) or under something solid (so things don't fall on you). It's not like you'd have enough time to drive out of the area. This is an improvement to older days (yesterday) but that's the best we've got.

I want it on the thing that sets off my Apple Watch with an amber alert. Loud AF

If it's just a text, it may not get checked until it's too late.
A special alarm that vibrates the phone a couple of times and then squeals "EARTHQUAKE ALERT!" would be more effective.