Sirens apparently work best if there is actually time for a warning. Word on the street here is, "If you feel the ground shaking, THAT IS YOUR SIREN! Do not wait, do not check the news media, head uphill immediately." Also practical advice.
Just one concern, the signs marking the route and area (as above) are often missing or stolen. According to a recent article in the Headlight Herald, a good deal of the highway sign budget is spent replacing tsunami signs. The assumption being there are dorm rooms, garages, man caves and other classy spots festively decorated with tsunami evacuation route signs. In fact, they are the #1 highway sign stolen in America. My guess is the signs would fetch you a pretty penny in the Midwest.