It looks like the local elementary school came to the same conclusion we did about local tsunami risk. South New Brighton elementary has bought life jackets for all the students; we still need to figure out where to source a family-pack.
Any large tsunami is likely to come with plenty of evacuation notice as it would reach us after a large quake off the coast of South America. But there also is some risk of a locally generated one that would come with less than 20 minutes notice. The Avon River separates Southshore, South Brighton, and New Brighton from any higher land except that which might be reached by a very long drive North. After the February earthquake, none of the bridges could be crossed by vehicles. So it could very easily be very impossible to evacuate after a local tsunami-causing earthquake.
Our emergency plan for anything big and local? Sit on the roof of our two-story house with a life-jacket. Our house is on a two meter rise from the street; the street is about two meters above sea level; the roof is about 4 meters from the ground. I can't see how we can do better other than by having a quick-inflate emergency life raft up there. But those aren't cheap. And a locally generated tsunami would likely to be small enough that a life jacket could reasonably reduce the risk.