Those seams are probably covered by the plywood sheathing the outer hull. For that purpose plywood is very good. As has been mentioned though, impacts/punctures are very likely in a tsunami, particularly with a tsunami passing through suburbia. Hardening the outer hull with a layer of galvanized steel might help a lot.
As constructed it looks like it would have plenty of buoyancy. A boat would probably benefit from a keel and ballast, but a boat designed for blue water may have a rather long keel under the hull, a keel that would catch on "stuff" in a tsunami and how does that work when the water is less deep than the keel? It doesn't work..
Because of the dynamics and churning water of a tsunami, I'm not sure if even a short keel would help this design. This design may be intended to bob like a cork and will probably sit high in the water above all the turmoil below. Might work, might not, no way to really test it. A scale model for testing in a shallow tank might be beneficial.
Getting back to hardening the hull -- hardening the lower half of the hull may help it when making contact with hard pointy objects below the surface. The upper half stays light, the lower half benefits from more weight (think distributed ballast) and is reinforced from punctures.
All that said, the best way to ensure it survives a tsunami intact is to move it to high ground