this is something that i can totally build at small scale to test it in all of the situations i anticipate, first, it is buried to its equator, and then covered with a natural wavelet (bell curve) dirt structure, how to cover its outer parts so it it exposes the water sealed underlying structure (it needs to shed the upper part of the covering effectively so it becomes fully exposed)

next, it is anchored using cables and a chain from the bottom, anchored in a very large, heavy concrete slab, anchored with chains (i think 5 is needed).

also, the internal floor support tensegrity grid and cable system helps such that the weight of the stuff on the floors sitting on the convex mesh support, increases its vertical compression weight distribution

basically, it would be possible to build a scale version of this about the size of a beach-ball, and contrive all of the states it needs to handle, from buried, to floating on the anchors, to detaching the anchor and floating to the surface, and when the water drains away, it needs supports that keep it vertical while on muddy ground. probably an inverted umbrella with a fabric so it can provide surface tension on a mushy surface, and then rope ladders from the upper opening to exit the structure.

didn't exactly mention this but its main entrance is one of the equatorial hexagons, on the upper side, with the lower flooring making its bottom edge, and a large double door sprung convex so when it closes, it has tension to resist the extra force that it will get horizontally and vertically... probably for this reason, it needs to be hinged so in emergency mode you can close this door, would need to be double layer, and voila. ready to float.

anyway, this is a great hobby project, if i can build a small prototype, maybe someone can fund turuning it into a kit that can be assembled to provide a tsunami survival refuge that withstands a full tidal tsunami, without significantly risking being sucked back out to sea, and obviously, built at higher altitude so the distance of the tether is sufficient to keep it anchored while exposing the upper part so you can have normal air access, and survey the surroundings to watch for the water to drain and bring it back down to ground. and all of it, i think, can be controlled manually, so it would need to be big enough for 6-8 people who would need to coordinate to tighten and loosen the turn buckles for actuating the things, as well as a leveraged manual pump for draining out any leaking water buildup like in a ship's hull.

i'm going to call it "Mleku's Ark"