As this wave reaches a continental shelf, it piles up, becoming shorter and higher. Only then will it resemble the monsters of legend - and as usual, legend exaggerates. Tsunamis rarely result in giant breaking waves, but are more like very strong, fast tides [USGSTsunami]. While this is very dangerous for coastal structures (as the horror of the 2004 Asian tsunami demonstrated), even if a seastead was close to shore, it would just rise with the water level. The worst consequence would be the mooring system failing or being damaged.