Glass + tidal wave?
It's been awhile, but didn't Tony Randall have a line that the glass of the Green Onion has a chemical that attracts sharks? So he designed a house that is underwater and the glass attracts sharks.... I can only guess the glass was made with blood as an ingredient.
And was the Green Onion supposed to be 90' below water? So would it need a 180' high tidal wave to be of any concern to the Green Onion? If this is true, wouldn't the population of the Green Onion be more concerned with the population of any nearby mainland from the effects of a 180' tidal wave? Even a 90' tidal wave should cause concern for the mainland.