The collapsing sea

With almost all of the world now fallen into the abyss, each separate collapse tends to blend into each other only being half-remembered by the people who have long since given up on the idea of a stable home. There's one collapse that's stayed in people's memories, however. The day the sea collapsed. No other collapse has changed the world as quickly as it did, and the effects it had spread much further than just at the point where the ground fell. Because much like pulling the plug on a bath, a single crack in the seafloor soon rapidly drained the sea. The rushing water making the crack bigger and bigger, making the water rush out faster and faster. Near some harbors people survived, the water leaving like a rapid tide and letting them walk back to the previous shore, but those further out at sea weren't as lucky. Even those who landed on stable ground hit it with such force few survived, and those that did weren't guaranteed to be saved in time despite rescue airships quickly being dispatched. Some never had a chance as they got pulled along with the water into the abyss. This single event affected countless settlements along the previous coast and really made people realize how big of a catastrophe was coming. The sudden lack of a sea also affected the surrounding environment and would've changed the weather of the whole world if it hadn't fallen right with it during the coming years. The former island nations started organizing the move of thousands of people, and the former coasts were quickly abandoned as people took what belongings they had and started making their way towards the world star and the middle of the world. Towards the falling city.