There have been a few sinkholes in southeastern Florida, but mostly it's the central part of the state.
In any case, the ground doesn't seem particularly stable. Sand on top of bedrock, and much of the bedrock is limestone.
Wikipedia:"In the 1920s, Fisher and others created much of Miami Beach as landfill by dredging Biscayne Bay; this man-made territory includes Star, Palm, and Hibiscus Islands, the Sunset Islands, much of Normandy Isle, and all of the Venetian Islands except Belle Isle."